Single crystals of Sr-bearing neodymium silicates with the oxyapatite structure were grown by using the float-zone method. The grown crystals were free from any macroscopic defects and their quality was sufficient for electrical measurements. The electrical conductivity was enhanced by about 3 orders of magnitude by the introduction of cation vacancies into Sr2Nd8(SiO4)6O2; a compound without cation or O ion vacancies. The introduction of O ion vacancies to Sr2Nd8(SiO4)6O2 and Nd9.33(SiO4)6O2 did not significantly affect their electrical conductivity. Cation vacancies could play an important role in O ion conduction in oxyapatite type rare-earth silicates.

Single Crystal Growth and Oxide Ion Conductivity of Oxyapatite Type Sr-Bearing Neodymium Silicate. Y.Masubuchi, M.Higuchi, S.Kikkawa, K.Kodaira, S.Nakayama: Solid State Ionics, 2004, 175[1-4], 357-60