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Browsing by Author "Petrova, D."

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    Effect of Ba incorporation on pressure-induced structural changes in the relaxor ferroelectric PbSc0.5Ta0.5O3
    Welsch, A. M.; Maier, B. J.; Engel, J. M.; Mihailova, B.; Angel, R. J.; Paulmann, C.; Gospodinov, M.; Friedrich, A.; Stosch, R.; Guttler, B.; Petrova, D.; Bismayer, U. (American Physical Society, 2009-09-28)
    Pressure-induced structural changes in the canonical relaxor Pb0.78Ba0.22Sc0.5Ta0.5O3 were studied with both in-house and synchrotron single-crystal x-ray diffraction as well as Raman spectroscopy at pressures up to 9.8 GPa. The results reveal that the substitution of Ba for Pb in ABO(3) perovskite-type structures, i.e., the substitution of a two-valent element with an isotropic electron shell for an isovalent element with a stereochemically active lone pair, leads to a "diffuse pressure-induced phase transition," a structural transformation over a broad pressure range, without a well-defined critical pressure point. The smeared phase transition of the average structure results from the existence of local structural deformations in the vicinity of A-positioned Ba cations.
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    Effect of La doping on the ferroic order in Pb-based perovskite-type relaxor ferroelectrics
    Maier, B. J.; Welsch, A. M.; Mihailova, B.; Angel, R. J.; Zhao, J.; Paulmann, C.; Engel, J. M.; Marshall, W. G.; Gospodinov, M.; Petrova, D.; Bismayer, U. (American Physical Society, 2011-04-07)
    The structural alteration induced by the substitution of three-valent cations with an isotropic electronic outermost shell for Pb2+ in perovskite-type relaxors was investigated in the solid solutions Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PST-La) and Pb1-xLaxSc(1+x)/2Nb(1-x)/2O3, x = 0.23 (PSN-La). In order to distinguish the "charge" effects from "strain" effects associated with the incorporation of La3+ in the structure, Sr-containing PbSc0.5Nb0.5O3 was characterized as well. The structure of the compounds was analyzed by in situ Raman spectroscopy, single-crystal x-ray diffraction, and powder neutron diffraction at different temperatures or pressures. It is shown that the embedding of La3+ strongly affects the ferroic structural species due to strain effects through a disturbance of the system of lone-pair electrons associated with Pb2+ and a decrease in the tolerance factor. La doping suppresses the dynamical coupling between off-centered Pb and B-site cations and enhances antiphase BO6 octahedral tilting which, depending on the level of doping, may lead to long-range order of antiphase BO6 tilts at ambient conditions and frustrated antiferroelectric order of Pb ions at low temperatures.