Lattice dynamics and the compression curves of cobalt

The phonon dispersion relations along symmetry directions in cobalt have been obtained using a nearest neighbor central force model for hcp lattices. The third-order elastic (TOE) constants obtained in this model have been used to determine the changes in the lattice parameters due to high pressure, using Thurston's extrapolation formula. The variation of volume with pressure has been calculated using Murnaghan's logarithmic equation. The agreement of the calculated values with the experimental shock wave data up to 1.2 Mbar pressure is remarkably good.Supported in part by the Council of Scientific and Industrial Research, Government of India, through the grant of a Research Fellowship to A.R.