2.1. Barium Titanate (BT) - Information and Library...

Preparation And Tunable Properties Of Modified Dielectric Ceramics

DEPARTMENT OF PG STUDIES AND RESEARCH IN MATERIALS SCIENCE, GUG. Page 25

2.1. Barium Titanate (BT):

One of the most versatile compounds in the field of ceramic science and

engineering is BaTiO3, (BT) which belongs to ABO3 family. It has typical crystal

structure and illustrates phase transition with change in temperature. Researchers are

making many attempts to study BT compound by synthesizing it by various well-known

and modified procedures to get a BT in various forms such as single crystal, thin film,

etc.

Another powerful technique is to perform substitution studies at cationic sites of

BT ceramics. Doping can be done at one site or at both the sites by iso-valent and or alio-

valent ions, individually or simultaneously. This practice is to explore the novel

applications of BT.

The extensive research work done on BT compounds are mentioned below:

Before 1940, only two types of ferroelectrics were known, Rochelle salt and

potassium dihydrogen phosphate and its isomorphs [1]. In the early 1940’s, the discovery

of BT ceramics, the first ferroelectric ceramic without hydrogen bonds, has led to the

discovery of a large number of similar type of perovskite ceramics viz. KNbO3, LiNbO3,

PT etc. [2].

Polycrystalline ceramics have advantage over single crystals, because

polycrystalline ceramics can be formed into any desired shape, the orientation of polar

axis can be chosen and synthesis process is cheaper than the single crystal growth

process. The major breakthrough in the research on ferroelectric materials came in the

early 1950’s with the widespread use of BT based ceramics in capacitor applications and

piezoelectric transducer devices [3].


DEPARTMENT OF PG STUDIES AND RESEARCH IN MATERIALS SCIENCE, GUG. 6

After 1950, many other ferroelectric ceramics including lead titanate (PT), lead

zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT) etc. (particularly lead

oxide based) have been developed, which find their use in various applications and

devices. These lead oxide based systems are the most widely used materials for

piezoelectric transducers, actuators and transformers due to their excellent piezoelectric

properties close to the morphotropic phase boundary (MPB) compositions [4].

H. Diamond et al (1961) studied the variation of ε with E in perovskite-like

ferroelectrics. It was reported that the variation of incremental ε is associated with an

induced ferroelectric state rather than being directly a property of domain processes, and

that a large variation with E must necessarily be accompanied by strong thermal

sensitivity [5].

K. M. Johnson et al (1962) reported the variation of ε with voltage in

ferroelectrics and its application to parametric devices, functional relationship between ε

and voltage for a ferroelectric in the paraelectric state was derived, and Fourier

capacitance coefficients for different applied voltage functions were computed. It was

showed that because the Tan δ of a ferroelectric in the paraelectric state is proportional to

frequency, it can be represented in the same way as a varactor [6].

K. Uchino et al (1989) shows that there is a relationship between the particle size

and the c/a ratio for ferroelectric materials. Smaller particle sizes leads to a c/a ratio close

to 1.00(c/a=1.00 implies a cubic structure) [7].

K. Uchino et al (1989) investigated the effect of the sample particle size on the

crystal structure and the Tc of BT powder in the particle size range 0.1 to 1.0μm and

reported that the transformation from tetragonal to cubic symmetry occurs at a critical



particle size of 0.12μm at room temperature, the Tc drops below room temperature at the

critical particle size [8].

A.I. Kingon et al (1996) reported that the high r perovskite for the application of

ferroelectric films is their incorporation into DRAMs as the storage node capacitor

dielectric. DRAMs represent a large market that is experiencing strong growth, but they

were particularly significant as the technology leader for semiconductor devices [9].

H.Takasu (2000) discussed the ferroelectric memory was not only an ideal

memory with clear advantages such as non-volatility, low power consumption, high

endurance and high speed writing, but is also the most suitable device for memory

embedded applications. The ferroelectric memory based reconfigurable devices can be

used as Dynamic Programmable Gate Array (DPGA), which were able to be reconfigured

from their original logic in a system under an operation mode [10].

S.B.Park et al.(2000) prepared of Pb(Yb1/2Ta1/2)O3-PT by the solid solution, the

crystal structure and the dielectric properties were investigated in terms of the PT

concentration. As the PT concentration increases, the crystal structure changes from

monoclinic to pseudocubic to tetragonal [11].

E. Tuncer et al (2002) reviewed the current state of understand of dielectric

mixture properties, and approaches to use numerical calculations for their modeling are

presented. It is shown that interfacial polarization can yield different non-Debye

dielectric responses depending on the properties of the constituents, their concentrations

and geometrical arrangements and discussed the future challenges on dielectric mixtures

[12].



Christos D. et al (2002) reviewed the Organic thin-film transistors (OTFTs)

conduction mechanisms and performance characteristics, as well as opportunities for

modeling properties of OTFTs. The shifted focus in research from novel chemical

structures to fabrication technologies that optimize morphology and structural order is

underscored by chapters on vacuum-deposited and solution-processed organic

semiconducting films and discussed in the growing field of the n-type OTFTs [13].

