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Surface Concentration of Defects at Grain Boundaries in Sintered Alumina Determined by Positron Annihilation Lifetime Spectroscopy

100%

Kansy J., Si Ahmed A., Liebault J., Moya G.

Acta Physica Polonica A

2001

vol. 100

issue 5

737-742

Sintered alumina samples of grain diameters spanning from 1.2 to 4.5μm have been investigated by positron annihilation lifetime spectroscopy. One series of samples was produced from material containing about 150 ppm impurities (mainly SiO_2). The second one was made from material having about 2700 ppm of various elements (SiO_2, MgO, CaO). Two models of positron trapping at grain boundaries are compared: The first one relates to the diffusion-limited regime; and the other one - to the transition-limited regime of trapping. As a result the relative change of surface concentration of defects at grain boundaries is determined. Additionally, the positron diffusion constant in bulk alumina at room temperature, D_+=0.36±10 cm^2/s, is estimated.

Defect Recovery in α-Fe e^{-}-irradiated at 300 K

88%

Dai G., Li X., Moser P., Moya G., Van Duysen J.

Acta Physica Polonica A

1993

vol. 83

issue 3

277-286

Defect annealing recovery has been studied, by measuring positron lifetime spectra, in high-purity α-iron irradiated at 300 K with 3 MeV electrons to a fluency of 7 × 10^{19} cm^{-2}. Vacancy clusters containing 6-10 single vacancies were observed immediately after irradiation during which they were possibly forming (the so-called "irradiation annealing"). With increasing temperature, the agglomerates continually grow in size at the expense of their concentration, giving rise to the formation of microvoids (> 15 vacancies). Also present were other types of defects, probably immobile vacancies trapped by impurity (e.g. carbon) atoms and dislocation/loops generated presumably from collapse of voids during the relatively high dose irradiation and/or the annealing. The immobile vacancies eventually became movable at around 350 K, supplying the growing clusters and thus leading to a stabilization in their concentration till around 500 K. Between 500 and 700 K, microvoids gradually evaporated, but the dislocation-associated defects were able to survive annealing at temperatures as high as 700 K. The void size and concentration and their evolution have been evaluated on the basis of both the to date theoretical and experimental studies. The temperature dependence was also, observed of positron trapping into vacancy agglomerates of various sizes.

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2 Acta Physica Polonica A

1 2001

1 1993

2 Moya G.

1 Dai G.

1 Kansy J.

1 Li X.

1 Liebault J.

1 Moser P.

1 Si Ahmed A.

1 Van Duysen J.

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Surface Concentration of Defects at Grain Boundaries in Sintered Alumina Determined by Positron Annihilation Lifetime Spectroscopy

Defect Recovery in α-Fe e^{-}-irradiated at 300 K