Vacancy-related diffusion correlation effects in a simple cubic random alloy and on the Na-K sublattice of alkali feldspar

Wilangowski F., Stolwijk N.

Abstract

Motivated by the need to analyse experimental data on ionic conductivity in alkali feldspar, we performed Monte Carlo (MC) simulations of vacancy diffusion in random binary systems. We employed an efficient procedure for the calculation of the vacancy correlation factor fV, which includes the computation of the associated partial correlation factors (PCFs) fVA and fVB. Test simulations on a simple cubic lattice show the improvements compared to previous MC data and the discrepancies with the Manning model. Vacancy correlation factors on the Na-K sublattice in the monoclinic structure of alkali feldspar proved to be dependent on crystal orientation. For the c∗-direction, PCFs related to the four different jump types were calculated. We also examined the percolation behaviour for extreme ratios of the atomic jump frequencies. The results are found to agree with known data for the simple cubic lattice. In the case of feldspar, we provide the first useful estimates for the percolation threshold and the associated critical exponent using a simplified set of jump frequencies.