K.F. Astafiev et al (2003) investigated the influence of addition of a low-loss

linear dielectric material to a tunable ferroelectric material in terms of the electrostatic

consideration. The calculations of the Tan δ and dielectric non-linearity of ferroelectric-

dielectric composites have been performed by using three different models. On the basis

of results obtained, the figure of merit of the composite material has been evaluated. No

improvement of the figure of merit of composite material compared to the pure

ferroelectric has been observed for the considered models [14].

A. K. Tagantsev et al (2003) reviewed the properties of ferroelectric materials that

are relevant to µw tunable devices and discussed the theory of dielectric response of

tunable materials and presented the techniques for characterization of tunable

ferroelectrics and applications of these materials [15].

V.Buscaglia et al. (2004) reported the preparation and the properties of BT

ceramics and thick films .The ceramics were prepared by spark plasma sintering at 800˚C

of nanopowders produced by a wet chemical process, while films were fabricated by air

flow deposition of mixed fine and coarse powders at room temperature followed by

isothermal firing. The transition from ferroelectric to paraelectric state was broadened



over a wide range of temperature with Curie–Weiss parameters strongly depressed in

comparison to grained ceramics [16].

M. Cernea (2005) synthesized the BT powder of particle size range 80nm,

calcined at 950°C, X-ray analyses indicates that the material exhibits a tetragonal, poorly

crystallized. The powder pressed and sintered at 1275°C show high , i.e. 1300 at 25°C

and, 3020 at the Tc (104°C). The melting point for BT prepared by sol-gel technique is

1290°C [17].

C.Pithan et al. (2005) studied the progress in the synthesis of nanocrystalline BT

powders for using highly volume efficient MLCC from the synthesis approach of both

liquid and solid precursors that is oxalate or citrate route. The technically and industrially

most relevant technique for the synthesis of nano sized BT powders, for practical

application was also highlighted [18].

A Sreenivasalu et al (2007) reported that the optimization of the sintering

temperatures of dielectric material such as BT and LiNbO3 in the form of pellet ceramics.

The optimized temperature for BT is 9500C and in LiNbO3 it is 900

0C based on the

temperature optimization studied carried out in the temperature range 800-10000C. The

crystallanity nature has symmetrically been analyzed through the XRD and FTIR spectral

measurements. Crystallization nature of the materials has been found to be tetragonal

based on the XRD. Such tetragonal crystalline natured dielectric materials are of

technological importance and significant relevance in the progress of wide variety of

opto-electronic materials [19].

F.F.Hammad et al.(2008) studied the XRD study on structural characteristics of

pure and doped perovskite BT. They reported that transformation from tetragonal to



cubic system and values of tetragonality (c/a = 1.0084-1.0095) are in agreement with that

of the pure BT of perovskite structure. Gd is not recommended as additive to get single

phase BT [20].

W.Li et al. (2009) studied the structure and electrical properties of BT prepared

by sol-gel process. The results indicated that both the grain size and the relative density

of the ceramics increased with the increase in sintered temperature. The at the room

temperature was not sensitive to the grain size [21].

E.E.Oren et al.(1999) reported the preparation of mono size and crystalline BT

by using hydrothermal synthesis. This process commonly uses the starting materials of

water-soluble inorganic Ba(OH)2·8H2O salt and insoluble TiO2 powders, to be mixed an

aqueous solution kept at room temperature near its boiling point for prolonged times.

Hydrothermal synthesis involves the formation of crystalline materials from the starting

materials in such aqueous media, under strongly alkaline conditions. Hydrothermal

processing of BT powders has always required the use of a certain quantity of excess

barium hydroxide in the starting mixture to speed up the hydrothermal reactions. Showed

that successful preparation of BT by hydrothermal processing required a pH>12 in

aqueous solution kept near the boiling point. They also underlined the importance of

eliminating CO2 from the reaction vessel to avoid the formation of BaCO3 [22].

C.Pithan et al. (2006) reported comprehensive review of preparation, processing

and characterization of BT powders and ceramics derived from micro-emulsion mediated

synthesis [23].

Y.Mao et al. (2010) prepared BT nanoparticles with various particle sizes by a

solvothermal method. SEM reveals that all the particles of BT with different size are



dispersed homogeneously and have uniform size. The effects of the reaction parameters,

such as the concentration of reactant, the polarity of solvent, the reaction temperature

and the amount of surfactant, on the size, morphology and uniformity of BT

nanoparticles are studied [24].

2.2. Modification of ABO3:

Viswanath et al (1997) studied the nature of the ferro-paraelectric transition

(FPT) of BT depends on its crystallite size. The ε values were determined from the

complex-impedance plot in the frequency range between 100Hz and 107Hz at various

temperatures and reported that the ε values obtained at the transition region (around

120°C) are very low and the spectra obtained are quite broad. Ferroelectricity vanishes on

doping BT with different valence state elements (Sn, Zr, Bi, Sb, Fe, Zn, Cu and Pb) in

92:8 mol. ratios [25].

