Non-linear elastic characterization of hexagonal cadmium selenide

The complete set of non-vanishing second- and third order elastic constants and the pressure derivatives of second order elastic constants of hexagonal wurtzite phase of cadmium selenide (CdSe) are obtained from the homogeneous deformation theory. The strain energy is derived using finite strain elasticity theory by considering interactions up to four nearest neighbors of each atom in the unit cell of CdSe. We then compare this strain energy with the strain dependent lattice energy density from the continuum model to obtain the expressions for the second- and third order elastic constants. The calculated third order elastic constants show that, the longitudinal wave velocities C111, C222 and C333 are greater than their shear mode, indicating an increase of vibrational frequencies under stress along these directions. Furthermore, the pressure derivatives of SOECs of the shear modes, C44 and C66, are negative, which show the possibility of a structural transformation. Bulk modulus and its pressure derivative are calculated and comparison with experimental values is made