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

A pyrochlore-type strontium bismuthate, (Sr0.75Bi0.25)2Bi2O6.83 was synthesized by a hydrothermal method using NaBiO3·nH2O as a starting material. The crystal structure was refined using synchrotron powder X-ray diffraction data. The final R-factors were Rwp = 8.07 % and Rp = 5.87 %, and the lattice parameter was a = 11.0195 (2) Å. This compound had a mixed bismuth valence state involving Bi3+ and Bi5+, where Bi3+ partially occupied the A-site (Sr2+) as well as the B-site (Bi5+) 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.