The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
R L Lichti - One of the best experts on this subject based on the ideXlab platform.
-
Muonium donor in rutile tio 2 and comparison with hydrogen
Physical Review B, 2015Co-Authors: R C Vilao, R L Lichti, J M Gil, H V Alberto, A Weidinger, R B L Vieira, B B Baker, P W Mengyan, J S LordAbstract:Muonium is like hydrogen, but with a positively charged muon instead of a proton at the center. Observing muon spin rotation in a single crystal of TiO${}_{2}$, and comparing to existing data for hydrogen, the authors demonstrate that the defect configuration and electronic structure are the same for both. This provides important support for research which uses muons as a substitute for hydrogen in semiconductors.
-
evidence for a shallow Muonium acceptor state in ge rich cz si1 xgex
Physica B-condensed Matter, 2009Co-Authors: B R Carroll, Y G Celebi, P J C King, R L Lichti, K H Chow, Ichiro YonenagaAbstract:Abstract We have observed muon spin rotation ( μ SR ) features that are consistent with a shallow Muonium (Mu) acceptor state for several Ge-rich silicon germanium alloy compositions. The Mu T [ 0 / - ] defect level crosses into the valence band at a Ge content of roughly 92%, indicating that a shallow acceptor state should be formed for muons that stop in the acceptor related T-site. For Si 0.09 Ge 0.91 , the difference between the diamagnetic amplitudes from RF-driven resonance measurements compared to TF- μ SR indicates a slowly formed state at temperatures below 50 K, consistent with a valence-band resonant Mu - that would form the core of a shallow Mu acceptor. We report a summary of hyperfine characterization and transition energies of the various T-site Muonium states in Ge-rich alloys and discuss options for the conditions under which shallow acceptor states may be observed by μ SR .
-
shallow donor state of hydrogen in in 2 o 3 and sno 2 implications for conductivity in transparent conducting oxides
Physical Review B, 2009Co-Authors: P D C King, Y G Celebi, R L Lichti, J M Gil, H V Alberto, R C Vilao, Piroto J Duarte, Dj Payne, R G Egdell, Iain MckenzieAbstract:Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In2O3 and SnO2. The paramagnetic charge state is stable below similar to 50 K in In2O3 and similar to 30 K in SnO2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.
-
novel Muonium centers magnetic polarons in magnetic semiconductors
Physica B-condensed Matter, 2009Co-Authors: V G Storchak, R L Lichti, J H Brewer, Oleg E Parfenov, Peter L Russo, Scott L Stubbs, D G Eshchenko, E Morenzoni, V P Zlomanov, A A VinokurovAbstract:Muonium centers are readily formed in a wide variety of insulators and semiconductors due to enormous capture cross sections of the unscreened Coulomb potential produced by positive muons. Following the initial capture, different processes of electron localization produce two basically different Muonium atoms—deep centers with the characteristic length scale of about the Bohr radius and shallow centers where electron is delocalized over many dozens of lattice spacings. In magnetic semiconductors, additional localization mechanism—exchange interaction–causes electron localization around the muon within about one lattice spacing. This novel Muonium center—bound magnetic polaron—is found in Eu and Sm chalcogenides and ferromagnetic spinels.
-
acceptor level of interstitial Muonium in znse and zns
Physical Review B, 2008Co-Authors: R C Vilao, R L Lichti, K H Chow, S P Cottrell, J M Gil, H V Alberto, Piroto J Duarte, Ayres N De Campos, A Weidinger, S F J CoxAbstract:, and subsequent emission of an electron from Mu to the conduction band.In this model, the emission step yields the binding energy for the second electron to place the Muoniumacceptor levels at 0.10 2 and 0.33 5 eV below the conduction-band edge for ZnSe and ZnS, respectively. Anapproximate constancy of the Muonium electron affinity for Zn and Cd semiconductor compounds is suggestedand the consequences for the observed Muonium states are discussed.DOI: 10.1103/PhysRevB.77.235212 PACS number s : 61.72.uj, 71.55.Gs, 76.75. i
S F J Cox - One of the best experts on this subject based on the ideXlab platform.
