Positron annihilation studies in single and polycrystals of Zn_1−xCu_xCr₂Se₄ spinel series

T. GroŃ Universität Göttingen, IV, Physikalisches Institut, Bunsenstraße 13–15, 37073, Göttingen, Germany; University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007, Katowice, Poland

J. Wolff Universität Göttingen, Institut für Metallphysik, Hospitalstraße 3–7, 37073, Göttingen, Germany

Th. Hehenkamp Universität Göttingen, Institut für Metallphysik, Hospitalstraße 3–7, 37073, Göttingen, Germany

K. Bärner University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40–006 Katowice, Poland

I. Okońska-Kozłowska University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40–006 Katowice, Poland

I. Jendrzejewska University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40–006 Katowice, Poland

E. Malicka University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40–006 Katowice, Poland

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Abstract

Positron annihilation studies were carried out on single and polycrystals of Zn_1−xCu_xCr₂Se₄ spinels. The largest average positron lifetime is observed for the single crystals, suggesting that for the spinel structure single crystals contain more vacancies than polycrystals. The positron lifetime connected with vacancies increases with x (copper concentration) as long as the crystals are semiconducting and decreases with x in the metallic region. These effects are probably caused by the different electron densities in the semiconducting and metallic regions of the Zn_1−xCu_xCr₂Se₄ spinel series together with different vacancy concentrations. In particular, the results are in good agreement with a vacancy model which allows to calculate the vacancy concentration using a single vacancy parameter.

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Positron annihilation studies in single and polycrystals of Zn_1−xCu_xCr₂Se₄ spinel series

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Positron annihilation studies in single and polycrystals of Zn_1−xCu_xCr₂Se₄ spinel series