Projects running in 1996
[Department of Semiconductor Physics]
[Section of Physics, Faculty of Mathematics and Physics]
[Faculty of Mathematics and Physics]
[Charles University]
[CSCA - Czech and Slovak Crystallographic Association]
V. Valvoda, D. Rafaja, R. Kuzel, H. Sichova, L. Dobiasova1, A.J. Perry2, J.R. Treglio 1
- X-Ray Group
- ISM Technologies Inc., San Diego, CA, USA
Present models describing the microstructure of thin polycrystalline coatings were extended to be able to explain the effects observed in the X-ray diffraction measurements. The regular effects are: (i) a dependence of the interplanar spacing on the inclination of the diffraction vector with respect to the sample surface, (ii) an anisotropy of the cubic lattice parameters calculated from positions of diffraction lines and
(iii) an anisotropy of the line broadening. Moreover, these effects appear in a different measure when using different diffraction geometry. Our extension of the present microstructural model combines the well-known anisotropy of the X-ray elastic constants with an anticipated anisotropy of the system induced by the presence of one free-expansion direction (perpendicular to the sample surface) and with an interaction between adjacent crystallites. The free parameters of the model are the maximum size of the lateral lattice deformation and a "stress free" lattice parameter. The model can explain the diffraction effects mentioned above successfully. The agreement can further be improved if a possible preferred orientation of crystallites is taken into account. The model has, of course, to yield plausible results for different diffraction geometries. This was applied as a criterion for the reliability of the model. Vice versa, a simultaneous use of various diffraction geometries supplies complementary data, which are necessary to obtain a correct insight into the structure.
Another study done on implanted polycrystalline TiN coatings was devoted to the investigation of depth profiles of microstructural parameters, the residual stress and the stress free lattice parameter in particular. The related measurements were carried out with aid of the parallel beam optics at a series of angles of incidence. This technique allows to vary the penetration depth of X-rays in materials. Consequently, integrated information over different distance from the sample surface can be obtained. Using a simplified deconvolution routine, it was found that the depth profile of residual stress follows a Gaussian function, which is also typical for distribution of the implanted atoms or ions in the host structure. Results were compared for implanted metal ions of different species, energy and momentum.
Thin films of CuNx, prepared by a supersonic plasma chemical reactor with a hollow copper anode were investigated. Two types of substrate were used: glass plate and silicon single crystal plate. Glancing angle diffraction geometry has been found necessary to get a sufficiently resolved X-ray diffraction patterns. Several structural phases were observed as a function of nitrogen flow. The most stable structure was identified as Cu3N.
D. Rafaja, V. Valvoda, A.J. Perry, J.R. Treglio: Depth profile of residual stress in the metal-ion implanted TiN coatings, Surf. Coat. Technol., submitted.
V. Valvoda, M. Chladek, D. Rafaja 1, C. Dorner, H. Hoffmann 2,
V. Holy, J. Grim3, A. Buchal, T. Sikola4, R. Krishnan5
- X-Ray Group
- Institute of Advanced Physics, University of Regensburg, Germany
- Masaryk University, Brno
- Technical University, Brno
- CNRS, Meudon, France
Structure of Ag/NiFe multilayers as a function of annealing temperature was examined in situ together with their electrical properties. The changes observed in the high-angle reflections indicate a gradual breaking down of the multilayer arrangement of layers with simultaneous growth of permaloy grains embedded in the silver matrix. Samples were also measured carefully in the low-angle region using reflectivity, off-scan, omega-scan and area scan in reciprocal space. The data were analyzed using the modified program of V. Hole which is based on the distorted wave Born approximation. The whole formalism allows to determine thickness and density of both materials, bilayer period, interface roughness, lateral correlation length and a degree of vertical roughness replication.
First results obtained on the multilayer system Ni/Au were completed by investigations carried out on Co-Ni/Au and Fe/V. The choice of these systems is advantageous for examination of methods of data reduction. Whereas the interface roughness is expected to be dominant in the systems Ni/Au and Co-Ni/Au, the interface quality in the system Fe/V is mainly governed by interdiffusion effects. Comparison of the diffraction pattern obtained in the high-angle region with the reflectivity curve and with the diffuse scattering helped us to distinguish the basic sources of the interface roughness.
