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Abstract : The energetics of formation of isolated vacancies in a family of CsCl type crystals the halides of caesium, thallium and ammonium are reexamined by using an energy minimisation approach. An increased relaxation and decreased electronic moment of the nearest neighbour ions resulted in overall energy terms leading to values of Schottky defect formation energies which are consistently larger relative to the previous results 1. Comparison with ionic conductivity and diffusion studies suggests that the transport properties in caesium and thallous halides may be understood in terms of Schottky defect mechanisms. We have made measurements on the electrical conductivity and dielectric loss of Co++ doped NH4Cl crystals. The observed dielectric loss peaks can be attributed to the reorientation of interstitial impurity-vacancy type dipoles. For a single bound vacancy the loss peak frequencies are determined by the first neighbour vacancy jumps. These results suggest that a vacancy charge transport mechanism cannot be ruled out in the ammonium halides.





Autor: Y. Murti C. Murthy

Fuente: https://hal.archives-ouvertes.fr/



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