Domain walls in bcc to hcp reconstructive phase transformations

The bcc (body-centered cubic) phase to hcp (hexagonal closed pack) phase tr ansformation in certain elements (e.g. Ti) and alloys is induced either by quenching or application of pressure. To study domain walls in these materi als we have extended the Landau model of Lindgard and Mouritsen by includin g a spatial gradient (Ginzburg) term of the scalar order parameter. Through first-principles calculations, we show that the bcc structure is unstable with respect to the shuffle of atoms rather than the shear. Therefore, we c an reduce the multiple (two) order parameter (OP) Landau free energy (LFE) to an effective one OP (shuffle) potential, which is a reasonable approxima tion. In general, the effective LFE is a triple-well potential. From the va riational derivative of the total free energy we obtain a static equilibriu m condition. By solving this equation for different physical parameters and boundary conditions, we obtain different quasi-one-dimensional soliton-lik e solutions which correspond to four types of domain walls between the bcc phase and the hcp phase. (C) 1999 Published by Elsevier Science S.A. All ri ghts reserved.