Simple Molecular Solids at Ultrahigh Pressure

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

This research concerns experimental studies of pressure-induced transformations and novel behavior of simple molecular systems to ultrahigh static pressures above 300 GPa (3 megabars) over a broad temperature range. The experiments will focus on transformations in representative solids formed from low-Z diatomic and triatomic systems, rare gases, and dense compounds and alloys containing these species. The project takes advantage of recent developments in diamond-anvil cell techniques, and a variety of theoretical predictions based on first-principles calculations. New synchrotron x-ray and neutron diffraction techniques will be used for crystal structure determination, including low temperature phases of oxygen and hydrogen isotopes. Recently developed high-pressure x-ray inelastic scattering techniques will be used to measure pressure effects and to understand the density dependence of electronic excitations, their bandwidths, and dispersion. Transport methods will be used to study superconductivity and possible transformations to novel states of in a range of materials, including oxygen and hydrogen-rich solids. There will be a systematic effort to extend the pressure range, accuracy, and sensitivity of static high-pressure techniques important for the high-pressure community, including those used at national user facilities. Numerous other fields, including chemistry, materials science, and planetary science should also benefit. A major goal of this project is the training of young scientists in physics and materials science. A graduate student and a post-doctoral fellow will be supported directly under this grant. Undergraduates and exceptional high-school students also participate. All are prepared for future positions in academia, national laboratories, and high-technology industries. The effect of ultrahigh pressures on simple molecules is a classic problem in physics and chemistry. Under the very high-pressures that can now be reached in the laboratory, molecules such as hydrogen, nitrogen, oxygen, water, and related substances transform to novel materials, including dense metals, unique superconductors, and unusual compounds. Many of these were unanticipated theoretically, and their discovery has greatly enhanced understanding of matter as a whole. In this project, new experiments on the novel behavior of simple molecules at ultrahigh static compressed to above 300 GPa (3 megabars) over a broad temperature range will be carried out using a powerful device known as the diamond anvil cell. The project takes advantage of recent developments in techniques that couple the diamond-anvil cell with sensitive analytical methods, and new theoretical predictions for these materials. A large portion of the experiments will take place at major national facilities such as synchrotron radiation and neutron sources, where new techniques will be developed and scientists trained. A variety of laser techniques as well as highly sensitive electrical and magnetic methods will be used, for example to study superconductivity from greatly compressing molecular materials. There will be a systematic effort to extend the pressure range, accuracy, and sensitivity of high-pressure techniques important for the high-pressure community, including major programs at national facilities. Numerous other fields, including chemistry, materials science, and planetary science should benefit. Finally, this project will train a number of young scientists, including graduate students and post-doctoral fellows as well as undergraduate interns and even exceptional high-school students. The research will prepare these students for positions in academia, national laboratories, and high-technology industries.