Stabilising elements in high oxygen coordination numbers: topo-structural implication on glass strength

玻璃拓扑学通常描述玻璃结构中结构元素的短到中间排列，并且约束理论的最新进展已成功地用于预测某些玻璃系统的机械性能。在这里，我们将采用以下方法的组合来确定玻璃网络的实际拓扑结构：将使用最先进的固态NMR光谱来表征短和中等长度尺度上的玻璃拓扑结构。虽然高分辨率（多量子）魔角旋转NMR实验提供了关于短程结构基序（1 - 2 π）的决定性信息，从而允许识别网络多面体的性质，采用基于现代均偶极和异偶极的NMR实验的全部清单，在中间长度尺度（2 - 8 μ m）上追踪结构图案将使我们能够阐明所识别的网络多面体朝向扩展的玻璃网络的互连。X射线吸收近边结构（XANES）光谱和红外和拉曼光谱等互补技术的结果将有助于改进玻璃拓扑结构的描述。具有低浓度非桥接氧的玻璃系统，因此，主要由共价键组成，被认为是实现更强玻璃的选择组合物。与局部增加的配位数的组合由于增加的堆积密度而可以提供优点，但是这可能取决于处于高配位的原子的键合情况是更具离子性（Al）或更具共价性（Si）。在短和中等长度尺度上的拓扑结构研究结果将与从微米和纳米压痕实验、布里渊光谱和（协作）原位机械测试获得的机械数据相关。其目的不仅是了解杨氏模量、抗裂性、断裂韧性和硬度如何受各种长度尺度上的玻璃拓扑结构的控制，而且还为实现强度显著提高的玻璃铺平了道路。

Glass topology usually describes the short-to-intermediate arrangement of structural elements in the glass structure, and recent advances in the constraint theory have been successfully used to predict mechanical properties of certain glass systems. Here, we will characterise the actual topology of the glass network employing a combination of methods: State of the art solid-state NMR spectroscopy will be used to characterize the glass topology on short and intermediate length scales. While high resolution (Multiple Quantum) Magic Angle Spinning NMR experiments provide decisive information about short range structural motifs (1 - 2 Å) and thus allows to identify the nature of the network polyhedra, the employment of the full inventory of modern homo- and heteronuclear dipolar based NMR experiments, tracing structural motifs on an intermediate length scale (2 - 8 Å) will enable us to elucidate the interconnection of the identified network polyhedra towards an extended glass network. Results from complementary techniques such as X-ray absorption near edge structure (XANES) spectroscopy and infra-red and Raman spectroscopy will help to refine the description of glass topology .Glass systems with low concentrations of non-bridging oxygens and, thus, consisting of mostly covalent bonds are considered the compositions of choice to achieve stronger glasses. The combination with locally increased coordination numbers may offer advantages owing to increased packing densities, but this may depend on the bonding situation of the atom in high coordination being of a more ionic (Al) or a more covalent character (Si). The topo-structural findings on short and intermediate length scales will be correlated with mechanical data obtained from micro- and nanoindentation experiments, Brillouin spectroscopy and (in collaboration) in situ mechanical testing. The aim is not only to understand how Young's modulus, crack resistance, fracture toughness and hardness are controlled by the glass topology on various length scales, but to pave the way towards glasses with significantly increased strength.