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

Mikroszerkezet karakterizációja röntgen vonalprofil analízis alapján = Characterization of microstructure by X-ray line profile analysis

A "" Mikroszerkezet karakterizációja röntgen vonalprofil analízis alapján"" c. T-046990, OTKA pályázat rövid szakmai összefoglalója, zárójelentés A deformációs anizotrópia jelenségét kihasználva részletes elméleti és kísérletes kutatásokat végeztünk a mikroszerkezet kvalitatív és kvantitatív karakterizációjára vonatkozóan köbös, hexagonális és ortorombos kristályrendszerekben a röntgen vonalprofil analízis módszerével. A földkéregben mintegy 100 km-es mélységben fekvő ortorombos MgSiO3 perovszkitokat szimuláló mintát állítottunk elő magas hőmérsékletű nagynyomású présben. Megállapítottuk, hogy csak és Burgers vektorú diszlokációk jönnek létre. 700 és 1000 K közötti hőmérsékleteken összenyomással deformált Ge egykristályokban helyfüggő mikrodiffrakcióval megállapítottuk, hogy a mikroszerkezet jelentős fluktuációkat mutat. [001], [011] és [111] textúrájú NiAl emlékező ötvözet mintákban meghatároztuk a különböző textúra komponensekhez tartozó kemény illetve puha krisztallit populációkban az aktív Burgers vektor típusokat valamint diszlokációsűrűségeket. Golyósmalomban őrölt alkáli földfém fluoridok krisztallitméret és diszlokációsűrűség meghatározása során felfedeztük, hogy pormintákban is létrejön röntgen optikai interferencia. Módszert dolgoztunk ki Burgers vektor típusok meghatározására hcp kristályokban. Kidolgoztuk a rétegződési hibák és ikerhatárok gyakoriságának meghatározási módszerét köbös kristályokban. A módszert számos esetben sikeresen alkalmaztuk. | ""Characterization of microstructure by X-ray line profile analysis"" Short summary of the T-046990, OTKA project, final report On the basis strain anisotropy detailed theoretical and experimental work has been carried out for the characterization of the microstructure in cubic, hexagonal and orthorhombic crystal structures by using the method of X-ray line profile analysis. A synthetic orthorhombic MgSiO3 perovskite was prepared the high temperature and pressure. We have found that only and type Burgers vectors are present in the deformed crystals. Ge single crystals were deformed by compression between 700 and 1000 K. Position sensitive microdiffraction has revealed that the deformed microstructure is strongly fluctuating on different length scales. NiAl shape memory alloys with [001], [011] and [111] textures were deformed by compression. We have determined the active Burgers vector types and dislocation densities in the different texture components for different grain orientation populations. Alkali-halide fluorides were ball milled to different extent. We have shown that X-ray optical interference can occur in nanocrystalline powder specimens. A method has been worked out to determine active Burgers vector types in hexagonal crystal systems, and the frequency of stacking faults and twin boundaries in cubic crystals. The methods have been applied successfully in several different cases