MWP-fit: a program for multiple whole-profile fitting of diffraction peak profiles by ab initio theoretical functions

A computer program has been developed for the determination of micro-structural parameters from diffraction profiles of materials with cubic or hexagonal crystal lattices. The measured profiles or their Fourier transforms are fitted by ab initio theoretical functions for size and strain broadening. In the calculation of the theoretical functions, it is assumed that the crystallites have log-normal size distribution and that the strain is caused by dislocations. Strain and size anisotropy are taken into account by the dislocation contrast factors and the ellipticity of the crystallites. The fitting procedure provides the median and the variance of the size distribution and the ellipticity of the crystallites, and the density and arrangement of the dislocations. The efficiency of the program is illustrated by examples of severely deformed copper and ball-milled lead sulfide specimens

Crystallite size distribution and dislocation structure determined by diffraction profile analysis: principles and practical application to cubic and hexagonal crystals

Two different methods of diffraction profile analysis are presented. In the first, the breadths and the first few Fourier coefficients of diffraction profiles are analysed by modified Williamson-Hall and Warren-Averbach procedures. A simple and pragmatic method is suggested to determine the crystallite size distribution in the presence of strain. In the second, the Fourier coefficients of the measured physical profiles are fitted by Fourier coefficients of well established ab initio functions of size and strain profiles. In both procedures, strain anisotropy is rationalized by the dislocation model of the mean square strain. The procedures are applied and tested on a nanocrystalline powder of silicon nitride and a severely plastically deformed bulk copper specimen. The X-ray crystallite size distributions are compared with size distributions obtained from transmission electron microscopy (TEM) micrographs. There is good agreement between X-ray and TEM data for nanocrystalline loose powders. In bulk materials, a deeper insight into the microstructure is needed to correlate the X-ray and TEM results

Microstructure of a rapidly quenched nanocrystalline Hf11Ni89 alloy from X-ray diffraction

A rapidly quenched nanocrystalline Hf(11)Ni(89) alloy was produced by melt-spinning. The X-ray phase analysis shows that the as-quenched ribbon consists of mainly nanocrystalline fcc HfNi(5) although a small amount of Ni is also detected. The crystallite size distribution and the dislocation structure of the dominant HfNi(5) phase were determined by a recently developed method of diffraction profile analysis. In this procedure, by assuming spherical shape and log-normal size distribution of crystallites, the measured physical intensity profiles are fitted by the well established ab initio functions of size and strain peak profiles. The anisotropic broadening of peak profiles is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. It was found that the median and the variance of the crystallite size distribution are 3.3 nm and 0.70, respectively. The dislocation density is 5.7x10(16) m(-2) and the character of dislocations is nearly pure screw

X-ray diffraction study of crystallite size-distribution and strain in carbon blacks

The crystallite size and size-distribution in the presence of strain is determined in carbon blacks by a recently developed procedure of X-ray diffraction peak profile analysis. The Fourier coefficients of the measured physical profiles are fitted by Fourier coefficients of well established ab initio functions of size and strain peak profiles. Strain anisotropy is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. Crystallite shape anisotropy is modelled by ellipsoids incorporated into the size profile function. The Fourier transforme of the size profile is given as an explicite formula making the fitting procedure fast. The method is applied to carbon balcks terated at different preassures and temperatures. The microstructure is characterised in terms of crystallite size-distribution, dislocation density and crystallite shape anisotropy

Results of the photometry of the spotted dM1-2e star EY Draconis

We have observed EY Draconis with the 24`` telescope of Konkoly Observatory in Budapest for 64 nights. In the first obse rving season the star produced a stable light curve for more than 60 rotation periods, however, the light curves observe d in the next season and the spot modelling show clear evidence of the evolution of the spotted stellar surface. The chan ges of the maximum brightness level suggests the existence of a longer period of about 300 days, which seems to be confir med by the ROTSE archival data.Comment: 4 pages, 7 figures with 12 image files, N+N+N conference, accepted for publication in A

Crystallite size distribution and dislocation density in nanocrystalline silicon nitride powders produced by two different procedures

Két különböző eljárással készült nanokristályos szilicium-nitrid por mikroszerkezetét vizsgáltuk röntgen vonalprofil analízissel. Az egyik mintát termikus plazmában SiCl(4) és NH(3) gőzfázisú szintézisével majd kristályosításával készítettük, míg a másik egy a kereskedelmi forgalomban kapható por, amit szilicium nitridálásával majd őrlésével állítottak elő. A porok szemcseméreteloszlását és diszlokációsűrűségét röntgen vonalprofil analízissel határoztuk meg. Megállapítottuk, hogy a nitridálással és őrléssel előállított por szemcséinek átlagos mérete kisebb, míg eloszlásuk szélesebb mint a plazmában előállított mintáé. Mindkét por diszlokációsűrűsége 10(14) és 10(15) m(-2) között volt. A röntgen diffrakciós mérésből meghatározott szemcseméret jól egyezik a fajlagos felületből számolt értékkel és az elektronmikroszkópos megfigyelésekkel. | Two silicon nitride powders were investigated by high resolution X-ray diffraction. The first sample was crystallized from the powder prepared by the vapor phase reaction of silicon tetrachloride and ammonia in thermal plasma while the second was a commercial powder produced by the direct nitridation of silicon and milling. Their crystallite size and dislocation density were obtained by the recently developed procedure of diffraction profile analysis. In this procedure assuming spherical shape and log-normal size distribution of crystallites, the Fourier coefficients of the measured physical profiles are fitted by the Fourier coefficients of well established ab initio functions of size and strain peak profiles. The anisotropic broadening of peak profiles is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. The area-weighted average particle size calculated from nitrogen adsorption isotherms was in good agreement with that obtained from X-rays. The powder produced by silicon nitridation and milling has a wider crystallite size distribution with a smaller average size than the powder prepared by vapor phase reaction in thermal plasma and subsequent crystallization. The dislocation densities were found to be between 10(14) and 10(15) m(-2)

