Positron annihilation in disordered binary alloys

Lock, Duncan; West, R N

doi:10.1088/0305-4608/4/12/014

Cited by 53 publications

(10 citation statements)

References 12 publications

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“…The value t L-188 ps is closer to the lifetime value characteristic of pure A1 than to that for Li, which has been reported to be t = 300 ps (Lock andWest 1974, Kubica et a1 1975). Recent theoretical results on the Zn clustering in Al-Zn alloys predict a dependence of the positron lifetime as a function of the cluster size ranging from the A1 bulk value, when no Zn clustering takes place, to the Zn bulk value when the cluster contains about 12 or more Zn atoms (Bharathi and Chakraborty 1988).…”

Section: Resultssupporting

confidence: 49%

“…Since the positron is sensitive to the local core potential, in an alloy it can show a tendency towards being localised and annihilated in zones where the Coulomb repulsion is lower. The positron affinity for one of the components in a metallic alloy has been treated both theoretically and experimentally (Lock and West 1974, Kubica eta1 1975, Koenig 1978. Dlubeketal(1979Dlubeketal( ,1981Dlubeketal( ,1986 have also proved experimentally that in Al-Zn alloys the positrons tend to be localised in Znrich zones.…”

Section: Introductionmentioning

confidence: 99%

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Collective emission of atoms in photonic bandgap materials

Yukalov

2000

Quantum Electron.

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The behaviour of two AI-Li dilute alloys having two different Li contents (1.7 and 3.7 at.%Li) has been studied using positron annihilation. The lifetime value is about 20 ps higher than that measured for pure AI and is independent of the Li content. When the specimens are cold rolled the lifetime increases to a value that is lower than the one currently associated with dislocations in A1 and does not depend on the Li concentration. After isochronal annealing the lifetime achieves the initial value t = 185 ps. The results are interpreted in terms of Li clustering.

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Section: Resultssupporting

confidence: 49%

Section: Introductionmentioning

confidence: 99%

Collective emission of atoms in photonic bandgap materials

Yukalov

2000

Quantum Electron.

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“…Compared with the parameters F A and FB of the constituent pure metals, FZ and Fg are effective values being affected by alloying effects such as changes in lattice structure and lattice constant and charge transfer between cells occupied by different types of atoms. For F, the use of the mean annihilation rate A = 1 /~ and of the S parameter S" = AS normalized to the annihilation rate was suggested by Lock and West [2], whereas Kubica et al [4] have used the core electron annihilation rate Ac. c; and c i denote the fractions of A and B atoms in the alloy as felt by positrons.…”

Section: Discussionmentioning

confidence: 99%

Positron Studies of the Chemical Composition of Guinier‐Preston Zones in AlZn Alloys

Dlubek

Gerber

1991

Physica Status Solidi (b)

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Various decomposed Al-Zn alloys are investigated by positron lifetime and angular correlation technique in order to study the potential of positron method in estimating the composition of Guinier-Preston zones. From experiments the curve shape parameters, S, the core annihilation rate, A,, and the number of free conduction electrons, z, derived from the zeros of the one-dimensional Fourier-transform of the angular correlation curve are estimated. The response of the various annihilation parameters to zone composition, positron affinity, and alloying effects (lattice change, charge transfer) is discussed. The number of free electrons per atom reflects most clearly the chemical composition of the GP zones.Verschiedene entmischte A1-Zn-Legierungen werden mit der Positronenlebensdauer-und Winkelkorrelationstechnik untersucht, um das Potential der Positronenmethode zur Bestimmung der Komposition von Guinier-Preston-Zonen zu untersuchen. Aus den Experimenten wird der Kurvenformparameter S, die Annihilationsrate mit gebundenen Elektronen und die Zahl von freien Leitungselektronen z, die aus den Nullstellen der Fouriertransformierten der Winkelkorrelationskurve abgeleitet wird, bestimmt. Es wird die Empfindlichkeit der verschiedenen Annihilationsparameter beziiglich Zonenkomposition, Positronenaffinitat und Legierungseffekten (Gitteranderung, Ladungsiibergang) diskutiert. Die Zahl freier Elektronen pro Atom widerspiegelt am deutlichsten die chemische Zusammensetzung der GP-Zonen.

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“…For the estimation we use the so-called reduced annihilation parameter F is a suitably chosen parameter such as the annihilation rate /z = l/z or the S-parameter normalized to the annihilation rate, S" = AS (see Lock and West [34]). A F corresponds to the concentration c i g of Ag as felt by positrons.…”

Section: Temperature Dependence Of Gp Zone Compositionmentioning

confidence: 99%

A positron study of guinier-preston zones and γ′-precipitates in an AlAg alloy

Dlubek

Wendrock

Pawelzyk

1993

Phys. Stat. Sol. (a)

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Positron lifetime τ and momentum distribution (curve shape parameter S) measurements are performed to study the decomposition in an Al5.9 at% Ag alloy during isochronal and isothermal heat treatment of water‐quenched samples. The positron studies are supplemented by small‐angle X‐ray scattering experiments. It is proved that positrons become trapped by G.P. zones being free of any vacancy‐type or dislocation‐type defect and by semicoherent γ′‐precipitates. Positron trapping rates show the coarsening of G.P. zones simultaneously with the formation and growth of γ′ during isothermal aging above 170 °C. From the temperature dependence of τ and S the transformation of η‐zones into τ‐zones is concluded. The Ag content of zones changes from about 60 at% at 120 °C (η‐zones) to 35 at% at 190 °C (η‐zones) which is in good agreement with SAXS and AP‐FIM experiments. Evidence of a reversible change of the G.P. zone composition when alternating the temperature between 190 and 120 °C is found in both positron and SAXS experiments.

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Positron annihilation in disordered binary alloys

Cited by 53 publications

References 12 publications

Collective emission of atoms in photonic bandgap materials

Collective emission of atoms in photonic bandgap materials

Positron Studies of the Chemical Composition of Guinier‐Preston Zones in AlZn Alloys

A positron study of guinier-preston zones and γ′-precipitates in an AlAg alloy

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