Diffusion correlation and isotope effects in high-defect-content solids

The tracer correlation factor for diffusion via non-interacting vacancies has been calculated by a Monte Carlo method for the simple-cubic lattice with a variable vacancy content. Particular emphasis has been placed on obtaining results of very high precision. The results are in excellent agreement with the recent analyses by Nakazato and Kitahara, and Tahir-Kheli and Elliott. In a separate calculation the tracer correlation factor in the same model has been calculated using a Monte Carlo method analogous to the experimental method used for measuring diffusion isotope effects. Good agreement was obtained with the direct method, indicating that in this model the tracer correlation factor can be well represented by the impurity correlation factor form.