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.