Study of superconducting properties of NiO Nano

particles/CuTl-1223 composite.

LAYIQ ZIA

Department of Physics

Quaid-i-Azam University

Islamabad, Pakistan

2015

Study of superconducting properties of NiO Nano particles/CuTl-1223 com-

posite.

A dissertation submitted to the department of physics, Quaid-i-Azam University,

Islamabad, in the partial fulfillment of the requirement for the degree of

Master of Philosophy

in

Physics

By

LAYIQ ZIA

Material Science Laboratory

Department of Physics

Quaid-i-Azam University

Islamabad, Pakistan

2015

Beginning with the name of ALLAH ALMGHTY the most beneficent and

merciful, and the most sovereign among all of us.

Certificate

This is to certify that Layiq Zia S/O Lajbar Khan has carried out the

experimental work in this dissertation under my supervision in Materials Sci-

ence Laboratory, Department of Physics, Quaid-i-Azam University, Islama-

bad and satisfying the dissertation requirement for the degree of Master of

Philosophy in Physics.

Supervisor

Dr. Nawazish Ali Khan Department of Physics Quaid-i-Azam University Islamabad, Pakistan.

Submitted through Chairman Prof. Dr. Arshad M.Mirza (S.I) Department of Physics Quaid-i-Azam University Islamabad, Pakistan.

DEDICATED

TO

MY LATE FATHER

ACKNOWLEDGEMENTS

All the praises to Almighty ALLAH, the most merciful and the sovereign

power, who made me able to accomplish this research work successfully. I offer my

humble and sincere words of thanks to his Holy Prophet Muhammad (P.B.U.H)

who is forever a source of guidance and knowledge for humanity.

This work would have not been possible without the invaluable contributions

of many individuals. First and foremost, I wish to thank my supervisor Dr. Nawa-

zish Ali Khan for all of his support, advice, and guidance during the whole period

of my study. I am thankful to chairman, department of physics, for the provision of

all possible facilities and cooperation.

I would like to acknowledge the Higher Education Commission of Pakistan

(HEC) for their financial support by awarding me the fellowship via Indigenous

5000 Ph.D Fellowship Program.

My humble and heartfelt gratitude is reserved for my beloved Parents, and

especially for my respectful brother Asif Zia and sister. Without their prayers, sup-

port and encouragement the completion of this study task would have been a

dream.

My sincere regards and thanks are overdue to my best friend Fai-

zullah,Abida Saleem, S.Qamar Abbas, S.Hamza safeer, M.Usman, M.Nadeem, and

all other friends and Lab fellows for their constructive suggestions and technical

guidance.

Layiq Zia

i

Abstract

Nix/(Cu0.5Tl0.5)Ba2Ca2Cu3O10- composite superconductors samples are synthesized at

normal pressure by two step solid state reaction method. The samples have shown ortho-

rhombic crystal structure with increase in the cell parameters with the increase in the

added concentration of Ni-nano-particles showing that Ni diffuses partially into the unit

cell of final compound. A metallic variation of resistivity from room temperature down to

onset of superconductivity is typical feature of these samples with Tc(R=0) varying be-

tween 92 and 94K. The magnitude of diamagnetism is significantly enhanced in 7 and

10% nano-particle added samples. The softening of apical oxygen modes of type Cu(1)-

OA-Cu(2) has confirmed the diffusion of Ni into the unit cell of the final compound. The

excess conductivity analyses of conductivity data have shown enhancement in the values

of Bc(0), Bc1 and Jc with the addition of Ni-nano-particles. This shows that added Ni-

nano-particles act as efficient pinning centers, which also confirmed in the suppression of

the London penetration depth.

ii

1 Table of Contents Chapter 1.1

1 Superconductivity ................................................................................................................................. 1

1.1. Electrical Resistivity ....................................................................................................................... 1

1.2 Some fundamental facts and historical review of superconductivity .......................................... 4

1.3 High temperature superconductors ............................................................................................. 7

1.4 . Structure of (CuTl) based high temperature superconductors ................................................. 10

1.5 Types of superconductors ........................................................................................................... 11

1.5.1 According to their magnetic properties ............................................................................................. 11

I. Type-(I) superconductors ............................................................................................................ 11

II. Type-(II) superconductors ........................................................................................................... 12

1.6. Characteristics and fundamentals of superconductivity ................................................................ 13

1.6.1 Zero resistivity .................................................................................................................................... 13

1.6.2.Meissner effect .................................................................................................................................. 14

1.6.3. Critical temperature .......................................................................................................................... 17

1.6.4. Critical magnetic field ....................................................................................................................... 18

1.6.5. The Isotope effect ............................................................................................................................. 19

1.6.6. Critical current density ( ) ............................................................................................................. 20

1.6.7. Correlation of three critical values in superconductivity .................................................................. 20

1.6.8. London penetration depth ......................................................................................................... 21

1.6.9. Coherence length .............................................................................................................................. 22

1.6.10. Specific heat .................................................................................................................................... 23

1.6.11. Energy gap ....................................................................................................................................... 23

1.6.12. Vortex formation ............................................................................................................................ 24

1.6.13.Magnetic Flux quantum ................................................................................................................... 24

1.6.14. Josephson Effect ............................................................................................................................. 25

I.DC Josephson effect .................................................................................................................................. 25

II. AC Josephson effect ................................................................................................................................ 25

1.6.15. Order parameter ............................................................................................................................. 25

1.6.16.Proximity effect ................................................................................................................................ 25

1.7 Theories and development of superconductors ......................................................................... 26

iii

1.7.1. London theory ................................................................................................................................... 26

1.7.2. Ginzburg landau theory .................................................................................................................... 27

1.7.3. BCS Theory ........................................................................................................................................ 28

1.7.3.1. Cooper pair formation ................................................................................................................... 28

1.8. Nano Technology and Nanoparticles ................................................................................................... 29

1.9. Application of superconductors ........................................................................................................... 30

1.9.1. Based on Zero resistivity ................................................................................................................... 30

I.Power transmission line ............................................................................................................................ 30

II. Superconducting motor .......................................................................................................................... 30

1.9.2. Based on magnetic properties .......................................................................................................... 31

II. Superconducting trains ........................................................................................................................... 31

III. Magnetic Resonance Imagining ............................................................................................................. 31

IV. Particle Accelerators .............................................................................................................................. 31

1.9.3. Based on Josephson Effect ................................................................................................................ 31

I. SQUID ...................................................................................................................................................... 31

1.10. References .............................................................................................................................. 32

Chapter 2 44

2.1. Literature review on (Tl-1223) superconductors ................................................................................. 34

2.2. Literature review on Nano-particle dope High temperature Superconductors (CuTl-1223) ......... 37

2.3. Literature Reviews on Fluctuation induced conductivity of high temperature superconductors

44

2.4. References ...................................................................................................................................... 47

Chapter 3 .. 59

3.1. Nanoparticles Synthesis procedure ..................................................................................................... 48

3.1.1. Co-precipitation method................................................................................................................... 48

3.1.2.Synthesis of NiO nanoparticles .......................................................................................................... 49

3.2. Sample preparation ............................................................................................................................. 49

