Characterization of BaIn0.25Zr0.75O2fy.chalmers.se/gsms/Projects2003/HelenoMaths.pdf · 2004. 11....

Characterization of BaIn0.25Zr0.75O2.875

Project report in the course FTF 155, Material Science; Characterization

Maths KarlssonHelén Jansson

Project in Material Science course (Characterisation part, FTF155) 04-03-03Maths KarlssonHelén Jansson--------------------------------------------------------------------------------------------------------------------------------------

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1. INTRODUCTION 2

2. THEORY 2

2.1 X-RAY POWDER DIFFRACTION 22.2. SECONDARY ION MASS SPECTROMETRY, SIMS 3

3. THEORY OF SOME EXPERIMENTAL TECHNIQUES NOT USED IN THIS PROJECT 5

3.1. AUGER ELECTRON SPECTROSCOPY. AES 53.2. X-RAY PHOTOELECTRON SPECTROSCOPY, XPS 53.3. SCANNING ELECTRON MICROSCOPY, SEM 63.4. TRANSMISSION ELECTRON MICROSCOPY, TEM 63.5. DIFFRACTION TECHNIQUES 73.6. ATOM PROBE FIELD ION MICROSCOPY, APFIM 73.7. VIBRATIONAL SPECTROSCOPY 83.8. NUCLEAR MAGNETIC RESONANCE, NMR 83.9. STM (SCANNING TUNNELLING MICROSCOPY) 83.10. AFM (ATOMIC FORCE MICROSCOPY) 9

4. EXPERIMENTAL - MATERIAL AND SAMPLE PREPARATION 9

4.1 SAMPLE PREPARATION FOR THE X-RAY DIFFRACTION 94.2 SAMPLE PREPARATION FOR THE SIMS EXPERIMENT 10

5. RESULTS 10

5.1 X-RAY DIFFRACTION 105.2 SIMS 13

6. CONCLUSIONS AND DISCUSSION 16

7. PROPOSAL FOR A SECOND PROJECT 17

8. ACKNOWLEDGEMENTS 17


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1. IntroductionIn this paper we describe the different measurements we have performed on a

polycrystalline sample of composition BaIn0.25Zr0.75O2.875. This material has a perovskitestructure, but is distorted from an ideal perovskite structure ABO3, due to the dopant In. Dueto the doping of In, with lower valence than Zr, oxygen vacancies that compensate for the net-negative charge are present. These vacancies make the sample very hygroscopic. This is whythe sample is stored in an inert atmosphere of Ar. The material is proton conducting and canbe used in a fuel cell working at intermediate temperatures, ~200-400 °C. Protonating of thismaterial is performed by treating the material in water vapour at elevated temperatures. Watermolecules then enter the sample and the water molecules oxygen occupy the oxygenvacancies, and they release the protons.

In this study we exploited the experimentally techniques, dynamic SIMS (SecondaryIon Mass Spectroscopy) and X-ray diffraction, to study the homogeneity and composition inthe sample.

2. TheoryThis chapter deals with the theory behind the experimental techniques, X-ray diffraction andSIMS, we used in our work. The theory is based on [1] and [2].2.1 X-ray powder diffraction

Regular, repeating planes of atoms that form a crystal lattice defines the three-dimensional structure of non-amorphous materials. Each material diffracts X-rays differently,depending on what atoms make up the crystal lattice and how these atoms are arranged.

Since a beam of X-rays consists of a bundle of separate waves, the waves interact withone another. Such interaction is termed interference. If all the waves in the bundle are inphase, the waves will interfere constructively. If the waves are out of phase destructiveinterference will occur. The atoms in crystals interact with X-ray waves in such a way as toproduce interference. The interaction can be thought of as if the atoms in a crystal structurereflect the waves. But, because a crystal structure consists of an orderly arrangement ofatoms, the reflections occur from what appears to be planes of atoms.

