O-H wag vibrations in hydrated BaInxZr1-xO3-xO2 investigated with inelastic neutron scattering

The nature of O-H wag vibrations in the cubic proton conducting perovskite-type oxides, BaInxZr1-xO3-x/2 (x=0.20-0.75) have been investigated by means of inelastic neutron scattering. Our spectroscopic results show that the O-H wag vibrations are manifested as a broad band between 600 and 1300 cm(-1). With increasing In concentration, the O-H wag band increases in intensity and broadens with an increased weight of the high frequency part. The intensity increase of the O-H wag band is a result of the increasing concentration of protons in the perovskite structure while the increased weight of the high frequency part results from an increased fraction of protons in strongly hydrogen bonding configurations. Such strongly hydrogen bonding configurations of the proton is primarily a result of the presence of oxygen vacancies and dopant atoms, which act as charged defects, but also of local structural distortions caused by the introduction of dopant atoms. From the temperature dependence of the O-H wag band we find that the mean square displacement of the protons increases only slightly as the temperature is raised from 30 to 300 K, which implies that it is unlikely that the protons undergo long-range diffusion for temperatures below 300 K. Comparing the In concentration dependence of different components of the O-H wag band with the proton conductivity of the reported compositions indicates that protons in weak or intermediate hydrogen bonding configurations are likely the main charge carriers.