Crystallization and conductivity of 2CaO–La 2O 3–5P 2O 5 glass–ceramic with Al 2O 3 addition

Abstract

Al 2O 3 was added to a 2CaO–La 2O 3–5P 2O 5 metaphosphate, to replace 10% of the Ca 2+ ions by Al 3+, forming a phosphate with the nominal composition 1.8CaO–0.1Al 2O 3–La 2O 3–5P 2O 5. The effect of Al 2O 3 addition and heat treatment on the microstructure and conductivity of the resulting glass–ceramics was investigated by XRD, SEM, TEM, and AC impedance spectroscopy. Upon transformation from glass to glass–ceramic, conductivities increased significantly. The glasses were isochronally transformed at 700 and at 800 °C for 1 h or 5 h, in air, following heating at 3 or 10 °C/min. With Al 2O 3 addition, after a heat treatment at 700 °C, 100–300 nm nano-domains of LaP 3O 9 crystallized from the glass matrix. Annealing at 800 °C produced a further order of magnitude conductivity increase for the Al-free glass, but less so for the Al-containing glass.