Role of interstitial hydrogen in SrCoO2.5 antiferromagnetic insulator

Abstract

Hydrogen exhibits qualitatively different charge states depending on the host material, as nicely explained by the state-of-the-art impurity-state calculation. Motivated by a recent experiment [Nature 546, 124 (2017)], we show that the complex oxide SrCoO2.5 represents an interesting example, in which the interstitial H appears as a deep-level center according to the commonly-used transition level calculation, but no bound electron can be found around the impurity. Via a combination of charge difference analysis, density of states projection and constraint magnetization calculation, it turns out that the H-doped electron is spontaneously trapped by a nonunique Co ion and is fully spin-polarized by the onsite Hund's rule coupling. Consequently, the doped system remains insulating, whereas the antiferromagnetic exchange is slightly perturbed locally.

A Computational Study of Fast Proton Diffusion in Brownmillerite Sr2Co2O5

“…32 Using Bader charge analysis, 43 we quantified the Bader charge around Co ions in H x SCO structures at different H concentrations and showed that the valence of Co reduces upon H insertion (Figure S3), consistent with a prior computational study. 44 Therefore, the multivalence of Co 2+/3+ accounts for the charge compensation of hydrogen insertion.…”

“…This lack of the proton preference among interlayer and octahedral layers in H x SCO compared to dilute H in SCO may be caused by the increased H−H interactions and the valence change of the Co cation, which reduce the small site energy difference of less than 0.3 eV between proton sites (H1−H5) in the octahedral layer and interlayer. 44 The small energetic preference of proton sites among interlayer and octahedral layers in H x SCO is greatly beneficial for proton transport. In H x SCO, a significant fraction of proton sites in the octahedral layer and interlayer are available for proton hopping, and small energy changes during the transition of proton sublattice suggest a low energy barrier for proton migration.…”

“…Therefore, in H x SCO at high H concentration, protons are distributed among interlayer and octahedral layer sites. This lack of the proton preference among interlayer and octahedral layers in H x SCO compared to dilute H in SCO may be caused by the increased H–H interactions and the valence change of the Co cation, which reduce the small site energy difference of less than 0.3 eV between proton sites (H1–H5) in the octahedral layer and interlayer . The small energetic preference of proton sites among interlayer and octahedral layers in H x SCO is greatly beneficial for proton transport.…”

Surface Stability Analysis with H Adsorption Affected the Magnetic Fluctuation of Brownmillerite SrCoO2.5 Based on the Electron Counting Model by Layers

“…According to the compositions and neighboring layers, we can define three types of layers along [001] in bulk as L-Co (6) O, L-SrO, and L-Co (4) O, respectively, as shown in Figure 1. The L-Co (6) O and L-Co Co (4) O. Theoretically, BM-SCO has several different phases that correspond to different space groups, namely, Ima2, 11,22 Imma, 23 and Pmc2 1 . 10 According to our previous calculations, Pmc2 1 is the most stable.…”

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

“…9 Inside this cell, to understand the complex diffusion pathways, it is essential to define each atomic layer and important atomic sites. We denote the four-coordinated and six-coordinated Co ions as Co (4) and Co (6) , respectively. There are three types of atomic layers along the [001] direction, and we denote the layer consisting of Co (6) and O ions as L-Co (6) O, the layer consisting of Co (4) and O ions as L-Co (4) O, and the layer consisting of Sr and O ions as L-SrO.…”