Influence of cluster formation on localization of optical phonons in two-dimensional pseudobinary substitutional solid solutions

The influence of the composition and short-range order of the cluster formation type on optical phonon localization in two-dimensional pseudobinary substitutional solid solutions is studied. Direct numerical calculations of the so-called inverse participation ration (IPR) are carried out, and the scaling of this parameter is studied for the fundamental modes of the spectral density of states at the Brillouin zone center of the averaged crystal. It is shown that cluster formation promotes phonon delocalization, although the nature of this effect is different for resonant and local (in the low-concentration limit) modes. The influence of the ionicity of a solid solution on localization is considered. It is shown that the Coulomb interaction neutralizes the effect of cluster formation while simultaneously decreasing the observed IPR. Based on the form of the distribution of local site absorption of an external electromagnetic field, a new physical criterion is suggested, which allows one to analyze the localization degree of phonon modes in ionic alloys.