Positron annihilation studies in single and polycrystals of Zn1-xCuxCr2Se4 spinel series

Abstract Positron annihilation studies were carried out on single and polycrystals of Zn1−xCuxCr2Se4 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 Zn1−xCuxCr2Se4 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.

[1]  I. Jendrzejewska,et al.  The single crystals Cu1 − xZnxCr2Se4 , 1995 .

[2]  T. Groń.  Influence of vacancies and mixed valence on the transport processes in solid solutions with the spinel structure , 1994 .

[3]  K. Wokulska,et al.  Growth of Cu1−xGaxCr2Se4 single crystals by chemical vapour transport and their electrical properties , 1992 .

[4]  F. Lu.  Point defects and cation tracer diffusion in (Co, Fe, Mn)3$minus;$delta;O4 spinels: I. Mixed spinels (CoxFe2yMny)3$minus;$delta;O4 , 1992 .

[5]  T. Hehenkamp,et al.  Positron Trapping Rates and Lifetimes of Vacancy-Impurity Complexes in α-AgSb Alloys , 1992 .

[6]  M. Puska.  Theory of Positron Annihilation and Trapping in Semiconductors , 1992 .

[7]  J. Kusz,et al.  Crystal and Magnetic Structure of the Magnetically Modulated Spinels Zn1-xGa2x/3Cr2Se4 Where (X=0.0, 0.1, 0.2, 0.3, 0.5) , 1991 .

[8]  Duda,et al.  Influence of the valence of the substituted cations on the electrical properties of the magnetically modulated spinels Zn1-xAxCr2Se4 (A=Cu, Ga2/3). , 1990, Physical Review B (Condensed Matter).

[9]  T. Hehenkamp,et al.  Positron lifetime spectroscopy in copper , 1986 .

[10]  Peter Kirkegaard,et al.  POSITRONFIT: A versatile program for analysing positron lifetime spectra , 1984 .

[11]  A. Bombik,et al.  Transition from helimagnetism to ferromagnetism in CuxZn1-xCr2Se4 , 1983 .

[12]  I. Okońska-Kozłowska,et al.  Mischkristallbildung im System CuxZn1−xCr2Se4 , 1978 .

[13]  R. D. Shannon.  Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides , 1976 .

[14]  K. Kudo,et al.  A classification of normal spinel type compounds by “Ionic packing factor” , 1974 .

[15]  Tsuneo Watanabe.  Electrical Resistivity and Hall Effect of ZnCr2Se4 , 1974 .

[16]  T. Watanabe.  Electrical properties of FeCr2S4 and CoCr2S4 , 1973 .

[17]  L. Friedman,et al.  Mixed-Conduction Model for Charge Transport in n -Type Cd Cr 2 Se 4 , 1970 .

[18]  F. Lotgering,et al.  Metal-deficient sulphospinels , 1969 .

[19]  R. Bachrach.  The optical absorption of orthorhombic thallous iodide , 1969 .