Thermoelastic properties of ReB2 at high pressures and temperatures and comparison with Pt, Os, and Re

Abstract

We have measured the phase stability and thermoelastic equation of state of ultrahard rhenium diboride at pressures up to 30 GPa and temperatures up to 2500 K using a laser heated diamond anvil cell in conjunction with synchrotron X-ray diffraction. ReB2 is shown to be stable throughout this pressure and temperature region. The ratio of the c-axis to the a-axis provides a monitor of the annealing of plastic stresses during compression. We show that ReB2 has a small thermal anisotropy but a large mechanical anisotropy. Combining this new data set with previously existing results from a large volume press yields a thermoelastic equation of state with a Grüneisen parameter of 2.4 (0.08) and a q of 2.7. A comparison of ReB2 with other high electron density incompressible metals—Os, Re, and Pt—shows that ReB2 has the lowest thermal pressure and the highest bulk modulus.