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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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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.
3
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Topographic and Reflectometric Investigation of Crystallographic Defects and Surface Roughness in 4H Silicon Carbide Homoepitaxial Layers Deposited at Various Growth Rates

76%
Wierzchowski W., Wieteska K., Mazur K., Kościewicz K., Balcer T., Strupiński W., Paulmann C.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
915-919
EN
Undoped 4H silicon carbide epitaxial layers were deposited by means of CVD method with growth rates of 2 μm/h, 5 μm/h and 11 μm/h at 1540°C on n-doped 8°, 4° and 0° off-cut 4H-SiC (00·1) substrates. The structural defects were studied before and after growth of the epitaxial layers by means of conventional Lang topography, synchrotron white beam and monochromatic beam topography and by means of X-ray specular reflectometry. The topographic investigations confirmed the continuation of the dislocations in the epitaxial deposit on the 8° and 4° off-cut substrates without new extended defects. The important difference occurred in the surface roughness of the epitaxial layers, which increased for higher growth rates. The epitaxial layers grown on 0° off-cut substrates at analogous condition contained usually other SiC polytypes, but the influence of the growth rate on the distribution of the polytypes was observed.
4
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Synchrotron Diffraction topography in Studying of the Defect Structure in Crystals Grown by the Czochralski Method

64%
Wierzchowski W., Wieteska K., Malinowska A., Wierzbicka E., Lefeld-Sosnowska M., Świrkowicz M., Łukasiewicz T., Pajączkowska A., Paulmann C.
Acta Physica Polonica A
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2013
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vol. 124
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issue 2
350-359
EN
The synchrotron diffraction topography had been widely used for investigation of the structural defects in crystals grown by the Czochralski method. Similarly as conventional diffraction topography, the synchrotron topography consists in recording with high spatial resolution of the beam formed by the Bragg reflection from the crystal. The advantages of synchrotron sources come from the possibilities of using the wavelength from a wide spectral range, improved high spatial resolution and collimation of the beam as well as from shortening the time necessary for the investigation. The synchrotron diffraction topography includes experimentally simpler white beam topography and more complicated monochromatic beam (multicrystal) topography, where the beam is formed by monochromators. In the case of Czochralski-grown crystals the synchrotron diffraction topography can be used for studying of the individual dislocations and their complexes such as glide bands or sub-grain boundaries, individual blocks, twinning, the domain structure and various segregation effects negatively affecting crystal properties. In addition, the topographical investigation can provide information concerning the reasons for the generation of defects, useful in the improving of the technology. In the present paper the possibilities of the synchrotron diffraction topography are discussed on the basis of several investigations of the Czochralski-grown oxide and semiconductor crystals, performed by the authors at HASYLAB. The majority of the results concern the oxide crystals grown at the Institute of Electronic Materials Technology, in particular garnets, orthovanadates, mixed calcium barium and strontium niobates as well as praseodymium lanthanum aluminates.
5
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Synchrotron Topographic Studies of Domain Structure in Czochralski Grown Pr_xLa_{1-x}AlO_3 and Pr_xLa_{1-x-y}Mg_yAlO_3 Crystals

64%
Wieteska K., Wierzchowski W., Malinowska A., Turczyński S., Lefeld-Sosnowska M., Pawlak D., Łukasiewicz T., Paulmann C.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
910-914
EN
A domain structure and crystallographic defects in Czochralski grown single crystals of Pr_xLa_{1-x}AlO_3 and Pr_xLa_{1-x-y}Mg_yAlO_3 were characterised with a number of methods including conventional and synchrotron X-ray diffraction topography, and polariscopic micrography. The observed twin domain systems were located perpendicularly to 〈100〉_{pcub} and 〈110〉_{pcub} (pseudocubic) directions. It has been confirmed that the domains are of the same orientation and a twin character as those described in literature for LaAlO_3 and LaGaO_3 crystals. The use of section transmission topography enabled to indicate that the domains are perpendicular to the (100)_{pcub} surface of the samples. The misorientation of lattice in the domains was evaluated from the white beam topographs and a tendency of its increase with increasing concentration of praseodymium was revealed.
6
Content available remote

Characterisation of the Defect Structure in Gadolinum Orthovanadate Single Crystals Grown by the Czochralski Method

64%
Wierzbicka E., Malinowska A., Wieteska K., Wierzchowski W., Lefeld-Sosnowska M., Świrkowicz M., Łukasiewicz T., Paulmann C.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
906-909
EN
The GdVO_4 single crystals, both undoped and doped with erbium or thulium, were studied by means of X-ray diffraction topographic methods exploring laboratory and synchrotron radiation sources. Variously developed block structure, caused probably by thermal stresses, was revealed. The highest crystallographic perfection was observed in the crystal doped with 4 at.% of thulium, which was free of the grain boundaries in the end part. Contrary to that, the differences in structural perfection between samples cut out from various regions of the crystal and for different kinds of doping, were less distinct in other crystals. The diffraction topographic methods enabled the statement that the misorientation between various blocks is in the range of several arc minutes.
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