Tellurium‐Tantalum Oxides

The rather complex mixed oxide system TeO 2 Ta 2 O 5 has been studied by means of x‐ray powder diffraction, at room temperature, using samples prepared in the interval of 500 to 900°C. Four whitish coloured stable mixed oxide phases have been found, corresponding to the formulas 3TeO 2 · Ta 2 O 5 , 7TeO 2 · 3Ta 2 O 5 and 2TeO 2 · Ta 2 O 5 ( in a low and high temperature form). The latter compound is not isostructural with 2TeO 2 V 2 O 5 . Approximate stability ranges are: up to 850°C, 3TeO 2 · Ta 2 O 5 ; 700–900°C, 7TeO 2 · 3Ta 2 O 5 ; 850°C and higher, 2TeO 2 · Ta 2 O 5 ( H ); 700–800°C, 2TeO 2 Ta 2 O 5 ( L ).