1.IntroductionDunn and Farrington[1]found that theNa ion in Naβ″-alumina single crystal canbe exchanged completely or partially withGd~(3+),Nd~(3+),Eu~(3+),Yb~(3+),Sm~(3+),Tb~(3+),Dy~(3+),Bi~(3+)and Pr~(3+)ions,but no reports havebeen published about the ion exchange reac-tion between La3+ and Naβ″-alumina.If anion exchanged polycrystalline β″-alumina isavailable and its ionic conductivity is highenough to be applied as a solid electrolyte inthe galvanic cell,it can be used in various 1. Introduction Dunn and Farrington [1] found that NaN ion in Naβ “-alumina single crystal canbe exchanged completely or partially with Gd ~ (3 +), Nd ~ (3 +), Eu ~ (3 +), Yb ~ (3+ ), Sm ~ (3 +), Tb ~ (3 +), Dy ~ (3 +), Bi ~ (3+) and Pr ~ (3+) ions, but no report havebeen published about the ion exchange reac tion between La3 + and Naβ ”-alumina.If anion repeated polycrystalline β" -alumina isavailable and its ionic conductivity is highenough to be applied as a solid electrolyte inthe galvanic cell, it can be used in various