Synthesis and characterization of potassium, rubidium, and cesium thiogermanate glasses

Glass-forming regions were investigated for the binary xM(2)S + (1-x)GeS2 (M = K, Rb, Cs) systems. Glasses were prepared from 0 less than or equal to x less than or equal to 0.20 mole fraction alkali sulfide using a novel preparation route involving the decomposition of the alkali hydrosulfides in situ. At higher alkali concentrations near x = 0.33, the glass-forming regions are limited by the readily formed adamantane-like M4Ge4S10 crystals. Structural characterization of the glasses and polycrystals for x less than or equal to 0.33 were performed using Raman scattering and IR absorption. Terminal Ge-S- vibrational modes, observed between 473 and 479 cm(-1), increased in intensity and decreased in frequency with increasing alkali modifier content. Glass transition temperatures decreased with increasing alkali modifier, ranging from 250 to 215 degreesC. Corresponding crystallization onset temperatures were between 340 and 385 degreesC. DC conductivity values of the glasses ranged from 10(-10) to 10(-7) (Omegacm)(-1) with activation energies between 0.54 and 0.93 eV for the temperature range of similar to100-250 degreesC. Higher ionic conductivities were observed with increasing alkali concentration and decreasing alkali radii. Additionally, an increase in the activation energy was observed above the glass transition temperature. (C) 2004 Published by Elsevier B.V.