On the stability and mobility of di-vacancies in tungsten

Properties of small vacancy clusters in tungsten were studied with first-principles calculations. The binding and formation energies of the vacancy clusters increase with the cluster size. Dynamic characteristics of a di-vacancy were specified between room temperature and 700 K with lattice kinetic Monte Carlo calculations, which were parametrised with the present first-principles results for the dissociation barriers. An Arrhenius fit for the di-vacancy diffusion yielded $D=0.04\exp (-1.65eV{kT}^{-1})$ ${cm}^2{s}^{-1}$, and for the mean lifetime, $\tau =0.093\exp \left(1.7eV\right){kT}^{-1}$ ps. The di-vacancy system was found to be stable up to 500 K, due to the high energy needed for its dissociation. Having a carbon impurity was found to increase the tungsten di-vacancy binding energy. (paper)