The Influence of Nanostructure and Pressure on the Properties of Low and Negative Thermal Expansion Materials

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

TECHNICAL SUMMARY: Thermal expansion plays a very important role in determining if a material will be suitable for a particular application. The proposed work will lead to an enhanced understanding of both structure property relationships in low and negative thermal expansion (NTE) materials, and strategies for controlling thermal expansion. The pressure dependence of thermal expansion (TE) in a variety of low and negative TE materials will be examined to establish the factors that lead to highly pressure dependent coefficients of thermal expansion (CTEs) in such materials. It is hypothesized that low pressure phase transitions in NTE materials will lead to the quite widespread occurrence of extreme pressure sensitivity. The pressure dependence of CTEs is a design consideration for composites where a NTE filler may experience stresses. The control of thermal expansion, by modifying the O:F ratio, in oxyfluorides with a ReO3 framework structure, will be examined and the underlying structure property relationships established by separately interrogating the response of M-F-M and M-O-M links to temperature and pressure using total scattering methods. Substitution of fluoride for oxide, as a means of controlling thermal expansion, is an unexplored arena with great potential for interesting findings. The local structures of AX2O7 (A - Zr, Hf; X - P, V) will be examined using total scattering to better understand their high temperature phase transitions and how the nanostructure (local structure) of their disordered high temperature phases can lead to low or negative thermal expansion, as only the disordered forms of these materials display interesting expansion characteristics NON-TECHNICAL SUMMARY: The thermal expansion characteristics of a material play a very important role in determining if it is suitable for use in a wide variety of applications. The proposed work will lead to an enhanced understanding of strategies for controlling thermal expansion, and the preparation of new materials. This will be of value in the search for new useful engineering materials. As an integral part of this work, graduate and undergraduate students will be trained in a wide variety of synthetic and materials characterization techniques, introduced to important concepts in materials chemistry/science, and engaged in activities that develop professional skills. These skills are of considerable value to the US economy. A significant component of the proposed experimental work will be conducted using major x-ray and neutron scattering facilities located at Department of Energy (DOE) national laboratories. The work at DOE laboratories enhances the educational experience of students, and leads to collaborations that professionally benefit both university and government laboratory employees.