The X-rays in X-ray diffraction are generated within a sealed tube that is under vacuum.A current is applied that heats a filament within the tube; the higher the current the greater thenumber of electrons emitted from the filament. A high voltage, typically 15-60 kilovolts, isapplied within the tube. This high voltage accelerates the electrons, which then hit a target,commonly made of copper. When these electrons hit the target, X-rays are produced. Thewavelength (l) of these X-rays is characteristic of that target. In our case, the target is copperwhich give a wavelength l=1.54 Å. These X-rays are collimated and directed onto thesample, which consists of a fine powder sealed in a glass capillary. A detector , which in ourcase was a scintillation detector, detects the X-ray signal; the signal is then processed eitherby a microprocessor or electronically, converting the signal to a count rate. A measurement isperformed by changing the angle between the X-ray source, the sample, and the detector in acontrolled rate. The principle of an X-ray diffraction measurement is shown in figure 1.

When an X-ray beam hits a sample and is diffracted, we can measure the distancesbetween the planes of the atoms that constitute the sample by applying Bragg's Law, figure 2.Bragg's Law is:


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2dsinq=ml (1)

where the integer m is the order of the diffracted beam, l is the wavelength of the incident X-ray beam, d is the distance between adjacent planes of atoms (the d-spacing), and q is theangle of incidence of the X-ray beam.

Figure 1. The principle of X-ray diffraction

The characteristic set of the d-spacings generated in a typical X-ray scan provides aunique "fingerprint" of the compounds present in the sample. When properly interpreted, bycomparison with standard reference patterns and measurements, this "fingerprint" allows foridentification of the material.

Figure 2. The d-spacing between atom planes is given by Bragg's law

2.2. Secondary Ion Mass Spectrometry, SIMSSecondary Ion Mass Spectrometry, SIMS is a technique for analysis of the composition

of a material, from its surface down to a depth of several microns. The sample is bombardedby a high-energy ion source and the secondary ions sputtered from the sample are thenanalysed for their mass to charge ratios. SIMS provides measurements of trace levels of allelements of the periodic table with isotope separation. SIMS also provides a high resolutionanalysis of lateral and depth distribution of these elements in the sample.

Primaryvariable slit

Sample Secondaryvariable slit

X-ray-source

Soller slitsSoller slits

Detector


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Two different classes must be distinguished, dynamic and static SIMS. Static SIMS isused to analyse the outermost layer of the sample surface and is designed to cause as smalldamages to the surface as possible. The static SIMS is often combined with a time-of-flightanalysis of the sputtered ions. Dynamic SIMS on the other hand, is used to obtain informationof the sample composition from the surface down to a depth of several micrometers. Withdynamic SIMS, a crater is formed by the bombardment of primary ions and is hence adestructive method. For dynamic SIMS, there are a few different types of analysers for thesecondary ions. Non-imaging ion probes provide depth profiles of the concentrations in thesample. Direct-imaging ion microanalysers provide a mass separated image of the samplesurface with a lateral resolution of down to 0.5 micrometers. Another imaging analysis is thescanning ion microprobe-microscope with a lateral resolution of about 10 micron.

The primary ions are usually produced by either ionizing a gas by plasma discharge orby ionizing atoms from the surface of a solid or liquid metal field emission. The primary ionsfrom the source pass through a primary mass filter to filter out all ions but those of a givenmass to charge ratio. The ions are then accelerated by an electric field through the primary ioncolumn. Electrostatic lenses in the column determine the width and intensity of the primaryion beam and also scan the ion beam over the analyzed area of the sample.

When the primary ion beam hits the sample surface, secondary particles from thesurface are emitted. Holding the sample at a high voltage and connecting the massspectrometer to ground, accelerates the secondary ions to the spectrometer. The acceleratedions pass through two electrostatic lenses to focus the ions on the entrance slit of the massspectrometer.

The mass spectrometer consists of two parts, an electrostatic ion selector and a massanalyser, figure 3. The electrostatic ion selector filters out all ions but those that have aspecific kinetic energy. In general, molecular ions will have a lower initial kinetic energy thanmonatomic ions as they can store energy from the sputtering process as vibrational androtational energy. By choosing an offset in the electrostatic ion selector one may thereforefilter out the lower energy molecular ions from the ion beam in order to favour the mono-atomic ions.