-
Muonium chemistry and spin dynamics in sulphur modelling interstitial hydrogen
Journal of Physics: Condensed Matter, 2011Co-Authors: S F J Cox, J S Lord, Iain Mckenzie, Jean Joseph Adjizian, M I Heggie, Upali A Jayasooriya, Roger Grinter, I D ReidAbstract:The nature of the elusive Muonium centre in sulphur is re-examined in the light of new data on its level-crossing resonance and spin–lattice relaxation. The aim is to provide a model for the solid-state chemistry of interstitial hydrogen in this element, which is as yet unknown, as well as to solve one of the longest standing puzzles in μSR spectroscopy, namely the surprisingly strong depolarization of muons mimicking ion-implanted protons in this innocuous non-magnetic material. The paramagnetic Muonium (and by inference hydrogen) centre is confirmed to have the character of a molecular radical, but with huge anisotropy at cryogenic temperatures and a striking shift of the resonance at ordinary temperatures, the hyperfine parameters appearing to collapse and vanish towards the melting point. New density-functional supercell calculations identify a number of possible structures for the defect centre, including a novel form of bond-centred Muonium in a closed-ring S8Mu complex. Simulations of the spin dynamics and fits to the spectra suggest a dynamical equilibrium or chemical exchange between several configurations, with occupancy of the bond-centre site falling from unity at low cryogenic temperatures to zero near the melting point.
-
Muonium as a model for interstitial hydrogen in the semiconducting and semimetallic elements
Reports on Progress in Physics, 2009Co-Authors: S F J CoxAbstract:Although the interstitial hydrogen atom would seem to be one of the simplest defect centres in any lattice, its solid state chemistry is in fact unknown in many materials, not least amongst the elements. In semiconductors, the realization that hydrogen can profoundly influence electronic properties even as a trace impurity has prompted its study by all available means-but still only in the functionally important or potentially important materials-for the elements, Si, Ge and diamond. Even here, it was not studies of hydrogen itself but of its pseudo-isotope, Muonium, that first provided the much needed microscopic pictures of crystallographic site and local electronic structure-now comprehensively confirmed by ab initio computation and such data as exists for monatomic, interstitial hydrogen centres in Si. Muonium can be formed in a variety of neutral paramagnetic states when positive muons are implanted into non-metals. The simple trapped atom is commonly only metastable. It coexists with or reacts to give defect centres with the unpaired electron in somewhat more extended orbitals. Indications of complete delocalization into effective mass states are discussed for B, α-Sn, Bi and even Ge, but otherwise all the Muonium centres seen in the elemental semiconductors are deep and relatively compact. These are revealed, distinguished and characterized by μSR spectroscopy-muon spin rotation and resonance informing on sites and spin-density distributions, muon spin relaxation on motional dynamics and charge-state transitions. This Report documents the progress of μSR studies for all the semiconductors and semimetals of the p-block elements, Groups III-VI of the Periodic Table. The striking spectra and originally unanticipated results for Group IV are for the most part well known but deserve summarizing and updating; the sheer diversity of Muonium states found is still remarkable, especially in carbon allotropes. The interplay of crystallographic site and charge state in Si and Ge at high temperatures, or under illumination, reflects the capture and loss of charge carriers that should model the electrical activity of monatomic hydrogen but still challenges theoretical descriptions. Spin-flip scattering of conduction electrons by the paramagnetic centres is revealed in heavily doped n-type material, as well as some modification of the local electronic structures. The corresponding spectroscopy for the solid elements of Groups III, V and VI is rather less well known and is reviewed here for the first time; a good deal of previously unpublished data is also included. Theoretical expectations and computational modelling are sparse, here. Recent results for B suggest a relatively shallow centre with molecular character; P and As show deeper quasi-atomic states, but still with substantial overlap of spin density onto surrounding host atoms. Particular attention is paid to the chalcogens. Muonium centres in Te show charge-state transitions already around room temperature; the identification of those in S and Se has been complicated by unusual spin dynamics of a different character, here attributed to spin-orbit coupling and interstitial reorientation. In the metals and semimetals, Muonium is not formed as a paramagnetic centre. Here the implanted muons mimic interstital protons and interest shifts to a variety of other topics, including aspects of charge screening (α-Sn, Sb, Bi), site preference and quantum mobility (Al, β-Sn, Pb). The post-transition metals receive only a brief mention, by way of contrast with the nonmetals. Systematic studies of local susceptibility via measurements of muon Knight shifts extends in favourable cases to revealing the elusive high-field Condon domains (Al, Sn, Pb, Bi). Some new information is available on the superconducting phases. Appendices include a derivation of the spin Hamiltonian for paramagnetic Muonium centres or molecular radicals having varying admixtures of orbital angular momentum, including the extreme case of orbital degeneracy, and examine the consequences of significant spin-orbit coupling for μSR spectroscopy and muon spin relaxation. This is the framework for the tentative assignments made here for the Muonium defect centres formed in sulphur and selenium, namely diatomic species resembling the chalcogen monohydrides. Equally, it provides guidelines for eventual solid-state detection of OMu-the elusive muoniated hydroxyl radical.
