Broadly speaking, our NSF-funded project has trained PhD students, has resulted in new understanding of how thermal conductivity of materials may vary with pressure, and during a phase transformation, and has supported the UCLA mineral physics group in training undergraduate and graduate students, collecting new data on the high temperature behavior of materials, and helped contribute to enhanced technological infrastructure for mineral physicists at shared user facilities, especially at the Advanced Light Source.

1. Student support [Broader Impacts] This grant provided partial support to two PhD students, Dr. Chris McGuire (2018, PhD) who is now a postdoctoral fellow at LLNL, and Dr. Krista Sawchuk (2021, PhD) who is now a postdoctoral fellow at LANL. In addition, this grant provided partial support to an undergraduate student, Rupini Kamat, who is now a PhD student in the Physics Department at Stanford University.

2. Discoveries and increased understanding [Intellectual Merit] We measured the pressure- dependent laser heating power-temperature properties of NaCl as a function of pressure. By combining the experimental results with a heat flow model of the diamond anvil cell, the results suggest that there is a sharp decrease in thermal conductivity as the material undergoes the phase transformation from the low pressure B1 phase to the high pressure B2 phase. A similar study was performed on iron-bearing oxide, which may be one of the important components of the Earth's lower mantle. We showed that while thermal conductivity tends to increase with pressure, we also observe a thermal anomaly coincident with the high-spin to low-spin transition in this material. The thermal anomaly can be interpreted as a decrease in thermal conductivity that is assocated with this electronic transition. less likely, but also possible, is that the electronic transition results in changes to the sample absorption/reflection behavior, that change the relationship between laser power and sample heating. These thermal property changes may be relevant for the Earth's interior, and are coincident with observed changes in mantle mixing dynamics at the top of the lowermost mantle. These discoveries have been presented at annual conferences and published in journals. Some material is still under review and revision. In addition, this grant helped support measurements of the thermal properties of a variety of transition metals, their oxides, silicates, carbonates, and sulfates at pressure and temperature conditions of the Earth's interior.

3. Service, Infrastructure support, and technology [Broader Impacts] During the term of this project, PI Kavner also served as chair of the Executive Committee of COMPRES, an NSF-funded consortium of institutions where Earth scientists take advantage of large scale shared user facilities (such as synchrotron light sources) to perform some of our measurements and experiments that could not be done without the support of the entire community. As a result, PI Kavner developed an appreciation of the importance of community building in order to get our best work done. In addition, within PI Kavner's research group, we developed methods to measure temperature during laser heating in the diamond anvil cell, methods to interpret the relationship between laser power and sample temperature in terms of a combination of the sample geometry, absorption properties, and/or thermal conductivity. Finally, we developed new methods to extract additional statistcal information from spotty ("bad") powder patterns from X-ray diffraction. These new methods are being used with our new data sets to infer highly precise thermoelastic properties for materials.

Last Modified: 07/21/2021
Modified by: Abby Kavner