The state of POnb non-bridging oxygen and proton incorporation in binary MO·P2O5 (M = Ca, Mg) phosphate glasses

Binary xMO·(100 − x)P2O5 (mol%; M = Ca, Mg) glasses were prepared using a conventional melting method, and the proton conduction mechanism in the glasses was investigated. The proton conductivities of the glasses were measured under various hydrogen (H2) gas concentrations from 0 to 100 vol.% using Pt electrodes. The CaO·P2O5 glasses show higher proton conductivities than MgO·P2O5 ones. Fourier-transform infrared (FTIR) measurements showed that protons dissociated from H2 gas at the Pt electrodes are incorporated into the glasses, and the proton conductivity increases as a result of an increase in the carrier (proton) concentration. There is a good linear relationship between the peak wavenumber of POnb (Onb indicates non-bridging oxygen) and the proton conductivity measured in a 100 vol.% H2 atmosphere. Furthermore synchrotron radiation X-ray diffraction (SRXRD) and FTIR results suggest that the π-electron of PO double bond is localized significantly in MgO·P2O5 compared with CaO·P2O5 glasses, which is the origin of higher proton conductivity in CaO·P2O5 glasses.