HYDROTHERMAL SYNTHESIS AND STRUCTURE OF A POTASSIUM TANTALUM DEFECT PYROCHLORE

The synthesis and crystal structure of potassium tantalate (KTa2(O,OH)6·1.8H2O) with a defect pyrochlore structure are reported. The compound was crystallized directly from tantalum pentoxide in basic solution under hydrothermal conditions at temperatures as low as 200 °C. Ion exchange of this substance in acid yielded an H-type defect pyrochlore. Both highly crystalline K-type and H-type materials absorb argon and have BET surface areas of about 14 m2/g. The crystal structures were refined by the Rietveld least-squares method from powder X-ray diffraction data. The final Rwp and χ2 were 7.70% and 2.79, respectively. The high thermal stability and control of acidity of these materials, along with the simple and cheap synthesis, may find many applications in sorption, catalysis, and microelectronics.