STABILITY OF CRYSTAL STRUCTURE OF (Fe, V)3M AND (Fe, Ni)3M (M equals Si, Ge, Sn) AND ITS ANALYSIS BASED ON RIGID BAND MODEL.

Abstract

The crystal structure of binary alloys T//3M, where T is a 3d transition metal and M is Si, Ge and Sn, varies as A15 to bcc (DO//3) to hcp (DO//1//9) or fcc (L1//2) with increasing number of the electron of T. According to X-ray studies on (Fe//1d// minus //xV//x)//3M, the crystal structures are A15 and DO//1//9 in Si alloys, A15, DO//3 and DO//1//9 in Ge alloys, and A15 and DO//1//9 in Sn alloys. Pseudobinary alloys Fe//3Si (DO//3)-Ni//3Si(L1//2) have only DO//3 and L1//2 solid solutions, but the alloys Fe//3Ge(DO//1//9)-Ni//3Ge(L1//2) and Fe//3Sn(DO//1//9)-Ni//3Sn(DO//1//9) form a bcc (DO//3) phase and an orthorhombic phase with a distorted DO//3 structure in their intermediate compositions, respectively. The energy of electron is calculated from the density of states curves of A15, DO//3 and DO//1//9 structures in the rigid band model and explained the dependence of the crystal structure on the average electron/atom ratio. In Fe//3Si, the coulomb energy between Fe atoms on two inequivalent sites is calculated based on the Thomas-Fermi model and the site preference of 3d transition metal impurity is explained.