Effective Volumes of Vacancies of Divalent Ions and Their Diffusion Coefficients in Alkali Halides

Photoelastic effects induced by divalent ions Sr⁺⁺ and Ba⁺⁺ diffused into KCl have been observed and measured experimentally. The theoretical analysis allows the calculations of the diffusion coefficients D(Sr⁺⁺)=9.0×10^-5e^-0.77/kT cm²/sec and D(Ba⁺⁺)=2.5×10^-2e1.1/kT cm²/sec, and of volume changes due to impurity-vacancy complexes. By following the thermal dissociation of these complexes, it was possible to conclude that the isolated vacancy causes a lattice expansion larger than the contraction due to the isolated divalent ion.