Nevertheless, a true insight into the real structure of polycrystalline multilayers can only be achieved if the contribution of specular diffraction and the contribution of diffuse scattering are correctly separated from the measured reflectivity curves, as the information on the real structure of multilayers results mainly from the reflectivity measurement. An additional problem is the separation of instrumental effects from experimental data. Extent of the instrumental effects was recognized when mapping the reciprocal space.
Besides the regular multilayers, metallic or ceramic single layers having a very small thickness were studied. The starting materials (Al, Al2O3, Mo, Ti and ZrO2) were electron-beam deposited applying a series of different voltages for each material. Two complementary methods, X-ray diffraction using the parallel beam technique and the reflectivity measurement using a double-crystal diffractometer, were performed to examine the chemical homogeneity, thickness, crystallinity and surface quality of samples in dependence on starting material and bias voltage. In crystalline coatings a value of the lattice deformation and a direction of the residual stress were estimated. In materials with a certain chemical inhomogeneity, number of particular layers was estimated. Thickness, electron density and roughness were calculated for each individual layer in the system.
The project was supported by the Charles University Fund, grant No. GAUK-140.
M. Chldek, C. Dorner, M. Mattner, H. Hoffmann and V. Valvoda, Structural and magnetic analysis of Ni81Fe19/Ag multilayers with ultrathin Ni81Fe19 sublayers, J.Phys.C., submitted.
V. Valvoda, R. Cerny, M. Chladek, D. Rafaja 1
- X-Ray Group
Generalized empirical correction for preferred orientation of crystallites in a powder sample was tested. Treatment of other than symmetrical diffraction geometries was also included. The texture correction procedure has been implemented in the computer program DBWS-9006PC for Rietveld refinement and in POWLS-80 for refinement of powder intensities measured at several sample inclinations. Monoclinic CrCl3 was used as a testing compound. Powder patterns were measured on Bragg-Brentano, transmission Seemann-Bohlin and glancing angle (thin film attachment) diffractometers. Data were treated by Rietveld refinement. Joint texture refinement was based on the data measured on 4-circle diffractometer.
V. Valvoda: Texture effects in powder diffraction and their correction by simple empirical functions, in: R. Snyder, J. Fiala, H.-J. Bunge, eds, Real Structure Analysis by XRD, Oxford University Press, manuscript submitted.
V. Valvoda, D. Rafaja, R. Kuzel, L. Dobiasova1 , R. Jenkins2
- X-Ray Group
- International Centre for Diffraction Data, Newtown Square, PA, USA
The most recent Round Robin Test organized in our laboratory was oriented on the Quantitative Phase Analysis of three-phases' mixtures. Pure starting components, which was the corundum (a-Al2O3), calcite (CaCO3) and quartz (SiO2), were mixed in four different weight ratios. The composition of two samples was known; these samples were to be used as calibration standards. The composition of the other two samples had to be determined.
The aim of the Round Robin Test was to inspect, how the sample preparation, the arrangement of the diffraction measurement and the method of data reduction influence the quality of results. Therefore, the participants of the test were asked to handle the samples using the technique, which is most frequently applied in their laboratory. For the data reduction, an external standard method was recommended. Besides, the participants were encouraged to submit results obtained with the method of data reduction which they prefer. The most popular alternative methods of data reduction are the Rietveld refinement and the intensity calculation.
The Round Robin Test confirmed that the quality of results obtained in the Quantitative Phase Analysis is first of all influenced by the technique of sample preparation and by the instrumentation of the diffraction measurement. The choice of the method of data reduction plays a minor role. It can be expected that the accuracy of the Quantitative Phase Analysis depends strongly on the precision, which can be reached at the measurement of the diffracted intensities. Nevertheless, as the intensity measurement itself can be done very precisely, the influence of the intensity measurement on the results of the Quantitative Phase Analysis is of the second order.
The project was supported by the U.S. - Czechoslovak Science and Technology Joint Fund, in cooperation with the International Centre for Diffraction Data (USA) and Ministry of Economy (CR), under grant No. 93008.
D. Rafaja1, W. Lengauer, P. Ettmayer2
- X-Ray Group
- Institute for Chemical Technology of Inorganic Materials, Technical University Vienna
Our preliminary work related to the study of ceramic-metal composites (CERMETS) included mainly the investigation of diffusion kinetics in nitrides and carbides of transition metals. We started with the following binary compounds: titanium nitrides, hafnium nitrides, niobium carbides, tantalum carbides and vanadium carbides. Although the CERMETS are commonly created by ternary or quaternary compounds, the study of diffusion kinetics in binary systems is important, as it contributes to understanding the diffusion process itself. Moreover, the material characteristics of binary systems (phase diagrams, individual diffusion coefficients) can be applied when explaining more complex systems.
