Thermoelastic equation of state of molybdenum

We report some high P-T diffraction experimental results on molybdenum usin g synchrotron x-ray and time-of-flight neutron-diffraction techniques. Unit -cell dimensions, measured up to P = 10 GPa and T = 1475 K, were derived fr om the refinement results and fitted to a high-temperature third-order Birc h-Murnaghan equation of state. The derived thermoelastic parameters for mol ybdenum are: isothermal bulk modulus K-T0 = 266(9) GPa with a pressure deri vative of bulk modulus partial derivative K/partial derivative P = 4.1(9), temperature derivative of bulk modulus partial derivative K/partial derivat ive T = -3.4(9) X 10(-2)GPa/K, volumetric thermal expansivity alpha = a + b T having a = 1.32(14) x 10(-5) K-1 and b = 1.26(15) X 10(-8) K-2. Further, all of the previous experimental data involving shock wave, ultrasonic, the rmal-expansion measurements were also analyzed and fitted to a high-tempera ture Birch/Vinet equation of state (EOS) and the thermal pressure approach of Mie-Gruneisen EOS, respectively. With the greatly extended P-V-T data co verage, we refined the thermoelastic parameter set for molybdenum as isothe rmal bulk modulus K-T0 = 268(1) GPa with pressure derivatives of bulk modul us partial derivative K/partial derivative P = 3.81(6), partial derivative K-2/partial derivative P-2 = -1.41(13) X 10(-2), temperature derivative of bulk modulus partial derivative K/partial derivative T = -2.13(31) X 10(-2) GPa/K, volumetric thermal expansivity alpha = a + bT having a = 1.31(10) x 10(-5) K-1 and b = 1.12(11) X 10(-8) K-2, and an invariant of alpha K-T,= 5.43(5) X 10(-3) GPa/K over a wide P-T range. We have conducted a neutron-d iffraction study at simultaneous high pressures and high temperatures. Ther mal vibrations of atoms (Debye-Waller factors) of molybdenum were derived a s a function of pressure and temperature. The experimental results of therm oelastic equation of state parameters are compared with previous experiment al data derived from shock wave and ultrasonic elasticity measurements.