Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA.
J Chem Phys. 2019 Jan 28;150(4):044506. doi: 10.1063/1.5080225.
The composition dependence of the fragility of SiSe liquids with 0.05 ≤ x ≤ 0.33 is determined using the calorimetric method and is found to be rather similar to that characteristic of their Ge analogues. In addition, the nature and the time scale of the structural relaxation of the SiSe glass during aging at 40 K below T are measured using Raman spectroscopy. The structural relaxation in this glass, which belongs to the so-called intermediate phase, involves progressive conversion of the doubly edge-shared SiSe tetrahedra E into singly edge-shared E and corner-shared E tetrahedra upon lowering of temperature. This tetrahedral speciation can be expressed in the form of the reaction 2 E → E + E. The time scale of this tetrahedral conversion reaction corresponds well with that of shear relaxation. This result is inconsistent with the claim made previously in the literature that intermediate phase compositions do not undergo aging. Moreover, when taken together, the fragility and the structural relaxation results suggest that the constraint counting scheme typically adopted in the literature for edge- vs. corner-shared tetrahedra in chalcogenide networks may need to be revised. A rigid-polytope based constraint counting approach is shown to be more consistent with the experimental results.
使用量热法确定了 0.05≤x≤0.33 的 SiSe 液体的组成依赖性，发现其与 Ge 类似物的特征相当相似。此外，还使用拉曼光谱测量了 SiSe 玻璃在 40 K 以下老化时的结构弛豫的性质和时间尺度。在这种属于所谓中间相的玻璃中，结构弛豫涉及在降低温度时，双边缘共享的 SiSe 四面体 E 逐渐转化为单边缘共享的 E 和角共享的 E 四面体。这种四面体形的分类可以用反应 2E→E+E 表示。这种四面体转化反应的时间尺度与剪切弛豫的时间尺度非常吻合。这一结果与文献中先前提出的中间相组成物不经历老化的说法不一致。此外，综合脆性和结构弛豫的结果表明，在硫属化物网络中边缘共享与角共享四面体的典型约束计数方案可能需要修改。基于刚性多面体的约束计数方法与实验结果更一致。
