Wilson C M, Ganesh R, Crandles D A
Department of Physics, Brock University, St. Catharines, Ontario L2S 3A1, Canada.
J Phys Condens Matter. 2024 Apr 18;36(29). doi: 10.1088/1361-648X/ad2ff1.
The recently-discovered high-entropy oxides (HEO's) 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 localised vibrational excitations. In this article, we explore the possibility of disorder-induced localisation in MgCoNiCuZnO, the prototypical HEO 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 and optical conductivity. The resulting phonon spectrum shows wave-like propagating modes at low energies and localised modes at high energies. Localisation is reflected in signatures such as participation ratio and correlation amplitude. Finally, we argue that mass disorder can be increased to enhance localisation. We consider a hypothetical material, high-entropy telluride-oxide, where tellurium atoms are admixed into the anion sublattice. This shows a larger localised fraction, with additional localised modes appearing in the middle of the spectrum. Our results demonstrate that HEO's are a promising platform to study Anderson localisation of phonons.
最近发现的高熵氧化物（HEO）呈现出晶体排列与高度无序的矛盾组合。它们在性质上不同于诸如玻璃和合金等无序固体的既定范例。在这些后一种体系中，众所周知无序会引发局域振动激发。在本文中，我们探讨了在具有岩盐结构的典型HEO——MgCoNiCuZnO中无序诱导局域化的可能性。为了描述声子激发，我们通过拟合母体二元氧化物的物理性质来模拟阳离子 - 氧相互作用的原子间势。我们根据实验测定的晶体结构和光导率验证了我们的模型。所得的声子谱在低能量处显示出波状传播模式，在高能量处显示出局域模式。局域化反映在诸如参与率和相关振幅等特征中。最后，我们认为可以增加质量无序以增强局域化。我们考虑一种假设的材料，即高熵碲化物氧化物，其中碲原子混入阴离子亚晶格中。这显示出更大的局域化部分，并且在谱的中间出现额外的局域模式。我们的结果表明，HEO是研究声子安德森局域化的一个有前景的平台。