-
acceptor level of interstitial Muonium in znse and zns
Physical Review B, 2008Co-Authors: R C Vilao, R L Lichti, K H Chow, S P Cottrell, J M Gil, H V Alberto, Piroto J Duarte, Ayres N De Campos, A Weidinger, S F J CoxAbstract:, and subsequent emission of an electron from Mu to the conduction band.In this model, the emission step yields the binding energy for the second electron to place the Muoniumacceptor levels at 0.10 2 and 0.33 5 eV below the conduction-band edge for ZnSe and ZnS, respectively. Anapproximate constancy of the Muonium electron affinity for Zn and Cd semiconductor compounds is suggestedand the consequences for the observed Muonium states are discussed.DOI: 10.1103/PhysRevB.77.235212 PACS number s : 61.72.uj, 71.55.Gs, 76.75. i
-
location of the h level experimental limits for Muonium
Physica B-condensed Matter, 2006Co-Authors: R L Lichti, K H Chow, J M Gil, R C Vilao, S F J Cox, D L StripeAbstract:Abstract The defect energy levels for Muonium, a light pseudo-isotope of hydrogen, are investigated to define the equivalent of the H [ + /- ] level which is predicted to be fixed at a universal energy. Existing results for Mu at donor and acceptor sites in silicon tentatively place Mu [ + /- ] approximately 0.5 eV above the predicted hydrogen level. Measured donor ionization energies in other materials in which two neutral Mu centers are observed define a range for the Mu acceptor energies. We discuss possible reinterpretation of known energies and the current state of investigations to obtain these Muonium acceptor levels in order to further refine a determination of the Mu [ + /- ] energy.
-
Muonium spectroscopy in znse metastability and conversion
Physical Review B, 2005Co-Authors: R C Vilao, R L Lichti, K H Chow, J M Gil, H V Alberto, Piroto J Duarte, Ayres N De Campos, A Weidinger, S F J CoxAbstract:High-precision spectroscopic information is obtained on the Muonium states in ZnSe by high-field transverse $\ensuremath{\mu}\mathrm{SR}$ measurements. At low temperatures, two Muonium states ${\mathrm{Mu}}_{I}$ and ${\mathrm{Mu}}_{II}$ are observed with isotropic hyperfine parameters of ${\mathrm{A}}_{I}=3283.63\ifmmode\pm\else\textpm\fi{}0.51\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and ${\mathrm{A}}_{II}=3454.26\ifmmode\pm\else\textpm\fi{}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ (74% and 77% of the vacuum value, respectively). State I is thermally unstable and converts to state II at approximately $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. State II is stable up to $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, at least. We assign ${\mathrm{Mu}}_{II}$ to the cation interstitial tetrahedral site and discuss the possibility that ${\mathrm{Mu}}_{I}$ may correspond either to Muonium at the same site but in the unrelaxed lattice or to the anion interstitial tetrahedral site. The temperature dependence of the hyperfine interaction was fitted with a local vibrational model giving an oscillator energy of approximately $8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. The amplitudes and the depolarization rates are measured over the entire temperature range and are discussed in the text.
M Iwasaki - One of the best experts on this subject based on the ideXlab platform.
