Hyperfine Interactions of Defects in Metals

Recknagel, E.; Schatz, G.; Wichert, Th.

doi:10.1007/978-3-642-81969-8_4

Cited by 54 publications

(11 citation statements)

References 124 publications

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“…4 Since the efg is characteristic of a particular environment of the probe atom, the presence of intrinsic lattice defects and their mobility can be monitored at the same time. That will be of utmost importance in the case of He atoms introdued by implantation, since vacancies are thereby created whose strong interaction with He atoms influences the behavior of He considerably.…”

Section: Migration Of Helium Atoms In Copper At 25 Kmentioning

confidence: 99%

Migration of Helium Atoms in Copper at 25 K

et al. 1985

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The dynamics of He atoms, which were implanted into copper at 10 K, were observed via their trapping at ni In atoms, using the perturbed yy angular correlation technique. During annealing in the temperature range 10 to 300 K, two types of In-He complexes were detected with the He atom occupying either a trapped single vacancy or an octahedral interstitial lattice site. The formation of the latter He complex shows that He atoms migrate via interstitial sites in Cu already at 25 K.PACS numbers: 66.30.Jt, 61.70.Tm 76.80. + y Whether single He atoms can find stable interstitial positions in metals and what their activation energies would be are still unsettled questions, which have been touched upon mainly theoretically. 1 The lack of experimental information is opposed to an increasing scientific interest in the dynamics of He atoms in metals. 2 The only experimental evidence for a stable interstitial He position and its activation energy comes from field-ion microscopy of W implanted with He of a few hundred electronvolts. 3 In this Letter we present results where the migration of He atoms is detected via the trapping of the He by radioactive impurities (probe atoms) and we show that interstitial He in Cu is mobile at 25 K.Using the perturbed yy angular correlation technique (PAC), the formation of probe-atom-He pairs is detected via the short-range electric field gradient (efg) induced by the He atom at the probe site. 4 Since the efg is characteristic of a particular environment of the probe atom, the presence of intrinsic lattice defects and their mobility can be monitored at the same time. That will be of utmost importance in the case of He atoms introdued by implantation, since vacancies are thereby created whose strong interaction with He atoms influences the behavior of He considerably. From previous PAC experiments the efg's caused by self-interstitials, vacancies, and defect clusters trapped at in In probe atoms in Cu are already well known. 5 Whereas in thermal-desorption experiments (which have provided the most detailed atomistic description for He in metals) the formation of different vacancy-He pairs and their stability is inferred from the observed He release of the sample, 6 in PAC experiments the formation of different probe-atom-He pairs is observed directly and is characterized by different efg's.In order to study the mobility of He atoms at low temperatures, polycrystalline foils and single crystals of Cu were doped with probe atoms by implanting in In atoms of 350 keV at 295 K. Afterwards, the samples were annealed at 800 K to remove the damage created by the implantation and were doped with 4 He atoms of 30 keV at 10 K. For the detection of the efg caused by the arrival of He atoms or intrinsic defects at the probe site, the 173-245-keV y cascade was mea-sured in coincidence; the y rays are emitted during the decay of the probe atom m In (r 1/2 = 2.8 d) into its daughter ni Cd. The efg acting on the probe atom manifests itself by modulating the coincidence probability in time, where the time r...

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Section: Migration Of Helium Atoms In Copper At 25 Kmentioning

confidence: 99%

Migration of Helium Atoms in Copper at 25 K

et al. 1985

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“…The hyperfine interaction of such impurities, meaning the interaction between the nuclear moments of (the concerned isomeric state of) the impurities and electromagnetic fields at their sites in a sample (Recknagel et al 1983), provides a powerful method for studying the behaviour of helium in metals (Rinneberg et al 1978). The hyperfine interaction induced perturbation of angular correlation of γ rays emitted in cascade (separated by the isomeric state of interest) by suitable radioactive probe atoms introduced in the sample, has been established as a powerful technique for studying defects in solids (Gary et al 1990).…”

Section: Introductionmentioning

confidence: 99%

Helium implantedAlHf as studied by181Ta TDPAC

2000

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Time differential perturbed angular correlation (TDPAC) measurement on AlHf reference sample has shown that a fraction 0⋅ ⋅88 of probe nuclei are defect free and are occupying the substitutional sites in fcc Al matrix, and the remaining are associated with Hf solute clusters. Measurements on helium implanted sample indicate the binding of helium associated defects by Hf solute clusters. Isochronal annealing measurements indicate the dissociation of the helium implantation induced defects from Hf solute clusters for annealing treatments beyond 650 K. On comparison of the present results with that reported in CuHf subjected to identical helium implantation, it is inferred that the Hf solute clusters in AlHf bind less strongly the helium associated defects than in CuHf.

