Effect of very slow O diffusion at high temperature on very fast H diffusion in the hydride ion conductor LaH2.75O0.125

TL;DR

This study uses neural network-based molecular dynamics to investigate how slow oxygen diffusion at high temperatures influences rapid hydrogen diffusion in the hydride ion conductor LaH2.75O0.125, revealing temperature-dependent diffusion mechanisms.

Contribution

It demonstrates the temperature-dependent diffusion behavior of oxygen and hydrogen in LaH2.75O0.125 using advanced MD simulations with neural network potentials.

Findings

O begins diffusing above ~550 K

Two diffusion processes coexist above Tc with different activation barriers

O and La exhibit strongly anharmonic behavior

Abstract

Neural network potential based molecular dynamics (MD) simulations on the excellent H conductor LaH2.75O0.125 show that O starts diffusing above a critical temperature of Tc~550 K, according to the variance of atom positions regardless of the time step. The original diffusion process at temperatures below Tc has an activation barrier of 0.25 eV. Use of MD simulations with various O and La mass revealed, at above Tc, the coexistence of the 0.25 eV process and an additional diffusion process with an activation barrier of 0.20 eV. The O and La have strongly anharmonic characters.