-
new precise spectroscopy of the hyperfine structure in Muonium with a high intensity pulsed muon beam
Physics Letters B, 2021Co-Authors: S. Kanda, Y Fukao, Yutaka Ikedo, Kunio Ishida, M Iwasaki, D Kawall, N KawamuraAbstract:Abstract A hydrogen-like atom consisting of a positive muon and an electron is known as Muonium. It is a near-ideal two-body system for a precision test of bound-state theory and fundamental symmetries. The MuSEUM collaboration performed a new precision measurement of the Muonium ground-state hyperfine structure at J-PARC using a high-intensity pulsed muon beam and a high-rate capable positron counter. The resonance of hyperfine transition was successfully observed at a near-zero magnetic field, and the Muonium hyperfine structure interval of ν HFS = 4.463302 ( 4 ) GHz was obtained with a relative precision of 0.9 ppm. The result was consistent with the previous ones obtained at Los Alamos National Laboratory and the current theoretical calculation. We present a demonstration of the microwave spectroscopy of Muonium for future experiments to achieve the highest precision.
-
study of Muonium emission from laser ablated silica aerogel
Progress of Theoretical and Experimental Physics, 2020Co-Authors: J Beare, J H Brewer, K Ishida, M Iwasaki, N Kawamura, G Beer, T Iijima, S Kamal, Kazuyoshi Kanamori, Ryo KitamuraAbstract:The emission of Muonium ($\mu^+e^-$) atoms into vacuum from silica aerogel with laser ablation on its surface was studied with various ablation structures at room temperature using the subsurface muon beams at TRIUMF and Japan Proton Accelerator Research Complex (J-PARC). Laser ablation was applied to produce holes or grooves with typical dimensions of a few hundred $\mu$m to a few mm, except for some extreme conditions. The measured emission rate tends to be higher for larger fractions of ablation opening and for shallower depths. More than a few ablation structures reach the emission rates similar to the highest achieved in the past measurements. The emission rate is found to be stable at least for a couple of days. Measurements of spin precession amplitudes for the produced Muonium atoms and remaining muons in a magnetic field determine a Muonium formation fraction of $(65.5 \pm 1.8)$%. The precession of the polarized Muonium atoms is also observed clearly in vacuum. A projection of the emission rates measured at TRIUMF to the corresponding rates at J-PARC is demonstrated taking the different beam condition into account reasonably.
-
new precise measurement of Muonium hyperfine structure interval at j parc
Hyperfine Interactions, 2017Co-Authors: Yasuhiro Ueno, Y Fukao, Yutaka Ikedo, Kunio Ishida, M Aoki, Y Higashi, T Higuchi, H Iinuma, Takashi U Ito, M IwasakiAbstract:MuSEUM is an international collaboration aiming at a new precise measurement of the Muonium hyperfine structure at J-PARC (Japan Proton Accelerator Research Complex). Utilizing its intense pulsed muon beam, we expect a ten-fold improvement for both measurements at high magnetic field and zero magnetic field. We have developed a sophisticated monitoring system, including a beam profile monitor to measure the 3D distribution of Muonium atoms to suppress the systematic uncertainty.
-
new Muonium hfs measurements at j parc muse
Hyperfine Interactions, 2016Co-Authors: P Strasser, Y Fukao, Yutaka Ikedo, Kunio Ishida, M Aoki, Y Higashi, T Higuchi, H Iinuma, Takashi U Ito, M IwasakiAbstract:At the Muon Science Facility (MUSE) of J-PARC (Japan Proton Accelerator Research Complex), the MuSEUM collaboration is planing new measurements of the ground state hyperfine structure (HFS) of Muonium both at zero field and at high magnetic field. The previous measurements were performed both at LAMPF (Los Alamos Meson Physics Facility) with experimental uncertainties mostly dominated by statistical errors. The new high intensity muon beam that will soon be available at MUSE H-Line will provide an opportunity to improve the precision of these measurements by one order of magnitude. An overview of the different aspects of these new Muonium HFS measurements, the current status of the preparation, and the results of a first commissioning test experiment at zero field are presented.
-
enhancement of Muonium emission rate from silica aerogel with a laser ablated surface
arXiv: Instrumentation and Detectors, 2014Co-Authors: G Beer, S. Kanda, H Kawai, K Ishida, M Iwasaki, N Kawamura, Y Fujiwara, S Hirota, Ryo Kitamura, S L LeeAbstract:Emission of Muonium ($\mu^+e^-$) atoms from a laser-processed aerogel surface into vacuum was studied for the first time. Laser ablation was used to create hole-like regions with diameter of about 270$~\mu$m in a triangular pattern with hole separation in the range of 300--500$~\mu$m. The emission probability for the laser-processed aerogel sample is at least eight times higher than for a uniform one.
