Crystal structure of the defect pyrochlore potassium tantalate on ion-exchanging dipping in sodium aqueous solution by rietveld analysis

Potassium tantalate was synthesized in a condition of about 150 °C by using hydrothermal synthesis method. In this study, it was found that the pyrochlore type potassium tantalate synthesized using this hydrothermal synthesis method was a defect type structure. Potassium tantalate having a defect type pyrochlore structure changed to sodium tantalate by dipping in an aqueous sodium solution. To investigate the crystal structure in more detail, the crystal structure of these samples was simulated by Rietveld analysis. Potassium tantalate synthesized by the hydrothermal synthesis method have water of crystallization and OH-group, and potassium had a nonstoichiometric composition calculated by Rietveld. In the pyrochlore type tantalate, the Na⁺ ion is considered to replace with the K⁺ ion through the tunnel of the octahedral structure made by TaO₆.