Preparation of pyrochlores. A 1−xH xTaO 3·nH 2O (A=Na, K)

Abstract

Pyrochlores of A 1−xH xTaO 3·nH 2O (A=Na,K) were prepared under the hydrothermal conditions. The values of x for these compounds were increased from 0.3 to 0.5 for A=Na and from 0.2 to 0.5 for A=K by treatment with the distilled water. The compounds with x<0.5 were decomposed to a mixture of NaTaO 3 and Na 2Ta 4O 11 for A=Na, or to a mixture of KTaO 3 and a tetragonal tungsten bronze phase, and those with x=0.5 to a single phase of A 2Ta 4O 11 at elevated temperatures. Below the decomposition temperatures, defect pyrochlores with oxygen vacancies, A 1− x TaO 3− x 2 , were produced. They were hygroscopic, and in the case of A=K and x=0.5 the original phase was recovered by leaving in air for several hours.