Diffusion of Rubidium Ion and Potassium Ion in Silver-Bromide and Silver-Chloride

The diffusion of Rb('+) in AgBr and AgCl was performed using the standard tracer and serial sectioning technique. For AgBr in the temperature range 184-420(DEGREES)C and AgCl in the temperature range 184-447(DEGREES)C, the temperature dependence of the diffusivity follows the normal, linear relationship D = D(,0) e('-H/kT). The pre-exponential factor for AgBr is. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). and for. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). The diffusion activation energy for AgBr is H = (1.33 (+OR-) 0.02) eV and for AgCl is H = (1.20 (+OR -) 0.02) eV. It is argued that the lack of curvature in these Arrhenius plots, which is predicted on the basis of a temperature dependent defect formation enthalpy, is intimately associated with the elastic strain field set up in the vicinity of the oversized Rb('+) ion. The diffusion of the smaller K('+) ion was also studied in AgBr and AgCl using the same technique. The temperature range investigated for AgBr was 248-418(DEGREES)C and for AgCl was 264-448(DEGREES)C. In this case, the Arrhenius plots describing the temperature dependence of the diffusion coefficient do show a continuous positive curvature as you approach the melting point. However, it is shown that the curvature is not completely accounted for by the the temperature dependent defect enthalpy model. Again, it is argued that small, but nevertheless temperature dependent, elastic binding does exist which affects the degree of curvature in the Arrhenius graphs.