GGA-FPKKR 法による Fe 基希薄合金中の点欠陥エネルギーの第一原理計算

抄録

  We present systematically ab-initio calculations for defect energies of 3d and 4sp impurities (Sc~Ge) in Fe. The calculations are based on the Generalized-Gradient-Approximation in the density-functional formalism and the full-potential Korringa-Kohn-Rostoker (FPKKR) Green's function method. We first examine the distance dependence, from the 1st- to 10th-nearest neighbors, of the impurity-impurity (I-I; I=Sc~Ge) interaction energies (E_int) and show that for most cases, the 1st-nearest neighboring I-I interaction energies (E_int¹) are dominant. We found that fundamental features of phase diagrams of Fe-based binary alloys, such as segregation, solid solution, and order, known experimentally, may be classified by use of the sign and magnitude of E_int¹. Second we discuss the calculated results for the 1st- and 2nd-nearest neighboring interaction energies of perturbed-angular-correlation (PAC)-probe Sn with 3d and 4sp impurities in Fe. The comparison of the calculated results with available experimental results shows that the observed attraction for Sn-Co, Sn-Ni, and Sn-Cu may be understood by the 1st-nearest neighboring interaction energies of these impurity pairs, while the observed repulsion for Sn-Ga, and Sn-Ge by the 2nd-nearest neighboring interaction energies of these impurity pairs. We also discuss the magnetism of single impurities X (=Sc~Cu) in Fe. The anti-parallel coupling to the bulk magnetization of the neighboring Fe atoms is stable for Sc~Mn, while the parallel coupling for Fe~Cu.