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(-1.65 eV kT(-1)) cm(2) s(-1), and for the mean lifetime, tau = 0.093 exp(1.7 eV) 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.