a Perturbed Angular Correlation Investigation of Defects in Silver Chloride.

The interaction of vacancies with trivalent ^{111}In atoms and the daughter ^{111}Cd ions was studied by the perturbed-gammagamma -angular correlation (PAC) method. Measurements below 110 K showed that the ^{111}In ions occurred predominantly in two well-defined lattice defects. Defect AgCl:In-1 is attributed to a right-angle indium-divacancy complex in which the indium ion occupies a silver lattice site and is probably bound to two vacancies occupying next-nearest Ag sites at right angles with respect to the indium ion. Defect AgCl:In-2 is attributed to a linear indium-vacancy complex in which two vacancies occupy next-nearest silver sites on either side of the substitutional indium site. As the temperature is increased above 110 K these complexes convert dynamically to two new complexes; AgCl:In -3 and AgCl:In-4, whose structure has not yet been determined. This conversion indicates a change in the equilibrium structure of the defect complexes with temperature. These new defect centers reach their maximum concentration at 180 K. Under certain conditions AgCl:In-3 converts in time to a new cubic-symmetric defect, AgCl:In-5. This defect is attributed to an indium-vacancy configuration in which the indium probe ion occupies an interstitial position surrounded by a tetrahedron of vacancies. As the temperature is raised above 210 K the spectra resulting from AgCl:In-3 and -4 are gradually damped out by a dynamic effect, most likely the escape and diffusion of one of the trapped vacancies following the decay of trivalent ^{111}In to divalent ^{111}Cd. A different dynamic effect dominates all spectra above 300 K, characterized by an activation energy of 0.48 eV and an attempt frequency of 3 times 10 ^{14}s^ {-1}. We have observed and exploited a new effect, an orientation dependence of the dynamic damping constant, to gain detailed information on the diffusion mechanism. We have identified this mechanism as the rotational diffusion of a silver vacancy between next-nearest silver sites to the cadmium probe ion.