Structural and lithium ion transport studies in borophosphate glasses

Lithium ion transport process and glass network modification upon the variation of network modifier (M) to former (F) ratio (M/F) in 30% LiBO2–70% [(M Li2O–F P2O5)] glasses have been investigated. The glasses with different M/F ratios (0.42–1.0) were prepared by melt quenching technique and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman and impedance spectroscopy techniques. The glass transition temperature, Tg increased with increasing M/F ratio suggesting an increase in overall connectivity of the network structure. Dc conductivity showed an enhancement of three orders of magnitude with increasing M/F. The observed increase in Tg and dc conductivity with modifier concentration has been explained on the basis of the competition between network breaking/forming events, leading to an increase in overall connectivity of the network and the formation of continuous channels for ion migration. Ac conductivity data were analyzed by fitting the data to Almond-West type power law equation, σ′(ω) = σ(0) + Aωn. The power law exponent, n, was found to be temperature dependent and exhibited a minimum, nmin. The observation of nmin has been explained in the light of diffusion controlled relaxation (DCR) model. Furthermore, the scaling of both ac conductivity and electrical modulus data showed an excellent collapse on to a single master curve indicating that there is a good time–temperature superposition and that conduction mechanism remains unchanged in this glass system.