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The local binding and migration behavior of the proton defect in cubic yttria-stabilized zirconia (YSZ) is studied by first-principles calculations and muon-spin spectroscopy (μSR) measurements. The calculations are based on density-functional theory (DFT) supplemented with a hybrid-functional approach with the proton defect embedded in quasi-random supercells of 10.3 mol% yttria content, where the yttrium–zirconium substitutional defects are charge compensated by oxygen vacancies. Representative migration pathways for the proton comprising both transfer and bond reorientation modes are analysed and linked to the underlying microstructure of the YSZ lattice. The μSR data show the evolution of the diamagnetic fraction corresponding to the muon-isotope analogue with an activation energy of diffusion equal to 0.17 eV. Comparisons between the calculations and the experiment allow an assessment of the character of the short-range migration of the proton particle in cubic YSZ. [ABSTRACT FROM AUTHOR]

Muonium, a positive muon and an electron, is often used as an experimentally accessible substitute for hydrogen in materials research. In semiconductors and insulators, a large amount of information on the hydrogen behavior is deduced from this analogy; however, it is seldom demonstrated that this procedure is justified. We show here, via a comparison of the hyperfine interactions, that in TiO2 muonium and hydrogen form the same configuration with the same basic electronic structure. A detailed description of the bonding characteristics of the muon to the Ti3+ polaron is presented. The special role of muon motion within the so-called oxygen channel in the rutile structure, which occurs at a lower temperature than for hydrogen, is emphasized. [ABSTRACT FROM AUTHOR]

We present a systematic study of isolated hydrogen in diverse forms of ZrO2 (zirconia), both undoped and stabilized in the cubic phase by additions of transition-metal oxides (Y2O3,Sc2O3, MgO, CaO). Hydrogen is modeled by using muonium as a pseudoisotope in muon-spin spectroscopy experiments. The muon study is also supplemented with first-principles calculations of the hydrogen states in scandia-stabilized zirconia by conventional density-functional theory (DFT) as well as a hybrid-functional approach which admixes a portion of exact exchange to the semilocal DFT exchange. The experimentally observable metastable states accessible by means of the muon implantation allowed us to probe two distinct hydrogen configurations predicted theoretically: an oxygen-bound configuration and a quasiatomic interstitial one with a large isotropic hyperfine constant. The neutral-oxygen-bound configuration is characterized by an electron spreading over the neighboring zirconium cations, forming a polaronic state with a vanishingly small hyperfine interaction at the muon. The atom-like interstitial muonium is observed also in all samples but with different fractions. The hyperfine interaction is isotropic in calcia-doped zirconia [Aiso=3.02(8) GHz], but slightly anisotropic in the nanograin yttria-doped zirconia [Aiso=2.1(1) GHz, D=0.13(2) GHz] probably due to muons stopping close to the interface regions between the nanograins in the latter case. [ABSTRACT FROM AUTHOR]

We present a systematic study of isolated hydrogen in α-TeO2 (paratellurite) by means of muon-spin spectroscopy measurements complemented by ab initio calculations based on density-functional theory (DFT). The observable metastable states accessible by means of the muon implantation allowed us to probe both the donor and the acceptor configurations of hydrogen, as well as to follow their dynamics. A shallow donor state with an ionization energy of 6 meV as well as a deep acceptor state are proposed, together with their atomic-level configurations and associated formation energies obtained from the DFT calculations. The latter show a tendency of interstitial hydrogen to bind strongly to bridging oxygen ions but also to coexist at sites deeper in the interior of the Te-O-Te rings with a more atomiclike character and a defect level in the gap. Atomlike interstitial muonium was observed; it has a hyperfine interaction of about 3.5 GHz. Charge and site changes with temperature are discussed. [ABSTRACT FROM AUTHOR]

The incorporation of interstitial hydrogen in yttria was studied by means of ab Initio calculations based on density-functional theory (DFT) and muonium spin polarization spectroscopy (μSR). The density-functional calculations, based on a semilocal functional within the GGA-PBE and a hybrid functional, uncovered multiple geometrical configurations for the neutral, H°, and the negatively charged, H~, states of hydrogen, thus demonstrating the existence of metastable minimum-energy sites. It was observed that the low-energy configurations for H° and H~ are similar: they prefer to relax in deep, interstitial sites, whereas the equilibrium configurations for the positively charged state, H+, were bond-type configurations with the hydrogen forming a covalent O-H bond with an Ο anion. For all neutral and negative configurations, localized defect levels were found inside the gap. Overall, the results for the formation energies obtained by the two different functionals are qualitatively similar; an amphoteric behavior was found for hydrogen after considering the lowest-energy structures for each charge state. The calculated acceptor transition level, obtained by the hybrid functional and seen near midgap, is consistent with μSR data from literature. The results are consistent with the present μSR data, where the observed diamagnetic signal is attributed to a donor-like muonium at the oxygen-bonded configurations and the paramagnetic signal to an acceptor-like deep muonium at the interstitial sites. [ABSTRACT FROM AUTHOR]