Electrical properties of various cation doped lanthanum silicates

Abstract

Effects of cation doping into La- and Si-sites of the apatite-type lanthanum silicate, La9.33Si6O26 on their electrical properties were investigated. Since it has been known that a slight Al or Mg doping into its Si-site is effective to enhance its ionic conductivity, dense pellets of La9.33+x(Si6-yAly)O26+1.5x-0.5y and La9.33+x(Si6-yMgy)O26+1.5x-y were fabricated and their electrical conducting properties were studied. In each case, the maximum electrical conductivity was found around x = 0.67 and y = 0.2. In addition, system of (La9.67M0.33)(Si5.8Mg0.2)O26.3+a (M; La, Y, Ce) was also investigated. It was found that the optimization of excess oxygen content, and the vacancy creation into SiO4 tetrahedra are key issues to improve its conductivity.