On the Sintering Behavior of Nb 2 O 5 and Ta 2 O 5 Mixed Oxide Powders.

A mixed oxide system consisting of Nb 2 O 5 and Ta 2 O 5, was subjected to annealing in air/hydrogen up to 950 °C for 1-4 h to study its sintering behavior. The thermogravimetric-differential scanning calorimetry (TGA-DSC) thermograms indicated the formation of multiple endothermic peaks at temperatures higher than 925 °C. Subsequently, a 30% Ta 2 O 5 and 70% Nb 2 O 5 (mol%) pellet resulted in good sintering behavior at both 900 and 950 °C. The scanning electron microscope (SEM) images corroborated these observations with necking and particle coarsening. The sintered pellets contained a 20.4 and 20.8% mixed oxide (Nb 4 Ta 2 O 15 ) phase, along with Ta 2 O 5 and Nb 2 O 5 , at both 900 and 950 °C, indicating the possibility of the formation of a solid solution phase. In situ high-temperature X-ray diffraction (XRD) scans also confirmed the formation of the ternary oxide phase at 6 and 19.8% at 890 and 950 °C, respectively. The Hume-Rothery rules could explain the good sintering behavior of the Ta 2 O 5 and Nb 2 O 5 mixed oxides. An oxide composition of 30% Ta 2 O 5 and 70% Nb 2 O 5 (mol%) and a sintering temperature of 950 °C appeared adequate for fabricating well-sintered oxide precursors for subsequent electrochemical polarization studies in fused salts.