Characterization of radiation-induced lattice vacancies in intermetallic compounds by means of positron-lifetime studies

Würschum, Roland; Badura-Gergen, K.; Kümmerle, Eberhard; Grupp, C.; Schaefer, H.

doi:10.1103/physrevb.54.849

Cited by 79 publications

(51 citation statements)

References 43 publications

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“…The maximum value of τ m is much shorter than that for vacancies. 21,22) The anomalous increase of τ m from 125 to 150 ps caused by the decrease in temperature from 335 to 200 K is quite similar to the increase of τ m observed above the M s temperature in Ni 51 Ti 49 alloy (Fig. 2).…”

Section: Resultssupporting

confidence: 76%

“…Positron mean lifetime at room temperature is much shorter than that in a vacancy, τ v = 197 ps, and is even shorter than that in the free positron state, τ f = 132 ps, for the Ni 51.7 Ti 48.3 alloy with the B2 structure reported by Wuerschum et al 21,22) It is obvious that the majority of positrons are not trapped in any lattice defects. In other words, non-stoichiometry in Ni 51 Ti 49 alloy is primarily compensated with anti-site atoms.…”

Section: Resultsmentioning

confidence: 85%

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Anomalous Temperature Changes of Positron Lifetime and Electrical Resistivity in B2-NiTi Alloys

et al. 2002

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The pre-martensitic phenomena in Ni-rich NiTi alloys have been studied by means of positron lifetime spectroscopy and electrical resistivity measurement. We have found anomalous positron lifetime changes above the martensitic transformation temperatures of Ni 50 Ti 50 -Ni 51 Ti 49 alloys. Positron lifetime increases anomalously with decreasing temperature even at temperatures 100 degrees higher than M s of Ni 51 Ti 49 alloys. Almost the same change in positron lifetime has been observed on the subsequent heating run with little hysteresis. We have also found the anomalous behavior of positron lifetime and negative temperature dependence of electrical resistivity even in NiTi alloys that do not exhibit martensitic transformation. The observed pre-martensitic changes of positron lifetime and electrical resistivity directly reflect the intrinsic electronic-structural changes of NiTi alloys that cause so-called pre-martensitic phenomena.

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Section: Resultssupporting

confidence: 76%

Section: Resultsmentioning

confidence: 85%

Anomalous Temperature Changes of Positron Lifetime and Electrical Resistivity in B2-NiTi Alloys

et al. 2002

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“…This complicated behavior of the effective formation energy of thermal vacancies in NiAl as a function of composition and temperature may partly account for the considerable scatter of the experimental data which can be found in the literature. 1,2,52,66,79,87 …”

Section: Effective Vacancy Formation Energymentioning

confidence: 99%

Constitutional and thermal point defects inB2NiAl

et al. 2000

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The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects ͑antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively͒ are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.

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“…[7,32] Section 2). The potentials of thermal vacancy detection by time-differential dilatometry have been confirmed in the case of crystalline intermetallics by comparison with the data of concomitant positron lifetime studies [5,7]. Since thermal vacancies could not be tested earlier because of the lack of specific experimental techniques, a rich paraphrasing has evolved such as free volumes, quasivacancies, delocalized defects, vacant spaces, or regions of lower density [44].…”

Section: à4mentioning

confidence: 93%

Vacancies and atomic processes in intermetallics – From crystals to quasicrystals and bulk metallic glasses

Schaefer¹,

Baier²,

Müller³

et al. 2011

Physica Status Solidi (b)

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A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1 2 -Ni 3 Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe 61 Al 39 and in MoSi 2 . In the icosahedral quasicrystal Al 70 Pd 21 Mn 9 the thermal vacancy concentration is low, whereas in the BMG Zr 57 Cu 15.4 Ni 12.6 Nb 3 Al 10 thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Fähnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics.

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Characterization of radiation-induced lattice vacancies in intermetallic compounds by means of positron-lifetime studies

Cited by 79 publications

References 43 publications

Anomalous Temperature Changes of Positron Lifetime and Electrical Resistivity in B2-NiTi Alloys

Anomalous Temperature Changes of Positron Lifetime and Electrical Resistivity in B2-NiTi Alloys

Constitutional and thermal point defects inB2NiAl

Vacancies and atomic processes in intermetallics – From crystals to quasicrystals and bulk metallic glasses

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