The migration of Ca in single crystals was studied by using a radio-tracer and sectioning method at temperatures of between 325 and 416C (table 4). The Arrhenius plot was found to consist of 2 linear branches, with a break at about 380C. The diffusion parameters which were deduced from the plot, for temperatures below 380C, were typical of a vacancy mechanism. The diffusion coefficients in the present material were always higher than those in AgCl. This was attributed to the relatively higher concentrations of intrinsic cation vacancies in AgBr. Upon assuming that diffusion occurred via impurity-vacancy complexes, the low-temperature data indicated that the activation enthalpy and entropy for impurity migration were 0.92eV and 4.2k, respectively. Significant deviations, which were observed at higher temperatures, suggested that simple concepts of mass action were insufficient at high defect concentrations.

Diffusion of Divalent Calcium in Silver Bromide. A.P.Batra, E.F.Ekpo, M.Dominique, N.U.Okorie: Physical Review B, 1990, 42[2], 1404-9

Table 4

Diffusion of Ca2+ in AgBr

Table 5

Diffusion of 36Cl in AgBr