Diffusion Studies of H of Different Charge States and Their Interplay with Co Spin States in SrCoO2.5

The tunable magnetism and reversible phase transformation of ionic-liquid-gated SrCoO2.5 (SCO) have attracted vast research interest in the material system. H atoms at different charge states may play important roles in energy and spintronic devices, yet no systematic studies are available. How the H atoms at different diffusion pathways interplay with the spin states of Co ions is also unknown. To answer these questions, we used the climbing image nudged elastic band (CI-NEB) method based on spin-polarized DFT calculation to study various diffusion pathways of H at different charge states. The diffusivity of H, the preferred diffusion pathway, and the magnetic fluctuation can be strongly affected by the charge states of the system. The diffusion of a proton on the Sr–O layer is the fastest among all pathways because the Sr ion is relatively inert. Magnetic fluctuation is observed for the neutral state because of the complex charge transfer mechanism from the neutral H to various Co sites. Contrary to the common belief that diffusion of a proton is always faster than that of a neutral H, in some pathways, the change of the local crystal field and overlapping of bond orbitals may hinder the diffusion of protons and make the diffusion of H in the neutral state easier than that of the proton. Finally, we proposed various experimental treatments to tune the preferred diffusers and diffusion pathways. Our study may shed light on potential electronic and spintronic applications of SCO and other similar perovskite systems.