3.3. Characterization of the samples .......................................................................................................... 50

3.3.1. X-ray diffraction technique ............................................................................................................... 50

I. X-ray diffraction and Braggs law .................................................................................................... 50

II. X-ray diffractometer ....................................................................................................................... 53

iv

3.3.2. Resistivity measurements ........................................................................................................... 54

Experimental setup ......................................................................................................................... 56

3.3.3. Ac magneto susceptibility technique .......................................................................................... 58

Experimental setup ......................................................................................................................... 61

I. Ac magnetic susceptometer ........................................................................................................... 61

3.3.4. Infrared spectroscopy ....................................................................................................................... 62

3.3.4.1. FTIR Components ........................................................................................................................... 63

I. Michelson interferometer........................................................................................................... 63

II. Source and detectors .................................................................................................................. 64

III. Detectors ................................................................................................................................. 64

IV. Fourier Transformation ............................................................................................................... 64

V. Moving mirrors ........................................................................................................................... 65

3.3.4.2. Operating procedure of FTIR Spectrometer ....................................................................... 65

3.4. Refrences ........................................................................................................................................ 66

Chapter 4.. 78

4. Introduction ........................................................................................................................................ 67

4.1. Experimental ................................................................................................................................... 67

4.2. Results and Discussion .................................................................................................................... 68

4.2.1. Theoretical Background .................................................................................................................... 68

4.2.2. Nano-superconductor (Ni)x/CuTl-1223 (x = 0, 3, 5, 7 and 10 wt. %) composites ............................. 73

4.3. Conclusions ..................................................................................................................................... 84

4.4. References ...................................................................................................................................... 85

Figures of contents

Figure 1.1: (a) Zero resistivity (b) Perfect diamagnetism..................................... 1

Figure.1.2:(a) lattice site (b) deformation of lattice site (c) attraction of second electron making cooper

pair ................................................................................................................................................................ 4

Figure .1.3: Evolution of Critical temperature(Tc) with time ........................ Error! Bookmark not defined.

Figure.1.4: Unit cell of CuTlBaCaCuO- superconductor ............... Error! Bookmark not defined.

Figure.1.5: Magnetization, versus applied magnetic field, for type-I superconductor. ............................. 12

Figure.1.6: magnetization, curve of a Type II superconductor ...................... Error! Bookmark not defined.

Figure.1 7: shows the expulsion of magnetic flux from superconductor .................................................... 15

v

Figure1 8: Meissner Effect .......................................................................................................................... 16

Figure1.9: Vanishing resistivity at Tc ......................................................................................................... 17

Figure 1.10: critical magnetic field (Hc) as a function of temperature ....................................................... 19

Figure1 11: Relation of Jc,Hc,and Tc graphically ...................................................................................... 21

Figure 1.12: Dependence of penetration depth , on temperature of superconductor. . Error! Bookmark not

defined.

Figure 1.13: Decay of magnetic field inside the superconducing material ................................................. 27

Figure 1.14: shows cooper pair formation inside superconductors lattice .................................................. 29

Figure 3.1: X-rays diffraction from a crystal. ............................................................................................... 52

Figure 3.2 X-ray diffractometer .................................................................................................................. 54

Figure 3.3 Phono contribution to the resistivity in normal metals ............................................................. 56

Figure 3.4: (a) Four probe resistivity setup (b) Equivalent circuit............................................................... 58

Figure 3.5: Phase diagram ........................................................................................................................... 61

Figure 3.6: Experimental arrangement of Ac magneto susceptibility ........................................................ 62

Figure 3.7: Systematic FTIR sketch .............................................................................................................. 64

Figure 4.1: X-ray diffraction scans for Ni nano-particles ............................................................................ 73

Figure 4.2: X-ray diffraction scans for Nix/CuTl-1223 (x = 0, 3, 5, 7 and 10 wt%) nano-superconducting

composites .................................................................................................................................................. 75

Figure 4.2(a): Variation in a,b-axis length because of Ni-contents. ............................................................ 76

Figure 4.2(b): Variation in c-axis length because of Ni-contents. ............................................................... 76

Figure 4.3: Combined resistivities for Nix/CuTl-1223 (x = 0, 3, 5, 7 and 10 wt%) nano-superconducting

composites. ................................................................................................................................................. 77

Figure 4.4: AC-susceptibility measurements for Nix/CuTl-1223 (x = 0, 3, 5, 7 and 10 wt%) nano-

superconducting composites ...................................................................................................................... 78

Figure 4.5: F.T.I.R spectrum for Nix/CuTl-1223 (x = 0, 3, 5, 7 and 10 wt%) nano-superconducting

composites. ................................................................................................................................................. 79

Figure 4.6(a): ln() vs ln() of Nix/CuTl-1223 x = 0 wt% nano-superconducting composites ................. 81

Figure 4.6(b): ln() vs ln() of Nix/CuTl-1223 x = 3 wt% nano-superconducting composites. ................. 82

Figure 4.6(c): ln() vs ln() of Nix/CuTl-1223 x = 5 wt% nano-superconducting composites. ................. 82

Figure 4.6(d): ln() vs ln() of Nix/CuTl-1223 x = 7 wt% nano-superconducting composites. ................. 83

Figure 4.6(e): ln() vs ln() of Nix/CuTl-1223 x = 10 wt% nano-superconducting composites. ............... 83

Table of contents

Table 1: Parameters estimated from ln() and ln() 82

Table 2: Superconducting parameters estimated from excess conductivity... 83

1

Chapter 1 Introduction and Historical Review

This chapter contains a brief historical review and an explanation of superconductivity,

theoretical models, necessary terms, and some important applications of superconductors. This

chapter also covers some of the fundamental experimental and theoretical facts about supercon-

ductors.

1 Superconductivity Superconductor are those conductors in which resistivity of the material goes to zero at

the critical temperature and the material become perfect diamagnetic mean all magnetic field

lines expel from the bulk of the material. In classical prospective superconductivity is a phenom-

ena in which the resistivity vanishes and material become perfect diamagnetic below the critical

temperature [1]. The zero resistivity and the perfect diamagnetism are shown in Figure.1.1.

The property that made superconductors attractive is zero resistance and the expulsion of a mag-

netic field. Before discussing property of superconductor, we have to first review resistive prop-

erties of normal materials in comparison with superconductors.

1.1. Electrical Resistivity The electrical resistivity is property of material how strongly it opposes the flow of the

current. The flow of the current opposes different in different materials. On the base of electrical

Figure 1.1: (a) Zero resistivity (b) Perfect diamagnetism

2

properties, materials classified into three groups, which are conductors, insulators, semiconduc-

tors, table 1 show electrical resistivity of these materials.

Materials Resistivity

Superconductors 0

Metals 10-8

Semiconductors Variable

Insulators 1016

Table 1: Shows resistivity range of superconductors, metals, semiconductors and

insulators.

Insulators having high electrical resistivity, while semiconductors have temperature de-

pendent electrical resistivity in contrast of these conductors show relatively very low electrical

resistivity. Metals are all conductors having low electrical resistance which is due to the very

large number of free electrons in metals while insulators and semiconductors having very low

free electron density at ambient temperature. Beside of high numbers of free electrons in metals

theirs is electrical resistance to the flow of the electrons when the electric field applied to metals.

