Synthesis of novel cation-ordered compounds with fluorite-related structure prepared by oxidation of Sn–Ta–O pyrochlore

Pyrochlore-type oxide, SnII1.64(Ta1.88SnIV0.12)O6.58 was oxidized for exploring novel metastable phases. Two novel SnIV0.82(Ta0.94SnIV0.06)O4.11 phases with a fluorite-related structure, which was obtained as a pure phase, and with a rutile-related structure appearing as an impurity for the fluorite-related phase were successfully obtained similar to the previous Sn–Nb–O system. The ordered arrangement of respective cations of Sn and (image) in the precursor SnII1.64(Ta1.88SnIV0.12)O6.58 was left in the both oxidized SnIV0.82(Ta0.94SnIV0.06)O4.11 phases. In contrast to the previous Sn–Nb–O system, the cation-ordered image-PbO2-related SnIV0.82(Ta0.94SnIV0.06)O4.11 could not be obtained in the present conditions. Such a difference between the Sn–Ta–O and Sn–Nb–O systems was interpreted by larger energy barrier of the transformation from the fluorite-related phase to image-PbO2-related phase in Sn–Ta–O system than in Sn–Nb–O system.