The following mass analyser separates the ions based on their mass to charge ratio.There are two kinds of mass analysers used in dynamic SIMS, magnetic sector analysers andquadrupole mass analysers. Magnetic sector mass analysers use a static magnetic field appliedat right angle to the incident ion beam. When the ions move through the magnetic field theywill experience a force perpendicular to their movement direction and thus move along acurve. The curvature depends on the mass to charge ratio of each ion, where ions with smallerratio will have a shorter curve radius than those with higher ratios. With a small slit, only ionswith a given mass to charge ratio pass on to the detector. In the quadroupole mass analyser theion beam goes through an oscillating electric field. Only those ions with a specific mass tocharge ratio can oscillate at a given frequency and are allowed through the analyser. Byvarying the voltage of the field one can change the allowed mass to charge ratio, which isdetected by the detector.


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Figure 3. The principle of Secondary Ion Mass Spectroscopy

3. Theory of some experimental techniques not used in this projectHere follows theory of some important techniques that can be used to characterize a material.

3.1. Auger Electron Spectroscopy. AESAES is a surface sensitive technique, where the sample is bombarded with an electron

beam in Ultra High Vacuum, UHV in order to eject an inner-shell electron and thereby createa vacancy in the shell. The vacancy is then filled with an electron from an outer shell andenergy is transferred to a third electron, which is ejected from the atom to the vacuum. Thiselectron, called Auger electron, leave the atom with a kinetic energy independent of the initialelectron energy which caused the ionisation, i.e. the Auger electron energy is characteristic ofthe target atom. If for example, the involved electrons come from K, L1 and L3 levels thekinetic energy is given byEKL1L3=EK-EL3-EL1where the energies are the binding energies for the levels involved in the Auger process. AESis sensitive to light elements, but since the technique is a two-electron process where two coreelectrons are involved, no Auger process is possible in H and He.

The instrument consists of an electron gun, focusing optics and an electron analyser.There are also an ion gun for depth profiling and a secondary electron detector for imagingaccessible.

3.2. X-ray Photoelectron Spectroscopy, XPSIn XPS (or ESCA) a photon of energy hn interact with an atomic core level electron of

binding energy Eb. If hn>Eb a photoelectron is ejected with a kinetic energy Ek. The emittedcore electrons have then kinetic energies related to their binding energies; Eb=hn-Ek-f, were fis the workfunction of the spectrometer.

Sample

Massspectrometer

Detector

Energyanalyser Mass spectrum

Depth profile

Image

Ion source


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XPS a surface sensitive technique, to achieve good sensitivity and avoid surfacecontamination Ultra High Vacuum (UHV) is required. The technique provides measurementof core level binding energies of constituent atom in a sample; both elemental and chemicalinformation can be obtained. Since no two elements have equal values of their atomic bindingenergy XPS can be used for elemental identification. The core level electron binding energiesare influenced by the valence-state of the atoms because of the electrostatic interactionbetween the valence, or bonding electrons. and the core level electron, which is photo-ionized.Such interactions result in a dependence of the binding energy of the core level electron uponthe chemical state of the atom

3.3. Scanning Electron Microscopy, SEMScanning electron microscopy (SEM) is a method for high resolution suface imaging of

conductive samples or samples coated with a thin conductive layer. In this techniqueselectrons are used for imaging. The advantages of SEM over light microscopy include greatermagnification and much greater depth of field. This technique is used for topographic images,microstructural analysis, and elemental analysis if it is equipped with an appropriate detector.Imaging is obtained using secondary electrons, electrons that interact with electrons in thetarget, for the best resolution of fine surface topographical features. Alternatively, imagingwith backscattered electrons, electrons that interact with the nuclei in the target atom, givescontrast based on atomic number to resolve microscopic composition variations, as well astopographical information. Qualitative and quantitative chemical analysis information can beobtained using an energy dispersive x-ray spectrometer with the SEM.

In SEM the electron beam follows a vertical path through the column of the microscope.In the column there are electromagnetic lenses which focus and direct the beam down towardsthe sample. When the electrons hit the sample, other electrons, backscattered or secondary areejected from the sample. Detectors collect the secondary or backscattered electrons, andconvert them to a signal, which produce an image on a screen.

