Polyamorphism and Structural Transitions during Glass Formation

玻璃形成过程中的多晶现象和结构转变

• 批准号: 0230662
• 负责人: John Kieffer
• 金额: $ 22.15万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-09-01 至 2005-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0230662&HistoricalAwards=false
• 关键词: Polyamorphism; Structural; Transitions; during; Glass

0072258KiefferThere is increasing evidence that the glassy and liquid states are structurally and thermodynamically distinct, although both amorphous. This implies that the glass transition is a "polyamorphic" transformation. Furthermore, a tendency of the substance to undergo structural transitions in the glassy state could affect materials properties such as non-linear optical responses and mechanical behaviors. This project comprises the investigation of the structural evolution in glass-forming materials as a function of pressure and temperature. The extent to which structural relaxation during glass formation involves polyamorphic structural transitions, as opposed to a viscous slowing within an invariant structure, will be determined. Structural characterization in supercooled melts will be accomplished using a combination of Brillouin and Raman light scattering and molecular dynamics simulations, which will allow one to identify the mechanical response of the structure and the nature of structural building blocks. Brillouin light scattering will be used to determine the high-frequency complex mechanical modulus of glass-forming melts at the molecular scale. The real component, or storage modulus, provides information on the structural integrity and network connectivity, while the imaginary component corresponds to the energy dissipated in aperiodic motions of small structural constituents (e.g., atomic hopping). Simultaneous Raman scattering will allow one to establish a direct correlation between this visco-elastic behavior and the symmetries and abundance of molecular building blocks. Molecular dynamic simulations will be used to reconcile the experimentally determined Raman spectra and visco-elastic properties with a detailed geometric description of the molecular structure. The manifestation of polyamorphism will be revealed by examining a series of glass-forming systems, chosen to systematically sample a wide range of glass-forming attributes, such as the valences, bonding types of the network elements, and melt fragility. Systems will include germanates, phosphates, tellurites, and chalcogenides. The relationship between the nature of the network former and the mechanisms of transitions between different non-crystalline polymorphs will be established by studying the effects of simultaneous pressure and temperature on the transition processes using heated diamond anvil cells.The objective of this project is to clarify the concept and manifestations of polyamorphism. With this clarification, our understanding of important issues in glass science will be advanced, since a tendency of a material to undergo structural transitions in the glassy state could affect its properties, such as non-linear optical responses and mechanical behaviors, which are important for high tech applications. Expanding the range of applicability of glasses will enable new technologies, including photonics, optical telecommunication and computing, drug and radiation delivery, bio-medical implants, sensors, energy storage and generation, nuclear waste containment, and light-weight metallic alloys.

0072258Kiefferthere越来越多的证据表明玻璃状和液态在结构和热力学上是不同的，尽管都无定形。 这意味着玻璃转变是“多态”转换。 此外，该物质在玻璃状态下进行结构过渡的趋势可能会影响材料特性，例如非线性光学响应和机械行为。 该项目包括对玻璃形成材料的结构演变的研究，这是压力和温度的函数。 将确定玻璃形成过程中结构弛豫的程度，涉及多形结构过渡，而不是在不变结构内的粘性减慢。 超冷熔体中的结构表征将使用布里渊和拉曼光散射和分子动力学模拟的组合来完成，这将使人们能够识别结构的机械响应以及结构构建块的性质。 Brillouin光散射将用于确定分子尺度上玻璃形成熔体的高频复合机械模量。 实际组件或存储模量提供了有关结构完整性和网络连接性的信息，而虚构的组件则与小结构成分的高度运动动作（例如原子跳跃）相对应。 同时的拉曼散射将使人们在这种粘弹性行为与对称性和丰富性分子构建块之间建立直接相关性。 分子动态模拟将用于调和实验确定的拉曼光谱和粘弹性特性，并详细介绍了分子结构的几何描述。 多态性的表现将通过检查一系列玻璃形成系统来揭示，该系统被选为系统地采样多种玻璃形成属性，例如价值，网络元素的粘结类型以及熔体脆弱性。 系统将包括德国人，磷酸盐，泰特里斯和葡萄干剂。通过使用加热的钻石砧室研究同时压力和温度对过渡过程的影响，将建立网络前者的性质与不同非晶体多晶型物之间的过渡机制之间的关系。该项目的目标是阐明多态性的概念和表现。通过这种澄清，我们对玻璃科学中重要问题的理解将是提出的，因为材料在玻璃状态下进行结构过渡的趋势可能会影响其特性，例如非线性光学响应和机械行为，这对于对此很重要，这对高科技应用。扩大玻璃的适用性范围将使新技术，包括光子学，光学电信和计算，药物和辐射输送，生物医学植入物，传感器，能源存储和发电，核废料遏制以及轻质金属合金。