Relative Influence of Topology, Dimensionality and Stoichiometry Toward the Properties of Covalent Network Glasses
Relative Influence of Topology, Dimensionality and Stoichiometry Toward the Properties of Covalent Network Glasses
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DOI：
10.3389/fmats.2019.00180
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发表时间：
2019-07
影响因子：
3.2
通讯作者：
P. Lucas
中科院分区：
文献类型：
--
作者：
P. Lucas
密度和脆弱性的趋势进行了分析，在Ge-As-Se，As-Se和Ge-Se系统的目的是识别相关的拓扑结构，化学计量学和维度的结构特征。Ge-As-Se系统提供了最具启发性的测试平台，因为它允许隔离个体效应。Ge-As-Se玻璃的脆性明显受化学计量因子的控制，而在=2.4处没有观察到拓扑转变。Ge-As-Se玻璃的密度随着平均配位而增加，但显示出以= 2.4和2.67附近为中心的两个异常。这些异常合并成一个单一的极值对应于化学计量组成时，对过量/硒不足，从而揭示了它们的共同联系，化学计量因素。然而，当化学计量因子是固定的，尺寸效应的形式揭示了一个线性依赖于四面体锗含量。类似地，当仅考虑Se过量组合物时，观察到= 2.4的拓扑转变处的扩散最大值。对于As-Se系统，在二维组成As 2Se 3处观察到脆性的局部最大值，与拓扑或化学计量因子的预测相反，从而表明尺寸效应控制脆性行为。最后，在Ge-Se系统中，当不存在来自化学计量和维度的贡献时，在= 2.4处发现与约束和自由度的平衡相关联的拓扑转变。在所有系统中，没有发现拓扑效应支配化学计量效应或尺寸效应的情况，因此可以得出结论，它是最小的主要贡献，而化学计量被发现是占主导地位的效应。
Trends in density and fragility are analyzed in the Ge-As-Se, As-Se and Ge-Se system for the purpose of identifying correlation with structural characteristics related to topology, stoichiometry and dimensionality. The Ge-As-Se system provides the most revealing testbed as it permits to isolate individual effects. The fragility of Ge-As-Se glasses is clearly controlled by stoichiometric factors while the topological transition at =2.4 is not observed in this system. The density of Ge-As-Se glasses broadly increase with average coordination but show two anomalies centered near = 2.4 and 2.67. These anomalies merge into a single extremum corresponding to stoichiometric compositions when plotted against excess/deficiency in Se, thereby revealing their common link to stoichiometric factors. Nevertheless, when stoichiometric factors are fixed, dimensional effects are revealed in the form of a linear dependence upon content of tetrahedral Ge. Similarly, a diffuse maximum at the topological transition of = 2.4 is observed when only Se-excess compositions are considered. For the As-Se system, a local maximum in fragility is observed at the two dimensional composition As2Se3, contrary to predictions from topological or stoichiometric factors, thereby indicating that dimensional effect control the fragile behavior. Finally, in the Ge-Se system, a topological transition associated with balance of constraints and degrees of freedom is found at = 2.4 when contributions from stoichiometry and dimensionality are absent. In all system, no case is found where topological effects dominate either stoichiometric or dimensional effects, hence it can be concluded that it is the least predominant contribution while stoichiometry is found to be the prevailing effect.