Influence of Lattice Dynamics on the Proton Transport in BaZrY-Oxide Perovskites under High Pressure

Abstract

Proton-conducting metal oxides such as Y-doped BaZrO3 have a wide application prospect as electrochemical energy converters at intermediate temperature. Understanding their proton transport mechanisms is important for improving the proton conductivity. Here, we investigate the influence of the crystal structure and the lattice dynamics of the BaZr0.9Y0.1O3-δ proton conductor using high-pressure Raman spectroscopy and high-pressure X-ray diffraction. A linear increase in the Raman shifts with pressure between 2.7 and 7.5 cm–1GPa–1 is observed for the vibrational modes higher than 450 cm–1 but almost invariant for vibrational modes less than 450 cm–1, highlighting the more significant phonon hardening effect of Zr–O stretching motions at high pressure than other motions. When the pressure increases from ambient pressure to 2 GPa, despite the 4 orders of magnitude enhancement in the Arrhenius prefactor and attempt frequency, the 2-fold increase in the activation energy results in a smaller proton conductivity at low temperature upon phonon hardening. A scenario of proton transfer combined with the Zr–O stretching motion to overcome the energy barrier is illustrated. According to the proton polaron model, the calculated polaron radius lies in the range of lattice parameters, suggesting the formation of lattice polarons in BaZr0.9Y0.1O3-δ. Our findings suggest that a softer lattice can enhance the low-temperature proton conductivity with a reduced energy barrier.