The electrical resistance arises from lattice vibration or impurities in the metals. Moving elec-

trons are scattered by lattice vibrations or impurities in the metal. Due to scattering, electron loss

there energy causes reduction in electric current in the metal. Lattice vibration depends on tem-

perature of metal by increasing temperature electrical resistance increase because lattice vibra-

tion of metal increase while by decreasing temperature of the metal electrical resistance decreas-

es but did not reach to zero value for normal metals. While the impurities were independents of

the temperature. In superconductors when the temperature goes down the electrical resistance

become zero at the critical temperature and below critical temperature superconductor is in zero

resistance state. In zero resistance, motion of moving electrons wasn't disturbed by the scattering

mechanism. Cooper and Schrieffer explained the zero resistance state giving a complete new

idea of cooper pair formation in the superconducting state. According to them, when normal

metals transform to superconducting state cooper pairs are formed in superconducting state due

to phonon induce electron-electron interaction. When electrons move across the positive core,

i.e. Lattice site they leave behind a small deformation by an account of its negative charge attrac-

3

tion on the positive lattice site cause the increasing density of positive charge due to the positive

charge on ion core. At this time, another electron attracted by this deformation of lattice site and

hence two electron pairs by this weak attraction. The pairing of the two electrons via phonons

called Cooper pairs [2].

By deformation of lattice sites for a short time due to electron attraction, creating a virtual

phonon which attracts the second electron, and thus two electrons come closer to become a

cooper pair. At this time the energy of the system decrease showing that force is attractive.

In normal metals, charge carriers are electrons or holes, but in superconductors, charge

carriers are cooper pairs. Electrons in normal metals come across the high resistance, but cooper

pairs encounter very low resistance, overall it shows very minimum resistance to electron

movement.

Electrical resistivity is due to lattice vibration and impurities in metals, lattice vibration is

decreasing with temperature and almost become vanishes at 0K, but impurities are independent

of temperature, which is always present in metals, at low temperature there is always residual

resistivity due to these impurities. Beside of these residual impurities metals can be transformed

into superconducting state.

Due to negligible resistance, heat loss is very little in superconductor wire, so they can

caries huge amount of current for a long time without any loss of energy. This huge amount of

caries current ability of superconducting wire challenges scientist and engineers technically to

develop this type of wire for transmission line of electric power supply to overcome energy loss

in transmission lines [3].

4

(a)

(b)

(c)

Figure.1.2: shows cooper pair formation in superconducting state, at (a) shows lat-

tice of positively charged ions of superconducting material (b) here a negative charge electron

moving through the positively ions lattice site (c) shows disturbance in positive lattice site in-

creasing density of positive charge as a result another electron is attracted by this disturbance.

1.2 Some fundamental facts and historical review of superconductivity All conductors show electrical resistance to the electrical current. To find a good con-

ductor that have no resistance scientist are struggling for centuries, in this way 19th

century was

very victorious because of the discovery of superconductivity in mercury by Onnes. Onnes dis-

covered the phenomenon of superconductivity, in the mercury during the validity of the Drude

theory. Onnes presented his research in 1911, in an article titled "On the Sudden Rate at

Which the Resistance of Mercury Disappears." Onnes define in that paper that the specific

resistance, became thousands of times less in amount relative to the best conductor at ordinary

temperature. Onnes later overturned the process and found that at 4.2 K, the resistance reim-

bursed to the material. The next year, Onnes presented more articles about the superconductivi-

Figure.1.2:(a) lattice site (b) deformation of lattice site (c) at-

traction of second electron making cooper pair

5

ty. Initially, Onnes called the phenomenon "supraconductivity" and, only later, approved the

term "superconductivity." For this research, Nobel Prize in Physics in 1911 granted to Onnes.

Two years later, after the discovery of superconductivity in mercury, conductivity of lead

had investigated in 1913 having superconductivity at 7K. After this long period, there is no such

element or compound was noticeable to have superconductivity. In 1941, Niobium Nitride had

reported to have superconductivity at 16K [4].

To understand this phenomena, different groups of scientist are working on this field

from the time of its discovery and discover a number of different properties and elements having

superconductivity. Up to half century from the discovery of superconductivity, there was no rea-

sonable theory that explains this phenomenon. From the discovery of high temperature super-

conductors up to now experimental mysteries of superconductors, mention that our knowledge

for understanding the complete phenomena of superconductivity is not enough [5].

In the history of superconductivity, one of the most important discoveries is the Meissner

Ochsenfeld effect. The Meissner effect is the expulsion of magnetic field line from the bulk of

the superconductors. The German physicists Walther Meissner and Robert Ochsenfeld discov-

ered the Meissner effect in 1933 by measuring the magnetic field distribution outside supercon-

ducting tin and lead samples. From above transition temperature sample is in normal state and

the field lines are passes through it, but after cooling below the transition temperature, Meissner

and Ochsenfeld observed all field lines ousted from the interior of the sample. The Meissner ef-

fect is the unique property of the superconductors, which make superconductors to become per-

fect diamagnetic. The minimization of energy, of the charge carriers in superconducting state is

the origin of the Meissner effect [6].

The expulsion of magnetic field line and vanishing resistivity in superconductors, shows

that the Maxwell equations are not most enough at superconducting state. To overcome this dif-

ficulty London brother in 1935 presented first phenomenological theory, which justifies the pres-

ence of Meissner effect. Although, the London theory did not completely describe superconduct-

ing state, but was an important step toward understanding the superconductivity. The London

theory had based on two fluid models of super fluidity. London brother assumed that in the su-

perconducting state, there are two types of electrons, normal and superconducting electrons; they

therefor consider two types of charge carries for the first time.

6

After the London theory, in 1950 there was another theory presented by Ginzburg and

Landau, which explain most macroscopic properties of superconductors. The phenomenological

Ginzburg Landau theory of superconductivity was first formulated by Landau and Ginzburg.

This theory, which joint Landau's theory of second-order phase transitions with a Schrdinger-

like wave equation, had great success in clarifying the macroscopic properties of superconduc-

tors. It can also be obtained from BCS theory, by applying suitable limits indicated by Gorkov

[7].

Abrikosov indicated that the Ginzburg-Landau theory expects the division of supercon-

ductors into the two types now referred to as type-I and type-II. Abrikosov and Ginzburg were

awarded the 2003 Nobel Prize for their work.

The dependence of the critical temperature of isotope mass had investigated by Maxwell and

Reynolds they observed that the Tc of superconductors is varies with the varying isotope mass.

From this observation, it was shown that phonon-electron interaction was necessary for super-

conductivity [8].

In 1957 John Bardeen, Leon Cooper and Robert Schrieffer developed a brief theory of

superconductors with the concept of electron pairing via phonon. Elemental and type-(I) super-

conductors obey this theory, but type two superconductors did not obey this theory and need

modification. Cooper pairs were considered a current carrier in superconductors according to this

theory. Cooper pairs were form when the conductors changes from the normal state to the super-

conducting state.