The work has been done in cooperation with the Technical University of Vienna. At the Technical University of Vienna, the thermodynamic characteristics (phase diagrams) of materials mentioned above were investigated. The part of the work done in our laboratory was devoted predominantly to the study of diffusion kinetics. A theory of diffusion processes in finite one-dimensional binary gas/solid diffusion couples containing several phases was created. This theory is based on an analytical solution of diffusion equations. It is able to describe the evolution of a phase structure at the reactive diffusion, the layer growth and the related phase boundary movement as well as the successive disappearance of individual phases if the homogeneity ranges of the individual phases, which exist in the sample at a given temperature, and the diffusion coefficients are known. This theory helped to explain the layer growth enhancement observed in finite diffusion couples. On the other hand, the theory of diffusion processes for finite samples can be used for estimation of diffusion coefficients in all phases from the phase boundary movement. It is impossible to obtain such a result from the theory derived for infinite samples. Although either the diffusion time or the sample thickness can be varied, the latter is more favorable, because a series of samples can be prepared in the same diffusion process. It means that the same experimental conditions (temperature, gas pressure, heating and cooling rate) can easily be kept. It is advantageous when the samples have a form of a wedge. Of course, the angle between the main diffusion planes has to be sufficiently low to fulfill the one-dimensional diffusion geometry.
However, this technique can yield only diffusion coefficients independent of concentration of in-diffusing species. In phases with a broad homogeneity range, the diffusion coefficients are expected to be concentration dependent. For that purpose a routine was developed that calculates the concentration dependent diffusion coefficients from the measured concentration profile. As the concentration dependent diffusion coefficients can be calculated from the concentration profile only if the quality of data is good enough (low scattering in the measured concentrations), the best way it to combine both methods.
The theory of diffusion processes mentioned above was derived still for one-dimensional samples. As this limitation is too strict when regarding the CERMETS, which are usually prepared by using the powder metallurgy methods, a finite difference's model of diffusion process was built. Using finite differences, more complicated geometries are easier to be handled. In addition, as the course of the diffusion process is always calculated successively, also change in the boundary conditions during the diffusion process can be taken into account. This is important when describing many diffusion phenomena, which are interesting from the technological point of view: the sample homogenization, successive phase evolution at the beginning of the diffusion process or a restricted diffusion flow through the sample surface.
The project was supported by the Fund of Charles University, grant No. GAUK - 4.
W. Lengauer, D. Rafaja, G. Zehetner, P. Ettmayer: The hafnium-nitrogen system: Phase equilibria and nitrogen diffusivities obtained from diffusion couples, Acta Metal. Mater., in press.
Rafaja, W. Lengauer, P. Ettmayer: Multiphase layer growth kinetics in finite gas/solid diffusion couples, Acta Metal. Mater., supplied.
P. Capkova , D. Janeba1, Z. Weiss, Z. Klika2, M. Numan, R. Driessen, H. Schenk3
- X-Ray Group
- Technical University of Mining and Metallurgy Ostrava
- Laboratory of Crystallography, University of Amsterdam
The study of natural and intercalated clay minerals can be devided into two main fields: 1/ The development of efficient sorbents for organic and inorganic pollutants in water resources and the development of catalysts. Structural investigation of intercalated clays is focused to the search of a suitable host structure and a proper intercalant with the aim to control the porosity of structure and consequently the selectivity of sorbents. 2/ The sorption of heavy metals into clay minerals - methods of identification and characterization of polluted clays with XRD methods. The X-ray diffraction method combined with molecular simulations is used for this study. Hydration and dehydration of clays is studied using molecular simulations and XRD measurements under the controlled humidity.
The structure of vanadyl phosphates and sulfates intercalated with alkali-cations and organic molecules have been studied to understand the relation between the structure and very interesting electrical and electrochemical properties of these compounds using the method described above.
