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Defects in Decomposing Copper Alloys Studied by Positrons

100%

Mikhalenkov V., de Lima A., Lopes Gil C.

Acta Physica Polonica A

1999

vol. 95

issue 4

615-622

The evolution of defect structure during isochronal annealing of water-quenched Cu-4.83 at.% In and Cu-4.94 at.% Sn alloys was studied by measuring positron lifetime and Doppler broadening of annihilation line. The behaviour of annihilation parameters in both alloys is found to be analogous. In as-quenched alloys one component of about 180 ps is detected in the lifetime spectra. It remains intact up to the annealing temperature of 450 K and is attributed to positron annihilation at quenched-in vacancies associated with alloying atoms. When going above this temperature, the short component appears in the lifetime spectra, while intensity of the long component starts to drop giving evidence to the reduction of defect concentration. This process is observed to develop up to 550 K; thereafter all annihilation parameters level off. After crossing the phase separation temperature they begin to vary again since the defect structure comes into dependence on cooling conditions. The obtained results are discussed in terms of defect structure evolution in the course of precipitate formation.

Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies

46%

Kajcsos Z., Liszkay L., Duplâtre G., Varga L., Lohonyai L., Pászti F., Szilágyi E., Lázár K., Kótai E., Pál-Borbély G., Beyer H., Caullet P., Patarin J., Azenha M., Gordo P., Lopes Gil C., de Lima A., Ferreira Marques M.

Acta Physica Polonica A

2005

vol. 107

issue 5

729-737

Positron annihilation techniques are used for the structural investigation of solids but the interpretation of results in grainy and porous media is still unclear. A unique picture can be obtained assuming that the dominant process is Ps trapping in competing "extended free volume" sites. In samples with a large amount of free volumes near-saturation Ps trapping will rule the lifetime pattern, and very long lifetimes of over 100 ns might arise from o-Ps trapped in mesopores. It is shown that lifetime parameters must be corrected for the 3γ/2γ counting efficiency ratio. The results demonstrate the high sensitivity of Ps to mesopores in zeolites but also that Ps-trapping poses limitations on the applicability of lifetime to structural investigation in porous systems. The evolution of the lifetime spectra upon changes in the sample and measuring conditions should be considered in a complex way, observing not only changes in some selected components but in the whole lifetime pattern simultaneously.

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2 Acta Physica Polonica A

1 2005

1 1999

2 Lopes Gil C.

2 de Lima A.

1 Azenha M.

1 Beyer H.

1 Caullet P.

1 Duplâtre G.

1 Ferreira Marques M.

1 Gordo P.

1 Kajcsos Z.

1 Kótai E.

1 Liszkay L.

1 Lohonyai L.

1 Lázár K.

1 Mikhalenkov V.

1 Patarin J.

1 Pál-Borbély G.

1 Pászti F.

1 Szilágyi E.

1 Varga L.

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Defects in Decomposing Copper Alloys Studied by Positrons

Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies