Theoretical study of phase forming of NaZn13-type rare-earth intermetallics

Abstract

By using the interatomic pair potential obtained with the lattice inversion method,the stability of RT13−xMx (R = La, Ce, Pr and Nd; T = Co and Fe; M = Si, Al, Cr, V andTi) of the NaZn13 type and its derivative structure are studied. The structuraltransition of LaT13−xSix (T = Co and Fe) between the cubic one with the space groupFm3c and the tetragonalone with I4/mcmis imitated from the viewpoint of energy. As for the function of the third elements,Al and Si are beneficial to the phase stability of RT13−xMx, whereas Cr, Tiand V are unfavourable to the stability. In the calculation, the range ofx,with which RT13−xMx could crystallize in the cubic or tetragonal structures,agrees with the experiments very well. The calculated crystallographic parameterscoincide with the experimental observation. In the cubic structure, Si and Alprefer the 96i site, and in the tetragonal structure Si first occupy the 16l(2) site,then the 16k site. In addition, all the site positions of the compounds with eitherthe cubic or tetragonal structure are really congruent with the experimental one.