HR: 0800h
AN: DI41A-0348    [Abstracts]
TI: Molybdenum and Tantalum at High Pressure and Temperature: Melting from Another Solid Phase
AU: * Burakovsky, L
EM: burakov@lanl.gov
AF: Los Alamos National Laboratory, Theoretical Division, T-1, MS B221, Los Alamos, NM 87545, United States
AU: Belonoshko, A B
EM: Anatoly.Belonoshko@fysik.uu.se
AF: Department of Material Science and Engineering, The Royal Institute of Technology, Stockholm, 10044, Sweden
AU: Belonoshko, A B
EM: Anatoly.Belonoshko@fysik.uu.se
AF: Institute of Theoretical Physics, AlbaNova University Center, The Royal Institute of Technology, Stockholm, 10691, Sweden
AU: Chen, S
EM: sc@lanl.gov
AF: Los Alamos National Laboratory, Theoretical Division, T-1, MS B221, Los Alamos, NM 87545, United States
AU: Johansson, B
EM: Borje.Johansson@fysik.uu.se
AF: Department of Material Science and Engineering, The Royal Institute of Technology, Stockholm, 10044, Sweden
AU: Johansson, B
EM: Borje.Johansson@fysik.uu.se
AF: Condensed Matter Theory Group, Department of Physics, Box 530, Uppsala University, Uppsala, 75121, Sweden
AU: Mikhaylushkin, A S
EM: Arkady.Mikhaylushkin@fysik.uu.se
AF: Department of Physics, Chemistry and Biology (IFM), Linkoping University, Linkoping, 58183, Sweden
AU: Preston, D L
EM: dean@lanl.gov
AF: Los Alamos National Laboratory, Physics Division, P-22, MS D410, Los Alamos, NM 87545, United States
AU: Simak, S I
EM: Sergei.Simak@fysik.uu.se
AF: Department of Physics, Chemistry and Biology (IFM), Linkoping University, Linkoping, 58183, Sweden
AU: Swift, D C
EM: dswift@lanl.gov
AF: Los Alamos National Laboratory, Physics Division, P-24, MS E526, Los Alamos, NM 87545, United States
AB: Considerable controversy exists as regards the interpretation of the melting of Mo and Ta in shock wave (SW) and diamond anvil cell (DAC) experiments. While SW experiments find a solid-solid phase transition in Mo, DAC experiments do not. We resolve this controversy by demonstrating from first principles phonon calculations within the quasiharmonic approximation that at higher pressure Mo, being stable in body-centered cubic (bcc) structure at low temperature, transforms into face centered cubic (fcc) structure on heating. This transformation occurs before melting, which is demonstrated by ab initio molecular dynamics (AIMD) simulations. Although Mo may not melt from fcc, if there is yet another more stable structure than fcc, Mo does certainly not melt from bcc. SW experiments in Ta suggest a solid-solid transformation before melting, as well as in Mo. Our AIMD simulations demonstrate that at higher pressure fcc is a more stable structure than bcc in Ta at high temperature, and therefore, like Mo, Ta does not melt from bcc. These findings suggest that DAC experiments do not correctly identify the high-pressure melting of both Mo and Ta.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3919 Equations of state
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting