Volume 33, Number 7, March I 1996
|533 - 538
|Condensed matter: structure, thermal and mechanical properties
|01 September 2002
Cross-over to incoherent tunnelling of substitutional defects in alkali halide crystals
Institut Laue-Langevin - B.P. 156X, 38042 Grenoble, France
2 Institut für Angewandte Physik, Universität Heidelberg Albert-Ueberle-Str. 3-5, 69120 Heidelberg, Germany
Accepted: 11 January 1996
The dielectric susceptibility of substitutional defects in alkali halides shows a surprising dependence on concentration c. In the dilute case ppm, the susceptibility is proportional to the number of defects. It reaches a maximum at a concentration where the average dipole-dipole interaction is equal to the bare tunnelling amplitude of a single defect and for still higher concentrations ppm it strongly decreases. The data for various defect systems are in quantitative agreement with a parameter-free master curve derived from a continued fraction expansion for the relevant correlation function. With increasing defect concentration a universal cross-over from coherent tunnelling to incoherent relaxation is driven by a novel relaxation mechanism, based on the dipolar interaction.
PACS: 61.72.Yx – Interaction between different crystal defects; gettering effect / 77.22.Gm – Dielectric loss and relaxation
© EDP Sciences, 1996
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