Hydrothermal synthesis and crystal structure of a mixed-valence pyrochlore-type strontium bismuthate, (Sr0.75Bi0.25)2Bi2O6.83

摘要

A pyrochlore-type strontium bismuthate, (Srsub0.75/subBisub0.25/sub)sub2/subBisub2/subOsub6.83/sub was synthesized by a hydrothermal method using NaBiOsub3/sub· n Hsub2/subO as a starting material. The crystal structure was refined using synchrotron powder X-ray diffraction data. The final R -factors were Rsubwp/sub = 8.07 % and Rsubp/sub = 5.87 %, and the lattice parameter was a = 11.0195 (2) ?. This compound had a mixed bismuth valence state involving Bisup3+/sup and Bisup5+/sup, where Bisup3+/sup partially occupied the A-site (Srsup2+/sup) as well as the B-site (Bisup5+/sup) in the pyrochlore-type structure. Moreover, the present compound was found to be a diamagnetic semiconductor with electrical resistivity of ～90 Ωm at room temperature.