  The recently-discovered high-entropy oxides offer a paradoxical combination
of crystalline arrangement and high disorder. They differ qualitatively from
established paradigms for disordered solids such as glasses and alloys. In
these latter systems, it is well known that disorder induces localized
vibrational excitations. In this article, we explore the possibility of
disorder-induced localization in (MgCoCuNiZn)O, the prototypical high-entropy
oxide with rock-salt structure. To describe phononic excitations, we model the
interatomic potentials for the cation-oxygen interactions by fitting to the
physical properties of the parent binary oxides. We validate our model against
the experimentally determined crystal structure, bond lengths, and optical
conductivity. The resulting phonon spectrum shows wave-like propagating modes
at low energies and localized modes at high energies. Localization is reflected
in signatures such as participation ratio and correlation amplitude. Finally,
we explore the possibility of increased mass disorder in the oxygen sublattice.
Admixing sulphur or tellurium atoms with oxygen enhances localization. It even
leads to localized modes in the middle of the spectrum. Our results suggest
that high-entropy oxides are a promising platform to study Anderson
localization of phonons.
