Thermal, physical, electrical and XPS studies of the Li 2O:P 2O 5: MoO 3 glass system

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The glass-forming region in the Li 2O:P 2O 5:MoO 3 system has been determined. Three series of glasses with 40, 50 and 60 mol% Li 2O have been studied. Maxima in glass transition temperature were observe around x = [MoO 3]/([MoO 3]+[P 2 O 5]) = 0.4. This was attributed to a convolution of the increasing cross-link density and decreasing mean bond strength with increasing x. DC conductivity, σ, was found to increase with x for a given Li 2O content, with the composition 0.5Li 2O:0.5(0.6P 2O 5:0.4MoOin3) having the highest σ at 25 °C. Linear correlation between the activation energy for conduction, Eact, and logarithm of the pre-exponential factor, σ 0, in the Arrhenius equation was attributed to strong entropy-enthalpy interaction. Binding energies of the Li 1s, P 2p, Mo3 d 5 2 and O1s core-levels have been determined from the respective XPS spectra. Upon deconvolution, the XPS O1s spectrum was found to consist of two peaks. Phosphate groups in the glasses were found to be preferentially modified by Li 2O compared with molybdate groups, consistent with the order of acidity, P 2O 5>MoO 3, of glass-forming oxides in melts. The presence of Li 2O is also believed to have promoted the formation of POMo units at the expense of POP and MoOMo units.