3.4. Transmission Electron Microscopy, TEMTEM is a technique in which microstructural analysis, interfacial analysis and crystal

structure analysis can be performed.In TEM there is an electron gun in the top of a column, which producing a

monochromatic wave of electrons. This wave is focused to a coherent electron beam by theuse of two condenser lenses (magnetic lenses). The first lens determines the size of the spotthat strikes the sample. The second lens changes the size of the spot on the sample; changingit from a wide dispersed spot to a pinpoint beam. The beam is restricted by the condenseraperture, which blocks out electrons with too large angles. When the beam hits the sample apart of it strikes the sample and parts of it is transmitted. The transmitted part is focused bythe objective lens into an image. Optional Objective and Selected Area metal apertures canrestrict the beam; the Objective aperture enhancing contrast by blocking out high-anglediffracted electrons, the Selected Area aperture enabling the user to examine the periodicdiffraction of electrons by ordered arrangements of atoms in the sample.

The image that is generated consists of dark and light regions. The darker areas of theimage represent those areas of the sample that fewer electrons were transmitted through (theyare thicker or denser). The lighter areas of the image represent those areas of the sample thatmore electrons were transmitted through (they are thinner or less dense)


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3.5. Diffraction techniquesDiffraction occurs when waves scatter from an object and constructively or

destructively interfere with each other.In diffraction experiments neutrons, electrons or x-rays can be used, which interact with

the sample in different ways. In an X-ray diffraction experiment the incoming radiation isscattered by the electrons in the sample. The interaction between X-rays and electrons isstrong, which gives a penetration depth on mm scale. The intensity varies with the atomicform factor, which scales with the number of electrons in an atom. Thus, heavier atoms areeasier to detect than lighter elements.

Incoming electrons in an electron diffraction experiment scatters by electrons in thesample by Coulomb interaction. This is a very strong interaction, which leads to a moresuperficial penetration depth than X-ray diffraction. The intensity varies as for X-raydiffraction with the form factor. Neutrons, on the other hand, are electrical neutral andinteracts therefore consequently very week with the atoms in the sample. This gives apenetration depth of about mm. In this technique the intensity varies with the nuclearscattering length, which varies from nucleus to nucleus. The scattering length is different fordifferent isotopes of an element.

Which one of the techniques you should use depends on what you want to investigate.Neutron diffraction is a very expensive method but with this method you are able to detectlight elements as hydrogen, which is not possible with electron or X-ray diffraction. Anotheradvantage with neutrons is the deep penetration depth, which gives information not onlyabout the surface but also about the bulk material. If you are interest about the structure andcontamination of the outermost surface layer electron diffraction is the best method to usesince this method is very surface sensitive due to very strong interaction with electrons in thesurface layer atoms.

3.6. Atom Probe Field Ion Microscopy, APFIMAtom probe field ion microscopy is the technique for surface analysis that has the

highest resolution, i.e. the best in atomic resolution. This technique has high requirements onthe specimen to be investigated. The sample must posses a certain degree of electricconductivity, it must have mechanical properties which counteract a break of the materialduring the analysis, and it has to allow a sharp tip (50 nm radius) to be made from the samplepreparation.

During measurement the sample is mounted in a vacuum system and at the samplesurface a high electric field is created. The high electric field causes evaporation andionization of the surface atoms. The charged ions are repelled by the electric field in radialdirection from the tip sample surface. The repelled ions hits an imaging screen 5 cm from thesample. For analysis of the sample composition, a pulsed voltage together with an ion detectorcan be used in time-of-flight analysis.

When APFIM is used to analyse the surface composition the sample is put in anatmosphere of a so-called imaging gas, usually an inert gas as He or Ne. When the gas atomsare in the vicinity of the highly charged surface field ionization, a quantum mechanicaltunnelling effect, may occur when the gas atoms are ionized and repelled from the surface.The probability of tunnelling is largest near atoms, i.e. each atom on the sample surface give


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rise to an ion beam in radial direction from the surface. This beam strikes a fluorescent screenand each beam give rise to a spot on the screen.

3.7. Vibrational SpectroscopyInfrared and Raman spectroscopy are two different techniques used to study molecular

vibrations. These techniques differ in how the radiation interacts with the samples. In infraredspectroscopy a broad spectrum of infrared light passes through the sample and an absorptionspectrum is obtained. When molecules absorb light of infrared wavelengths thevibrational/rotational states of the molecules are changed. For a vibrational transition to be IRallowed, the change in vibrational state must also give a change in the dipole moment of themolecule, i.e. IR spectroscopy produces strong absorption bands for polar functional groups.

