A dual phase glass-ceramic composite is produced by heating a CaLa(PO3)(5) glass at 800 degrees C for 20 h. The glass-ceramic consists of intertwined crystalline La(PO3)(3) and amorphous Ca(PO3)(2) with an overall conductivity of 1.52 x 10(-5) S/cm(-1) at 550 degrees C in humidified air. For the water vapor treated glass, the vibration modes of the incorporated water, as well as of P-OH groups, are detected by infrared spectroscopy in the range 3440-1660 cm(-1). The conductivity of the glass-ceramic is higher in humidified air than in dry air, consistent with proton conduction. Published by Elsevier B.V.