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

Abstract

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.

Keywords: Inorganic chemistry; Materials chemistry.

Fig. 1

XRD patterns of NaBi₂Ta₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 2

Infrared transmission spectra of NaBi₂Ta₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 3

Raman spectra of NaBi₂Ta₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 4

SEM images powders of NaBi₂Ta₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 5

Pressure versus density before and after sintering for NaBi₂NbTa₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 6

Dilatometry curves of NaBi₂NbTa₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 7

Sintering thermal cycle.

Fig. 8

SEM images of NaBi₂NbTa₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b) sintered at about 1350 °C.

Fig. 9

Frequency dependence of dielectric constant vs. temperature of NaBi₂Ta₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 10

Frequency dependence of dielectric losses vs. temperature of NaBi₂Ta₅O₁₆ (a) and TlBi₂Ta₅O₁₆ (b).

Fig. 11

Frequency Logarithmic temperature dependence of the frequency location at the dielectric losses peak for compound NaBi₂Ta₅O₁₆ heated from 25 °C to 500 °C.