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1
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Identification of the Domain Walls Configuration in the Ferroelastic Nanosize Material La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}

100%
Savytskii D., Paulmann C., Bismayer U., Berkowski M.
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issue 1
62-73
EN
This paper deals with the identification of multidomain configuration in ferroelastic phases of La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x} using polychromatic synchrotron X-ray radiation (Laue method). A nondestructive approach for the determination of domain misorientations, orientation of domain walls and their configuration in the nanosize ferroelastic domain structure was developed. The proposed approach can be used to study the nanosize ferroelastic domain structure in small crystals of submillimeter sizes at different external fields, including temperature. The ferroelastic domain structure in the orthorhombic as well as in the rhombohedral phases of La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x} crystals has been identified. The intersection of walls leads to the formation of a chevron-like pattern. The observed reversibility of domain patterns during temperature cycles is probably caused by the interaction of domain boundaries with point defects, most likely oxygen vacancies.
2
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Symmetry Pattern and Domain Wall Structure in GdFeO_{3} Perovskite Type

100%
Savytskii D., Tataryn T., Bismayer U.
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issue 1
78-85
EN
Symmetry relations between the domain states in GdFeO_{3} type crystals have been obtained using group-theoretical analysis for prototype and ferroelastic space groups. Models for possible domain pairs are developed. The ion locations on the domain boundary were estimated as intermediate positions between the sites in crystal structure of neighboring domain states. It is shown that the crystalline structure of the boundary approaches to the prototype phase structure - the ideal ABO_{3} perovskite-type structure, however certain deformations remain. In addition to the shifts of the all ions the tilts of oxygen octahedra of the some type and related displacements of A ions should take place during the switching of orientation states. The tilts of octahedra and displacements of A ions are sufficient to form translation states (antiphase domains). Antiphase domains can have boundaries between themselves basically along the three faces of the orthorhombic cell.
3
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Theoretical Study of the Ferroelastic Domain Structure in La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}

100%
Savytskii D., Tataryn T., Martynyuk N., Bismayer U.
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issue 1
48-61
EN
Theoretical analysis of the ferro-elastic domain structure of a La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{2.925} crystal in three different crystallographic phases is presented. Parameters of these configurations are obtained using group theoretical approach, the method of spontaneous deformation as well as theoretical interpretation of twinning resulting from mechanical deformation (mechanical twinning theory). In the three phases of La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{2.95} - trigonal, orthorhombic and monoclinic - the parameters of ferro-elastic domain structures are determined; namely the quantity of orientation states, symmetry elements of connection between states, orientations and types of domain walls, tensors of spontaneous deformations of the perovskite-type cells for every orientation state, elements of twin shifts, which are needed for the reorientation of some orientation states to others. By using the found parameters of bidomain configurations a mechanism is proposed, which causes chevron-like domain configurations in compounds with martensitic phase transitions.
4
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Local Phenomena in meta-mict Titanite

100%
Bismayer U., Paulmann C., Groat L., Zhang M.
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issue 1
74-77
EN
Pure titanite is a mineral with chemical composition CaTiSiO_{5}. Its structure consists of corner linked TiO_{6}-octahedra, SiO_{4}-tetrahedra and sevenfold coordinated Ca positions. In nature various impurities like U and Th can be incorporated in the structure showing alpha and beta radiation. On meta-mictization, a process which occurs in nature when a mineral is exposed to radioactive irradiation, strong modifications of the structure are observed. Recoil processes due to alpha radiation change over geological time scales the originally periodically structured material into a quasi-amorphous state with persisting short-range order but destroyed long-range order. We report IR and Raman spectra as well as X-ray diffraction data of meta-mict and heat treated titanite from the Cardiff mine, Canada. IR as well as the Raman modes are strongly broadened in the meta-mict material and sharpen on annealing. The OH-stretching mode at 3486 cm^{-1} indicates strong changes in the local environment of OH in meta-mict titanite. The appearance of the Raman excitations between 620 and 750 cm^{-1} in meta-mict titanite, which in IR spectra are due to Ti-O stretching from TiO_{6} octahedra, indicates the breakdown of the Raman selection rules. This points to the breaking of the octahedral symmetry of TiO_{6} polyhedra.
5
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Diffraction Studies of Nanocrystals: Theory and Experiment

64%
Palosz B., Grzanka E., Gierlotka S., Stel'makh S., Pielaszek R., Bismayer U., Neuefeind J., Weber H., Palosz W.
Acta Physica Polonica A
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2002
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vol. 102
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issue 1
57-82
EN
Based on theoretical calculations of powder diffraction data it is shown that the assumption of the infinite crystal lattice for small particles is not justified, leads to significant changes of the diffraction patterns, and may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called "apparent lattice parameter", alp, is proposed.
6
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Generation and Relaxation of Microstrains in GaN Nanocrystals under Extreme Pressures

64%
Grzanka E., Palosz B., Gierlotka S., Pielaszek R., Bismayer U., Janik J., Wells J., Palosz F., Porsch F.
Acta Physica Polonica A
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2002
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vol. 102
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issue 2
167-174
EN
Nanocrystalline powders of GaN with grain sizes ranging from 2 to 30 nm were examined under high external pressures by in situ diffraction techniques in a diamond anvil cell at DESY (HASYLAB, Station F3). The experiments on densification of pure powders under high pressure were performed without a pressure medium. The mechanism of generation and relaxation of internal strains and their distribution in nanoparticles was deduced from the Bragg reflections recorded in situ under high pressures at room temperature. The microstrain was calculated from the full-width at half-maximum (FWHM) values of the Bragg lines. It was found that microstrains in GaN crystallites are generated and subsequently relaxed by two mechanisms: generation of stacking faults and change of the size and shape of the grains occurring under external stress.
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