Synthesis and properties of La 2(Mo 1 - XM x) 2O 9 (M = Nb, Ta) ionic conductors

La 2(Mo 1 - xM x) 2O 9 (M = Nb, Ta; 0 < x ≤ 0.2) solid solutions were prepared, and their physicochemical and electrical properties were studied. Second harmonic generation measurements indicate that the solid solutions have a noncentrosymmetric structure and undergo a structural phase transition accompanied by a sharp increase in ionic conductivity, similar to that of La 2Mo 2O 9. The transition temperature is found to decrease with increasing Nb or Ta content. The introduction of 5 wt % Nb increases the 800°C conductivity of the material.