Influence of Yttrium Concentration on Local Structure in BaZr1-xYxO3-δ Based Proton Conductors

The evolution of local structure, coordination of protons, and proton conductivity in yttrium-doped barium zirconate, BaZr1-xYxO3-delta (x = 0-0.5), has been investigated using thermal-gravimetric analysis, impedance spectroscopy, and infrared spectroscopy. Low-frequency (50-1000 cm(-1)) infrared absorbance spectra provide evidence of increasing local structural distortions as a function of yttrium concentration as well as subtle differences, mainly linked to the oxygen sublattice, between the dry and hydrated samples. High-frequency (1700-4500 cm(-1)) spectra of the hydrated samples, distinguished by a broad O-H stretch continuum, manifest a varying degree of hydrogen bond interactions between the protons and nearest neighbor oxygens due to the disordered crystal structure with a general weakening in. particular of the strongest hydrogen bonding interactions with increasing dopant levels. It is argued that compositions within the range 0.15 <= x <= 0.3 possess a favorable level of local structural distortions to facilitate high proton conductivity, and this, coupled with a significant proton concentration, may be a factor in explaining the high proton conductivity these phases display.