The study of superconducting properties with mathematical tools was first time devel-

oped by Bogolyubov in 1958 which was an important contribution to this field.

Unification of Ginzburg landau theory with Bardeen, Cooper Schrieffer near the critical tempera-

ture was explained by L.P Gorkov in 1959. Gorkov also solved the BCS theory using green

function after one year later in 1958.

Practical use of superconductor was first time come into the world in 1962, when scien-

tists made first superconducting wire of niobium titanium, hence making superconducting mag-

net.

The tunneling effect was discovered in 1962 by Josephson, which explains the current

flow between two superconducting blocks, which was separated by an insulator, the phenomena

were known as Josephson effect.

7

1.3 High temperature superconductors

Since after the discovery of superconductors scientists were struggling to find supercon-

ductors that have a high critical temperature. More than Half decay after superconductors were

discovered scientists only made superconductors having a critical temperature 18K in Nb3Sn and

23K for Nb3Ge. However, for practical use of these superconductors, low temperatures were re-

quired, which made superconductivity to be explored to get high temperature superconductors

for the practical use. Having no such discovery more than half decay, field of superconductivity

was considered to be at a dead end. The 1980's were a decade of unequaled discovery in the field

of superconductivity. Before 1986, in 1964, Bill Little of Stanford University had suggested the

possibility of organic (carbon-based) superconductors. These superconductors are synthesizing

effectively in 1980, by Danish researcher Klaus Bechgaard of the University of Copenhagen and

3 French team members. (TMTSF)2PF6 had to be cooled to an incredibly cold 1.2K critical tem-

perature and exposed to high pressure to super conduct.

Then, in 1986, a true discovery was made in the superconductivity. Alex Mller and

Georg Bednorz (above), researchers at the IBM Research Laboratory in Rschlikon, Switzerland,

made an inelastic ceramic compound that super conducted at the highest temperature then known

30K [9]. This discovery was so remarkable because of that ceramics are normally insulators.

They do not conduct electricity. Because of that, researchers had not dignified them as likely

high-temperature superconductor candidates. The Barium, Oxygen, Copper and Lanthanum

compound i.e. LaBaCuO, which Mller and Bednorz synthesized, behaved in a not yet tacit way.

The discovery of this first of the superconducting copper-oxides (cuperates) won the two men a

Nobel Prize the following year. It was also found that small quantities of this material were in

fact superconducting at 58 K. Mller and Bednorz' discovery started a rash of activity in the field

of superconductivity. Researchers began around the world, making up ceramics of every pre-

sumable combination in a quest for getting higher and higher critical temperature.

A research group In January of 1987 at the University of Alabama-Huntsville replaced

Yttrium for Lanthanum in the Mller and Bednorz molecule and attained incredible 92K critical

temperature superconductivity in YBa2Cu3O10- [10]. A material (today referred to as YBCO)

was for the first time had found that would super conduct at temperatures higher than that of

boiling temperature liquid nitrogen, which is an easily available coolant. Further milestones had

done using exotic and frequently toxic elements in the vile perovskite ceramic.

8

These ceramic superconductors are called cuperates because Cu2O is a common constitu-

ent in all these high temperature superconductors. The Superconducting behavior of the cuper-

ates was astonishing at that time, because in normal un-dopant form they are Mott insulators.

The superconducting behaviors of these cuperates are depending on the magnetic impurities, the-

se magnetic impurities, reduce the critical temperature of cuperates.

The newly discovered superconductors also called un-conventional superconductors, and

had a clear difference from all conventional superconductors, which obey BCS theory. Scientist

repeated all conventional method on these cuperates for understanding superconductivity in these

cuperates, but did not get any satisfactory results. The importance of Cu2O in high temperature

superconductors were for the first time identified by Anderson, he realizes there is week inter

planer coupling in cuperates, thus the important physics behind superconductivity in cuperates is

quasi two dimensional[11].

The current classes of ceramic superconductors with the highest critical temperatures are

the mercuric-cuperates. In 1993 at the University of Colorado and the team of A. Schilling, M.

Cantoni, J. D. Guo, and H. R. Tot of Zurich, Switzerland for first time synthesis of one of these

compounds. A thallium-doped, mercuric-cuperates included of the elements Mercury, Thallium,

Barium, Calcium, Copper and Oxygen had a highest critical temperature at 138K, and was con-

firmed in February of 1994 by Dr. Ron Goldfarb at the National Institute of Standards and Tech-

nology Colorado. On the application of extreme pressure its T can be increased up higher approx-

imately 25 to 30 degrees more at 300,000 atmospheres.

In 1988, Sheng and Hermann discovered thallium based superconductors [12-13]. Thalli-

um based superconductors are the most finest amongst all other cuperates superconductors, due

to its high critical temperature and having a low surface resistance. Because of these quality ef-

forts had done on thallium-based superconductors, for making thin film and bulks [14-20]. They

are existing in different phases according to its general formula TlpBa2Caq-1CqO2q+2 (p=1, 2; q=1,

2, 3, 4, 5) [21-24].

According to this general formula, different phases are synthesized, in which Tl-2223 is

at best having high critical temperature 127K, having tetragonal symmetry with p4/mmm space

group [25, 26].

9

In recent years, various discoveries regarding the novel nature of superconductivity have

been made. In 1997 researchers found, an alloy of gold and indium was superconductor and a

magnet near at zero absolute temperature, which contradicts that both a magnet and supercon-

ductivity, could not exist at the same time. Since then, more than a half-dozen such compounds

had discovered.

In 2001 magnesium Debride had been found to be a super conduct at 39K, which was an ex-

traordinary discovery because any of the elemental or binary alloy do not super conduct above

30K. However, 39 K is still well below the transition temperature of the high temperature ceram-

ic superconductors.

The most recent groups of superconductors to be discovered are the "pnictides". They are

iron-based superconductors having a high critical temperature at 50K.they are first discovered by

Japanese researcher in 2006. Similar to the high-T copper-oxides, the precise mechanism that

aids superconductivity in them is a mystery.

Figure.1.3: Evolution of Critical temperature (Tc) with time

10

1.4 . The Structure of (CuTl) based high temperature superconductors

Number of characterization has been done on superconducting systems such as Cu-

Ba2CanCun+1Oy and TlBa2CanCun+1Oy. Both of these systems are differ because of position of

oxygen in charge reservoir layers. The Charge carriers dominating superconducting properties of

these samples and on change concentration of charge carriers superconducting properties get

change. Charge concentration can be changed by applying pressure or doping cations [27,28].

Addition of TI in Cu-12(n-1)n, results in the growth of a new subfamily Cu1-xTlx-12(n-1)n,

which is quite near to the compound. The Preparation of Cu-Tl compound has been done at nor-

mal as well as high pressure, having properties similar to those of Cu-based compounds [29, 30-

33]. The slight increase in the anisotropy of Cu-Tl superconducting compounds is mainly due to

semi insulating charge reservoir layer Cu1-xTlxBa2O4-, but the anisotropy remains lower as com-

pared to that of Tl-based superconductors.

