title: Clapeyron slope reversal in the melting curve of AuGa2 at 5.5 GPa.
abstract: We use x-ray diffraction in a resistively heated diamond anvil cell to extend the melting curve of AuGa2 beyond its minimum at 5.5 GPa and 720 K, and to constrain the high-temperature phase boundaries between cubic (fluorite structure), orthorhombic (cottunite structure) and monoclinic phases. We document a large change in Clapeyron slope that coincides with the transitions from cubic to lower symmetry phases, showing that a structural transition is the direct cause of the change in slope. In addition, moderate (~30 K) to large (90 K) hysteresis is detected between melting and freezing, from which we infer that at high pressures, AuGa2 crystals can remain in a metastable state at more than 5% above the thermodynamic melting temperature.
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, USA.
authors.forename: Z M
authors.initials: ZM
authors.lastname: Geballe
authors.forename: S V
authors.initials: SV
authors.lastname: Raju
authors.forename: B K
authors.initials: BK
authors.lastname: Godwal
authors.forename: R
authors.initials: R
authors.lastname: Jeanloz
mesh_terms: D003198:Computer Simulation; D005708:Gallium / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D011312:Pressure; D013816:Thermodynamics; D044366:Transition Temperature
chemical_list: D006046:Gold; D005708:Gallium