Ion-exchange reaction of a-site in A₂Ta₂O₆ pyrochlore crystal structure

Na⁺ or K⁺ ion rechargeable battery is started to garner attention recently in Place of Li+ ion cell. It is important that A+ site ion can move in and out the positive-electrode materials. When K₂Ta₂O₆ powder had a pyrochlore structure was only dipped into NaOH aqueous solution at room temperature, Na₂Ta₂O₆ was obtained. K₂Ta₂O₆ was fabricated from a tantalum sheet by a hydrothermal synthesize with KOH aqueous solution. When Na₂Ta₂O₆ was dipped into KOH aqueous solution, K₂Ta₂O₆ was obtained again. If KTaO₃ had a perovskite structure was dipped, Ion-exchange was not observed by XRD. Because a lattice constant of pyrochlore structure of K-Ta-O system is bigger than perovskite, K⁺ or Na⁺ ion could shinny through and exchange between Ta⁵⁺ and O^2- ion site in a pyrochlore structure. K⁺ or Na⁺ ion exchange of A₂Ta₂O₆ pyrochlore had reversibility. Therefore, A₂Ta₂O₆ had a pyrochlore structure can be expected such as Na⁺ ion rechargeable battery element.