P.K.Panda (2009) reviewed on the developments in environment friendly

piezoelectric materials was done by Symptoms and signs of lead Lead (Pb) poisoning

properties of some selected Pb-free compositions, for example, BT, Bi0.5Na0.5TiO3,

(Na0.5Bi0.5)0.92 Ba0.08TiO3, (Na0.5Bi0.5)0.92 Ba0.08TiO3+xNb2O5 etc. Effects of dopants on

their various properties along with phase relation between the individual components

involved in the formation of solid state solution of perovskite structure materials [26].

Ching-Fang Tseng et al (2009) discussed a new ultra low Tan δ μw dielectric

ceramic, Mg(Sn0.05Ti0.95)O3(MSnT). The compounds were prepared by the conventional

solid-state route, and sintered at 1360°–1480°C for 2–6h. The investigations show that

the MgTi2O5 secondary phase was observed. Moreover, dielectric properties were



correlated with the formation of second phase. The excellent μw dielectric properties

were obtained from the new MSnT ceramics sintered at 1390°C for 4h [27].

Takashi Teranishi et al (2010) analysed the polarization behavior in relaxation of

BT-based ferroelectrics using wideband dielectric spectroscopy in dielectric spectra from

the kilohertz to terahertz range. Ceramics of BT, BST, and BZT were selected as normal

ferroelectrics, DPT ferroelectrics, and relaxor ferroelectrics, respectively. The variation

of ionic polarization in both BT and BST ceramics with temperature are explained by the

softening of the soft phonon mode. In BZT, found ε anomaly at the ε maximum

temperature (Tm) at low frequencies is not attributed to the softening of the soft phonon

mode, but originates from the ε derived from the dipole polarization. Relaxor behavior in

BZT is derived from the increase in the depression of ε dipole on cooling across the Tm

with increasing frequency. In dipole polarization, BT, BST, and BZT all exhibited a

similar tendency of ε dipole above the Tc and Tm. However, behavior of ε dipole below

the Tc can be explained by the ferroelectric domains in BT, whereas the variation of ε

dipole below the Tm could be explained by growth process of polar nano-regions [28].

2.3. A-site modification of ABO3:

I.M.Reaney et al. (1994) studied the dielectric and structural characteristics of Ba-

and Sr-based complex perovskite as a function of temperature. Tolerance factor

influences the structure and the value coefficient of the ε studied [30].

A.I. Kingon et al. (1996) investigated the temperature dependent dielectric

behavior of BST [29].

L.C.Sengupta et al. (1999) reported that the BST combined with other non-

electrically active oxide ceramics was useful for low Tan δ, tunable dielectric materials



which are important for phased array antenna and other device applications. The ε , Tan δ

of these composites have been reduced to enhance the overall impedance matching and

thereby lowering the overall insertion loss of the device and discussed the material

fabrication methods and the electronic properties of these composites [30].

P.H.Chen et al. (2000) estimated the microstructural characteristics and non-

equilibrium core-shell phase in (PbxSr1-x) TiO3 materials and their electrical properties

shows that the specimens prepared by μw sintering exhibited a single Tc, whereas those

prepared by conventional sintering show a double Tc behavior [31].

S. Ezhilavan et al. (2000) reviewed the developments, deposition techniques,

post-annealing, physical, electrical, dielectric characteristics and the effects of electrode

materials, dielectric relaxation and defect analysis and the reliability phenomena

associated with the BST thin films for future Giga bit era DRAM applications [32].

R.Wang et al. (2001) studied the dielectric properties of BST solid solution. The

ε, pyroelectric measurements have confirmed the quantum paraelectric to the quantum

ferroelectric phase transition in solid solution with [33].

B.D.Stojanovie et al. (2001) have studied the structural and electrical

characteristics of semiconducting BPT ceramics. In this they investigated that the

addition of 5 mol% of Al2O3, SiO2 and TiO2 as additives to the Sb2O3 MnSO4 and ZnO

doped BPT system controlled the abnormal grain growth of this system [34].

D.Shiwen et al. (2001) hypothesized theoretically that the Tc of BT may be

lowered and broadened when either the large Ba2+

ions are partially replaced by small-

sized Sr2+

or Zn2+

, or the active Ti4+

ions are partially replaced by non-active Zr4+

or

Sn4+

[35].



K.Park et al. (2002) studied the microstructure and electrical properties of porous

BST ceramics, they reported that the crystalline structure of the porous BST ceramics

strongly depended on the oxygen content and these ceramics can be used for humidity

and gas sensors [36].

P.Pookmanee et al. (2004), studied the effect of sintering temperature on

microstructure of hydrothermally prepared bismuth sodium titanate ceramics,they

reported that the hydrothermal route has an advantage over other synthesis processing’s,

that BNT powders can be obtained without additional heat treatment. The grain size and

surface densification of BNT ceramics becomes higher and denser with increasing

sintering temperature [37].

H.Miao et al. (2006) reported hydrothermal synthesis, to be considered as one of

the best methods used to prepare mono-disperse nanometer BT powders, which presents

the major advantages: narrow particle size distribution, low concentration, high purity

and fine crystallization of powders, little pollution during the preparation process, short

preparation time and low cost. Fine Dy and Mg-doped BT powders were prepared by

hydrothermal method at 240˚C with BaCl2·2H2O, TiCl4 and NaOH as the main reactants,

Dy2O3 and MgCl2·6H2O as additives respectively. It is confirmed that Dy or Mg enters

into the BT lattice. Ba site is replaced if a little Dy2O3 is doped but some more Dy will

take up the positions of Ti. Mg always substitutes for Ti site. Dy and Mg are both useful

to obtain the microstructure with small grains and high density, and the former results in

a better microstructure [38].

