Sintering temperature is used to control the microstructure of Li(1+x+y)Al(x)Ti(2-x)Si(y)P(3-y)O(12)(x=0.3, y=0.2), a NASICON-type glass-ceramic. Scanning Electron Microscope imaging, X-Ray Diffraction, and Electrochemical Impedance Spectroscopy are employed to show that increase in sintering temperature increases conductivity while generating secondary crystalline phases. Total conductivity is as high as 3.81 x 10(-4) S cm(-1) for sintering temperatures above 1000 degrees C. Crystallization of dielectric phases places the optimal sintering temperature in the 900 degrees C to 1000 degrees C range. Thermal analysis of the glass precursor reveals the glass transition, and crystallization temperatures. (C) 2010 Elsevier B.V. All rights reserved.