Solid State Chemistry of Low and Negative Thermal Expansion Frameworks

该项目将研究材料的热膨胀特性，以确定各种应用的适用性。例如，在高温下显示低热膨胀或负热膨胀的框架通常在冷却到具有较高热膨胀系数的致密形式时经历相变。石英的相变可以通过“填充物”来抑制，填充物就是用锂或铝代替一些硅来生产诸如商业上有用的-长晶石之类的材料。将探索用磷酸锆结构“填充”相作为一种生产具有有趣热膨胀特性的新材料的手段。此外，用金属+ 3和+ 5离子的混合物代替锆+ 4离子将被研究作为抑制这种不想要的相变的一种手段。许多负热膨胀材料在适度压力下变成非晶，这限制了它们的应用。这种非晶化的机制将使用包括高压下x射线吸收精细结构测定在内的技术进行研究。建议的工作将为一些研究生和本科生提供在材料科学/化学领域广泛实用的各种方法的经验。材料的热膨胀特性在决定它是否适用于特定应用方面起着非常重要的作用。低热膨胀或零热膨胀在尺寸稳定性是一个主要问题的领域是必要的，例如在精密光学器件的制造中。在暴露于热冲击的陶瓷中，也需要低热膨胀或零热膨胀，例如用于炊具和一些内燃机和航空航天应用的陶瓷。负热膨胀在小众应用中非常有价值，例如补偿微电子中另一个组件的正热膨胀。这个项目的重点是制备低热膨胀或负热膨胀的新材料，并扩展我们对它们的制备和物理性质的理解。所获得的知识将对寻找新的工程材料有价值。该项目为几名研究生和本科生提供了各种合成和表征方法的经验，这些方法在材料化学和材料科学领域具有重要和普遍的用途

This project will investigate the thermal expansion characteristics of materials that determine suitability for various applications. For example, frameworks that display low or negative thermal expansion at high temperatures often undergo a phase transition on cooling to a denser form with a higher coefficient of thermal expansion. The phase transition of quartz can be suppressed by "stuffing", that is replacing some silicon with lithium or aluminium to produce materials such as the commercially useful beta-eucrytpite. The "stuffing" of phases with the zirconium phosphatre structure will be explored as a means of producing new materials with interesting thermal expansion characteristics. Additionally, the replacement of zirconium plus four with mixtures of metal plus three and plus five ions will be examined as a means of suppressing this unwanted phase transition. Many negative thermal expansion materials become amorphous at modest pressures and this limits their application. The mechanism of this amorphization will be investigated using techniques that include x-ray absorption fine structure determinations at high pressure.The proposed work will provide several graduate and undergraduate students with experience of a wide variety of methods that are of general utility in the field of materials science/chemistry.%%%The thermal expansion characteristics of a material play a very important role in determining if it will be suitable for a particular application. Low or zero thermal expansion is necessary in areas where dimensional stability is a major issue, such as in the fabrication of precision optical devices. Low or zero thermal expansion is also necessary in ceramics that are exposed to thermal shock, such as those used in cookware and in some internal combustion engine and aerospace applications. Negative thermal expansion can be very valuable in niche applications, such as compensating for the positive thermal expansion of another component in microelectronics. This project focuses on the preparation of new materials displaying low or negative thermal expansion and extending our understanding of both their preparation and physical properties. The knowledge gained will be of value in the search for new engineering materials. The project provides several graduate and undergraduate students with experience in a wide variety of synthetic and characterization methods that are of great and general utility in the fields of materials chemistry and materials science.***