HR: 0830h
AN: V11D-0523    [PDF]
TI: The Role of Shear in the Onset of Iron's {\it bcc} to {\it hcp} Stress--Induced Phase Transition
AU: * Lew, A
EM: lewa@caltech.edu
AF: Dept. of Mechanical Engineering Stanford University, Durand 259, Stanford, CA 94305 United States
AU: Caspersen, K
EM: kcasper@chem.ucla.edu
AF: UCLA Dept. of Chemistry and Biochemistry, Box 951569, Los Angeles, CA 90095-1569 United States
AU: Ortiz, M
EM: ortiz@aero.caltech.edu
AF: GALCIT, California Institute of Technology, 1200 East California Blvd MSC 105-50, Pasadena, CA 91125 United States
AU: Carter, E
EM: eac@chem.ucla.edu
AF: UCLA Dept. of Chemistry and Biochemistry, Box 951569, Los Angeles, CA 90095-1569 United States
AB: Iron presents a martensitic phase transition from {\it bcc} to {\it hcp} at an approximate pressure of 13 GPa. The exact onset pressure has been determined to have values ranging from 9 to 16 GPa by several different experimental results. We propose a multiscale model for Iron, with all necessary quantities computed exclusively from first--principles. In this model, we account for all shear components of the deformation, finding that they play a crucial role in its onset, even for very small amounts of shear. Briefly, the model consists of constructing the energy landscape in all six-components of strain. Then, for a given deformation of a representative sample, we minimize its energy by possibly accomodating martensitic laminates inside it, in the spirit of a spinodal decomposition. We will describe the model in detail and show how the onset pressure varies when shear is present, as well as the mixed states encoutered upon transformation.
DE: 3210 Modeling
DE: 3924 High-pressure behavior
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting