A (3 + 3)-dimensional “hypercubic” oxide-ionic conductor: type ii bi2o3–nb2o5

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ACS Publications
The 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.
Bismuth oxides, Thermal conductivity, Transition elements, Crystals, Zone melting, Diffraction
Ling, C.D., Schmid, S., Blanchard, P.E.R., Petříček, V., McIntyre, G.J., Sharma, N., Maljuk, A., Yaremchenko, A.A., Kharton, V.V., Gutmann, M., & Withers, R.L. (2013). A (3 + 3)-dimensional “hypercubic” oxide-ionic conductor: type ii bi2o3–nb2o5. Journal of the American Chemical Society, 135(17), 6477-6484. doi:10.1021/ja3109328