Raman spectroscopy is a process where the molecules scatter incident monochromaticlight, usually in the visible region of the spectrum. In Rayleigh scattering, the molecule isexcited by the incident light and immediately relaxes down to its ground state. If the moleculedoes not relax to the state it came from, there is inelastic (Stokes and anti-Stokes) scattering.This inelastic scattering has its origin in a change in polarizability of the vibrational modes.This gives that Raman spectroscopy show strong peaks for non-polar functional groups andthereby complements the IR spectroscopy.

Raman and IR spectroscopy share common absorption bands, but complementingmeasurements with both techniques give more information on the vibrations in the material. Afundamental difference is however, that IR uses transmission and the sample must thereforebe more or less transparent, whereas Raman can be done by studying the scattering from asurface.

3.8. Nuclear Magnetic Resonance, NMRNuclear magnetic resonance, NMR, is a phenomenon that occurs when the nuclei of

certain atoms are immersed in a static magnetic field and exposed to a second oscillatingmagnetic field. Some nuclei experience this phenomenon, and others do not, dependent uponwhether they possess a spin or not. In an applied magnetic field the nuclei with spin angularmomentum respond by shifting the spin between different discrete spin states. The nucleuscan have 2I+1 distinct energy states and apart from the nuclei with I=0 all other exhibit, intheory, the NMR phenomenon. Nuclei with I=1/2 align either with or against the appliedmagnetic field H0, producing two different energy levels according to DE=mH0=ghH0/2p,where I is spin quantum number, m the magnetic moment and g the gyro magnetic ratio. Thenuclei presses about the axis of H0 with the Larmor frequency w0=2pn0, which is different foreach type of nuclei observed. A resonance condition, i.e. an energy transition occurs whenDE=n0 is obeyed by the irradiating energy. The precession frequencies are fingerprints of thechemical environment of the nucleus in the molecule, producing chemical shifts from a peakreference (frequency shift in Hz) or even reported as ppm after factorization. The mostcommon nucleus in NMR is 1H, 13C and 29Si, though they differ quite much in gyromagnetic ratio.

3.9. STM (Scanning tunnelling microscopy)In STM one uses a sharpened, conducting tip with a bias voltage applied between the

sample and the tip. When the tip is brought within about 10 Å of the sample, electrons begin


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to tunnel between the tip and the sample. The resulting current varies with the distancebetween the tip and the sample. Therefore one can image the surface of the sample bymeasuring the magnitude of the tunnelling current. Two modes of measurement are possible:constant-height and constant current. In constant-height mode, the tip is scanned in ahorizontal plane over the surface. The tunnelling current will depend on the sample’stopography and the local electronic properties of the surface. The magnitude of the currenttherefore gives a measure of the surface topography of the sample. In constant-current modethe tip moves up and down to keep the magnitude of the current constant. The verticalposition of the tip therefore gives a measure of the sample’s topography in this mode. Due tothe fact that one uses a very sharp tip (atomic size laterally) and that the tunnelling current isan exponential function of distance, one obtains a very high sensitivity. Only metals andsemiconductors can be studied in STM

3.10. AFM (Atomic Force Microscopy)In AFM a sharp tip is scanned over the surface. The tip is located at the free end of a

100 – 200 mm long cantilever. The weak van der Waal forces between the surface and the tipcause the cantilever to bend. The magnitude of the bending gives therefore a topographicimage of the sample’s surface. In contradiction to STM, AFM can also be used to studyelectronically insulating materials.

4. Experimental - material and sample preparationThe studied material has the composition BaIn0.25Zr0.75O2.875. This material has been

synthesized from the starting materials BaCO3, ZnO2 and In2O3. The reaction for thesynthesizing is BaCO3 + 0.75ZrO2 + 0.125In2O3 Æ BaIn0.25Zr0.75O2.875. The different steps inthe synthesizing process are listed below.

1. Grinding and mixing of reactants2. Heating, 1000°C, 15 h.3. Regrinding and compacting4. Heating 1300 °C, 40 h.5. Regrinding and compacting6. Heating 1300 °C, 40 h.7. Product formation to a pellet, 7 mm in diameter.

