Thermal equation of state of stishovite

The pressure-volume-temperature (P-V-T) behavior in SiO₂-stishovite has been studied using a DIA-type, cubic-anvil apparatus (SAM85) interfaced with in situ synchrotron X-ray diffraction at the superconducting wiggler beamline (X-17B) of the National Synchrotron Light Source, using a polycrystalline specimen previously hot-pressed in a 2000-ton uniaxial split-sphere apparatus (USSA-2000). The P-V-T data up to 10 GPa and 1273 K were analyzed using several approaches based on the Birch-Murnaghan equation-of-state (EOS) and related thermodynamic relations. The results obtained from different approaches are internally consistent. With the pressure derivative K'(T)₀ fixed at the ultrasonically determined value of K'₀ = 5.3, we obtained the isothermal bulk modulus K'(T)₀ = 294(2) GPa and its temperature derivative (partial differential K(T)/partial differential T)(P) = -0.041(11) GPa K^-1, and the thermal expansion coefficients a₀ = 1.40(8) X 10^-5 K^-1 and a₁ = 10.9(20) X 10^-9 K^-2. The room temperature bulk modulus (K(T)₀) of the present study is in agreement with the adiabatic values obtained previously from Brillouin scattering and diamond-anvil cell X-ray diffraction studies on single crystal stishovite and ultrasonic studies on polycrystalline specimens.