4TH-ORDER NONLINEAR ELASTIC COEFFICIENTS OF HEXAGONAL CLOSE-PACKED LATTICE

The expressions for the fourth-order elastic constants of a hexagonal close packed lattice is derived using the sublattice displacements to the second order in strains. These expressions together with the expre ssions for the second- and third-order elastic constants have been use d to obtain the higher order nonlinear elastic coefficients in some he xagonal metals. These expressions are used to find the second-order, t hird-order and fourth-order elastic constants of cadmium. The pressure derivatives of their elastic constants are also obtained. The results obtained are compared with the available experimental results.