Kinetic fragility of melts of conditional glass former oxides

条件玻璃原氧化物（cgf）在高度专业化和光学玻璃的生产中发挥着至关重要的作用。由于不能立即结晶，它们通过熔体淬火形成玻璃的能力受到很大限制，实际上它们只能通过与其他氧化物的二元或多组分混合物形成玻璃。然而，基于结构和/或动力学标准的CGFs有限玻璃形成的起源仍然没有令人满意的解决。因此，本研究计划的目的是研究焓弛豫与粘性流动之间的关系及其结构起源。实验是基于现代闪光差示扫描量热计（FDSC）的能力，以高速率（高达50,000 K s-1）淬火小液滴（几微米大小）的熔体，并同时确定玻璃化转变的特征温度，在第二步中，粘度和动力学脆性得到。通过将含CGF玻璃的改进剂的粘度与量热数据相联系的组成回路，提供了平行移位因子。利用FDSC和平行位移因子，工作假设验证了期望，即脆性gfs在玻璃化转变时的焓松弛和粘性流动是解耦的。工作将集中在三种CGFs上：类金属氧化物Sb2O3，过渡金属氧化物V2O5和重金属氧化物Bi2O3，由于它们在玻璃中的吸引力，它们的熔体的热稳定性以及金属/类金属阳离子的不同电子构型而被选择。通过收集小玻璃液滴的拉曼强度，可以获得近中程阶的结构信息，为此已经建立了专门的设备。由此，可以推导出动态非均质性的程度，并与粘度/量热结果相关联。通过比较研究进一步阐明了功假设所处理的问题，强调了当CGF熔体接近不纯水平时，玻璃化转变温度与改性剂分数之间的非线性关系。反过来，温度依赖约束理论将用于提供CGF玻璃网络的连通性和玻璃化转变温度的成分依赖之间的定量联系。

Conditional glass former oxides (CGFs) do play an essential role as components in the production of highly specialized and optical glasses. Their readiness for glass formation by melt-quenching is strongly limited due to immediate crystallization and in practice they form glasses only by binary or multicomponent mixtures with other oxides. However, the origin for limited glass formation of CGFs based on structural and/or kinetic criteria is still not satisfactorily settled. The objective of the research proposal is therefore to study the relation between enthalpy relaxation and viscous flow ranged by the strong–fragile pattern of kinetic fragility and its structural origin. Experiments are based on the capability of modern flash differential scanning calorimeter (FDSC) to quench a small droplet (few microns in size) of melt at high rate (up to 50,000 K s-1) and to simultaneously determine characteristic temperatures of the glass transition from which, in a second step, viscosity and kinetic fragility are obtained. Parallel shift factors are provided by performing a compositional loop linking viscosity with calorimetric data of modifier containing CGF glasses. With the use of FDSC and parallel shift factors, the work hypothesis is to verify expectations, that enthalpy relaxation and viscous flow at the glass transition of fragile CGFs are decoupled. Work will be focussed on three CGFs: the metalloid oxide Sb2O3, the transition metal oxide V2O5, and the heavy metal oxide Bi2O3 that are selected due to the attractive properties in glasses, thermal stability of their melt and the different electronic configuration of the metal/metalloid cation. Structural information on the near- and mid-range order will be gained by collection of Raman intensities from the small glassy droplet, for which special equipment has been built up. From it, the degree of dynamic heterogeneity will be deduced and correlated to the viscometric/calorimetric results. The issues dealt with by the work hypothesis are furthermore elucidated by comparative research in terms of highlighting the expected non-linear relation between glass transition temperature and modifier fraction of CGF melts when approaching inpurity level. In turn, temperature-dependent constraint theory will be used to provide a quantitative connection between the connectivity of the CGF glass network and the compositional dependence of the glass transition temperature.