Solid State Chemistry of Low and Negative Thermal Expansion Frameworks

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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.***