Positive muons as light isotopes of hydrogen

Seeger, A.

doi:10.1007/3540087052_52

Cited by 31 publications

(1 citation statement)

References 61 publications

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“…In FCC metals possible directions for migration are the [110] direction and the [11 11 direction. Along the [l lo] direction the impurity wavefunction will be strongly localized at the octahedral site and it is only for positive muons that sometimes the [110] path is adopted [41]. In general interstitial impurities in FCC metals at elevated temperatures are assumed to migrate by an overbarrier jump via the tetrahedral position to a neighbouring octahedral site (see figure l ( a ) ) .…”

Section: Fcc Systemsmentioning

confidence: 99%

Electromigration in transition metals. II. Light interstitials in Cu, Ag, Ni, Pd, Al, V, Nb and Ta

Lodder

1991

J. Phys.: Condens. Matter

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The electromigration wind valence of interstitial hydrogen in a series of transition metals is calculated using a state-of-the-art computational scheme accounting for the real band structure and local lattice deformation plus charge transfer in the impurity cluster. A microscopic picture of the oscillatory motion and the mobility of the proton explains the remarkable difference between the wind valence of hydrogen in Nb and Ta. A zero-point motion model explains the H/D isotope effect in the eiiective valence as observed in many systems. From a comparison of experimental effective valences with calculated wind valences. it is concluded that the direct valence, in systems where the wind valence is not dominant, has a value close to unity. Thermal effects are investigated and shown to be unimportant at moderate temperatures. In addition wind valences of interstitial boron in Pd, carbon in Pd and Nb and oxygen in Nb are presented.

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Section: Fcc Systemsmentioning

confidence: 99%

Electromigration in transition metals. II. Light interstitials in Cu, Ag, Ni, Pd, Al, V, Nb and Ta

Lodder

1991

J. Phys.: Condens. Matter

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The Study of Positron Diffusion in Solids by Positron Spin Relaxation (e+SR) Experiments

Seegee

Major

Banhart

1987

Phys. Stat. Sol. (a)

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A method is given for investigating the temperature dependence of the positron (e+) diffusivity that is analogous to the study of the diffusion of positive muons in solids through the longitudinal relaxation of the muon spin polarization. It makes use of the facts that e+ emitted from radioactive sources with velocity v are longitudinally polarized with helicity v/c and that the e+ spin polarization is essentially preserved during the implantation and slowing-down process. The residual polarization of the annihilating e+ is determined by their "magnetic history", i.e., by the magnetic fields "seen" by the e+ magnetic moments during their movement through the solid. Information on the residual polarization may be obtained by measuring the annihilation characteristics (in the present set-up the Doppler broadening of the 2y annihilation line) in magnetically saturated ferromagnetic substances. I n this case the "polarimeter" serves also as the sample in which the e+ diffusivity is studied. The theory relating the polarization t o the e+ diffusivity is developed for the specific case of a-iron. Experiments on a-iron single crystals between 77 and 770 K indicate that the mechanism of e+ diffusion is rather complicated and cannot be adequately described by propagation in band states or hopping alone. Eine Methode zur Bestimmung der Temperaturabhangigkeit des Positronendiffusionskoeffizienten wird vorgestellt, die darauf beruht, daD von einer radioaktiven Quelle mit der Geschwindigkeit v emittierte Positronen mit der Helizitit v/c longitudinal polarisiert sind, und die enge Analogien zur Untersuchung der Diffusion positiver Myonen mit Hilfe der Myonspinrelaxation aufweist. Die Spinpolarisation der Positronen bleibt beim Eindringen in die Probe und beim Abbremsvorgang weitgehend erhalten. Die bei der Zerstrahlung noch vorhandene Restpolarisation wird durch die ,,magnetische Vorgeschichte" der Positronen bestimmt, d. h. durch die Magnetfelder, rnit denen ihre magnetischen Momente wahrend der Diffusion durch die Probe wechselwirken. Information uber die Restpolarisation kann durch Messen der Zerstrahlungscharakteristik (im vorliegenden Experiment der Dopplerverbreiterung) in magnetisch gesattigten ferromagnetischen Substanzen gewonnen werden. Hierbei dient die Probe, in der die Positronendiffusion untersucht wird, auch als Polarimeter. Die zur Verknupfung der Depolarisierung mit dem Diffusionskoeffizienten der Positronen benotigte Theorie wird fur den speziellen Fall von a-Eisen entwickelt. Ihre Anwendung auf experimentelle Ergebnisse an a-Eiseneinkristallen zwischen 77 und 770 K zeigt, da13 der Diffusionsmechanismus der Positronen recht kompliziert ist und nicht ausschlieBlich mit der Positronenausbreitung in Bandzustlnden oder rnit Hupfprozessen zutreffend beschrieben werden kann.

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Theory of Multi‐Phonon Transitions beyond the Condon Approximation

Teichler

1981

Physica Status Solidi (b)

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For light interstitials in deformable host-materials ("small-polaron"-like systems) the theory of multi-phonon transitions is developed beyond the so-called Condon approximation, i.e., the effect of phonon fluctuations on the defect transfer-integrals J is explicitly taken into account. In particular the rate of incoherent defect transitions is evaluated up to second order in J and the temperature dependence of the multi-phonon processes is discussed in the regime above half of the Debye temperature.Fur leichte Zwischengitterteilchen in deformierbaren Wirtsmaterialien (Systeme vom Typ des kleinen Polarons) wird die Theorie der Viel-Phononen-Ubergange jenseits der sogenannten CondonNiiherung entwickelt, d. h., die Auswirkungen der Fluktuationen des Phononensystems auf die Ubergangs-Integrale J des Defekts werden explizit berucksichtigt. Insbesondere wird die Rate der inkoharenten Uberglnge in zweiter Ordnung in J bestimmt und die Temperaturabhangigkeit der VieI-Phononen-Prozesse im Bereich oberhalb der halben Debye-Temperatur diskutiert.

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Positive muons as light isotopes of hydrogen

Cited by 31 publications

References 61 publications

Electromigration in transition metals. II. Light interstitials in Cu, Ag, Ni, Pd, Al, V, Nb and Ta

Electromigration in transition metals. II. Light interstitials in Cu, Ag, Ni, Pd, Al, V, Nb and Ta

The Study of Positron Diffusion in Solids by Positron Spin Relaxation (e+SR) Experiments

Theory of Multi‐Phonon Transitions beyond the Condon Approximation

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