Characterization and densification of defect pyrochlore oxide powders ABi₂Ta₅O₁₆ (A=Na, Tl)

Defect pyrochlore oxide powders ABi₂Ta₅O₁₆, in the pseudo-binary systems BiTaO₄-ATa₃O₈ (A = Na, Tl), were prepared by solid state method. The structural study showed that all oxides crystallize in a cubic system with the space group Fd3m, the lattice parameter "a" were determined using Rietveld refinement method. For systematic study on densification from powders, the samples were pressed with a uniaxial pressure into pellets; sintering temperature, holding time and heating rate were optimized. Techniques, including X-ray diffraction, IR-Raman, MEB, dilatometry, were employed to investigate the structure and the morphology of the synthesized powders and sintered materials. The dielectric characteristics, relative permittivity and dielectric losses (tgδ), determined at room temperature are comparable to those of other pyrochlores.