A.Jamil, et al (2007) reported that the ferroelectric capacitors made from BST are

applied as varactors in tunable, high-frequency circuit applications. In that context, a

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voltage-controlled oscillator (VCO) had been designed and implemented using discrete

RF bipolar junction transistor (BJTs) and tunable ferroelectric capacitor [39].

2.4. B-site modification of ABO3:

D.Hennings et al (1982) reported that the very high and broad Curie maxima are

observed in ceramic BZT mixed crystals, which are often used for the preparation of

ceramic dielectrics and studied the ferroelectric-to-paraelectric phase transition of

ceramic BZT using dielectric measurements, XRD, and determination of the Pr. At higher

Zr concentrations, it was found that ferroelectric and paraelectric phases coexist in a wide

temperature region [40].

Z.Yu et al (2000) reported that the successful growth of BZT single-crystal fibers

by the laser-heated pedestal growth technique, a single-phase perovskite structure of the

materials had been identified by the XRD technique. Dielectric properties as function of

temperature and frequency and room-temperature hysteresis loops were measured. Pr and

Ec are obtained and compared for both single crystals and ceramics and observed the

small dielectric relaxation behavior [41].

R.Maier et al. (2001) studied the structural and physical properties of pseudo

cubic thin film BaTi1-xFexO3 grown by pulsed laser deposition. They suggest a substantial

increase of the ferroelectric transition temperature relative to that of bulk BT is to lattice

expansion induced by Fe doping [42].

A. Dixit et al (2002) studied XRD confirmed the structural phases in the powder

and films of BZT and various structural transitions of BT, as a function of different Zr

content, and compared well with the published result on ceramics and single crystalline

BZT. The deposited films were smooth, crack-free and have homogeneous



microstructure, and Zr content strongly influences the evolution of the microstructures of

the films. Some selected compositions of these films are characterized in terms of their

dielectric properties and phase transition behavior. BZT films with 20% of Zr have

shown a ferroelectric to paraelectric transition in the vicinity of room temperature [43].

Zhi Yu et al (2002) studied the Ferroelectric-relaxor behavior of BZT ceramics in

the temperature range from 150 to 450K and observed broad dielectric peak with a high-

dielectric maximum exhibits frequency dispersion. The polarization hysteresis loops were

observed with a Pr of 10μC/cm2 at 175K. The high- ε and high-polarization properties are

expected to find practical applications at low temperatures [44].

S.Wang et al. (2005) studied the effect of sintering atmosphere on the

microstructure and dielectric properties was endorsed to the change of solubility of the

acceptor ions in this core-shell-structured materials. The core-shell- structure is

considered to be a state of the inhomogeneous grains, in which the unreacted grain core is

pure BT, whereas the shell consists of reacted BT severely doped additives [45].

M.Tanmoy et al (2006) reported that the E-field tunable behavior of the

environmental friendly lead-free perovskite BZT relaxor ceramics in the temperature

range from 300 to 30 K and studied the E dependence of dielectric behavior of the

ceramics, It was shown that manipulating the Zr:Ti concentration in BZT ceramics and

optimizing the applied dc bias field the properties for specific applications in tunable

filters, phase shifters, antennas, etc., can be tailored in the temperature range from

100 to 300 K [46].

B.Li et al. (2007) investigated the microstructure and dielectric properties of Y/Zn

co-doped BT ceramics sintered in reducing atmosphere. They concluded that proper



amount of Y2O3 and ZnO can notably progress the dielectric temperature characteristics

due to the formation of grain core-shell a structure [47].

Tanmoy Maiti et al (2011) reported that the mechanism and nature of relaxor

ferroelectric behavior in the environmental friendly lead free BZT system. A revised

complete phase diagram of BZT, with different compositions has been developed based

on their electrical properties. Two different kinds of relaxor behaviors have been

observed in the BZT system; one is dominated by polar Ti-rich regions and another by

non-polar Zr-rich regions. All the BZT relaxor compositions are characterized by

dielectric properties with and without bias, pyroelectric and thermal expansion

measurements in the wide range of temperatures. The structure of the BZT compositions

has been evaluated by XRD, Neutron diffraction study. Further the local structure of the

BZT compositions has been probed by micro-Raman spectra. Although the global

structure of BZT relaxors is cubic as observed in Neutron diffraction studies, the local

symmetry is non-cubic as evident in the micro-Raman spectra of BZT relaxors as well as

in their thermal strain measurement, dielectric and pyroelectric behavior [48].

2.5. A-site and B-site modification ofABO3:

L.C.Sengupta et al (1995) reported that BST doped with MgO, has low ε,

extremely low Tan δ and high η such novel materials possess superior electronic

properties; and they may be employed in various antenna systems at both μw and

millimeter wave range frequencies [49].

