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Perovskites (ABO3) with mixed transition-metal cations are of particular interest for high-temperature electrochemical and electrocatalytic devices. In this regard, the effects of Sr doping on the structural and electrical properties of the double perovskite La2NiTiO6have been studied. High-resolution neutron powder diffraction (NPD) indicates that the symmetry of the La2−xSrxNiTiO6−δseries changes from monoclinic (space group, P21/n) for low Sr contents, associated with B-site cation ordering, to orthorhombic (Pnma) for x> 0.1 with increasing B-site disorder. The substitution of Sr for La is primarily charge compensated by the creation of oxygen vacancies, as indicated by NPD and analysis of the Ni oxidation state by chemical titration thermal analysis and magnetic measurements. The system exhibits p-type electronic conductivity for oxygen partial pressures (pO2) > 10−18atm, increasing with increasing Sr content (σ= 1.18 S cm−1at 900 °C for x= 0.5 in air). A p–n transition is observed in the range 10−18≤ pO2≤ 10−19atm. Sr-doped materials are less conductive in the n-type regime than the Sr-free parent phase; however, n-type conductivity increases with greater xin the range 0.1–0.5, most probably due to increasing reducibility associated with a higher degree of B-site disorder and defect association. [ABSTRACT FROM AUTHOR]

We provide a full description of the first single-crystal synthesis of the low-dimensional quantum spin compound (CuCl)LaNb2O7through the low-temperature topotactic ion exchange route. Very fast diffusion of ion-exchanged CuCl and Cs ions is observed. In addition, thorough structure determination at very low temperature is outlined following use of single-crystal X-ray diffraction and powder neutron diffraction, taking advantage of the better sensitivity of the latter method for describing O and Cl atoms. State-of-the-art calculations (Maximum Entropy Method) are used for visualising the fine structural features of this unusual pseudo-tetragonal superstructure. Our study unambiguously throws light on the long-standing controversy concerning the crystal structure of this compound, and allows for a relevant description of its magnetic properties. Incidentally, it is demonstrated that the low-temperature structural model tentatively proposed very recently by Tsirlin et al.(Phys. Rev. B, 2010, 82, 054107), according to powder synchrotron X-ray diffraction, is correct. [ABSTRACT FROM AUTHOR]

Cation non-stoichiometry is now recognised to have a significant influence on the electrical-transport properties of proton-conducting oxides. The effects of A-site-cation deficiency in the Sr1−xCe0.9Yb0.1O3−δperovskite system with potential use in electrochemical devices are examined. Electron diffraction is used to verify the orthorhombic perovskite structure (space group, Pnma) of compositions 0 ≤ x≤ 0.06. Combined Rietveld refinements of high-resolution neutron and X-ray diffraction data confirm a previously reported anomalous evolution of the lattice parameters within the series, with a maximum in specific free volume observed for x= 0.04. Analysis of the ion-site occupancies indicates that A-site and oxygen vacancies form up to x= 0.04, with partial partitioning of the Yb dopant over the Sr and Ce sites taking place for higher levels of Sr deficiency. The change in defect chemistry is likely to be responsible for the anomalous evolution in structural parameters, and may arise from the alleviation of strain associated with substantial octahedral tilting which occurs for a high A-site vacancy content. In addition to lattice parameters, electrical transport and stability in CO2are also affected by dopant partitioning. The proton conductivity appears to be well correlated with both the nominal oxygen-vacancy content and the specific free volume. The stability of the series towards carbonation is not correlated to the Sr chemical potential but, instead, is lowest for the composition of greatest specific free volume. [ABSTRACT FROM AUTHOR]