Figure.1.4: Unit cell of CuTlBaCaCuO- superconductor

11

The member of cuperates family 1-x x 1 has P4/MMM space group and tetrago-

nal structure [34]. In addition, as the result, the prepared compound 1-x x 2 n-1 n 2n+4-

have showed the low anisotropy as well as the critical temperature is high too. In a unit cell,

there are four 2 planes and a charge reservoir layer. In a unit cell, the four 2 planes are

separated by three calcium atoms from other. The Ba atom connected the superconducting 2

planes with each other, making the pyramid, type, unit cell and known as a p-plane. Where, the

central planes or s-planes are those, which come between these two p-planes. When the carriers

are doped to superconductors compounds, the s-planes are optimally doped, whereas p-planes

are over doped. Overall, p-planes play an important role in carrying supplies from the charge

reservoir layer to the s-plane [35]. The Cu atom of the p-plane mentioned as whereas the

oxygen atom of the p-plane is termed as , on the other hand the copper atoms in the charge

reservoir layer are named as [36-37]. The oxygen atom links the charge reservoir

layer 1-x x 2 4- and the p-plane. The charge passage mechanism is controlled by the

oxygen atom from the p-plane to the charge reservoir layer. The oxygen atom at the center of the

charge reservoir layer 1-x x 2 4- is named as atom [38]. This oxygen atom has

secondary bonding either and atoms of the charge reservoir layer.

1.5 Types of superconductors

Superconductors have classified into two main types according to their physical and

magnetic properties. However, it can further classify according to our understanding.

1.5.1 According to their magnetic properties

According to their magnetic properties, they are divided into two main types. They are type-(I)

and type-(II).

I. Type-(I) superconductors These types of superconductors have a lower critical temperature, and have an abrupt transition from

a normal state to a super state in a magnetic field. Type-(I) superconductors are soft superconductors, they

are composed of pure elements, alloys, they have also low critical magnetic field. Type-(I) are consist of

elemental and binary alloy superconductors. The maximum critical magnetic field of type-(I) supercon-

ductor is , which is very low value compare to the type-(I) superconductors. The Type-(I) super-

12

conductor mostly consists of those superconductors, which obeyed BCS theory and called as conventional

superconductors. Figure.1.5. Shows that up to the material is pure diamagnetic and above it

becomes paramagnetic.

II. Type-(II) superconductors

They are consisting of all non-conventional superconductors, and having a high critical

temperature. They are mostly made of ceramic, so due to their physical properties they are hard

superconductors. In comparison with type-(I) superconductors, type-(II) superconductors not

have sharp or abrupt transition from a perfect diamagnetic state to a paramagnetic state. As a re-

sult, there has a two state combine region, where vortices are formed having a normal core inside

and outside the region is in the superconducting state. Figure.1.5.(b) Shows that negative mag-

netization rises continuously up to Hc1(T) while above Hc1 it decreases gradually. The material

between Hc1 and Hc2 is partial diamagnetic, i.e. The magnetic field can penetrate into the materi-

al and above Hc2 material become paramagnetic.

Figure.1.5: Magnetization, versus applied magnetic field, for

type-I superconductor.

13

Figure.1.6: Magnetization, versus applied magnetic field, for type-II superconductor

1.6. Characteristics and fundamentals of superconductivity

As any state of matter, has its own elementary properties, so any superconducting state

independently exhibits its own mechanism of superconductivity. Hence, a high temperature su-

perconductor will also exhibit them. The key basic properties of the superconducting state are the

following: zero resistance, the Meissner effect, the Josephson effects, the magnetic flux quantiza-

tion, the presence of an energy gap, and the proximity effect. An obstacle in specific heat was

marked in all superconducting transition. Finally, the behavior of type-II superconductors, in the

mixed state has the same pattern.

1.6.1 Zero resistivity

At any temperature below the critical temperature all superconductor has zero electrical

resistivity, mean that infinite electrical conductivity, for small amplitude of DC current. The re-

sistivity of a superconductor is smaller than 1023-m. This value is 18 orders of magnitude less-

er than the resistivity of copper at ambient temperature. Such a small value of resistivity in a su-

perconductor indicates that in zero magnetic field the current lifetime in a superconducting ring

is not less than 105 years. Superconductors have properties having zero electrical resistivity be-

14

low the critical temperature, which make superconductivity a thermodynamically unique phase

of matter [39]. The relation of electrical resistivity with electrical conductivity is followed as:

(1.1)

Now, as

(1.2)

Here m is the mass of the electron, e represent charge on the electron, is mean free time,

where n is the number of the electron. A scattering of electrons in solid decrease with decrease of

temperature, with resulting of decrease in lattice vibrations in solid. In superconducting state

when scattering of electron with lattice decrease mean free time increases, which results in de-

crease in electrical resistivity, and at very low temperature below the critical temperature of su-

perconductors, mean free time become so large that resistivity become vanishes and the material

become a superconductor [40]. Electrical resistivity vanishing at below critical temperature is

the intrinsic properties of all superconductors, which is widely used in practical applications.

1.6.2. Meissner effect

Meissner effect is the intrinsic property of all superconductors, below the critical field all

superconductors shows expulsion of magnetic field line from the bulk of the material. It was

first observed by Meissner and Ochsenfeld in 1911, that magnetic flux lower than Hc was ex-

pelled by the sample below Tc[41]. Meissner effect is the consequence of perfect diamagnetism

of the superconductors. Every superconductor shows perfect diamagnetism. Inside the supercon-

ductor magnetic field is zero in placing in the applied external field. This due to surface current

which arise when superconductor is placed in the external field current was built up on the sur-

face of superconductor which produce magnetization in opposite direction which cancel out the

effect of external magnetic field.

15

The magnetic field expulsion from superconductor vanishes when the temperature in-

creased or field strength is increased. Surface current remains on the surface of superconductor

in the temperature below the critical field because the resistivity is zero, so a dissipation of ener-

gy is zero and the material remain in the perfect diamagnetic state. Relation of external magnetic

field to magnetization is as follows

(1.3)

Here, Hex shows the external magnetic field, M denotes magnetization, and shows magnetic

susceptibility.

But inside the superconductor at

So equation 1.3 becomes

Figure.1 6: shows the expulsion of magnetic flux from su-perconductor

16

Also from (1.3)

(1.4)

Negative sign shows opposite magnetization produce inside the superconductor. This

shows that the magnetization of superconductors have ve value and susceptibility of supercon-

ductors have -1 value [42].

From a classical point of view every superconductor exhibit perfect diamagnetism, i.e.

