Elasticity of hcp Metals at High Pressure and Temperature: the Quasi-harmonic Case of Cobalt
Abstract
High-resolution inelastic x-ray scattering (IXS) measurements have been carried out on a single crystal of hcp cobalt at simultaneous high pressure and high temperature. Four out of five independent moduli of the elastic tensor have been derived from simultaneous velocity and density determinations. Our experiments indicate that the elasticity of hcp-Co at high pressure and temperature is well described within the frame of the quasi- harmonic approximation, and that anharmonic high-temperature effects on the elastic moduli, sound velocities and elastic anisotropy are minimal at constant density. These new results on hcp-cobalt are particularly interesting in light of the controversial case of iron, where, on one hand, nuclear resonant inelastic x-ray scattering measurements [1] suggest a negative correlation between the aggregate sound velocities and temperature at constant density, in violation of the "Birch law", and, on the other hand, ab initio finite temperature molecular dynamics simulations [2] support the validity of the "Birch law" for a large number of systems, including bcc- and hcp-Fe. Finally, these measurements highlight the current capabilities of the IXS technique for the studies of elasticity and phonon dispersion of materials under extreme thermodynamic conditions. [1] J.F. Lin et al., Science 308, 1892 (2005). [2] L. Vočadlo, Earth Planet. Sci. Lett. 254, 227 (2007).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFMMR43C1523A
- Keywords:
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- 3909 Elasticity and anelasticity;
- 3924 High-pressure behavior;
- 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction