Phase relations and spectral properties of new phases in Sc2O3-V2O5-Nb2O5-Ta2O5 system

Phase relations in the Sc2O3-V2O5-Nb2O5-Ta2O5 system up to 950 °C have been analyzed. Solid solutions ScNb1 − xTaxO4 (x = 0-1) with the wolframite structure (FeWO4, the space group P21/n) and ScNb2 − 2xTa2xVO9 − δ (x = 0-1) with the tetragonal structure (the space group I4¯), and also a region of a three-dimensional solid solution based on VNb9O25, which is limited by compounds TaNbV2O10, ScNb2VO9, ScTa2VO9, VNb9O25 and VTa9O25, were detected in this system. Elementary tetrahedrons have been found in the Sc2O3-V2O5-Nb2O5-Ta2O5 system. Solid solutions ScNb1 − xTaxO4 and ScNb2 − 2xTa2xVO9 − δ were studied by the methods of vibrational and optical spectroscopy. It was found that the forbidden gap in these solid solutions increased and decreased with growing concentrations of tantalum and niobium atoms, respectively. A correlation between optical and IR spectroscopic data was established.