XRD profile analysis of smectites is usually limited to the apparent d-spacing estimated from the peak maxima from the raw data. This can lead to the wrong d-spacings and consequently to the wrong conclusions about mixed layering (interstratification) and wrong structural model of interlayer. The interference function is modulated by the angle dependent instrumental factors (Lorentz-polarization, diffraction geometry) and physical factors (structural factor, volume absorption, surface roughness absorption) which lead to profile distortions and to the shift of the peak maxima. This effect is especially significant at low diffraction angles and for broadened diffraction lines (FWHM>1o).
Attention has been paid to detailed analysis of these effects, their corrections and their consequences for the interpretation of diffraction patterns. The proposed methodology was successfully used on montmorillonites (MMT) intercalated with Zn, Cd cations and Al-hydroxy complexes. The "true" d-spacings corrections are in good agreement with those calculated from molecular simulations (Crystal Packer module in Cerius2 modeling environment). The differences between the d-spacings from data without corrections and after corrections can be even 0.2 nm which is very much especially because of the d-spacing is often the limiting factor for the use of intercalated clays. Very important results following from the profile analysis are also the conclusions about interstratification.
P.Capkova, R.A.J.Driessen, M.Numan, H.Schenk, Z.Weiss, Z.Klika: Molecular simulations of montmorillonite intercalated with aluminium complex cations. Part I. Intercalation with [Al13O4 (OH)24+x(H2O)12-x](7-x)+, Clays&Clay Minerals, submitted.
P.Capkova , R.A.J.Driessen, M.Numan, H.Schenk, Z.Weiss, Z.Klika: Molecular simulations of montmorillonite intercalated with aluminium complex cations. Part II. Intercalation with Al(OH)3-fragment polymers, Clays&Clay Minerals, submitted.
D.Janeba, P.Capkova, Z.Weiss, H. Schenk: Characterization of Intercalated Smectites Using XRD Profile Analysis in Low Angle Region, Clays&Clay Minerals, submitted.
D.Janeba, P.Capkova, Z.Weiss: XRD Profile Analysis of Intercalated Montmorillonites, Geologica Carpathica Clays, in press.
P.Capkova , R.A.J.Driessen, M.Numan, H.Schenk, Z.Weiss, Z.Klika: Molecular simulations: Montmorillonite intercalated with aluminium complex cation, Koninlijke Nederlandse Akademie van Wetenschappen, submitted.
P.Capkova , R.A.J.Driessen, M.Numan, H.Schenk, Z.Weiss, Z.Klika: Modeling of intercalated clay minerals, Chemick' listy, submitted.
D. Rafaja, R. Kuzel 1, P. Kratochvil, J. Kopecek 2
- X-Ray Group
- Department of Metal Physics, our faculty
Aim:The intermetallic compounds based on the intermetallic phase Fe3Al are expected to be used in many technical and technological applications, where good mechanical properties together with a large chemical resistance are needed. The mechanical properties are significantly influenced by the stage of the long-ordering in the atomic structure. The aim of our study is to establish the exact course and temperature of the phase transformation and to estimate the diffusivities of atoms.
Recent results: The whole X-ray diffraction pattern was used for a study of the long range ordering in stoichiometric iron-aluminium alloy Fe3Al. The diffraction pattern of fcc Fe3Al can be split into three groups. Intensities of diffraction lines related to the first group are sensitive to the arrangement of atoms at the octahedral positions. Intensities of reflections of the second group vary with a variable distribution of atoms at the tetrahedral positions. Finally, the intensities of diffraction lines that belong to the third group remain constant independent of the stage of the long range order.
L. Dobiasova, V. Valvoda1, P. Glogar 2, V. Stary3
- X-Ray Group
- Institute of Minerals Structure, Prague
- Technical University, Prague
Carbon fibers and their composites subjected to the heat treatment at 1000, 2200 and 2800 oC have been studied by XRD analysis using Bragg-Brentano and parallel beam diffractometer settings. Advantages and disadvantages of these methods for the structure parameters characterization are discussed. The lattice spacing of (0001) planes was used as a measure of the degree of graphitization. The apparent size of coherently diffracting domains ranges from about 3.0 to 30.0 nm and the angle of carbon layers inclination from the fiber axis was found to be between 7 and 30o.
The project was supported by the Grant Agency of Czech Republic, grant No. 106/95/0359.