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“…There it experiences a different EFG which should be axially asymmetric. 2 With a further increase in temperature, a situation of maximum damping is reached around 100 K and the pattern practically vanishes. At even higher temperatures the jump rate becomes so high that the probe nucleus feels an EFG averaged between the central position and the three possible vacancy sites, which leads again to an undamped QI frequency and axial symmetry, i.e., 77=0.…”

Section: Gnu) = X S2n(t])cos[c N (7])vnt]mentioning

confidence: 98%

Dynamics of an Indium Impurity in the Relaxed Divacancy in Iridium

Vianden

Feuser

1988

Phys. Rev. Lett.

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Perturbed y-y angular correlation experiments reveal an unexpected dynamical behavior of U1 ln atoms in a trivacancy complex in iridium. The measured quadrupole interaction is static at 12 K but becomes strongly time dependent around 100 K resulting in a typical damping of the interaction pattern. At 293 K again a static interaction of different magnitude is observed. This behavior can be described by a jump motion of the indium atom between a stable position in the center of the (111) three-vacancy triangle at low temperatures and the surrounding vacant sites at high temperatures.PACS numbers: 61.70. Yq, 66.30.Jt, Since the first applications of nuclear methods to the study of defects in metals, the dynamic behavior of defect-probe-atom complexes has been a main point of interest. The reason is that it is directly related to the mechanism of the elementary diffusion jump in the various host matrices. And in contrast to the classical diffusion studies employing tracer atoms, whose macroscopic distribution is determined, e.g., through sectioning techniques, the nuclear methods are able to give direct information about the movement of the probe atom on a microscopic scale and thus improve our understanding of the diffusion process.Generally, the nuclear methods exploit the hyperfine interaction between the nuclear moments of a probe nucleus and the electromagnetic fields generated by a defect in the vicinity of the probe. In the case of a trapped defect, this causes a static hyperfine interaction, which gives information about the nature of the defect and the geometrical configuration of the probe-defect complex. Distortions of the complex during the time of observation lead to time-dependent hyperfine interactions which can be directly related to the dynamical behavior of the probe atom or its surrounding. In recent review, Petry and Vogl x discuss the application and specific advantages of the various nuclear methods for diffusion studies.The y-y perturbed-angular-correlation (PAC) technique has been particularly successful in the investigation of vacancies in metals. 2~4 It observes the perturbation of the directional correlation of two y rays emitted consecutively in the decay of an unstable parent nucleus. The hyperfine interaction between the quadrupole moment of the nuclear state intermediate to the y-y cascade and electric-field gradients caused by disturbances of the cubic charge symmetry surrounding the probe atom causes a characteristic perturbation pattern. It can be described by a perturbation function of the form "max GnU) = X S2n(T])cOs[c n (7])vnt] .Here VQ ^eQV zz lh is the quadrupole interaction (QI) frequency with Q the quadrupole moment of the inter-mediate nuclear state and V zz the largest component of the electric-field-gradient (EFG) tensor. 5 rj^iVxx -V yy )/V zz varies between 0 and 1 and describes the asymmetry of the EFG. The Fourier coefficients sm and the frequency factors c n are well known functions of r\. 5 rt max is determined by the spins and multipolarities of the levels and tran...

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Hyperfine Interactions of Defects in Metals

Cited by 54 publications

References 124 publications

Migration of Helium Atoms in Copper at 25 K

Migration of Helium Atoms in Copper at 25 K

Helium implantedAlHf as studied by181Ta TDPAC

Dynamics of an Indium Impurity in the Relaxed Divacancy in Iridium

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