Protons in lattice confinement: Static pressure on the Y-substituted, hydrated BaZrO3 ceramic proton conductor decreases proton mobility

TL;DR

This study investigates how high mechanical pressure affects proton conductivity in Y-substituted BaZrO3 ceramics, revealing that pressure influences activation energies and proton mobility, with implications for material design.

Contribution

It provides new insights into the pressure-dependent proton conduction mechanisms in BaZrO3 ceramics, highlighting the effects of synthesis method and pressure on activation energies and mobility.

Findings

Bulk activation energy increases with pressure, more so in solid-state samples.

Grain boundary activation energy peaks at 1.25-1.5 GPa, then decreases.

Pressure-induced sintering reduces grain boundary resistance.

Abstract

Yttrium substituted BaZrO3, with nominal composition BaZr0.9Y0.1O3, a ceramic proton conductor, was subject to impedance spectroscopy for temperatures 300 K < T < 715 K at mechanical pressures 1 GPa < p < 2 GPa. The activation energies Ea of bulk and grain boundary conductivity from two perovskites synthesized by solid-state reaction and sol-gel method were determined under high pressures. At high temperature, the bulk activation energy increases with pressure by 5% for sol-gel derived sample and by 40% for solid-state derived sample. For the sample prepared by solid-state reaction, there is a large gap of 0.17 eV between the activation energy at 1.0 GPa and > 1.2 GPa. The grain boundary activation energy is around a factor two times as that of the bulk, and it reaches a maximum at 1.25 - 1.5 GPa, and then decrease as the pressure increases, indicating higher proton mobility in the grain boundaries at higher pressure. Since this effect is not reversible, it is suggested that the grain boundary resistance decreases as a result of pressure induced sintering. The steady increase of the bulk resistivity upon pressurizing suggests that the proton mobility depends on the space available in the lattice. In return, an expanded lattice with a/a0 > 1 should thus have a lower activation energy, suggesting that thin films expansive tensile strain could have a larger proton conductivity with desirable properties for applications.