Lattice Dynamics Calculations for Mg_1-XZn_xO Solid Solutions

In this study, Mg_1-xZn_xO solid solutions are studied by modelling lattice dynamics, using the methods of classical molecular dynamics. These time-efficient methods are of great interest since they allow using large crystallic structures, which reduce artificial defect periodicity. The main program used is General Utility Lattice Program (GULP). The Buckingham potential is used for modelling interatomic forces. The parameters for this potential are found for different effective ionic charges by using lattice parameters and vibrational frequencies obtained from ab initio calculations performed in the program CRYSTAL14. With these potentials, the dispersion relations and densities of states have been calculated for MgO, ZnO and Mg_1-xZn_xO. Calculations have been made for different Mg and Zn contents in the wurtzite and cubic phase solid solutions, respectively, using the supercell method and a large number of Brillouin zone sampling points.

New interatomic potentials for interactions Mg-O, O-O, Zn-O have been obtained. These potential parameters have been verified and the phonon dispersion curves and DOS for MgO and ZnO utilising these potential parameters have been compared to other studies, both experimental and theoretical. By adding more Zn in the cubic phase (c-MgO) solution, no local vibrational modes are observed; however, there is a clear spectral widening and a noticeable change in the low frequency region (100–300 cm⁻¹) of the DOS. Adding more Mg in wurtzite phase (w-ZnO) solution, on the other hand, results in local vibrational modes in the mid (350 cm⁻¹) and high frequency (650 cm⁻¹) regions.