Unified analyses for P‐V‐T equation of state of MgO: A solution for pressure‐scale problems in high P‐T experiments

Abstract

[1] In order to determine an accurate and reliable high-pressure and high-temperature equation of state (EOS) of MgO, unified analyses were carried out for various pressure-scale-free experimental data sets measured at 1 atm to 196 GPa and 300-3700 K, which are zero-pressure thermal expansion data, zero-pressure and high-temperature adiabatic bulk modulus (K S ) data, room temperature and high-pressure K S data, and shock compression data. After testing several EOS models based on the Mie-Grüneisen-Debye description for the thermal pressures with the Vinet and the third-order Birch-Murnaghan equations for the 300-K isothermal compression, we determined the K 0 T0 and g(V) using a new functional formb À 1]} to express the volume dependence of the Grüneisen parameter. Through least squares analyses with prerequisite zero-pressure and room temperature properties of V 0 , K S0 , a 0 , and C P0 , we simultaneously optimized a set of parameters of K 0 T0 , g 0 , a, and b required to represent the P-V-T EOS. Determined new EOS models of MgO successfully reproduced all the analyzed P-V-T-K S data up to 196 GPa and 3700 K within the uncertainties, and the total residuals between calculated and observed pressures were found to be 0.8 GPa in root mean squares. These EOS models, even though very simple, are able to reproduce available data quite accurately in the wide pressure-temperature range and completely independent from other pressure scales. We propose these models for primary pressure calibration standards applicable to quantitative high-pressure and high-temperature experiments.Citation: Tange, Y., Y. Nishihara, and T. Tsuchiya (2009), Unified analyses for P-V-T equation of state of MgO: A solution for pressure-scale problems in high P-T experiments,

The thermal equation of state of FeTiO3 ilmenite based on in situ X-ray diffraction at high pressures and temperatures

“…MgO unit-cell volumes were converted to pressures using the Speziale et al (2001) thermal equation of state. At the P-T conditions of this study, this EOS gives results that are identical within error to those derived using the more recent MgO EOS of Tange et al (2009).…”

Equation of state and high-pressure/high-temperature phase diagram of magnesium

“…A temperature difference of 1000 K corresponds to a pressure difference of approximately 7 GPa. 32 Upon heating, the integrated diffraction peaks from the MgO were noticeably broader than those from the sample. The additional width of the MgO peaks suggests a temperature gradient of around 500 K at a sample temperature of 1000 K, rising to around 700 K at a sample temperature of 2500 K. The stated pressures may thus be systematically 3-6 GPa too high, with the higher discrepancies at the higher temperature and higher pressure region of the phase diagram.…”

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

“…(14) and (15) Calculated results of this work are compared to selected experimental data obtained by hydrostatic or quasi-hydrostatic compression in the diamond-anvil cell [90][91][92][93] and ultrasonic measurements [94][95][96][97]. The results of semi-empirical assessments [98,100], other ab initio LDA [59], GGA [61] and empirically-corrected GGA [101] calculations and MD simulations [60,84] are also shown for comparison. , as compared to ambient-pressure experimental data [57] and a thermodynamic assessment [102].…”

“…Figure 7 and Table 4 show the results obtained for the P-V-T equation of state of periclase, as compared to different kinds of experimental data (i.e., static compression in the diamond-anvil cell, ultrasonic measurements, etc.) [89][90][91][92][93][94][95][96][97], semi-empirical modelling of experimental data [98][99][100] and other DFT [59,61,101] and MD [60,84] calculations. The EOS of MgO has been calculated according to Equation (15) in a range of conditions compatible with those realized in the Earth's lower mantle (i.e., P = 0-160 GPa, V/V 0 = 0.65-1.00, T = 0-3000 K).…”