Relationship between structure and mobility of proton carriers injected by electrochemical substitution of sodium ions with protons in 35NaO1/2-1 WO3-8NbO5/2-5LaO3/2-51PO5/2-based glasses

Using Raman and 31P magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies, we studied the structural changes in 35NaO1/2-1WO3-8NbO5/2-5LaO3/2-51PO5/2 glass upon introducing Al2O3 and/or Y2O3 in order to understand the reduced mobility of proton carriers in glasses with Al2O3 and/or Y2O3 in which proton carriers were injected by alkali-proton substitution (APS). The Raman and 31P MAS-NMR spectra showed that phosphate chains were shortened by the Al2O3 and/or Y2O3 introduced into 1W glass. This structural change increased the fraction of protons bound to oxygen atoms in the terminal PO4 (i.e., the Q1 unit) of the phosphate chains. Because the protons bound to terminal Q1 units in phosphate chains tightly bind to oxygen atoms, as opposed to the protons bound to inner Q2 units in phosphate chains, we attributed the reduced mobility of proton carriers upon introducing AlO3/2 and/or YO3/2 into 1W glass to the shortening of phosphate chains. From these results we propose that to obtain a highly proton-conducting glass after APS, the glass must have a composition of O/P < 3.5 and thus a sufficiently high fraction of Q2 units.