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要技术应用的氧化玻璃的结构和动力学，即含硼玻璃和氟化氧玻璃。我们将获得环境和高温下硼酸盐、硼硅酸盐、硼酸铝和氟氧化物玻璃的定量微观信息，包括含有稀土元素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，包括原位、高温测量和不同热历史制备的玻璃的研究，记录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、25Mg、27AI和29Si），必要时补充其他方法，如拉曼光谱和红外光谱。斯坦福大学现有的仪器包括配备9.4、14.1和18.8特斯拉磁体的光谱仪（后者是目前商业上可获得的最高磁场强度），配备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针。一种新开发的快速淬火装置，可以对小的、有价值的、同位素富集的样品进行热历史研究。新的核磁共振方法的应用，特别是多量子核磁共振，将继续发挥主要作用，正如核磁共振可观测物与已知晶体模型化合物结构的经验校准一样。连接微观和宏观的模型将继续被开发和测试，一个基于密度泛函理论的从头计算能量的新程序将被用来补充实验结果。含硼氧化玻璃广泛应用于耐腐蚀和耐温度的容器、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。作为组成和温度的函数，硼阳离子容易改变其局部结构环境，这不仅有助于这些材料的有用特性，而且使它们成为一个独特而有趣的科学课题。在氟化氧玻璃中，一些氧离子被氟化物取代，再次赋予玻璃和玻璃形成液体独特的性质，并再次提出了有关混合阴离子系统结构和动力学的大量基础科学问题。长期以来，氟化物一直被用于降低玻璃形成液的粘度和熔化温度，但其机理尚不清楚；在最近的高科技创新中，氟化氧玻璃作为稀土元素在激光和光放大器材料中的宿主正变得有趣。在所有这些材料中，为特定技术应用定制其特性的能力需要对其原子尺度结构的定量了解，以及该结构在前驱体高温玻璃熔化时变化的动力学。核磁共振通常以高度定量的方式“看到”氧化玻璃中许多最重要成分的选定同位素周围的局部原子结构和动力学。因此，核磁共振已被证明是研究此类非晶体材料的近乎理想的工具，并极大地增加了我们对它们的了解。这个项目应该对材料科学界有直接的兴趣，但它的结果也将对从事玻璃形成和其他复杂液体动力学研究的物理学家、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硅酸盐岩浆行为的地球化学家具有真正的意义。在过去，希望在未来，这种跨学科的研究性质已经拓宽了我们小组中具有光谱学或地球化学背景的学生的视野，进入了迷人且技术重要的玻璃和陶瓷科学世界。

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.