Rare-earth silicate with an apatite structure was a new type of oxide ion conductor, the electrical conductivity of which was higher at relatively low temperatures than that of stabilized zirconia. Single crystals were indispensable in order to reveal the intrinsic bulk properties such as anisotropy of electrical conductivity. A review was presented of recent research work on single crystal growth via the float-zone method and electrical properties of this material, including re-investigation of phase relations in Nd2O3–SiO2 system and structure refinement using neutron diffraction. A possible mechanism for the oxide ion conduction was proposed based on the existence of cation vacancies.

Single Crystal Growth and Oxide Ion Conductivity of Apatite-Type Rare-Earth Silicates. M.Higuchi, Y.Masubuchi, S.Nakayama, S.Kikkawa, K.Kodaira: Solid State Ionics, 2004, 174[1-4], 73-80