Al2O3 was added to a 2CaO-La2O3-5P(2)O(5) metaphosphate, to replace 10% of the Ca2+ ions by Al3+, forming a phosphate with the nominal composition 1.8CaO-0.1Al(2)O(3)-La2O3-5P(2)O(5). The effect of Al2O3 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 degrees C for 1 h or 5 h, in air, following heating at 3 or 10 degrees C/min. With Al2O3 addition, after a heat treatment at 700 degrees C, 100-300 nm nano-domains of LaP3O9 crystallized from the glass matrix. Annealing at 800 degrees C produced a further order of magnitude conductivity increase for the Al-free glass, but less so for the M-containing glass. (C) 2009 Elsevier B.V. All rights reserved.