B= 0 inside the superconductor, as shown in Figure.1.8. In fact, as we already know to cancel B,

a superconductor creates a DC current on the surface, which gives rise to a magnetization M, so

that in the interior of the superconductor. Since the resistivity of the superconductor is zero, this

surface current does not dissipate energy. If the magnetic field was applied to a superconductor

at T>Tc, and it is then cooled down to T

17

1.6.3. Critical temperature

Superconductivity appears in superconductors only below a certain temperature, which is known

as critical temperature. At room temperature the superconductor is a normal state and the current

dissipation occurs due to electrical resistivity. However, when the superconductor material

cooled down below its critical temperature the dissipation of current or energy become vanishes

and the state of the material is defined as superconducting state. Different superconductors have

different critical temperature, which mean that critical temperature depends on the superconduc-

tor materials. From the discovery of superconductors scientist remain in struggle for increasing

the critical temperature of superconductors. Although they had no good achievements in this re-

search up to 1986. At that time, the highest critical temperature was below 30K, which is no

good sign of research. In 1986, material having high a critical temperature above 77K was

Figure1.8: Vanishing resistivity at Tc

18

Discovered, and got attention because of having c above liquid temperature. In high tempera-

ture ceramic superconductors, YBa2Cu3O7 have 92K [43], and HgBa2Ca2Cu3 have Tc 133K. Fig-

ure 1.9 shows the resistance of normal and superconductor above and below Tc. Where, Table:

1.2 shows critical temperature of different superconductors

Table1.2: Critical temperature of some superconductors

1.6.4. Critical magnetic field

The superconductivity not only destroyed by the increasing of temperature, above its crit-

ical value, but it also destroyed by increasing the external applied magnetic field. Transition

from superconducting to normal state occurs below the critical temperature, by application of

high magnetic field. Therefore, the maximum external field at which the superconductivity de-

stroyed is called a critical magnetic field. This was first observed by Meissner when they analyze

the behavior of superconductors at different magnetic field, they observed that the superconduc-

tivity remains only at certain values of the applied external field after which the superconductors

is a normal state. Figure.1.10. Shows critical magnetic field versus temperature at T < Tc.

19

When the superconductor placed in external fields, induces current flow in the surface of

superconductors, which produce opposite magnetic field, which cancels the applied field and the

expulsion of the field line, occurred. Nevertheless, above a critical value of applied magnetic

field, the current do not present more and as a result, the magnetic field line penetrates into the

bulk and the material become normal. The critical magnetic field depends upon the critical tem-

perate of the sample and on the symmetry of the superconductor sample [44]. The critical mag-

netic field is low for type-(I) superconductors. In case of type-(II), superconductors, there are

intermediate region so there are different critical fields having mixed region.

1.6.5. The Isotope effect

The dependence of the critical temperature of the mass of the isotope was first observed

by Maxwell indicating that for a material different isotope, has different critical temperature.

From a number of different experiments, it proved, providing an equation between the mass of

the isotope and its critical temperature i.e.

(1.5)

Where a is fitting constant.

Figure 1.9: critical magnetic field (Hc) as a function of temperature

20

1.6.6. Critical current density ( )

In superconducting state the current in the superconductors have zero resistance so the

loss of heat energy is zero its reply that superconductors can carry a huge amount of current

without loss of energy due to resistance but there is a limit above which the loss of energy oc-

curs. Superconductors sustain up to a certain amount of current above which its superconducting

state destroyed. The maximum current at which the superconductivity destroyed is called critical

current density . The critical current depends on the material, different materials have differ-

ent value of critical current. The transition of state occurs because of the collision of electrons

with lattice site and the breaking of Cooper pairs. The critical current for type-(I) superconduc-

tors has low value then type-(II) superconductors. Its because of that type-(I) superconductors

have low Tc and also consists of elements superconductors, there for the electron density is high-

er than that in type-(II).

1.6.7. Correlation of three critical values in superconductivity

As superconductivity not only destroyed upon increasing temperature, but there are two

other critical values upon which the superconductivity depend as we discuss above, now the de-

pendence of these critical values on each other also importance in superconductors.

For superconductors have superconductivity the temperature, current and applied magnet-

ic field must be below of its critical values for that superconductor. This implies that the material

must be below of all critical values, then it can have superconductivity. In superconducting state

the materials have a lower energy state, so that all electrons that formed cooper pairs has lower

energy state. While electrons that are unpair have higher energy state and they are according to

London theory called normal electrons. The superconductors below its critical temperature at

and has supercondivity but upon increasing its temperature above its critical value

having no applied field and no current transform into a normal state. Because of breaking up of

cooper pairs become favorable and the current now only fascinated by normal electrons, which

have resistance to its motion.

21

Now, at below Tc increase in current density from its critical value vanish the super-

conductivity, on similar way when the superconductors placed in strong magnetic field above of

its critical value the superconducting state vanish beside it has lower value of temperature

and current. Figure 1.11 shows the relation among temperature , magnetic field , and current

density .

1.6.8. London penetration depth

From Meissner effect, it was first believed that external magnetic field completely ex-

pelled from the interior of the superconductors. Soon after the London theory, it was proved that

external magnetic field could penetrate into a thin layer of the superconductor, which is known

as the London penetration depth denoted as .The London theory was two fluid model in

which current is flowing by two different ways super electron and normal for which London

used Maxwell equation from which they developed useful equation, which is known as London

equations [45].

By solving London equations it proved that magnetic field exponential decay from the

surface to the interior of superconductors. This decay of the magnetic field is called London pen-

etration depth.

(1.6)

Figure1 10: Relation of Jc,Hc,and Tc graphically

22

Where e represents charge, me represent mass, ns represent density, of electrons is permeabil-

ity of free space.

London penetration depth also depends on the temperature and the nature of the materials which

is given as

*

+

(1.7)

Here is penetration depth at zero T. For about 1022

cm-3

, is nearly 60nm [46]. Fig-

ure.1.12. Shows the dependence of penetration depth on temperature.

Figure 1.11: Dependence of penetration depth , on temperature of superconductor.

1.6.9. Coherence length In 1953 Pippard give the idea of coherence length for the first time [47]. The coherence length is

basically the dimension over which the order parameter varies near the boundary of

superconductor. Abrikosov defined the ratio of penetration depth, and coherence length, as Ginzburg-

Landau parameter. It is denoted by

23

(1.8)

Ginzburg-Landau parameter basically distinguishes between type-I and type-II superconductors,

superconductors having

(1.9)

are termed as type-I superconductors while type-II superconductors has value of [48].

1.6.10. Specific heat

Another property that has a nonlinear behavior is specific heat, which has a jump at the

transition point. For normal metals specific heat given as

(1.10)

Specific heat has two parts, one from the conducting electron and second is from lattice vibration

or phonons. In normal metals, specific heat is linear with temperature at low temperature where

phonon contribution is negligible.

In case of superconductors, as the phonon at low temperature have no such contribution

to specific heat, only the electron contributes to specific heat capacity. In superconductors nor-

mal electron transforms into Cooper pairs, so that the value of specific heat has nonlinear be-

havior with temperature for superconductors.

(1.11)

From a thermodynamic of superconductors, define that heat capacity changes exponentially with

the temperature. There is the development of the energy gap, proof of the existence of the super-

conducting state.

1.6.11. Energy Gap

Fermi band theory of metals define that electron in metals has a definite energy band,

metals have conduction band having higher energy. In case of superconductors, there is for-

mation of cooper pairs, which reduce energy of electron than its normal state, so there has pro-

duced a band gap between normal electron state and pairs electrons states. The width of the

electron energy gap in Fermi surface is 2. This was developed from the BCS theory that the

electron in normal state has a higher energy state than electrons in a super state [49].

