The Intermediate Phase in Network Glasses

这个项目涉及玻璃的性质和它们的相变。在选定的硫系玻璃系统中，将软性相（FP）与刚性相（RP）分开的中间相（IP）的物理性质进行研究。这些特性将在四组不同的实验中进行研究。首先，将在78K到Tg+200 K的范围内对Ge-Se、As-Se和Ge-As-Se块体玻璃进行温度依赖的拉曼散射研究，以检查FP、IP和RP中发生的分子结构变化的性质。第二，同样的玻璃系统，但现在合成为倾斜沉积薄膜（倾斜角度在0到80度范围内），将在拉曼，119Sn穆斯堡尔效应和光收缩研究中，在其原始和光照射状态下进行检查。在多孔（倾斜）沉积膜中形成的柱状结构可能代表了中等范围结构的元素，负责IP中玻璃的相当独特的物理性质。第三，将在拉曼光谱、NQR光谱、EXAFS光谱和129I穆斯堡尔光谱研究中研究基于镍基玻璃系统，如as - se、as - s和as - ge - se玻璃，以阐明最近调制差示扫描量热法（MDSC）测量中发现的IP分子结构的新方面。最后，将选择的玻璃中的119Sn Lamb-Mossbauer因子作为平均配位数的函数，以比较IP中玻璃与FP和RP中的玻璃的局部弹性响应。学生将参与这项研究，从而为进入21世纪的科学技术工作做好准备。本研究涉及玻璃和玻璃系统的性质。眼镜的特点是软盘网络的渐进交联，这将使其在关键连接时变得刚性。这通常是通过系统地改变玻璃系统中的化学成分来实现的。然而，对含硫和含硒玻璃的实验表明，软相（FP）和刚性相（RP）被中间相（IP）分开。将进行四组不同的实验，以确定选定玻璃系统中IP的物理性质。不同的实验技术将带来承担选定的玻璃系统在一系列的玻璃成分，包括三个不同的阶段。实验将在包含相之间转变的较宽温度范围内进行。此外，还将研究这些玻璃的特殊制备薄膜。这些实验有望揭示在不同温度和成分条件下玻璃系统的复杂性，其结果将用于将新玻璃纳入先进的技术设备。学生将参与这些调查。因此，他们将获得凝聚态物理和材料科学这一当代重要领域之一的培训，并为进入工业、学术界和政府的科学/技术工作队伍做好准备。

This project concerns the properties of glasses and their phase transformations. The physical nature of the Intermediate phase (IP) that separates the Floppy phase (FP) from the Rigid Phase (RP) in select chalcogenide glass systems will be examined. These properties will be investigated in four different sets of experiments. First, temperature-dependent Raman scattering studies of Ge-Se, As-Se and Ge-As-Se bearing bulk glasses will be performed over the range from 78K to Tg+200 K to examine the nature of molecular structure changes taking place across Tg in the FP, IP and the RP. Second, the same glass systems, but now synthesized as obliquely deposited thin-films (obliqueness angle in the range from 0 to 80 degrees) will be examined in their virgin and photo-illuminated state in Raman, 119Sn Mossbauer effect and photo-contraction studies. The columns formed in the porous (obliquely) deposited films may represent the elements of medium range structure responsible for the rather unique physical properties of glasses in the IP. Third, pnictide based glass systems, such as As-Se, As-S and As-Ge-Se bearing glasses will be examined in Raman, NQR, EXAFS and 129I Mossbauer spectroscopic studies to elucidate new aspects of molecular structure recently inferred from the discovery of the IP in Modulated Differential Scanning Calorimetry (MDSC) measurements. Lastly, 119Sn Lamb-Mossbauer factors in select glasses will be established as a function of mean coordination number to contrast the local elastic response of glasses in the IP from those in the FP and the RP. Students will participate in this research and will thereby be prepared to enter the scientific technical work force of the 21st Century.This research concerns the properties of glasses and glass systems. Glasses are characterized by progressive cross-linking of a floppy network that will render it rigid at a critical connectivity. This is often realized by systematically changing the chemical composition in a glass system. Experiments on sulfur- and selenium-bearing glasses have shown however that a floppy phase (FP) and a rigid phase (RP) are separated by an intermediate phase (IP). Four different sets of experiments will be performed to establish the physical nature of the IP in select glass systems. Different experimental techniques will be brought to bear on selected glass systems over a range of glass compositions that encompass the three different phases. The experiments will be performed over a wide temperature range that embraces the transitions among the phases. Furthermore, specially fabricated thin films of these glasses will be investigated. These experiments are expected to shed light on the intricacies of glass systems under various conditions of temperature and composition and the results will be of use for the incorporation of new glasses in advanced technological devices. Students will participate in these investigations. They will thereby acquire training in one of the important contemporary areas of condensed matter physics and materials science and will be prepared to enter the scientific/ technical work force in industry, academe, and the government.