Well-aligned polycrystalline lanthanum silicate oxyapatite grown by reactive diffusion between solid La sub(2)SiO sub(5) and gases [SiO+1/2O sub(2)]

The c-axis-oriented polycrystalline lanthanum silicate oxyapatite, La sub(9.48)(Si sub(5.89)[squ sub(0.11))O sub(26 ) ([squ denotes a vacancy in the Si site), was successfully prepared by the reactive diffusion between randomly grain-oriented La sub(2)SiO sub(5) polycrystal and [SiO+1/2O sub(2)] gases at 1873 K 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 P6 sub(3)/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 super(-3) to 1.17 10 super(-2) S/cm with increasing temperature from 923 to 1073 K. The activation energy of conduction was 0.23(2) eV. We have successfully prepared the highly c-axis-oriented polycrystalline La sub(9.48)(Si sub(5.89)[squ sub(0.11))O sub(26 ) by the reactive diffusion between randomly grain-oriented La sub(2)SiO sub(5) polycrystal and [SiO + 1/2O sub(2)] gases at 1873 K in Ar atmosphere. The crystal structure (space group P6 sub(3)/m) showed the deficiency of Si site of ca. 1.9 %.