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Electronic Structure of Y_{3}Al_{5}O_{12}:V Single Crystals, Comparison with Sintered Ceramics

100%
Kruczek M., Talik E., Kusz J., Sakowska H., Świrkowicz M., Węglarz H.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
209-212
EN
Y_{3}Al_{5}O_{12} (YAG) single crystals doped with vanadium ions (V^{3+}) were obtained by the Czochralski method. The X-ray photoelectron spectra of YAG:V annealed in reducing atmospheres: H_{2}, vacuum and H_{2} + vacuum are presented and compared with the spectra of the YAG ceramics. The X-ray photoelectron spectra showed that the vanadium dopant concentration in YAG:V crystals is lower than a nominal one. For the "as grown" YAG:2.8at.%V crystal vanadium exists in the mixed valence state. The increase in lattice parameters for the samples annealed in hydrogen was found.
2
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Defect Structure Formed at Different Stages οf Growth Process in Erbium, Calcium and Holmium Doped YVO_{4} Crystals

84%
Malinowska A., Wierzbicka E., Lefeld-Sosnowska M., Wieteska K., Wierzchowski W., Łukasiewicz T., Świrkowicz M., Graeff W.
Acta Physica Polonica A
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2010
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vol. 117
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issue 2
328-331
EN
The defect structure of YVO_{4} single crystals doped with Er^{3+}, Ho^{3+} and Ca^{2+} were studied by X-ray diffraction topographic methods, using laboratory and synchrotron radiation sources. Variously developed block structure was the dominating imperfection of the investigated crystals observed both in conventional Lang and synchrotron topographs. The evaluation of block misorientation was realised by means of superimposed projection and section white beam synchrotron radiation topographs. More possibilities of following the mutual rotation of blocks were provided by means of white beam synchrotron radiation WBSR projection topographs exposed through the fine mesh.
3
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Synchrotron Diffraction topography in Studying of the Defect Structure in Crystals Grown by the Czochralski Method

84%
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.
4
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Characterisation of the Defect Structure in Gadolinum Orthovanadate Single Crystals Grown by the Czochralski Method

84%
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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