Vibrational properties of protons in hydrated BaInxZr1-xO3-x/2 -: art. no. 094303

We investigate the local proton dynamics in the proton conducting hydrated perovskite system BaInxZr1-xO3-x/2 (x=0.25-0.75) using infrared spectroscopy and first-principles calculations. We show that oxygen vacancies and dopant atoms in the vicinity of the proton tilt the proton toward a neighboring oxygen creating strongly hydrogen-bonded configurations. This is manifested as a strong redshift of the O-H stretch band in the infrared absorption spectrum. We also find considerable fluctuations of the nearest and next-nearest oxygen-proton distances with time, resulting in additional spectral broadening. By comparing the frequencies of computed O-H stretch modes we can relate specific local configurations to different parts of the broad O-H stretch band. Even though hydrogen-bonded configurations favor proton transfer they hinder the long-range migration by decreasing the reorientational rate. Thus, in order to optimize the proton mobility it is important to avoid extreme configurations caused by either oxygen vacancies or dopant atoms in the perovskite structure.