Na+-ion conductivity of double phosphate Na3Sc2(PO4)3 in the region of the β-γ transition

The Na + -ion conductivity σ of double phosphate Na 3 Sc 2 (PO 4 ) 3 in the region of the β-γ transition has been studied using impedance spectroscopy (1–10 6 Hz). The polycrystalline sample of Na 3 Sc 2 (PO 4 ) 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 3 Sc 2 (PO 4 ) 3 suffers a ∼1.5-fold jump at 470 ± 2 K upon heating and a ∼2.5-fold jump at 430 ± 4 K upon cooling (the temperature hysteresis of the jump in σ is 40 K). For double sodium-scandium phosphate γ-Na 3 Sc 2 (PO 4 ) 3 in the superionic state, σ attains 0.07 S/cm at 700 K and the ion transport activation enthalpy is 0.42 ± 0.02 eV.