Thermal equation of state of stishovite

Abstract

The pressure–volume–temperature ( P– V– T) behavior in SiO 2-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 (∂ K T /∂ T) P =−0.041(11) GPa K −1, and the thermal expansion coefficients a 0=1.40(8)×10 −5 K −1 and a 1=10.9(20)×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.