P.Hansen et al (1998) studied the dielectric properties of (Ba,Ca)(Ti,Zr)O3

ceramics containing various acceptor and donor dopants on the B sites and observed that



all acceptors cause a reduction of the Curie point and the maximum ε increases with the

average grain size almost independent of the acceptor incorporated [50].

M.W.Cole et al (2000) investigated the structural, microstructural, interfacial, and

surface morphological properties of BST doped with Mg, determined dielectric and

insulating characteristics. Single phase solid solution films were achieved at Mg doping

levels up to 5 mol%, while multiphased films were obtained for 20 mol%. Decreases in

the ε, Tan δ, η and leakage current characteristics were paralleled by a reduction in grain

size with increasing Mg dopant concentration and suggest that Mg doping serves to limit

grain growth and responsible for lowering the ε, Mg behaves as an acceptor-type dopant

at the grain boundary and is responsible for the low Tan δ and good leakage current

characteristics, reported the performance-property trade-offs advocates the 5-mol% Mg

doped BST film to be an excellent choice for tunable μw device applications [51].

Y.Tsur et al. (2001) investigated the rare earth cation substitutions into BT.

Analysis based upon crystal chemistry, defect chemistry and meta stable states is resented

to aid interpretation of experimental data. The detailed and highly precise XRD and

Electron Paramagnetic resonance experiments performed on samples produced with

different A/B ratios and fired under different oxygen partial pressure conditions give rise

to new insights into the material. Specifically, the site occupancy and the valence states

for the rare-earth dopants in BT are considered [52].

M.W.Cole et al (2002) analyzed by glancing angle XRD, SEM, AFM, and Auger

electron spectroscopy studies and measured the dielectric properties of un patterned films

at 10GHz using a coupled, tuned split dielectric resonator system, and at 100kHz using

metal–insulator–metal capacitors on the influence of low concentration of Mg doping on



the structural, microstructural, surface morphological, and dielectric properties of BST

thin films and shows The Mg-doped BST films exhibited improved dielectric and

insulating properties compared to the undoped BST thin films. The improved dielectric

properties, low leakage current, and good dielectric η of the low level Mg-doped BST

thin films merits strong potential for utilization in tunable μw devices [53].

K.Imai et al (2002) observed that Fe doping of BST films to be remarkably

effective for suppressing the decrease in and investigated the site where the doped Fe

ions are substituted in the crystal by means of electron standing wave method using

SrTiO3 single crystal, reported that most of the Fe ions are substituted at B sites (Ti sites),

which suggests that Fe ions as acceptors compensate donor electrons and reduce band

bending [54].

L.Radhapiyari et al (2003) studied the structural and the microstructural

properties of BST system substituted with iron by varying the amount of Ba and Sr and

investigated the dielectric properties of the system Ba1−xSrxFe0.01Ti0.99O3 as a function of

temperature, frequency and dc bias. The η of the system shows up to 42% for a particular

composition with Ba/Sr ratio of 70:30 [55].

X.F.Liang et al (2003) investigated the effect of doping Al2O3 on the BST

ceramics. A strong correlation was observed between the average grain size and Al2O3

content,shows the Tan δ and tunable properties of modified BST. The minimum of the

Tan δ was achieved at Al2O3 doping level up to 0.8 wt.% and obtained the maximum η of

30.1% at the doping level of 0.4 wt.% Al2O3 [56].

X. F. Liang et al (2004) investigated the effects of different concentrations of

Mn2+

, Mg2+

, Al3+

, Fe3+

, La3+

, and Nb5+

on the dielectric and tunable properties of BST



ceramics. It was observed that doping in small amounts with acceptor ions such as Mg2+

,

Fe3+

, and Al3+

could meliorate the dielectric properties clearly, Decrease of Tan δ was

attributed to the formation of compensating defects originating from acceptor substitution

and reported that the η was linked to both the ε and the grain size [57].

L.C.Sengupta et al (2004) reported that the electronically tunable materials

include an electronically tunable dielectric phase such as BST in combination with at

least two additional metal oxide phases. The additional metal oxide phases may include,

for example, oxides of Mg, Si, Ca, Zr, Ti and all such tunable materials are used in

devices such as phased array antennas, tunable filters also useful in many applications,

including the area of RF engineering and design [58].

K.T.Kim et al (2005) studied the effect of Cr doped BST prepared from alkoxide-

based sol–gel method on the Pt/Ti/SiO2/Si substrate. AFM and XRD analyzed and

showed that increasing the Cr-doping ratio causes increased grain size while the surface

remains smooth and crack-free. It was also reported that BST improves the and the

leakage-current characteristics, the figure of merit reached the maximum value of 72.3 at

the 5 mol% of Cr doping. Cr-doped BST thin films are prospective candidates for

applications in tunable devices [59].

Y.Chen et al (2005) investigated that the dielectric properties of BSTO/Mg2SiO4/

MgO composite ceramics. It was suggested that the dielectric properties were influenced

to a great extent by the microstructure, and the η [60].

