Third-order elastic constants of the alloy Fe72Pt28

The complete sets of second- and third-order elastic constants of the cubic Fe72Pt28 have been obtained using the strain energy density derived from interactions up to three nearest neighbours of each atom in the unit cell. The finite strain elasticity theory has been used to get the strain energy density of Fe72Pt28. The strain energy density is compared with the strain-dependent lattice energy density obtained from the continuum model approximation and the expressions for the second- and third-order elastic constants of Fe72Pt28 are given. The second-order potential parameter is deduced from the measured second-order elastic constants of Fe72Pt28 and the third-order potential parameter is estimated from the Lennard-Jones inter-atomic potential for Fe72Pt28. The inter-lattice displacements; the three independent second-order elastic constants and the six independent third-order elastic constants of Fe72Pt28 are also determined. The second-order elastic constants are compared with the experimental elastic constants of Fe72Pt28. We also study the effect of pressure on the second-order elastic constants of Fe72Pt28