Structure and Dynamics in Boron- and Fluoride-Containing Oxide Glasses and Liquids: High-Resolution and High-Temperature Nuclear Magnetic Resonance Studies

固体核磁共振将继续用于研究两类具有重大技术应用的氧化物玻璃的结构和动力学，即含硼玻璃和氟氧化物玻璃。我们将获得关于常温和高温下的硼酸盐、硼硅酸盐、硼铝和氟氧化物玻璃的定量微观信息，包括含有稀土元素的抗磁性类似物的系统，并将根据这些新发现解释和模拟现有的热力学和输运性质数据。我们将继续强调温度效应，包括现场高温测量和对不同热历史制备的玻璃的研究，这些历史记录了在一定温度范围内的液体结构。我们将使用广泛的核磁共振方法(核素包括11B、170、19F、23Na、25 mg、27Al和29Si)，并在需要时补充其他方法，如拉曼和红外光谱。斯坦福大学提供的仪器包括带有9.4、14.1和18.8特斯拉磁铁(后者是目前商业上可获得的最高场强)的光谱仪，具有复杂的高速魔角旋转、双重和三重共振以及高温核磁共振探头。一种新开发的快速淬火设备，将允许对小的、有价值的、同位素浓缩的样品进行热史研究。新的核磁共振方法的应用，特别是多量子核磁共振的应用，将继续发挥重要作用，对具有已知晶体模型化合物结构的核磁共振观测数据的经验校准也将如此。将继续开发和测试连接微观和宏观的模型，并将使用基于密度泛函理论的新的从头能量计算程序来补充实验结果。含硼氧化物玻璃广泛应用于耐腐蚀、耐高温的容器、管道和储罐、玻璃纤维复合材料、光学元件、计算机显示屏等。硼硅酸盐玻璃也可能在隔离放射性废物方面发挥重要作用。随着组成和温度的变化，硼阳离子很容易改变其局部结构环境，这不仅有助于这些材料的有用性质，而且使它们成为一个独特而有趣的科学课题。在氟氧化物玻璃中，一些氧离子被氟化物取代，这再次赋予了生成的玻璃和玻璃形成液体独特的性质，并再次提出了关于混合阴离子系统的结构和动力学的大量基础科学问题。长期以来，氟化物一直被用来降低玻璃形成液的粘度和熔化温度，但对其机理并不清楚；在最近的高科技创新中，氟氧化物玻璃正成为激光和光学放大器材料中稀土元素的主体，引起人们的兴趣。在所有这些材料中，为特定的技术应用量身定做它们的性能的能力需要对它们在原子尺度上的结构以及在前体高温玻璃熔化中结构变化的动力学的定量知识。核磁共振“看到”局部原子结构和动力学，通常是以高度定量的方式，围绕氧化物玻璃的许多最重要成分的选定同位素。因此，核磁共振已被证明是研究这种非晶态材料的一种近乎理想的工具，并极大地增加了我们对它们的理解。这个项目应该会引起材料科学界的直接兴趣，但它的结果也将对研究玻璃形成和其他复杂液体的动力学的物理学家、开发固态核磁共振新应用的物理化学家以及试图模拟和预测自然界中硅酸盐岩浆行为的地球化学家具有实际意义。在过去，希望在未来，这种类型的研究的跨学科性质拓宽了我们组中具有光谱学或地球化学背景的学生的视野，进入了玻璃和陶瓷科学这一迷人的、具有重要技术意义的世界。

Solid-state Nuclear Magnetic Resonance will continue to be used to study the structure and dynamics of two classes of oxide glasses that have major technological applications, namely boron-containing glasses and oxyfluoride glasses. We will acquire quantitative microscopic information on borate, borosilicate, aluminoborate, and oxyfluoride glasses at ambient and high temperature, including systems containing diamagnetic analogs of rare earth elements, and will interpret and model existing thermodynamic and transport property data in light of these new findings. We will continue to emphasize temperature effects, with both in situ, high temperature measurements and studies of glasses prepared with varying thermal histories, which record the liquid structure at a range in temperature. We will use a wide range of NMR methods (on nuclides including 11B, 170, 19F, 23Na, 25Mg, 27AI, and 29Si), supplemented where needed by other methods such as Raman and infrared spectroscopy. Instruments available at Stanford include spectrometers with 9.4, 14.1, and 18.8 Tesla magnets (the latter the highest field strength currently commercially obtainable), with sophisticated high-speed magic-angle spinning, double and triple resonance, and high temperature NMR probes. A newly-developed rapid quench apparatus that will allow thermal history studies of small, valuable, isotopically enriched samples to be done. Applications of new NMR methods, in particular multiple quantum NMR, will continue to play a major role, as will the empirical calibration of NMR observables with structure of known crystalline model compounds. Models linking the microscopic and macroscopic will continue to be developed and tested and a new program of ab initio energy calculations, based on density functional theory, will be used to complement experimental results. Boron-containing oxide glasses are widely used in corrosion- and temperature-resistant containers, pipes and tanks, in "fiberglass" composites, in optical components, computer display screens, etc. Borosilicate glasses are also likely to play a major role in sequestering radioactive wastes. The ease with which the boron cation changes its local structural environment as a function of composition and temperature not only contributes to the useful properties of these materials but makes them a unique and intriguing subject scientifically. In oxyfluoride glasses, some oxygen ion is replaced by fluoride, again giving the resulting glasses and glass-forming liquids unique properties, and again posing a wealth of fundamental scientific issues concerning the structure and dynamics of mixed-anion systems. Fluoride has long been used to lower viscosities and melting temperatures of glass-forming liquids without clear understanding of mechanism; in recent high-tech innovations, oxyfluoride glasses are becoming interesting as hosts for rare earth elements in laser and optical amplifier materials. In all of these materials, the ability to tailor their properties to specific technological applications requires quantitative knowledge of their structure at the atomic scale, and the dynamics with which that structure changes in the precursor high-temperature glass melts. Nuclear magnetic resonance "sees" the local atomic structure and dynamics, often in a highly quantitative way, around selected isotopes of many of the most important constituents of oxide glasses. NMR has thus proven to be a near-ideal tool for studying such non-crystalline materials, and has increased our understanding of them enormously. This project should have direct interest to the Materials Science community, but its results will also have real significance to physicists working on the dynamics of glass- forming and other complex liquids, to physical chemists developing new applications of solid-state NMR, and to geochemists trying to model and predict the behavior of silicate magmas in nature. In the past, and hopefully in the future, the discipline-crossing nature of this type of study has broadened the perspectives of students in our group, with backgrounds in spectroscopy or geochemistry, into the fascinating and technologically important world of glass and ceramic sciences.