Structural and electrical properties of Li2O–ZnO–P2O5 glasses

Lithium zinc phosphate glasses of the composition xLi2O–(40 − x)ZnO–60P2O5, (0 < x < 40), in mol%, were prepared by melting and analyzed by different thermal analysis (DTA), Raman and impedance spectroscopy in the frequency range from 0.01 Hz to 4 MHz and temperature range from 303 to 473 K. The systematic change in the variety of properties at 20 mol% Li2O is explained by changes in the nature of the oxygen bonds in glass network. The Raman spectra predominantly show the metaphosphate structure with barely detectable pyrophosphate units for all glasses in the series. However, replacing ZnO with Li2O in these glasses leads to the compositional dependent changes. This dependence is explained by different structural cross-linking of phosphate chains with increasing Li2O, which is correlated with the unusual Tg minimum at 20 mol% Li2O. The electrical conductivity as a function of Li2O concentration measured at lower temperatures (298 and 363 K) passes through a minimum at 20 mol% whereas linearly increases at higher temperatures. This suggests that the conductivity enhancement is directly related to the thermally stimulated mobility of Li+ ions in the high temperature region. The observed minimum in electrical conductivity at 20 mol% Li2O is due to the structural reorganization of the glass network. With increasing Li2O content up to 40 mol% the values of electrical conductivity increases for five orders of magnitude indicating ionic conductivity.