Influence of sintering temperature and pressure on crystallite size and lattice defect structure in nanocrystalline SiC

Microstructure of sintered nanocrystalline SiC is studied by x-ray line profile analysis and transmission electron microscopy. The lattice defect structure and the crystallite size are determined as a function of pressure between 2 and 5.5 GPa for different sintering temperatures in the range from 1400 to 1800 degrees C. At a constant sintering temperature, the increase of pressure promotes crystallite growth. At 1800 degrees C when the pressure reaches 8 GPa, the increase of the crystallite size is impeded. The grain growth during sintering is accompanied by a decrease in the population of planar faults and an increase in the density of dislocations. A critical crystallite size above which dislocations are more abundant than planar defects is suggested

Dislocation density and Burgers vector population in fiber-textured Ni thin films determined by high-resolution X-ray line profile analysis

Nanocrystalline Ni thin films have been produced by direct current electrodeposition with different additives and current density in order to obtain 〈100〉, 〈111〉 and 〈211〉 major fiber textures. The dislocation density, the Burgers vector population and the coherently scattering domain size distribution are determined by high-resolution X-ray diffraction line profile analysis. The substructure parameters are correlated with the strength of the films by using the combined Taylor and Hall–Petch relations. The convolutional multiple whole profile method is used to obtain the substructure parameters in the different coexisting texture components. A strong variation of the dislocation density is observed as a function of the deposition conditions.</jats:p

Dislocation density and graphitization of diamond crystals

Two sets of diamond specimens compressed at 2 GPa at temperatures varying between 1060 K and 1760 K were prepared; one in which graphitization was promoted by the presence of water and another in which graphitization of diamond was practically absent. X-ray diffraction peak profiles of both sets were analyzed for the microstructure by using the modified Williamson-Hall method and by fitting the Fourier coefficients of the measured profiles by theoretical functions for crystallite size and lattice strain. The procedures determined mean size and size distribution of crystallites as well as the density and the character of the dislocations. The same experimental conditions resulted in different microstructures for the two sets of samples. They were explained in terms of hydrostatic conditions present in the graphitized samples

Csúszási rendszerek, Burgers vektor és rétegződési hibák meghatározás köbös, ortorhombos és hexagonális rendszerekben a röntgen vonalprofil analízis módszere alapján = Active slip-systems, Burgers vectors and twinning in hexagonal, cubic and ortorhombic systems determined by X-ray line profile analysis

Polikristályos Ti mintában, krisztallitonként kiértékelve a szinkrotronos diffrakciós vonalprofilokat, meghatároztuk az egyes krisztallitokban a legvalószínűbb csúszási rendszereket. Krisztallitonként meghatároztuk a legvalószínűbb diszlokációkat az MgGeO3 poszt-perovszkitban. A mintát gyémánt cellában 90 GPa nyomással melegítés közben vittük a poszt-perovszkit fázisba. A Co-Ti és Co-Zr ötvözeteken méréseket végeztünk a Chicago-i APS szinkrtorton mellett az 1-ID szinkrotron nyalábbal. Ezzel áttörést sikerült elérni az itt fejlesztett egykristály-diffrakció polikristályos-aggregátumon módszerben. Az Co-Ti és Co-Zr ötvözet rendszerek eredményeinek mind a végső kiértékelése mind a publikálása túlmutatnak a jelen OTKA projekt keretein és jelenleg még folyamatban vannak. Új módszert dolgoztunk ki erőteljesen textúrált mintákban a különböző textúra komponensek mikroszerkezetének kísérletes meghatározására. Erőteljesen textúrált Cu-Nb nanokristályos multirétegekben meghatároztuk a diszlokáció és ikerhatár sűrűséget a rétegvastagság és a hengerlés függvényében. Nanokristályos Cu vékonyrétegben meghatároztuk a diszlokáció sűrűségeket és a nanoikerhatár távolságokat a porlasztott és a hengerelt állapotokban. Meghatároztuk különböző textúrájú Ni vékonyrétegek diszlokáció és ikerhatár sűrűségét a különböző textúra komponensekben. Meghatároztuk egy extrudált Mg ötvözetben a diszlokáció sűrűségeket a különböző textúra komponensekben. Az OTKA szám feltüntetésével 27 cikket publikáltunk. | We determined the most likely slip systems in the individual grains of polycrystalline Ti and MgGeO3 post-perovskite from line profiles measured in polycrystalline aggregates at the ESRF synchrotron in Grenoble. The post-perovskite phase was attained in a diamond-anvil-cell during heating. We did synchrotron measurements on the Co-Ti and Co-Zr alloys at the 1-ID beamline at the APS in Chicago. With the evaluation of these data we could achieve a breakthrough in the processing of the complex and several tens of gigabit data of such experiments. We developed a novel method to evaluate the substructure in the different texture components of strongly textured materials. This we applied to extruded Mg, to Ni thin films and several different types of multilayers of Cu-Nb and thin films with nanotwins. We worked out the procedure for the determination of twinning on the pyramidal and prismatic planes in hexagonal materials from X-ray line broadening. We published 27 research papers with indicating the OTKA-71594 number