A Monte Carlo study of oxygen diffusion on the (110) plane of tungsten

Abstract

Abstract A Monte Carlo study of oxygen diffusion on the (110) plane of tungsten has been carried out, by finding the time autocorrelation function of particle number fluctuations on a square lattice. Best results were obtained by the single site autocorrelation function, but do not differ much from those obtained from a finite probed region. The experimentally observed increase in activation energy with coverage could be reproduced almost quantitatively by using an attractive nearest neighbor interaction energy J 1 = 2.1 kcal, a repulsive next-nearest neighbor energy J 2 = −1.7 kcal, an attractive third nearest-neighbor energy J 3 = 0.7 kcal and a triplet energy J t = 0 or −1.2 kcal. With those parameters an increase in prefactor of > 100 was seen as coverage increased from 0 to 0.5. This increase still falls short of the experimentally observed one, as expected. The mean square number fluctuation was also calculated using the values of J 1 , J 2 and J 3 cited above in the grand canonical ensemble as function of temperature and coverage. The results agree qualitatively with the experimental ones, but are an order of magnitude larger. Reasons for the discrepancy are discussed.