Fluoride ion diffusion of superionic PbSnF4 studied by nuclear magnetic resonance and impedance spectroscopy

Super-ionic material PbSnF4 prepared by precipitation from aqueous solution was characterized by x-ray diffraction, DTA and F-19 nuclear magnetic resonance (NMR) techniques. The temperature and frequency dependence of the conductivity, the modulus and the dielectric properties were investigated by means of impedance spectroscopy. The Arrhenius plot of the dc conductivity shows a gradual slope change around 355 K from a high-activation-energy (E-sigma = 30 kJ mol(-1)) region to a low-activation-energy region (E-sigma = 22 kJ mol(-1)). At lower temperatures the real part of the ac conductivity exhibited a power-law behaviour as found in most ionic conductors. At high temperatures, on the other hand, a low-frequency dispersion of the conductivity was observed due to the space charge polarization, which resulted from the high ionic conductivity. An extremely large dielectric constant was observed with decreasing frequency due to the space charge polarization. A dielectric anomaly was also observed around the phase transition temperature. The modulus formalism was used to-estimate the conductivity relaxation times, and was compared with those from the line width transition of the F-19 NMR.