First-principles pressure-temperature phase diagrams in metals
Using interatomic potentials derived from first-principles generalized pseudopotential theory, finite-temperature phase transitions in both simple and transition metals can be studied through a combination of analytic statistical methods and molecular-dynamics simulation. In the prototype simple metal-Mg, where volume and pair forces adequately describe the energetics, a complete and accurate phase diagram has thereby been obtained to 60 GPa. A rapidly temperature-dependent hcp-bcc phase line is predicted which ends in a triple point on the melting curve near 4 GPa. In central transition metals such as Mo or Fe, on the other hand, the energetics are complicated by d-state interactions which give rise to both many-body angular forces and enhanced electron-thermal contributions. We have made a detailed study of these phenomena and their impact on melting in the prototype case of Mo and a full melting curve to 2 Mbar has been obtained. In the case of Fe, we are examining the high-pressure phase diagram and the question of whether or not there exists a high-pressure, high-temperature solid bcc phase, as has been speculated. To date, we have shown that the bcc structure is both thermodynamically and mechanically unstable at high pressure and zero temperature, with a large and increasing bcc-hcp energy difference under compression.
- Research Organization:
- Lawrence Livermore National Lab., CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 10193000
- Report Number(s):
- UCRL-JC-113300; CONF-930676-55; ON: DE94001056
- Resource Relation:
- Conference: 14. international conference of the International Association for the Advancement of High Pressure Science and Technology,Colorado Springs, CO (United States),27 Jun - 2 Jul 1993; Other Information: PBD: Jul 1993
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
METALS
PHASE DIAGRAMS
MAGNESIUM
MOLYBDENUM
IRON
TRANSITION ELEMENTS
INTERATOMIC FORCES
PRESSURE DEPENDENCE
VERY HIGH PRESSURE
MELTING
BCC LATTICES
HCP LATTICES
COMPRESSION
CALCULATION METHODS
360102
665000
STRUCTURE AND PHASE STUDIES
PHYSICS OF CONDENSED MATTER