Due to the samples ability to absorb water from air, the sample was stored in an inertatmosphere after the final step in the synthesizing process.

4.1 Sample preparation for the x-ray diffractionFor the x-ray diffraction experiment we made some powder of the pellet. This was done

by scratching the rough surface with a scalpel. The powder was filled up to approximately 2cm in a capillary, 0.3 mm in diameter. The capillary was then closed by burning of andtightening capillary with a match. This step was performed in air. The capillary was thenplaced in the sample holder in the diffractometer. In the Debye-Scherrer symmetry that wasused, the sample holder rotates during the measurement. This means that the placing of the


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capillary in the sample holder was of crucial importance when the rotating axis must gothrough the middle of the sample. The wavelength of the x-ray beam was 1.54 Å. Theexposure time was 20 hours.

4.2 Sample preparation for the SIMS experimentThe SIMS experiment turned out to be impossible without some special preparation.

This because the sample was not enough electrically conducting. The negatively chargedoxygen ions charged up the sample and made a reliable measurement impossible. The actionfor circumvent this was to evaporate a thin layer of golf on the samples surface. Weevaporated this layer of gold to a thickness of about 0.2 mm. In order to obtain a strongerpellet that could be handled more easily we painted some silver on the edge around the pellet.

5. ResultsIn the subsections below the results from the experiments are presented

5.1 X-ray diffractionThe X-ray diffraction pattern obtained from the measurement is shown in figure 4

below.

Figure 4. X-ray diffraction pattern for the sample BaIn0.25Zr0.75O2.875. The wavelength of the x-ray in this experiment was 1.54 Å. The exposure time was 20 hours.


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With use of a database [3] containing measured diffraction pattern for several materials, wehave analysed the obtained diffractogram. The two most similar diffraction patterns to ourmeasured diffractogram were the diffractogram for the materials BaZrO3 and(Ca0.25Sr0.50)(Bi0.5Cu0.5)O3-x.

Table 1 shows the diffraction angles for the observable peaks in the spectrum and thediffraction angles for the BaZrO3 and (Ca0.25Sr0.50)(Bi0.5Cu0.5)O3-x materials, taken from thedatabase. The numbers in parenthesis indicate the Miller indices and relative intensity. Thewavelength of the radiation associated to the data for these materials are 1.5406 Å and 1.5418Å respectively.


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Table 1. Diffraction angles.2q /°, (Investigated sample) 2q /°, (BaZrO3) 2q /°, ((Ca0.25Sr0.50)(Bi0.5Cu0.5)O3-x)21.2 21.165 (100, 10) 18.182 (110, 10)23.6 30.114 (110, 100) 18.470 (011, 7)24.7 37.103 (111, 10) 21.198 (101, 22)30.1 43.100 (200, 35) 21.198 (020)43.1 48.510 (210, 2) 23.753 (111, 5)53.5 53.490 (211, 40) 29.740 (200, 24)62.5 62.610 (220, 20) 30.148 (121, 100)71 71.038 (310, 18) 30.500 (002, 24)79 75.082 (311, 2) 35.205 (211, 4)86.8 79.042 (222, 6) 35.600 (031, 11)94.6 86.842 (321, 16) 38.756 (131, 10)102.3 94.586 (400, 4) 43.149 (202, 44)110.5 102.406 (330, 10) 47.990 (301, 5)119 110.473 (420, 8) 48.568 (222, 12)

119.010 (332, 6) 48.568 (141)128.298 (422, 6) 49.304 (311, 4)139.010 (510, 12) 53.037 (321, 27)

53.333 (240, 18)53.933 (123, 35)61.743 (400, 5)62.665 (242, 19)63.466 (004, 5)66.102 (420, 5)66.102 (152, 5)66.548 (341, 5)70.434 (402, 4)71.039 (323, 15)71.168 (161, 16)71.636 (204, 6)78.356 (440, 4)79.865 (044, 4)83.080 (262, 3)

It is clearly seen that the diffraction peaks for the investigated sample corresponds verywell with the data for BaZrO3. Due to the fact that the measurement was performed in theinterval 10° £ 2q £ 120°, there is no meaning to consider the two large-angle values forBaZrO3. Therefore we see that there are only 3 peaks in the data for BaZrO3 that do not fitwell with the measured diffraction pattern. As seen in the table, the intensity for 2 of these 3peaks is very small. This low intensity together with the high noise in the spectrum isprobably the explanation why we cannot observe these peaks in the spectrum. So, if wediscard these two low-intensity peaks, there is only one left in data for BaZrO3 that we cannotobserve in the spectrum. From this analysis it is rather clear that the sample underinvestigation has the BaZrO3 structure.