(1.12)

24

Here reperesent Fermi velocity, from equation its show that band gap depends on temperature

of the system. At 0K all electrons are transform to pairs form in superconductors while above 0K

there are two definite electrons normal and paired, above Tc the Cooper pairs are completely

broken.

(1.11)

Represent Boltzmanns constant.

1.6.12. Vortex formation

For type-(I) superconductor, there is one critical magnetic field, the value at which transi-

tion, from the super to the normal state occurs. In case of type-(II) superconductors, there is not

one critical magnetic field where the transition from normal to super state occur, but there are

more than one valued critical magnetic field at which super state transition occurs.

At first critical field the superconductor transforms to intermediate phase in which the

sample having both state normal and super state. In this region, there is formation of vortices

which has a dimension of cooper pair length i.e. coherence length. The Vortices has radius equal

to that of coherence length, and having a normal core inside while outside of vortices is super-

conducting state.

Due to this normal core vortex external magnetic field can penetrate through this core and

the superconductor has changed its purfying properties of perfect diamagnetic nature.

By increasing external magnetic field, density of these vortices increased which mean normal

region in the sample increase and the material become normal at a point called a third critical

field. Above which there is no superconductivity remain and all of the materials become trans-

ferred into a normal state.

1.6.13. Magnetic Flux quantum

Superconductor has another interesting property of magnetic flux quantization. The ap-

plied external magnetic field through a coil of superconductors has properties of quantization

that there is a discrete number of flux cross through that of the coil which is called flux quantiza-

tion. In 1961, B. S. Deaver and W. M. Fairbank discovered experimentally the phenomenon of

flux quantization [50]. It was predicted first theoretically by London theory 1948. Single magnet-

ic quanta has a value that pass through a loop of a superconductor is

25

(1.12)

1.6.14. Josephson Effect

In 1962, Josephson determined that current through a thin insulating barrier (the order of

a few nanometers thick) between two superconducting blocks flowing due to tunneling of pairs.

This tunneling of cooper pairs through an insulating barrier called Josephson Effect. The Joseph-

son Effect is two types, DC Josephson effect, and Ac Josephson effect.

I. DC Josephson effect

The current flow during tunneling of Cooper pairs through an insulating barrier at zero-voltage

known as the DC Josephson Effect.

II. AC Josephson effect

The flow of the oscillating current during tunneling of Cooper pairs across the insulating

barrier at a steady voltage is sustained across a tunnel barrier is known as the Ac Josephson Ef-

fect. These two phenomena was proved experimentally soon after its prediction. The oscillating

current in AC Josephson Effect has frequency calculated by Josephson has equal to

(1.13)

1.6.15. Order parameter

There are different parameters, which describe the properties of the system or its state. In

the superconducting state, the order parameter is the one of the most important parameter. This

represents the density of cooper pairs in the superconducting state. The Wave function has an

amplitude and phase the superconductors, wave function written as the order parameter has

unique properties similar to that of the wave function in quantum mechanics.

1.6.16. Proximity effect

When a superconductor is in good contact with normal metal, the cooper pairs from su-

perconductor transfer or tunnel into the thin layer of normal metal and this thin layer of normal

metal behave like a superconductor. This phenomenon, called proximity effect. Every supercon-

ductor shows this phenomena when it has a good quality connection with normal metal. During

proximity effect the order parameter from superconducting state alter, and hence inducing super-

26

conductivity in normal metal within a thin layer of the order of coherence length

[51].Induce superconductivity; depend on the contact of the two conductors, and on the tempera-

ture. Below critical temperature, density of cooper pairs is high, so the tunneling from supercon-

ductors to a normal state is also high.

1.7 Theories and development of superconductors

Scientists are developing theory on the phenomenon of superconductivity. To fully de-

scribe superconducting state many models and theory were presented at different time having

limitation in explaining the phenomena of superconductivity. In 1947, London brothers present

first phenomenological theory of superconductivity, which was successfully explained electro-

dynamics of superconductors at that time, but having a limitation of explaining other properties

of superconductors. With the passage of time, theories were produced for explaining a different

aspect of the superconductors, in the same way Ginzburg Landau presents a theoretical model in

which they for the first time introduce quantum mechanics and define a new parameter in a su-

perconducting state called order parameter. The first microscopic theory which explains the be-

havior of superconducting state at micro level was presented by three scientist Bardeen, Cooper

and Schrieffer in 1967, in which they introduce cooper pairs. In similar ways, Aslamsov and

Larkin presented his work on the thermal fluctuation in superconductors.

1.7.1. London theory

Fritz and Heinz London in 1935 present a phenomenological model of superconductivity,

which explain the macroscopic behavior of superconductors in external magnetic field. They

used the Maxwell equation to describe the electrodynamics of superconductors and considering

the super state as two fluid state in which they considered current in two class one due to normal

electron and other due to super electron, the super electron current has high density when a metal

change from a normal state to superconducting state. As in superconducting, state there is no op-

position for current so therefore they take the current in normal state as normal current and in

superconductor state, as superconducting current. The relation between magnetic

field, electric field, and current is linear and is described by London equations [52].

The London equations in terms of electric field and magnetic field are

(1.14)

27

Where is the density and is the velocity of superconducting fluid, is the mass and is

charge of the electron. is the electric field.

The magnetic fields penetrate into the superconductors in a thin, small layer called Lon-

don penetration depth as discussed above. This is of the order of ; having de-

pends on the temperature of the sample. Figure.1.17. Shows decay of magnetic field inside the

superconductor.

.

1.7.2. Ginzburg landau theory

Ginzburg Landau presented the second phenomenological theory in 1950. The GL theo-

ry used quantum mechanics into the explanation of superconductors. GL theory combined

Landau second order phase transition with a Schrdinger wave equation. They consigned a

wave function Subject on single distinct coordinate to the whole super-

conducting electrons. Electron in superconducting state has coherence behavior because of

single valued wave function behavior of all electron at single state. Categorically, the GL

theory assigns a single wave function to an electron in super state. The GL theory is only appli-

cable to a small region in the critical temperature range , because its used second

order phase transition of Landau theory. The Landau second order phase transition associated

Figure 1.12: Decay of magnetic field inside the superconducing material

28

with thermodynamic variable and singularity arises in the heat capacity. The probability of

order parameter or wave function, of superconducting electrons gives the density of cooper pairs

in the super state.

From London theory, it was proved that the magnetic field has small penetration depth in

the superconductor. This was also proved in the GL theory that defines the dependent of coher-

ence and penetration depth on temperature.

GL theory shows that the width of the wave function in type-(I) superconductors is larger than

that oh type two superconductors.

1.7.3. BCS Theory

The electron in superconductors has single state, and having lower energy from that of

normal electrons in normal state. This microscopic property of superconductors was first ex-

plained by BCS theory, developed by J.Bardeen, L. N. Cooperand J. R. Schrieffer [53] in 1957,

with the idea of attractive interaction between two electrons viva phonons. The BCS theory was

well educated in explaining superconductivity in type-(I) or elemental superconductors. Howev-

er, it fails to explain type-(II) superconductors.

