Elasticity of hexagonal-closed-packed cobalt at high pressure and temperature: a quasiharmonic case.

We performed high-resolution inelastic x-ray scattering measurements on a single crystal of hcp cobalt at simultaneous high pressure and high temperature, obtaining 4 of the 5 independent elements of the elastic tensor. Our experiments indicate that the elasticity of hcp-Co is well described within the quasiharmonic approximation and that anharmonic high-temperature effects on the elastic moduli, sound velocities, and elastic anisotropy are minimal at constant density. These results support the validity of Birch's law and represent an important benchmark for ab initio thermal lattice dynamics and molecular-dynamics simulations.