The explanation why we cannot observe the two low-intensity peaks is probably due tothe high level of noise as seen in the spectrum. However, there is in addition one peak withhigher intensity that we cannot detect either. There may be so that this is because the dopingwith In, that is, the substitution of Zr for In atoms.

There are also quite many peaks that fit well with the data for (Ca0.25Sr0.50)(Bi0.5Cu0.5)O3-x.Maybe the most interesting is that the only two observable peaks (23.6° and 24.7°) in the


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measured spectrum that do not fit well with the data for BaZrO3 fit much better with the datafor the distorted perovskite (Ca0.25Sr0.50)(Bi0.5Cu0.5)O3-x. That’s why we think that these twodiffraction peaks are due to the In doping in the sample we have investigated. How thesepeaks are correlated to the In doping is difficult to say. There may be some ordering of the Inatoms or the oxygen vacancies that give rise to these peaks.

5.2 SIMSThe mass spectrum is shown in figures 5-7 below. The three figures show the spectrum

for the mass numbers 1-71, 70-141 and 140-210 respectively. The spectrum is recorded at onepoint, where the size of the analysed area was around 100 mm in diameter. The sputtered areawas around 200*200 mm. An image of the sputtered crater is shown in figure 8.

From the mass spectrum it is obvious that the sample contain more than Ba, In, Zr andO. From a table of the relative abundance of the naturally occurring isotopes [4], we haveidentified the elements O16, Al27, Si28, K38, Ca40, Ti48, Fe56, Ga69, Sr88, Zr90, In115, Ba134, Hf180 andAu197. The peaks at 106 and 150 are due to Zr bonded to O and Ba bonded to O respectively.The “gold-peaks” are probably only due to the thin layer of gold that covers the surface of thesample. It must here be stressed that we have not regarded the very low intensity peaks in theidentification of additional elements.

After the mass spectrum was measured we measured the depth profile, see figure 9. Thedepth profile was measured for the selected elements Si, K, Ca, Ti, Fe, Sr, Zr, In, Ba, and Hf.The measurements were performed for 25-30 minutes, which corresponds to a sputtered depthof some 100 nm. The depth profile was only measured for one isotope for each of the selectedmaterials. Figure 10 and figure 11 show the depth profiles measured at 3 different places onthe sample’s surface. Due to the fact that we did not select the strongest isotope of eachelement (since that had required a change of detectors) you should not compare the intensitiesof the elements in these figures.

Looking at figures 10 and 11, it is observed that the concentration of Si, K and Fe ishigher in the surface layer (< 100 nm) of the sample. The concentration of Ca seems to berather constant through the sample. When we study the heavier elements Ti, Sr, Zr, In, Ba andHf it is observed that the concentration of these are less in the surface layer than in the bulk. Itis observed that the there is roughly no difference in concentration among the three differentmeasuring points. That is, the sample is homogenous (at least among these three points).

In figure 9, the depth analysis started after the mass spectrum was measured, whichmeans that the surface layer was already sputtered off when the measurement begins. We hereobserve the almost constant concentration for each element in the bulk.


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Figur 5. Measured mass spectrum (mass number 1-71) on a sample of BaIn0.25Zr0.75O2.875.

Figur 6. Measured mass spectrum (mass numbers 70-141).

Figur 7. Measured mass spectrum (mass numbers 140-210).


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Figur 8. Microscope image of the sample' surface. The dark areas (~200*200 mm) are thesputtered regions. The yellow colour of the gold layer is clearly seen.

Figure 9. Depth profile of selected elements. The spectrum is measured after and at the sameplace on the sample as the mass spectrum.

Figure 10. Depth profile of selected elements. Three different measurement places.


