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 (0.94Ta+0.06Sn) 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 α-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 α-PbO2-related phase in Sn-Ta-O system than in Sn-Nb-O system.