Subsolidus phase equilibria of in the La2O3-V2O5-Nb2O5-Ta2O5 system

X-ray phase analysis has been used to examine the phase composition of the La2O3-V2O5-Nb2O5-Ta2O5 system in the subsolidus region up to 1200 degrees C . It was found that solid solutions including the M-fergusonite and weberit e structures, as well as a limited series of LaTaO4-based solid solutions, are formed in the ternary La2O3-Nb2O5-Ta2O5 system. Solid solutions based o n the LaNb2VO9 and LaTa2VO9 compounds have been detected in the La2O3-V2O5- Nb2O5-Ta2O5 system. These solid solutions have been examined by IR and radi o spectroscopy. The number of defects in the vanadium sublattice is found t o depend on the composition and sintering conditions. Elementary tetrahedro ns have been found in the La2O3-V2O5-Nb2O5-Ta2O5 system. (C) 2000 Published by Elsevier Science S.A. All rights reserved.