Formation and transformation of 3TeO2·Nb2O5

Abstract

A compound so far denoted as 4TeO₂·Nb₂O₅ has been determined to be a metastable modification of 3TeO₂·Nb₂O₅. At a heating rate of 10 °C min^–1 the metastable modification crystallizes at 530–550 °C from an amorphous material prepared by the simultaneous hydrolysis of tellurium tetrachloride and niobium isopropoxide. It has a tetragonal unit cell with a= 1.2308 and c= 0.9924 nm. The structure consists of the Te₃O₈ unit, built up of two TeO₃ groups and a TeO₄ group. The tetragonal-to-orthorhombic phase transformation occurs at 620–655 °C.