Thermal equation of state of natural stibnite up to 25.7 GPa and 533 K

In situ energy dispersive X-ray diffraction experiments on a natural stibnite were performed by using an external resistive heating diamond anvil cell instrument with synchrotron radiation at Beijing Synchrotron Radiation Facility up to 25.7 GPa and 533 K. No phase changes are observed during compression or decompression. The compression of stibnite is anisotropic. The a-axis is the most compressible direction, followed by the b axis and the c axis. The a and b axis is thrice and twice as compressible as the c axis, respectively. A fit to the high temperature Birch-Murnaghan equation of state yielded an isothermal bulk modulus K-0 = 27.7(1.1) GPa, a temperature derivative of the bulk modulus (partial derivative K/partial derivative T)(p) = -0.0147(57) GPaK(-1), and a thermal expansion coefficient (alpha(0)) = 2.9(6) x 10(-4)K(-1). The derived K-0 value is in good agreement with previous results. The temperature derivative of the bulk modulus and thermal expansion coefficient of stibnite are obtained for the first time. An anomalous thermal behavior of stibnite along the c axis was found, and its possible reason was discussed.