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Structure Identification and Electrical Properties of the New Pyrochlore Phase in the Sr–Bi–Ta–Ti–O System

A new pyrochlore phase Sr0.5BiTaTiO6.5 has been successfully synthesized via a solid state reaction, and its crystal structure and electrical properties are also investigated in this study. When the amount of TiO2 added in the starting materials is insufficient, a secondary phase-SrBi2Ta2O9 is formed with the pyrochlore phase; however, when an ample amount of TiO2 is added, some excess TiO2 remains in the bulk. The structure refinement based on the Rietveld method corroborates the finding that Sr0.5BiTaTiO6.5 exhibits a cubic Fd3m structure with a lattice constant a0=10.424 Å, and the theoretical density is calculated to be 6.867 g/cm3. The exact position of each atom in Sr0.5BiTaTiO6.5 is determined, and the ideal crystal structure model is constructed. According to the dielectric measurement and polarization analysis, it is found that the densified Sr0.5BiTaTiO6.5 exhibits paraelectric characteristics at room temperature with a low dielectric constant (94.8 at 10 kHz). In addition, the dielectric constant of this pyrochlore phase shows a rather weak dependence upon temperature as well as frequency.