Excited configurations of hydrogen in the BaTiO3-xHx perovskite lattice associated with hydrogen exchange and transport

Year: 2017 DOI: 10.1103/PhysRevB.95.020301

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T. U. Ito, A. Koda, K. Shimomura, W. Higemoto, T. Matsuzaki, Yoji Kobayashi, Hiroshi Kageyama.   Physical Review B, 2017, 95, 1-5.


Excited configurations of hydrogen in the oxyhydride BaTiO3−xHx (x=0.1–0.5), which are considered to be involved in its hydrogen transport and exchange processes, were investigated by positive muon spin relaxation spectroscopy using muonium (Mu) as a pseudoisotope of hydrogen. Muons implanted into the BaTiO3−xHx perovskite lattice were mainly found in two qualitatively different metastable states. One was assigned to a highly mobile interstitial protonic state, which is commonly observed in perovskite oxides. The other was found to form an entangled two spin-12 system with the nuclear spin of an H ion at the anion site. The structure of the (H,Mu) complex agrees well with that of a neutralized center containing two H ions at a doubly charged oxygen vacancy, which was predicted to form in the SrTiO3−δ perovskite lattice by a computational study [Y. Iwazaki et al., APL Mater. 2, 012103 (2014)]. Above 100 K, interstitial Mu+ diffusion and retrapping to a deep defect were observed, which could be a rate-limiting step of macroscopic Mu/H transport in the BaTiO3−xHx lattice.