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The RietveldToTensor program is designed to study crystal lattice deformations using the Rietveld method from the X-ray powder diffraction data gathered under varying physical and chemical conditions. Using the program, it is possible to determine the tensor of thermal expansion, compressibility, or chemical deformations of the material. The program runs on the Microsoft Windows 7 and higher platforms. [ABSTRACT FROM AUTHOR]

The thermal expansion of magnesium borate (Mg3B2O6) is studied by the method of X-ray thermodiffraction in the temperature range 25–1100°C. The coefficients of thermal expansion are calculated as follows: αa = 13.0(5), αb = 8.5(5), αc = 8.0(5), αV = 30(1) × 10–6°С−1 at 25°C; and αa = 20.0(5), αb = 13.0(5), αc = 13.0(5), αV = 46(1) × 10–6°С−1 at 1100°С. The direction of the maximal thermal expansion (αa) is perpendicular to the preferred orientation of the BO3 triangles. [ABSTRACT FROM AUTHOR]

All thermal vibrations of atoms are in fact anharmonic – this is the underlying reason for the manifestation of many physical properties of solids, primarily its thermal expansion. By now, over three decades have passed from the seminal works of Kuhs [Kuhs Statistical description of multimodal atomic probability densities. Acta Crystallogr A. 1983;39:148–158.Kuhs Lead Article Generalized Atomic Displacements in Crystallographic Structure Analysis. Acta Cryst. 1992;A48:80–98. Kuhs The Anharmonic Temperature Factor in Crystallographic Structure Analysis. Aust J Phys. 1988;41:369], and 'anharmonic' approaches are now widely used for the description of thermal displacements of the atoms. Experimental data for studies of this phenomenon can be acquired from targeted diffraction experiments, and in this mini review, we analyse the current state of this area, mostly for the inorganic structures. The modern crystallographic hardware and software permits to correct the description of anharmonicity for the objects whereof one or two decades ago this phenomenon was either neglected or beyond the power of data processing. In general, the asphericity of electron density distribution is not necessarily caused by anharmonic motions; another possible reason is the displacement of valence electrons due to the formation of chemical bonds. We analyse the hitherto reported examples of anharmonic description of thermal motions; this phenomenon is most pronounced for univalent cations (like alkalis, silver, copper and thallium) and anions (halides). We also present the new Anharmonicity program suite which permits to determine the maxima of distribution of probability density. [ABSTRACT FROM AUTHOR]

A software is developed for determining the parameters of the thermal expansion tensor of the crystals of any system by a set of experimental diffraction data received using X-ray, synchrotron and other radiations at various temperatures. An algorithm is realized which allows carrying out all calculations from the experimental determination of the Bragg reflection angles to the calculation of the parameters of the thermal expansion tensor of the crystals, including the orientation of the tensor axes with respect to the crystallographic axes. The drawing of the 3D characteristic surface of the tensor and its 2D sections is also provided. The software is aimed at studying the anisotropy of the thermal expansion of the crystal materials and phase transitions, as well as revealing the mechanism and nature of the thermal behavior of substances. [ABSTRACT FROM AUTHOR]

Hydroxylclinohumite Mg5(SiO4)2(OH,F)2 is a common monoclinic orthosilicate of the humite group, which, on the one hand, is a prototype of promising materials, and, on the other hand, is an important source of information about both the transport and the presence of water in the Earth's mantle, and therefore studying its thermal behavior is of particular interest. In this paper, the mineral is studied by powder X-ray diffraction for the first time in a wide temperature range (–180 ≤ T ≤ 1000°C). The temperature limits for the existence of the phase are established, the principal values of the thermal expansion tensor are calculated, and a structural interpretation of thermal expansion is given. [ABSTRACT FROM AUTHOR]

The method of synthesis of sodium and potassium sulfates in a thermal X-ray machine is described for the first time; the synthesis is followed by cooling to study its thermal behavior. A mixture of sodium and potassium sulfates (in a 1 : 1 ratio) is obtained for the study. [ABSTRACT FROM AUTHOR]

In the Na2SO4–K2SO4 system, nine phases are known. In this study, for the first time, the values of the thermal expansion coefficients of continuous high-temperature solid solutions crystallizing in the P63/mmc crystal system, low-temperature limited solid solutions based on natroaphthitalite and aphthitalite (P3-m1), and polymorph II Na2SO4 (Pbnm) in the Na2SO4–K2SO4 system are provided. The genetic succession of polymorphs P3m1 and P3-m1 ↔ P63/mmc, which manifested itself in the double sulfates of this system, is revealed. [ABSTRACT FROM AUTHOR]