Well-aligned polycrystalline lanthanum silicate oxyapatite grown by reactive diffusion between solid La2SiO5 and gases [SiO+1/2O2

Abstract

The c-axis-oriented polycrystalline lanthanum silicate oxyapatite, La9.48(Si5.89□0.11)O26 (□ denotes a vacancy in the Si site), was successfully prepared by the reactive diffusion between randomly grain-oriented La2SiO5 polycrystal and [SiO+1/2O2] gases at 1873K in Ar atmosphere. The polycrystal was characterized using optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, X-ray diffractometry, and impedance spectroscopy. The crystal structure (space group P63/m) showed the deficiency of Si site at ca. 1.9%. The bulk oxide-ion conductivity along the grain-alignment direction steadily increased from 9.2 × 10−3 to 1.17 × 10−2S/cm with increasing temperature from 923 to 1073K. The activation energy of conduction was 0.23(2)eV.