Center for Alloy Innovation and Design (CAID), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
School of Microelectronics, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
Adv Sci (Weinh). 2023 May;10(15):e2300901. doi: 10.1002/advs.202300901. Epub 2023 Mar 30.
Metavalent bonding (MVB) is characterized by the competition between electron delocalization as in metallic bonding and electron localization as in covalent or ionic bonding, serving as an essential ingredient in phase-change materials for advanced memory applications. The crystalline phase-change materials exhibits MVB, which stems from the highly aligned p orbitals and results in large dielectric constants. Breaking the alignment of these chemical bonds leads to a drastic reduction in dielectric constants. In this work, it is clarified how MVB develops across the so-called van der Waals-like gaps in layered Sb Te and Ge-Sb-Te alloys, where coupling of p orbitals is significantly reduced. A type of extended defect involving such gaps in thin films of trigonal Sb Te is identified by atomic imaging experiments and ab initio simulations. It is shown that this defect has an impact on the structural and optical properties, which is consistent with the presence of non-negligible electron sharing in the gaps. Furthermore, the degree of MVB across the gaps is tailored by applying uniaxial strain, which results in a large variation of dielectric function and reflectivity in the trigonal phase. At last, design strategies are provided for applications utilizing the trigonal phase.
多键合（MVB）的特征是电子离域（如金属键合）与电子定域（如共价键或离子键合）之间的竞争，它是先进存储应用相变材料的重要组成部分。该结晶相转变材料表现出 MVB，这源于高度对齐的 p 轨道，并导致较大的介电常数。打破这些化学键的对齐会导致介电常数急剧降低。在这项工作中，阐明了多键合如何在层状 SbTe 和 Ge-Sb-Te 合金中跨越所谓的范德华类似间隙发展，其中 p 轨道的耦合显著降低。通过原子成像实验和从头算模拟，确定了在 SbTe 的薄膜中存在涉及此类间隙的扩展缺陷。结果表明，这种缺陷会对结构和光学性质产生影响，这与间隙中存在不可忽略的电子共享是一致的。此外，通过施加单轴应变来调整间隙处的多键合程度，这会导致三方相的介电函数和反射率发生很大变化。最后，提供了利用三方相的设计策略。