N Kawamura - One of the best experts on this subject based on the ideXlab platform.
-
new precise spectroscopy of the hyperfine structure in Muonium with a high intensity pulsed muon beam
Physics Letters B, 2021Co-Authors: S. Kanda, Y Fukao, Yutaka Ikedo, Kunio Ishida, M Iwasaki, D Kawall, N KawamuraAbstract:Abstract A hydrogen-like atom consisting of a positive muon and an electron is known as Muonium. It is a near-ideal two-body system for a precision test of bound-state theory and fundamental symmetries. The MuSEUM collaboration performed a new precision measurement of the Muonium ground-state hyperfine structure at J-PARC using a high-intensity pulsed muon beam and a high-rate capable positron counter. The resonance of hyperfine transition was successfully observed at a near-zero magnetic field, and the Muonium hyperfine structure interval of ν HFS = 4.463302 ( 4 ) GHz was obtained with a relative precision of 0.9 ppm. The result was consistent with the previous ones obtained at Los Alamos National Laboratory and the current theoretical calculation. We present a demonstration of the microwave spectroscopy of Muonium for future experiments to achieve the highest precision.
-
study of Muonium emission from laser ablated silica aerogel
Progress of Theoretical and Experimental Physics, 2020Co-Authors: J Beare, J H Brewer, K Ishida, M Iwasaki, N Kawamura, G Beer, T Iijima, S Kamal, Kazuyoshi Kanamori, Ryo KitamuraAbstract:The emission of Muonium ($\mu^+e^-$) atoms into vacuum from silica aerogel with laser ablation on its surface was studied with various ablation structures at room temperature using the subsurface muon beams at TRIUMF and Japan Proton Accelerator Research Complex (J-PARC). Laser ablation was applied to produce holes or grooves with typical dimensions of a few hundred $\mu$m to a few mm, except for some extreme conditions. The measured emission rate tends to be higher for larger fractions of ablation opening and for shallower depths. More than a few ablation structures reach the emission rates similar to the highest achieved in the past measurements. The emission rate is found to be stable at least for a couple of days. Measurements of spin precession amplitudes for the produced Muonium atoms and remaining muons in a magnetic field determine a Muonium formation fraction of $(65.5 \pm 1.8)$%. The precession of the polarized Muonium atoms is also observed clearly in vacuum. A projection of the emission rates measured at TRIUMF to the corresponding rates at J-PARC is demonstrated taking the different beam condition into account reasonably.
-
negative Muonium ion production with a c12a7 electride film
Journal of Physics: Conference Series, 2019Co-Authors: Masashi Otani, K. Shimomura, Y Fukao, N Kawamura, K Futatsukawa, Shiro Matoba, T Mibe, Yasuhiro Miyake, Takayuki Yamazaki, K HasegawaAbstract:Negative Muonium atom (μ + e – e –, Mu–) has unique features stimulating potential interesting for several scientific fields. Since its discovery in late 1980's in vacuum, it has been discussed that the production efficiency would be improved using a low-work function material. C12A7 was a well-known insulator as a constituent of alumina cement, but was recently confirmed to exhibit electric conductivity by electron doping. The C12A7 electride has relatively low-work function (2.9 eV). In this paper, the negative Muonium production measurement with several materials including a C12A7 electride film will be presented.
-
enhancement of Muonium emission rate from silica aerogel with a laser ablated surface
arXiv: Instrumentation and Detectors, 2014Co-Authors: G Beer, S. Kanda, H Kawai, K Ishida, M Iwasaki, N Kawamura, Y Fujiwara, S Hirota, Ryo Kitamura, S L LeeAbstract:Emission of Muonium ($\mu^+e^-$) atoms from a laser-processed aerogel surface into vacuum was studied for the first time. Laser ablation was used to create hole-like regions with diameter of about 270$~\mu$m in a triangular pattern with hole separation in the range of 300--500$~\mu$m. The emission probability for the laser-processed aerogel sample is at least eight times higher than for a uniform one.
