19F/119Sn/207Pb NMR studies on phase transition and ion dynamics in cubic PbSnF4

Abstract Phase transition and ion dynamics in cubic PbSnF4 (γ-PbSnF4), which shows high conductivity ~10−4 S/cm at room temperature, is examined by using 19F/119Sn/207Pb solid-state NMR at 7 T and 14 T. By comparing with the corresponding NMR data of tetragonal PbSnF4 (β-PbSnF4) obtained by annealing the γ form at 200 °C, we show that, while local structures around both Sn and Pb atoms are similar in the two forms, ion dynamics are markedly different. In the γ form, many F-vacancies existing around Sn and Pb lead the defect-driven ion conduction less effective as the fluoride ions tend to move locally. Further, we show that the γ-to-β phase transition is preceded by slowing down of a part of mobile fluoride ions at temperature ca. 100 °C below the transition temperature observed by DSC.