Q-Y Shao et al (2006) investigated that the Tc of Pb1−xSrxZr0.52Ti0.48O3 [(PSZT)

x=0.2–0.8] decreases with the increase of Sr contents and paraelectric PSZT films at



room temperature are demonstrated and the increase of Sr contents also leads to the

simultaneous decrease of ε, η and Tan δ [61].

R.X.Li et al (2006) investigated the dielectric response and tunable properties of

Cr-doped BST solid solution, observed that all of the doped specimens are cubic

perovskite phase, grain size increases with the increase of Cr content below 0.6 mol%,

The dielectric frequency spectra of the doped BST solid solution showed that an

additional relaxation of the doped specimens is observed at frequencies above 10 MHz

and shows that η and Tan δ were improved by doping with Cr concentration lower than

1.0 mol% compared with un doped material. The 0.6 mol% Cr-doped specimen reveals a

maximum η and figure of merit of 23.3% and 518.3, respectively. Extremely low Tan δ

in order of 5 × 10−4

is found for 0.4–0.6 mol% Cr-doped BST solid solution. The

dramatically low Tan δ of the specimen is explained by the reducing of Cr3+

to Cr2+

and

the acceptor action of Cr3+

and Cr2+

which neutralized the donor action of oxygen

vacancies [62].

X.J.Chou et al (2007) prepared BST-Mg2TiO4 composite ceramics via the

conventional solid-state reaction method. The microstructures, η, and μw properties of

composite ceramics were investigated. The ε is tailored from 335 to 35 by manipulating

the addition of Mg2TiO4 from 50% to 80% weight ratio and the η was 10.8% measured at

10 kHz for the 80% Mg2TiO4 addition. The composite ceramics with high Q value (>200)

are useful for potential tunable μw device applications in the wireless communication

system [63].

U.C.Chung et al (2008) reported that Spark plasma sintering (SPS) was an

efficient tool to obtain highly densified ferroelectric-dielectric ceramic composites with



clean interfaces and tunable properties. Dielectric MgO and ferroelectric BST were

combined in two-dimensional multilayer and three-dimensional random powders design.

Such SPS ceramics can be used as experimental input for simulation and were potential

candidates for high frequency applications [64].

2.6. Rare earth material modified ABO3:

A.Yamaji et al. (1977) studied preparation, characterization and properties of Dy-

doped BT ceramics. The effect of grain size on dielectric constant, lattice parameters and

linear thermal expansion coefficient are more pronounced than the chemical effects of Dy

doping in the ferroelectric state [65].

W.H.Su et al. (1986) synthesized and investigated double rare earth oxides of

ABO3 composition. Their analysis focused on the crystal structure of the compound

which was synthesized by using high pressure and high temperature methods [66].

A.S.Shaiks (1986) studied the structure and dielectric properties of BT doped with

Nd2O3 . Their results illustrated that Nd occupies the Ba2+

site and charge compensation

takes place by creation of Ti4+

vacancies. The addition of Nd2O3 leads to very drastic

shift in the Tc of BT [67].

E.Iguchi et al. (1991) synthesized La2O3, Gd2O3 doped BT, and studied their

dielectric and conductivy properties. They concluded theoretically, that the dominant

conduction in n-type BT is due to hopping motion of non-adiabatic polarons [68].

C.Eylem et al. (1992) reported the synthesis and properties of RxBa1-xTiO3 series

where R = La, Gd, Nd, Er and Y. These compounds display rare earth dependent metal to

semiconductor transition that co relate with the perovskite tolerance factor. Atomic

absorption and TGA of these samples were also studied [69].



M.Kuwabara et al. (1997) observed that with an increase in sintering temperature,

the rate of increase of Tc in La-doped BT ceramics increases. A phase transition

phenomenon was interpreted based on concentration change of lanthanum in the lattice

defects present in the material with sintering temperature. A distinct increase in the room

temperature bulk resistivity with an increase in sintering temperature was also observed

[70].

F.D.Morison et al. (1998) reported a novel doping mechanism comprising A-site

doping with creation of Ti vacancies for very high ε BT ceramics. A typical value of ε

10,000 at 130°C in undoped BT was reported with Tc 226

°C [71].

F.D.Morison et al. (1999) investigated ε of La3+

doped BT ceramics. They

obtained ε at the phase transition of 130°C for x = 0 and – 9

°C for x = 0.06 sampled fired

in O2 atmosphere were insulating and showed no signs of donor doping, whereas air fired

samples were semiconducting attributed to oxygen loss [72].

S.Urek et al. (2000) studied the electrical properties of La3+

doped BT samples

with donor concentration in the range from 0.3 to 12.5 mol% of La, results showed that

with the use of specific sintering profile PTCR ceramics containing an amount of donor

dopants >0.3 mol%, can be prepared [73].

D.Li et al. (2000) have prepared Ba1-xLnxTi1-xMxO3 (Ln=La, Sm, Gd, Dy. M=Al,

Fe, Cr) the tunable ferroelectric compositions ceramics and shown that, the simultaneous

doping of acceptor and donor ions in their polycrystalline BT can shift the Tc to a lower

temperature and increase the η [74].



T.Nagai et al. (2000) discussed the effect of MgO doping in the phase

transformation in BT. A change in Raman spectra with temperature showed that

orthorhombic to rhombohedral phase exist at high temperature [75].

