Equation of State of TiN at High Pressures and Temperatures - A Possible Host for Nitrogen in Planetary Mantles
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-12-20 |
| Journal | Journal of Geophysical Research Solid Earth |
| Authors | Kierstin Daviau, R. A. Fischer, Matthew C. Brennan, Junjie Dong, TerryâAnn Suer |
| Institutions | Toi Ohomai Institute of Technology, University of Waikato |
| Citations | 4 |
Abstract
Section titled âAbstractâAbstract Nitrogen, the most abundant element in Earthâs atmosphere, is also a primary component of solid nitride minerals found in meteorites and on Earthâs 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 Xâray diffraction to measure the thermal equation of state and phase stability of titanium nitride (TiN) in a laserâheated diamond anvil cell at pressures up to âź70 GPa and temperatures up to âź2,500 K. TiN maintains the cubic B1 (NaClâtype) crystal structure over the entire pressure and temperature range explored. It has K 0 = 274 (4) GPa, K 0 Ⲡ= 3.9 (2), and Îł 0 = 1.39 (4) for a fixed V 0 = 76.516 (30) Ă 3 (based on experimental measurements), q = 1, and θ 0 = 579 K. Additionally, we collected Raman spectra of TiN up to âź60 GPa, where we find that the transverse acoustic (TA), longitudinal acoustic (LA), and transverse optical phonon modes exhibit mode GrĂźneisen parameters of 1.66(17), 0.54(15), and 0.93 (4), respectively. Based on our equation of state, TiN has a density of âź5.6-6.4 g/cm 3 at Earthâs 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 Earthâs mantle, making it a plausible reservoir for deep planetary nitrogen if chemical conditions allow its formation.