R C Vilao - One of the best experts on this subject based on the ideXlab platform.
-
Muonium donor in rutile tio 2 and comparison with hydrogen
Physical Review B, 2015Co-Authors: R C Vilao, R L Lichti, J M Gil, H V Alberto, A Weidinger, R B L Vieira, B B Baker, P W Mengyan, J S LordAbstract:Muonium is like hydrogen, but with a positively charged muon instead of a proton at the center. Observing muon spin rotation in a single crystal of TiO${}_{2}$, and comparing to existing data for hydrogen, the authors demonstrate that the defect configuration and electronic structure are the same for both. This provides important support for research which uses muons as a substitute for hydrogen in semiconductors.
-
shallow donor state of hydrogen in in 2 o 3 and sno 2 implications for conductivity in transparent conducting oxides
Physical Review B, 2009Co-Authors: P D C King, Y G Celebi, R L Lichti, J M Gil, H V Alberto, R C Vilao, Piroto J Duarte, Dj Payne, R G Egdell, Iain MckenzieAbstract:Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In2O3 and SnO2. The paramagnetic charge state is stable below similar to 50 K in In2O3 and similar to 30 K in SnO2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.
-
acceptor level of interstitial Muonium in znse and zns
Physical Review B, 2008Co-Authors: R C Vilao, R L Lichti, K H Chow, S P Cottrell, J M Gil, H V Alberto, Piroto J Duarte, Ayres N De Campos, A Weidinger, S F J CoxAbstract:, and subsequent emission of an electron from Mu to the conduction band.In this model, the emission step yields the binding energy for the second electron to place the Muoniumacceptor levels at 0.10 2 and 0.33 5 eV below the conduction-band edge for ZnSe and ZnS, respectively. Anapproximate constancy of the Muonium electron affinity for Zn and Cd semiconductor compounds is suggestedand the consequences for the observed Muonium states are discussed.DOI: 10.1103/PhysRevB.77.235212 PACS number s : 61.72.uj, 71.55.Gs, 76.75. i
-
location of the h level experimental limits for Muonium
Physica B-condensed Matter, 2006Co-Authors: R L Lichti, K H Chow, J M Gil, R C Vilao, S F J Cox, D L StripeAbstract:Abstract The defect energy levels for Muonium, a light pseudo-isotope of hydrogen, are investigated to define the equivalent of the H [ + /- ] level which is predicted to be fixed at a universal energy. Existing results for Mu at donor and acceptor sites in silicon tentatively place Mu [ + /- ] approximately 0.5 eV above the predicted hydrogen level. Measured donor ionization energies in other materials in which two neutral Mu centers are observed define a range for the Mu acceptor energies. We discuss possible reinterpretation of known energies and the current state of investigations to obtain these Muonium acceptor levels in order to further refine a determination of the Mu [ + /- ] energy.
-
Muonium spectroscopy in znse metastability and conversion
Physical Review B, 2005Co-Authors: R C Vilao, R L Lichti, K H Chow, J M Gil, H V Alberto, Piroto J Duarte, Ayres N De Campos, A Weidinger, S F J CoxAbstract:High-precision spectroscopic information is obtained on the Muonium states in ZnSe by high-field transverse $\ensuremath{\mu}\mathrm{SR}$ measurements. At low temperatures, two Muonium states ${\mathrm{Mu}}_{I}$ and ${\mathrm{Mu}}_{II}$ are observed with isotropic hyperfine parameters of ${\mathrm{A}}_{I}=3283.63\ifmmode\pm\else\textpm\fi{}0.51\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and ${\mathrm{A}}_{II}=3454.26\ifmmode\pm\else\textpm\fi{}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ (74% and 77% of the vacuum value, respectively). State I is thermally unstable and converts to state II at approximately $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. State II is stable up to $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, at least. We assign ${\mathrm{Mu}}_{II}$ to the cation interstitial tetrahedral site and discuss the possibility that ${\mathrm{Mu}}_{I}$ may correspond either to Muonium at the same site but in the unrelaxed lattice or to the anion interstitial tetrahedral site. The temperature dependence of the hyperfine interaction was fitted with a local vibrational model giving an oscillator energy of approximately $8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. The amplitudes and the depolarization rates are measured over the entire temperature range and are discussed in the text.