1.7.3.1. Cooper pair formation

The electron that moves through the conductor, interacts with the nearby positive

charges in the lattice which results in the deformation of the lattice. Lattice deformation brings

another electron, of opposite spin and momentum, to move into the higher positive charge

density region [54] is the basic consideration of BCS theory. According to BCS theory, the atom-

ic excitations produce attractive interaction between two electrons and they form a pair. This

pairing of two electrons, correlate these electrons making a correlated system. Figure.1.18.

Shows the lattice of superconductors and formation of cooper pair.

29

Below the critical temperature, there are high numbers of these electron pairs produced

and all of them correlated with each other so they make a super condensate, which has higher

breaking energy. This suggests that in low temperature the lattice vibration has the small energy

so it cannot break these correlated electrons. In superconducting state these Cooper pairs have no

effect of lattice vibration and thus there is no resistance in motion for these Cooper pairs. The

breaking of any pair destroys the hole condensate of all pairs and the superconductivity dismiss

at that point which is above the critical temperature of superconductor. The coherence length at

which the cooper pair exists is a few angstroms.

1.8. Nano Technology and Nanoparticles

The term nanotechnology, and nano-science, is commonly used in past decades because it

is including an enormous range of disciplines and technologies. Nanotechnology is the science

that deals with the materials, studying their composition, structure and properties at the nanome-

ter scale [55]. The term nano-science discusses the applied science field, and technology, whose

basic aim is to control the matter at atomic and molecular scale and making of devices that lie

within this size range, most of 100 nanometers or smaller.

The material particles that have the order range from 1-100nm, is called nanoparticles.

They are different in shapes and dimension having zero-dimensional and shaped identical to

spheroids. Nanoparticles exhibit different properties by having size in the dimensions of nano-

Figure 1.13: shows cooper pair formation inside superconductors lattice

30

scale than normal materials. A particle at nano scale has more reactive than from bulk size be-

cause of having a greater surface per unit mass. Thus, the material in the nano-particles form will

be more reactive as compared to the mass of material made up of larger particles. The ordered

arrangement of atoms may be of ions in a nano-particle are called nano-crystallites.

1.9. Application of superconductors

Based on the properties of superconductors used in practical life, the applications of Su-

perconductors are categorized as Fellows.

1.9.1. Based on Zero resistivity

I. Power transmission line

The Energy loss in power transmission lines From power generation to home or city In-

dustries is 15% of the total power. This is bush energy loss due to resistance, so to remove or

minimize energy loss due to resistance, resistance less wire is needed for which superconduct-

ing wine is good choice, because of having no energy loss due to zero resistance.

There are various labs working, and developing superconducting wire for practical use.

One of which is Brookhaven Laboratory produces 50cm diameter of superconducting wire Ca-

pable of carrying power up to 1000MW, which is to time more than the power that the normal

conductor of same diameter can carry. Superconducting wires need special en closer that it must

be below from room temperature, because of superconductivity only take place below room

temperature. Niobium titanium wire is used in encloses of liquid helium. BSCCO in a tape form

is also a process of experiments with YBCO in thin film form. For practical application the op-

timum current density is approximately 1000 A/Cm. This is the largest value of current, incapa-

ble by copper wire.

II. Superconducting motor Recent motors and generators are efficient, but having large size for the production of

high power requirement. The superconducting coil of bismuth 2223 is used instead of conven-

tional coil; it has small size producing power up to 167HP, demonstrated in 1995 at Navel labor-

atory. Normal motors having copper wire used as a coil is large in size, it can be reduced in size

using super conducting coil instead of copper coil which make also these motors or Generators to

become more efficient.

31

1.9.2. Based on magnetic properties

II. Superconducting trains

The Meissner effect of superconductors has useful application in the modern world is

fastest train system. A train system of superconductors can be built having fewer fractions be-

tween the rail and train because of no contact due to Meissner effect. Engineering for this as-

sessment was done by oh nan and reported that superconducting trains would be faster and safer

than the conventional trains, The record speed of 32l miles/ hour was recorded in 1997 By mag-

netic aviation train made by Japanese engineers.

III. Magnetic Resonance Imagining In recent day MRI is commonly used for the diagnosis of different diseases. This tech-

nique helps doctors in the treatment of many hidden diseases. For MRI strong and uniform mag-

netic field is required. For this requirement superconducting magnet are used in modern type of

MRI.

IV. Particle Accelerators Particle accelerators require high power electromagnetic field. The LHC in CERN has

several thousand of superconducting magnets producing high magnetic field in the comparison

of normal superconductors, also has less energy requirement of about 10th timeless from normal

electromagnets, with the benefit of producing 4th time more power the that of normal magnets.

1.9.3. Based on Josephson Effect

I. SQUID Accuracy is important for any experimental measurement of any experiment. So for most

sensitive magnetic field experiment SQUID use as a magnetic field detector.

The superconducting quantum interference device (SQUID), is made up of two parallel

Josephson junctions. The SQUID device is a very sensitive magnetometer, which can detect ex-

tremely small magnetic fields. SQUID can be used to measure very small magnetic fields in be-

ings. It can be used for finding that if there is sufficient magnetism in mouse brains for the navi-

gational property to an internal compass. The SQUIDs sensitivity is linked with measuring vari-

ations in magnetic field related to one flux quantum, which can be written;

(1.15)

32

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34

Chapter 2 Literature review

2.1. Literature review on (Tl-1223) superconductors

L.Perez. Arrieta et al [1] prepared the 2 2 3 x superconductors and

studied their properties. For the preparation of these samples, they used two step process. They

used a two zone furnace by different thallium diffusion conditions at 5500C, they deposit

films of 2 2 3 x by spray pyrolysis techniques. From acetylacetonates, precursor of films

was formed and from different oxygen flow rates various 2 partial pressure were prepared to

get the pressure of thallousoxide in the range of -4 -2 0 by the

used of 2 pellets. They obtained films of phase having which is perpen-

dicular to the surface of substrate. They took the conclusion that the film has the mixture of

2 phase and phase, they got crystalline grain with longest side having super-

conductor behavior best overall for a thallous oxide pressure of -2atm. For these films

the (Tc) values were from

The Cu0.5Tl0.5Ba2Ca2Cu3-y FeyO10- specimen were produced by N.Hasan et al [2]. These

specimens were manufactured using a solid phase change of Ca(NO3)2,CuCN,Ba(NO3)2 and

Fe2O3 at 1atm for (y=0.0, 0.01, 0.03, 0.075) examples. They performed the XRD analysis, resis-

tivity, thermo gravimetric analysis, and AC susceptibility measurements, to observe the influence

of Fe doping on them. From the XRD data, they noticed changes in the cell function a and c

but the tetrahedral arrangement of particles remained the identical. The length was

shortened with the inclusion of Fe concentration in unit cell. From gravimetric analysis, they no-

ticed that on replacing Cu+2

with Fe+2

ions result the existence of oxygen in higher quantity and

produced some Fe-O defects, having influence on conductivity. Through the resistivity and sus-

ceptibility calculations they got that by putting Fe doping will damage CuO2 planes, ground ef-

fects and greater amount of oxygen will free up carrier to a great extent in turn it will lessen

down the charge density. The influences on the charge localization were studied and it was re-

sulted that F