F.D.Morrison et al. (2001) investigated the mechanism of doping BT with La by a

combination of XRD, electron probe microanalysis, scanning and transmission electron

microscopy and impedance measurements. Phase diagram results confirm that the

principal doping mechanism involves ionic compensation through the creation of titan-

ium vacancies. The change from insulating to semiconducting behavior is reversible, by

changing the atmosphere on heating at 1350 – 1400˚C [76].

Y.Tsur et al. (2001) studied issue of rare earth (Lu3+

-La3+

) cation substitutions in

BT. They have analyzed the crystal and defect chemistry with the formation of metal

state in their structural characteristics. EPR measurement shows the site occupancy of

various dopants along with their valence states. The nature of amphoteric ions defect and

site occupancy was also reviewed and compared with the early study [77].

J.H.Wang et al. (2001) reported that an electrical property of Ce-doped BT. The

Tc lowered when Ce3+

is incorporated in Ba site where as the substitution of Ce4+

for Ti4+

sites resulted in no change in Tc. There is no significant change in conductivity behavior

when compared with pure BT, clearly indicating the substitution of tetravalent Ce at Ti-

site of Ce doped BT ceramics [78].

A.M.Slipenyuk et al. (2001) prepared BT ceramics doped by Y and Ca and has

been studied by electron spin resonance (ESR). They reported that the grain size of BT

ceramics became smaller under Ca doping though the temperature region of the effect of

PTCR remain practically unaffected [79].



M.T.Buscaglia et al. (2002) investigated Er3+

substitution in BT ceramics by

having dopant concentration in the range 0.2, 0.5 and 10% Er3+

solubility at the Ba site

does not exceed,. However the resulting properties such as electrical conductivity were

sensitive to sintering condition [80].

M.B.Park et al.(2003) demonstrated that the chemical and electrical features of

the ceramics with grain boundary can be controlled and designed based on the diffusion

coefficient as well as grain boundary potential barrier height at particular heat-treatment

conditions [81].

J.Du et al. (2004) prepared the Ni/Graphite/BT composites are fabricated by

adding Ni and Graphite powders in to BT ceramics. They reported that the room

temperature resistivity of the composites is much lower than the prototype ceramics. The

magnitude of resistivity changes to some extent. Graphite added will prevent the

oxidation of Ni, but a lot of pores will be produced in the bulk with overdose of graphite

so that the resistivity of the composites increases subsequently [82].

Z.C.Li, et al. (2005) prepared Sm2O3 doped BT ceramics with a PTCR by solid

state reaction sintering. The grain size decreased with increasing dopant content

secondary phase and lattice parameters a = 10.6Å and c = 20.2Å formed in the ceramics.

The room temperature resistivity decreases with the increase of dopant content in the low

doping level and reaches the minimum value at a certain dopant content (about 0.2

mol%), then increases with the increasing of dopant content [83].

S.Qizhen et al. (2005) reported that the conventional doping method of solid

doping is associated with many disadvantages including the high impurity, poor powder

characteristics and compositional inhomogeneity. Thus, some authors have began to



prepare BT doped with additives using sol-gel processing by one step, which has many

advantages such as high purity and good distribution. But until now, few papers report

the influence of Ti/Ba ratio on the microstructure and dielectric property of rare earth

doped BT the Ti/Ba ratio of the samples significantly influences the ceramics'

microstructures. The Nd-doped BT nano crystalline powders and ceramics with different

Ti/Ba ratios were prepared by sol-gel method. Phases and microstructures of the Nd-

doped BT based powders and ceramics were characterized by XRD, SEM and TEM

methods. The results revealed that the powders synthesized by sol-gel method were

nanometer scale (30-60nm) and were mainly composed of cubic BT with a small amount

of BaCO3. After sintering at high temperature, both cubic BT, and BaCO3 were

transformed into tetrahedron BT phase [84].

S.Sen et al. (2005) polycrystalline sample of (Ba1-xCax) (Sn0.15Ti0.85) O3 (x = 0,

0.03, 0.06 and 0.09) of perovskite structure family have been prepared by a high

temperature solid state reaction technique. Dielectric studies shows the compound

undergo diffuse phase transition. DC and AC conductivities have been investigated over

a wide range of temperature and the activation energy was also calculated [85].

Z.Yumin et al. (2006) investigated the effect of Ce3+

and Eu3+

doping on the

structure, the microstructure and dielectric properties of BT ceramics. Ce-doped BT

exhibit pseudo-cubic perovskite structure while Eu doped BT ceramics exhibit tetragonal

perovskite structure [86].

Da-Young Lu et al. (2006) explained the role of Co-doping with La and Ce for

the first time in BT ceramics. Co-doping with lanthanum and Ce causes a strong

broadening of ferroelectric phase transition and resist the Curie peak, with rapid shift



these materials are promising candidate for future Y5V monolithic or even X7R MLCC

[87].

R.K.Dwivedi et al. (2007) have investigated the ferroelectric transition in valance

compensated Ba1-xLaxTi1-xCrxO3 ceramics. They reported that dielectric anomaly

corresponding to the ferroelectric to paraelectric transition has been found to shift the

lower temperature with the increase in concentration of La and Cr [88].

