Phonon Dispersion in Anisotropic Dilute Alloys by Weighted Dynamical-Matrix Approach

The calculation of phonon frequencies in dilute anisotropic alloys is not a simple undertaking and the successful methodologies are not well developed. We propose weighted dynamical-matrix (WDM) approach for calculating optical phonon spectra that is applicable to such complex alloys for a large range of alloying elements. Our WDM approach forms the dynamical-matrix for random alloys using the weighted average of parent structures mass and calculated force constants that allows us to calculate the phonon spectra. This WDM approach is computationally efficient and easily implemented. We demonstrate its use for the effect of Fe-doping on the phonon modes in dilute alloy of CuAl_1-xFe_xO₂ delafossite powders whose structural and magnetic properties have been reported previously^1,2 and the phonon frequencies are measured using Raman and FTIR spectroscopies. The observed phonon modes are in good agreement with our WDM approach calculations. These results are consistent with the lattice expansion accompanying the Fe-doping, weakening the bonds. Also, Fe-doping effect on optical properties of these alloys is explored and explained by the first-principle calculated band structures.
¹ M. Aziziha et al, J. Magn. Magn Mater. 471, 495 (2019).
² M. Aziziha et al,AIP Advances 9, 035030 (2019).