This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This proposal seeks ~$478K in funding to support developing a high pressure, high temperature calibration scale for diamond anvil cell (DAC) studies. Existing pressure scales are plagued with issues particularly at high temperatures. Developing a pressure scale is proposed by performing density measurements by x-ray diffraction and concurrent sound velocity measurements using Brillouin scattering on cubic boron nitride (cBN). In addition, Raman P and T measurements will be made. The PIs propose to reference other materials though their equation of state to cBN at varying temperatures and pressures by coupling methodologies into a single pressure scale. Because material properties change under high pressure and temperature, it has been difficult to ascribe pressure exerted on materials in DAC studies. Pressure and temperature effects have been noted for numerous materials and measurement techniques (X-ray, optical, fluorescent, etc). cBN is suggested as a potential pressure scale calibrant as it's crystal structure is theoretically stable to phase transformation up to at least 1000 GPa within the range of DAC studies. DAC studies along with the calibrated pressure scale will allow studies into material phase transitions in the Earth's interior, Earth material thermal property studies and equation of state determinations, and material phase stability and chemistry. This study will result in a primary pressure scale - calibrated on an inert material and suitable for high T&P work. The outcome will allow accurate X-ray diffraction, X-ray spectroscopy, and X-ray scattering measurements under high T&P. This, in turn, will allow theoretical equation of state calculations for deep Earth materials. Results will broadly impact geophysics, mineral physics, geochemistry and geodynamics. Studies will involve REU students (2-3 per summer). Graduate students are post-docs are also proposed for training.
