Browsing by Author "Petříček, V"
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- ItemA (3 + 3)-dimensional “hypercubic” oxide-ionic conductor: type ii bi2o3–nb2o5(ACS Publications, 2013-04-09) Ling, CD; Schmid, S; Blanchard, PER; Petříček, V; McIntyre, GJ; Sharma, N; Maljuk, A; Yaremchenko, AA; Kharton, VV; Gutmann, MJ; Withers, RLThe high-temperature cubic form of bismuth oxide, δ-Bi2O3, is the best intermediate-temperature oxide-ionic conductor known. The most elegant way of stabilizing δ-Bi2O3 to room temperature, while preserving a large part of its conductivity, is by doping with higher valent transition metals to create wide solid-solutions fields with exceedingly rare and complex (3 + 3)-dimensional incommensurately modulated ?hypercubic? structures. These materials remain poorly understood because no such structure has ever been quantitatively solved and refined, due to both the complexity of the problem and a lack of adequate experimental data. We have addressed this by growing a large (centimeter scale) crystal using a novel refluxing floating-zone method, collecting high-quality single-crystal neutron diffraction data, and treating its structure together with X-ray diffraction data within the superspace symmetry formalism. The structure can be understood as an ?inflated? pyrochlore, in which corner-connected NbO6 octahedral chains move smoothly apart to accommodate the solid solution. While some oxide vacancies are ordered into these chains, the rest are distributed throughout a continuous three-dimensional network of wide δ-Bi2O3-like channels, explaining the high oxide-ionic conductivity compared to commensurately modulated phases in the same pseudobinary system. © 2013, American Chemical Society.
- ItemStructural evolution of one-dimensional spin-ladder compounds Sr14−xCaxCu24O41 with Ca doping and related evidence of hole redistribution(American Physical Society, 2011-10-17) Deng, G; Pomjakushin, V; Petříček, V; Pomjakushina, E; Kenzelmann, M; Conder, KIncommensurate crystal structures of spin-ladder series Sr(14-x)Ca(x)Cu(24)O(41) (x = 3, 7, 11, and 12.2) were characterized by powder neutron scattering method and refined using the superspace group Xmmm(00 gamma)ss0 [ equivalent to superspace group Fmmm(0, 0, 1 + gamma)ss0; X stands for nonstandard centering (0, 0, 0, 0), (0, 1/2, 1/2, 1/2), (1/2, 1/2, 0, 0), (1/2, 0, 1/2, 1/2)] with a modulated structure model. The Ca doping effects on the lattice parameters, atomic displacement, Cu-O distances, Cu-O bond angles, and Cu bond valence sum were characterized. The refined results show that the CuO(4) planar units in both chain and ladder sublattices become closer to square shape with an increase of Ca doping. The Cu bond valence sum calculation provided new evidence for the charge transfer from the chains to ladders (approximately 0.16 holes per Cu from x = 0 to 12.2). The charge transfer was attributed to two different mechanisms: (a) the Cu-O bond distance shrinkage on the ladder and (b) increase of the interaction between two sublattices, resulting in Cu-O bonding between the chains and ladders. The low-temperature structural refinement resulted in the similar conclusion with a slight charge backflow to the chains.© 2011, American Physical Society