Local electronic structure of interstitial hydrogen in MgH2inferred from muon study

Ryosuke Kadono; Masatoshi Hiraishi; Hirotaka Okabe; Akihiro Koda; Takashi U Ito

doi:10.1088/1361-648X/acccc7

Local electronic structure of interstitial hydrogen in MgH₂inferred from muon study

J Phys Condens Matter. 2023 Apr 21;35(28). doi: 10.1088/1361-648X/acccc7.

Authors

Ryosuke Kadono¹, Masatoshi Hiraishi², Hirotaka Okabe³, Akihiro Koda^{1

4}, Takashi U Ito⁵

Affiliations

¹ Muon Science Laboratory and Condensed Matter Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK-IMSS), Tsukuba, Ibaraki 305-0801, Japan.
² Institute of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki 310-8512, Japan.
³ Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
⁴ Department of Materials Structure Science, The Graduate University for Advanced Studies (Sokendai),Tsukuba, Ibaraki 305-0801, Japan.
⁵ Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan.

PMID: 37054730
DOI: 10.1088/1361-648X/acccc7

Abstract

Magnesium hydride has great potential as a solid hydrogen (H) storage material because of its high H storage capacity of 7.6 wt%. However, its slow hydrogenation and dehydrogenation kinetics and the high temperature of 300 ^∘C required for decomposition are major obstacles to small-scale applications such as automobiles. The local electronic structure of interstitial H in MgH₂is an important fundamental knowledge in solving this problem, which has been studied mainly based on density functional theory (DFT). However, few experimental studies have been performed to assess the results of DFT calculations. We have therefore introduced muon (Mu) as pseudo-H into MgH₂and investigated the corresponding interstitial H states by analyzing their electronic and dynamical properties in detail. As a result, we observed multiple Mu states similar to those observed in wide-gap oxides, and found that their electronic states can be attributed to relaxed-excited states associated with donor/acceptor levels predicted by the recently proposed 'ambipolarity model'. This provides an indirect support for the DFT calculations on which the model is based via the donor/acceptor levels. An important implication of the muon results for improved hydrogen kinetics is that dehydrogenation, serving as areductionfor hydrides, stabilises the interstitial H^-state.

Keywords: electronic structure; hydrogen state; interstitial hydrogen; muon spin rotation.