Ion conductivity of double phosphate [Na.sub.3][Sc.sub.2][.sub.3] in the region of the β-γ transition

The [Na.sup.+]-ion conductivity a of double phosphate [Na.sub.3][Sc.sub.2][(P[O.sub.4]).sub.3] in the region of the β-γ transition has been studied using impedance spectroscopy (1-[10.sup.6] Hz). The polycrystalline sample of [Na.sub.3][Sc.sub.2][(P[O.sub.4]).sub.3] has been prepared by solid-phase synthesis and ceramic technology. It has been found that, upon the β-γ transition, the conductivity σ of [Na.sub.3][Sc.sub.2][(P[O.sub.4]).sub.3] suffers a ~1.5-fold jump at 470 [+ or -] 2 K upon heating and a ~2.5-fold jump at 430 ± 4 K upon cooling (the temperature hysteresis of the jump in a is 40 K). For double sodium--scandium phosphate γ-[Na.sub.3][Sc.sub.2][(P[O.sub.4]).sub.3] in the superionic state, a attains 0.07 S/cm at 700 K and the ion transport activation enthalpy is 0.42 ± 0.02 eV.