Proton-conducting BaO-P2O5 and BaO-La2O3-Al2O3-P2O5 glass thin films

BaO-P2O5 (BP) and BaO-La2O3-Al2O3-P2O5 (BLAP) glass thin films with a thickness of 80–160 nm, which have a high content of residual moisture and a high concentration of non-bridging oxygen (NBO) as a medium for proton movement, were fabricated through sol-gel spin coating using water as a solvent. All the fabricated glass thin films exhibited amorphous phase and glassy, defect-free surfaces. The thickness of the BP thin films decreased as the annealing temperature increased. The increase in the annealing temperature led to a decrease in NBO/BO ratio which is thought to affect proton mobility and an increase in mobile proton concentration. Therefore, it seems that high proton concentration by residual water appears to have a dominant effect on fast proton conduction. The calculated proton concentrations of the fabricated BP thin films were decreased from 55.9 mol/l to 45.5 mol/l as the annealing temperature increased from 300 °C to 400 °C. The conductivity of BP and BLAP thin films annealed at 400 °C were 2.52 × 10−6 S/cm and 1.32 × 10−5 S/cm, respectively, at 300 °C. BLAP thin film showed significantly improved conductivity compared to those of BP glass thin films due to its high proton concentration.