Abstract Inelastic X-ray scattering (IXS) experiments were carried out at room temperature at BL35XU of the SPring-8 on a single crystal Mg85Zn6Y9 alloy with a synchronized long-period stacking ordered (LPSO) phase of purely 18R type. The IXS measurements were carried out in both the longitudinal and transverse directions along the Γ -K and Γ -M (momentum vector q ⊥ lattice axis c ), and Γ -A ( q ∥ c ) directions for the energy transfers ω below 40 meV. Peaks arising from longitudinal and transverse acoustic (LA and TA) modes were clearly observed in the IXS spectra. The dispersion relations of the LA and TA modes in the Mg85Zn6Y9 LPSO alloy are mostly similar to those of previous INS data on single crystal pure Mg. New impurity-derived dispersion-less excitation modes are observed along all of the crystal directions at about 5, 10, and 17 meV. Partial vibrational density of states (vDOS) was obtained using an a b i n i t i o molecular dynamics simulation, and it was found that the ∼ 10 meV peak mainly originates from the phonon excitations inside the L12-type Zn6Y8 clusters and the ∼ 17 meV peak from those between the cluster and the host Mg atoms, and a small shoulder at 5 meV consists of motions of all the elements. These findings clarify that the dispersion-less modes mainly correspond to localized stretching and twisting modes around the impurity clusters in the LPSO alloys.

中文翻译：

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具有同步长周期堆积有序相的单晶 Mg 85 Zn 6 Y 9 中的声子激发

摘要 在室温下，在 SPring-8 的 BL35XU 条件下，对具有纯 18R 型同步长周期堆积有序 (LPSO) 相的单晶 Mg85Zn6Y9 合金进行了非弹性 X 射线散射 (IXS) 实验。IXS 测量沿 Γ -K 和 Γ -M（动量矢量 q ⊥ 晶格轴 c ）和 Γ -A ( q ∥ c ) 方向在纵向和横向上进行，用于能量转移 ω 低于 40 meV . 在 IXS 光谱中清楚地观察到由纵向和横向声学（LA 和 TA）模式产生的峰。Mg85Zn6Y9 LPSO 合金中 LA 和 TA 模式的色散关系与之前单晶纯 Mg 的 INS 数据基本相似。在大约 5、10 和 17 meV 的所有晶体方向上都观察到了新的源自杂质的无色散激发模式。使用abinitio分子动力学模拟获得了部分振动态密度（vDOS），发现~10 meV峰主要来自L12型Zn6Y8簇内的声子激发，~17 meV峰来自于L12型Zn6Y8簇之间的声子激发。簇和主体 Mg 原子，以及 5 meV 的小肩部由所有元素的运动组成。这些发现阐明了无色散模式主要对应于 LPSO 合金中杂质簇周围的局部拉伸和扭曲模式。5 meV 的小肩由所有元素的运动组成。这些发现阐明了无色散模式主要对应于 LPSO 合金中杂质簇周围的局部拉伸和扭曲模式。5 meV 的小肩由所有元素的运动组成。这些发现阐明了无色散模式主要对应于 LPSO 合金中杂质簇周围的局部拉伸和扭曲模式。