Incompressibility of osmium metal at ultrahigh pressures and temperatures

Abstract

Osmium is one of the most incompressible elemental metals, and is used as a matrix material for synthesis of ultrahard materials. To examine the behavior of osmium metal under extreme conditions of high pressure and temperature, we measured the thermal equation of state of osmium metal at pressures up to 50 GPa and temperatures up to 3000 K. X-ray diffraction measurements were conducted in the laser heated diamond anvil cell at GeoSoilEnviroCARS and the High Pressure at the Advanced Photon Source and beamline 12.2.2 at the advanced light source. Ambient temperature data give a zero pressure bulk modulus of 421 (3) GPa with a first pressure derivative fixed at 4. Fitting to a high temperature Birch–Murnaghan equation of state gives a room pressure thermal expansion of 1.51(0.06)×10−5 K−1 with a first temperature derivative of 4.9(0.7)×10−9 K−2 and the first temperature derivative of bulk modulus of be dK0/dT=−0.055 (0.004). Fitting to a Mie–Grüneisen–Debye equation of state gives a Grüneisen parameter of 2.32 (0.08) with a q of 7.2 (1.4). A comparison of the high pressure, temperature behavior among Re, Pt, Os, shows that Os has the highest bulk modulus and lowest thermal expansion of the three, suggesting that Os-based ultrahard materials may be especially mechanically stable under extreme conditions.