The effect of compressive strain on the Raman modes of the dry and hydrated BaCe0.8Y0.2O3 proton conductor

TL;DR

This study investigates how compressive strain and hydration affect the Raman modes and proton conductivity in BaCe0.8Y0.2O3, revealing strain-induced changes in lattice vibrations and activation barriers.

Contribution

It provides new insights into the anisotropic effects of strain on lattice dynamics and proton transfer in proton-conducting ceramics using high pressure Raman spectroscopy.

Findings

Hydration suppresses certain Raman mode variations.

Compressive strain increases the activation barrier for proton conduction.

Strain causes anisotropic phonon hardening and softening in the crystal lattice.

Abstract

The BaCe0.8Y0.2O3-{\delta} proton conductor under hydration and under compressive strain has been analyzed with high pressure Raman spectroscopy and high pressure x-ray diffraction. The pressure dependent variation of the Ag and B2g bending modes from the O-Ce-O unit is suppressed when the proton conductor is hydrated, affecting directly the proton transfer by locally changing the electron density of the oxygen ions. Compressive strain causes a hardening of the Ce-O stretching bond. The activation barrier for proton conductivity is raised, in line with recent findings using high pressure and high temperature impedance spectroscopy. The increasing Raman frequency of the B1g and B3g modes thus implies that the phonons become hardened and increase the vibration energy in the a-c crystal plane upon compressive strain, whereas phonons are relaxed in the b-axis, and thus reveal softening of the Ag and B2g modes. Lattice toughening in the a-c crystal plane raises therefore a higher activation barrier for proton transfer and thus anisotropic conductivity. The experimental findings of the interaction of protons with the ceramic host lattice under external strain may provide a general guideline for yet to develop epitaxial strained proton conducting thin film systems with high proton mobility and low activation energy.