CALCULATION OF SOME DEFECT PARAMETERS IN FCC METALS

The lattice statics model together with the atomistic continuum model is used for the calculation of relaxation due to a vacancy, the vacancy formation energy and divacancy binding energy in the case of some f.c.c. metals whose phonon dispersion curves are available. Using the measured phonon dispersion relations and the elastic constants as constraints the dynamical matrix is derived considering interactions up to the eight nearest neighbouring shell. The calculation shows that in all the cases the first twelve nearest neighbours relax towards the vacancy and the magnitude of the displacements of the distant neighbours decreases systematically. The available experimental values of the monovacancy formation energy and divacancy binding energy whereever available, show fairly good agreement. Relations among monovacancy formation energy, melting temperature, and activation energy for self-diffusion are proposed.