P.Yongping et al. (2007) showed the influence of rare-earths on electrical

resistivity and microstructure of BT ceramics doped with rare-earth ions Y, Dy, Ho, Er

and Y. Their result showed that a dramatic decrease in the resistivity occurred at the

concentration of 0.3% of La doped sample. However the range of concentration for

semiconducting samples doped with Dy, Ho, Er and Y was wider especially for Y-doping

[89].

E.Aizinger et al. (2007) studied the solubility of Pr in BT.The two series of

samples were investigated. First one was Ba-rich series and the second one had Ba/Ti

ratio equals 1. In Ba-rich series, it was found that the solubility limit is between 4 mol%

and 10 mol% Pr. In the second series the solubility limit was between 15 mol% and 20

mol% Pr [90].

L.Lingxia et al. (2007) studied the doping effect of Gd2O3 on BT based meta-

dielectric composite ceramics system was studied, that the doping effect of Gd2O3 could

restrain the growth of grain which could make the dimension of grain and small and

density high it could be broadened the Curie peak of the ceramics and increases at room

temperature. The replacement of B-sites by Gd3+

could lead some non ferroelectric areas

[91].



J.Zhang et al. (2008) prepared the BST with 0.5 mol% of various trivalent rare-

earth elements ceramics. Their structural and dielectric properties are studied. The XRD

pattern displays the addition of rare-earth changes the structure from cubic to tetragonal

and improve the tetragonality distortion of BST and rare earth element is found to be an

important factor in controlling the temperature dependency of the dielectric properties.

Due to their low ε, low Tan δ and moderate η, the Sm, Eu, Gd-doped samples are very

attractive for the tunable μw devices [92].

Z.Yao et al. (2008) investigated the structure and dielectric behavior of Ba1-

xNdxTiO3 perovskite fabricated by solid state mixed method. By increasing Nd doping

phase transition behavior appeared from tetragonal to cubic structure. Nd3+

addition

shifted the temperature of the ε maximum and decreases the grain size [93].

Y. B. Xu et al (2008) prepared BST-Sr(Ga0.5Ta0.5)O3 solid solutions by solid-state

reaction method, and investigated their dielectric and tunable characteristics. It was

observed that the addition of Sr(Ga0.5Ta0.5)O3 into BST causes a shift in the phase

transition peak to a lower temperature, depressed and broadened phase transition peaks,

resulted in decreased ε and Tan δ at room temperature. With the increase of Sr

(Ga0.5Ta0.5) O3 content, the ε, Tan δ, and η are decreased [94].

Y.Li et al. (2009) has prepared Sm doped BST ceramics, and investigated the

dielectric properties. They found that the substitution of Sm3+

for the host cations

perovskite lattice. Owing to the replacement of Sm3+

ions for A-site, Tc rises with the

increase of Sm2O3 doping when the doping content is below 0.1 mol%, meanwhile when

the content is more than 0.1 mol%, Sm3+

ions tend to occupy the B-site, causing a drop of

Tc. Owing to the modification of Sm3+

doping, more over the creation of oxygen



vacancies controls the ε when the addition is above 0.1 mol%, so the ε decreases with

increase of Sm3+

[95].

S.B.Reddy et al.(2009) studied the effect of La substitution on the structure and

dielectric properties of BZT ceramics. The ε maximum was observed at 2 mol% La

substitutions and with further increase in La content the phase transition was found to be

broad [96].

P.Pasierb et al. (2011) reported the barium create exhibits high protonic

conductivity, especially when doped by suitable trivalent ions. A possible approach to get

the protonic conductor stable in the presence of CO2 with relatively high protonic is the

preparation of solid solutions BaCe1-xMexO3-δ (Me = Zr, Ti) doped simultaneously with

acceptor ion [97].

P.Kumar et al. (2011) were synthesized Ba0.80-xCaxPb0.20Ti0.90Zr0.10O3 ceramics by

solid state reaction. Samples microstructure and dielectric, ferroelectric piezoelectric

properties studied. They reported that Tan δ was found to improve with increase in x

where piezoelectric charge coefficient d33 was found to decrease with increase in x [98].

Thus, with this review of literature, we have focused our attention on the

following aims and objectives:

Aims and objectives of the work:

The main aim of this work is to prepare modified dielectric ceramics and study

their tunable properties.

Following are the major objectives planned for this work:

1. Synthesis of BSZT in the form of (Ba0.6Sr0.4)(Zr1-xTix)O3 (x=0.40, 0.50 and 0.65) and

Modified BSZT with the stoichiometric (Ba0.6Sr0.4)(Zr0.6Ti0.4)O3-Nb2O5-Fe2O3-RE



(where, RE=La2O3, Gd2O3 ,Nd2O3, Sm2O3, HO2O3. Pr2O3, Er2O3).

2. Study of structural, micro-structural and surface morphology of synthesized

compounds.

3. Study of temperature and frequency dependent electrical and dielectric behavior in

order to understand their DPT, ferroelectric and tunable properties.



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2.1. Barium Titanate (BT) - Information and Library...

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