Equation Of State Of Tin At High Pressures And Temperatures: A Possible Host For Nitrogen In Planetary Mantles

Nitrogen, the most abundant element in Earth's atmosphere, is also a primary component of solid nitride minerals found in meteorites and on Earth's surface. If they remain stable to high pressures and temperatures, these nitrides may also be important reservoirs of nitrogen in planetary interiors. We used synchrotron X-ray diffraction to measure the thermal equation of state and phase stability of titanium nitride (TiN) in a laser-heated diamond anvil cell at pressures up to similar to 70 GPa and temperatures up to similar to 2,500 K. TiN maintains the cubic B1 (NaCl-type) crystal structure over the entire pressure and temperature range explored. It has K-0 = 274 (4) GPa, K-0 = 3.9 (2), and gamma(0) = 1.39 (4) for a fixed V-0 = 76.516 (30) angstrom(3) (based on experimental measurements), q = 1, and theta(0) = 579 K. Additionally, we collected Raman spectra of TiN up to similar to 60 GPa, where we find that the transverse acoustic (TA), longitudinal acoustic (LA), and transverse optical phonon modes exhibit mode Gruneisen parameters of 1.66(17), 0.54(15), and 0.93 (4), respectively. Based on our equation of state, TiN has a density of similar to 5.6-6.4 g/cm(3) at Earth's lower mantle conditions, significantly more dense than both the mantle of the Earth and the estimated densities of the mantles of other terrestrial planets, but less dense than planetary cores. We find that TiN remains stable against physical decomposition at the pressures and temperatures found within Earth's mantle, making it a plausible reservoir for deep planetary nitrogen if chemical conditions allow its formation.Plain Language Summary Understanding the incorporation of nitrogen into Earth's interior could account for discrepancies in Earth's nitrogen budget. Solid nitride materials have been suggested to store nitrogen in the mantle and/or core. We performed high pressure, high temperature experiments on the refractory nitride mineral osbornite titanium nitride (TiN) to explore its stability at Earth's mantle conditions. We measured its density and crystal structure at high pressures and temperatures, finding that TiN does not change structure or melt at deep Earth conditions. Additionally, we performed Raman spectroscopy measurements to further explore the properties of TiN at high pressures. We find that TiN is a plausible mineral for nitrogen storage within the deep Earth, provided that it is chemically stable within the mantle.