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Figure 11. Depth profile of selected elements. Three different measurement places.

6. Discussion and conclusionsThe X-ray powder diffraction experiment shows that the material under investigation

(BaIn0.25Zr0.75O2.875) has the BaZrO3 composition and structure. The spectrum fits very well toa known spectrum of BaZrO3. There is however two peaks in the measured spectra that wecannot identify to the known spectra of BaZrO3. We guess that this peak is due to someordering of the doping atoms or oxygen vacancies.

The SIMS experiment showed that there are more elements in the sample than it shouldbe, (should only be Ba, In, Zr and O). Si, K and Fe are to the highest degree present in thesurface layer (< 100 nm). The concentrations of Ti, Sr, Zr, In, Ba and Hf are higher in thebulk than in the surface layer. The concentration of Ca is rather homogenous thorough thematerial. Measurements at three different places on the sample showed that the sample ishomogenous (on the length scale measured). To really be sure that the sample is homogenouswe should though need to perform many more measurements at different places on thesample.

We do not know where all the extra elements in the mass spectrum come from. Thepresence of some of them is probably due to the sample’s inevitable exposure to air. Theconcentration of these elements should be low thorough the sample. However, theconcentration should be highest in the surface layer.

If we only treat the “extra” elements with highest concentration (Si, K, Ca, Ti, Fe, Srand Hf), it is not easy to say where these come from. Though, we think that some of themcome from the synthesizing and some are due to that the sample has been in contact withdifferent materials (sample chamber, cyvette). Because the concentrations of Si, K and Fe arehighest in the surface layer we think that these elements are due to the latter. The remainingelements may come from the fact that the starting materials used when synthesising thesample were not pure enough. That is, it may have been so that the starting materialscontained these “extra” elements (impurities). Nevertheless, as discussed above, one shouldremember that the X-ray diffraction spectrum resembles the X-ray spectrum for BaZrO3 verywell, why the impurity atoms cannot have disturbed the structure much.


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Both experiments did finally turn out well. Regarding the X-ray experiment our firsttrial exposure for 2 hours resulted in a very noisy spectrum. Therefore we set the exposuretime to 20 hours, which also resulted in a fairly good spectrum. Due to lack of time we couldnot exposure for longer time than 20 hours, but that would of course result in an even betterspectrum. We could also measure over a wider region, but that also takes more time of course.

Due to the electrically insulating sample we had to evaporate a layer of gold on thesample’s surface. After the first measurement we realised that the gold layer was to thin or notuniform (the sample became charged), where after we had to evaporate a thicker layer.Nevertheless, when the sample’s surface was covered with this thicker layer themeasurements turned out to be easy.

7. Proposal for a second projectWe have inherited an old gold coloured metal ring with an indistinct strange inscription

inside. We would like to know if the ring consists of gold and what the inscription says.(Maybe Frodo did not succeed)

We will start our analysis of the ring with vibrational spectroscopy (Raman and IRspectroscopy) for identifying vibrational modes of elements in the sample. This will give usinformation if there are different atoms and molecules in the sample or if it consists of puregold.

Since our sample is made of metal and thereby conductive we are able to use Augerelectron spectroscopy (AES) for element analysis. We want to investigate both the surfaceatoms composition and the elements in the bulk. For the bulk material we would like to do adepth profile to see if there is an oxide layer or other contaminations on the surface. If there issome kind of defects on the surface the depth profile will give us the thickness of this layer.

The surface topography can be analysed by Secondary Electron Imaging (SEM). Thistechnique will give an opportunity to investigate and create an image of the mystic inscriptioninside the ring.

8. AcknowledgementsWe are more than thankful to Hans Odelius and Vratislav Langer for excellent help with

the experiments.


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References1. Material Science and Technology; A comprehensive treatment vol 2., Edited by R.W.Cahn, P. Haasen and E.J. Kramer (1992)2. Handouts in the course3. Database, Vratislav Langer, Inorganic Chemistry (Gothenburg university).4. Table of isotopes, Hans Odelius, Applied Physics (Chalmers)

Characterization of BaIn0.25Zr0.75O2fy.chalmers.se/gsms/Projects2003/HelenoMaths.pdf · 2004. 11....

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