Defect levels and hyperfine constants of hydrogen in beryllium oxide from hybrid-functional calculations and muonium spectroscopy


The atomistic and electronic structures of isolated hydrogen states in BeO were studied by ab initio calculations and muonium spectroscopy (mu SR). Whereas standard density-functional theory with a semi-local GGA functional led to a detailed probing of all possible minimum-energy configurations of hydrogen further calculations with the hybrid HSE06 functional provided improved properties avoiding band-gap and self-interaction errors. Similarly to earlier findings for the other wide-gap alkalineearth oxide, MgO, hydrogen in BeO is also predicted to be an amphoteric defect with the pinning level, E(+/-), positioned in the mid-gap region. Both donor and acceptor levels were found too deep in the gap to allow for hydrogen to act as a source of free carriers. Whereas, hydrogen in its positively-charged state, H+, adopts exclusively hydroxide-bond OH configurations, H0 and H-instead show a preference to occupy cage-like interstitial sites in the lattice. H0 in particular displays a multitude of minimumenergy configurations: its lowest-energy ground state resembles closely a trapped-atom state with a nearly spherical spin-density profile. In contrast to the strongly ionic MgO, H0 in BeO was further found to stabilise in additional higher-energy elongatedbond OH configurations whose existence should be traced to a partial covalent character of the Be-O bonding. Calculations of the proton-electron hyperfine coupling for all H0 states showed that the ground-state interstitial H0 configuration is dominated by an isotropic hyperfine interaction with a magnitude very close to the vacuum value, a finding corroborated by the mu SR-spectroscopy data.



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Marinopoulos, AG; Vilao, RC; Vieira, RBL; Alberto, HV; Gil, JM; Yakushev, MV; Scheuermann, R; Goko, T

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This work was supported with funds from (i) FEDER (Programa Operacional Factores de Competitividade COMPETE) and from FCT Portugal - Fundacao para a Ciencia e Tecnologia under projects [UID/FIS/04564/2016] and [PTDC/FIS/102722/2008]; (ii) PhD [grant number SFRH/BD/87343/2012] from FCT - Fundacao para a Ciencia e Tecnologia (RBLV); (iii) RFBR [grant number 14-02-00080], [grant number 14-03-00121], [grant number 16-29-06410] (MVY); (iv) UB RAS [grant number 15-20-3-11] (MVY); (v) Act 211 of the Government of Russia 02.A03.21.0006 (MVY).

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