Oxide-ion conductivity enhancement of polycrystalline lanthanum silicate oxyapatite induced by BaO doping and grain alignment

摘要

We prepared the c-axis-oriented polycrystal of BaO-doped lanthanum silicate oxyapatite (LSO) by reactive diffusion technique. The sandwich-type ternary diffusion couple, which was made up of La2SiO5/[La2Si2O7 + BaO-doped LSO]/La2SiO5, was heated at 1873 K for 100 h. The thin-plate polycrystalline electrolyte was mechanically extracted from the inner part of the annealed couple, and characterized by optical microscopy, electron probe micro-analysis (EPMA), X-ray diffractometry (XRD), and impedance spectroscopy. Based on the numbers of cations determined by EPMA and structural data refined by single-crystal XRD, the chemical formula of the constituent crystallites was determined to be (La_(9.32)Ba_(0.37))(Si_(5.82)□_(0.18))O_(26), where □ denotes a vacancy in Si site. The combined use of BaO-doping and grain-alignment techniques effectively improved the oxide-ion conductivity, which steadily increased from 3.27 X 10~(-2) to 2.15 X 10~(-1) S cm~(-1) with increasing temperature from 773 to 1023 K.