Composition-dependent properties and phase stability of Fe-Pd ferromagnetic shape memory alloys: A first-principles study

摘要

The composition-dependent properties and their correlation with the phase stability of Fe_(75+x)Pd_(25-x) (-10.0 ≤ x ≤ 10.0) alloys are systematically investigated by using first-principles exact muffin-tin orbitals (EMTO)-coherent potential approximation (CPA) calculations. It is shown that the martensitic transformation (MT) from L1_2 to body-centered-tetragonal (bct) occurs in the ordered alloys with about -5.0 ≤ x ≤ 10.0. In both the L1_2 and bct phases, the evaluated a and c/a agree well with the available experimental data; the average magnetic moment per atom increases whereas the local magnetic moments of Fe atoms, dependent on both their positions and the structure of the alloy, decrease with increasing x. The tetragonal shear elastic constant of the L1_2 phase (C) decreases whereas that of the bct phase (C_s) increases with x. The tetragonality of the martens-ite (| 1 -c/a|) increases whereas its energy relative to the austenite with a negative value decreases with Fe addition. All these effects account for the increase of MT temperature (TM) with x. The MT from L1_2 to bct is finally confirmed originating from the splitting of Fe 3d E_g and T_(2g) bands upon tetragonal distortion due to the Jahn-Teller effect.