H. Sichova , L. Dobiasova , J. Charvat, S. Danis 1, J. Wild, J. Macl 2, P. Bohacek3
- X-Ray Group
- Department of Electronics and Vacuum Physics, our faculty
- Institute of Physics, Czech Academy of Sciences, Prague
Crystal structure of the high-Tc superconducting phase (Bi1-x Pbx)2 Sr2 Ca2Cu3Oy, (phase 2223) with transition temperature Tc = 105K have been studied. Structure changes in atomic configuration caused by different Pb concentration (x = 0.15, 0.20, 0.25, 0.30, 0.40) and different preparation conditions (slowly cooled and quenched samples) were in the focus of our study. Rietveld refinement of x-ray powder diffraction data was used for structure change analysis. The correlation among transition temperatures and structure parameters, phase concentrations and atomic configuration variations of bulk samples were found. Using the bond valence sum method Cu valence value of measured samples was investigated. Within the precision of our method no Cu valence changes were found. The temperature Tc of samples was closely related to the Bi-O bond distances. The precision of the used method was tested by the Rietveld structure analysis of CuO powder data for three samples with different oxygen stoichiometry.
The project was supported by the Foundation of Charles University, grant GAUK - 13.
J. Wild, J. Macl, H. Sichova, P. Bohacek, J. Pracharova, Z. Janu, S. Civis, P. Kubat, 8O K superconducting Bi-Sr-Ca-Cu-O layers prepared by laser ablation in the air, J.Appl. Phys., submitted.
J. Wild: Modifikovanametoda pripravy tenkych supravodivych vrstev, Technik, 1(1996)11.
H. Sichova, J. Charvat, S. Danis: X-ray structure study of high-Tc phase of Bi(Pb)-Sr-Ca-Cu-O system, ready for publication.
L. Dobiasova, H. Sichova: X-ray structure of copper bond valence study in CuO and high-Tc superconducting bismuth-cuprate ceramics, will be published.
R. Kuzel1, F. Chmelik2, P. Moravec3
- X-Ray Group
- Department of Metal Physics, our faculty
- Institute of Physics, Charles University, our faculty
The evolution of the mean crystallite size and strain with annealing temperature (within the range 20-1000oC is studied for ultrafine-grained copper, germanium and silicon produced by plastic deformation. In as-prepared samples of germanium and silicon a minor high-pressure tetragonal phases were found which dissapeared after annealing above 300oC (for germanium). An increase of mean crystallite size and decrease of strain with increasing temperature is obvious. The greatest reduction of XRD line broadening was observed in the range of 400-800oC whereas significant change in eletrical transport properties was found after annealing above 800oC.
Different techniques (e.g. TEM) have revealed that the thermal stability of samples is not determined only by a mean grain size but also by the grain-boundary dislocations. For the correct interpretation of XRD profiles an application of classical (Williamson-Hall or Warren-Averbach) methods seems to be insufficient and more sophisticated model would be desireable.
R.K. Islamgaliev, F. Chmelik, R. Kuzel, Thermal Stability of Submicron Grained Copper and Nickel, Materials Science and Engineering, in preparation
R. Kuzel1, C.R. Houska 2
- X-Ray Group
- Virginia Polytechnic Institute and State University, Blacksburg, USA
The research of early stage of precipitation in Cu-Be alloys was completed with two papers describing a new simplified method for characterization of precipitate size and concentration and the results obtained for Cu-Be samples aged at 200oC. The method is based on the fitting of experimental diffraction profiles with three Pearson functions corresponding to Bragg peak, static diffuse scattering and quasiline (diffuse scattering). The three components are interconnected via the static Debye-Waller factor 2M which is refined by fitting. Simultaneously, the factor and quasiline shifts are calculated using a simplified semi-analytical approximation of the precipitate displacement field including the effect of elastic anisotropy. The experimental and theoretical results are compared and dimensions of precipitates can be refined. Near surface preferred orientation of precipitate habit planes (100) leading to observed large anisotropy of 2M's and probable stair-step pairing of precipitates was found after aging. At 200oC, quantitative estimates of the diameters for disk-shaped stair-step pairs give 3.6 and 4.8 nm for 16 and 64 hrs aging, respectively, a height of one unit cell (0.29 nm), and a pair spacing which appears to increase with time.
C.R. Houska, R. Kuzel, Simplified Elastic Models for Disk-Shaped Precipitates, Journal of Materials Science, supplied
R. Kuzel, C.R. Houska, Baoping He, Characterization of Severe Matrix Distortions During Phase Separation from the Redistribution of Diffracted Intensities, Journal of Materials Science, accepted
Last page modification : 17. 11. 1997
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