STRUCTURAL-PROPERTIES OF A NOVEL MAGNETIC TERNARY PHASE - ND3(FE1-XTIX)29 (0.04-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.06)

A structural determination of the new magnetic ternary rare-earth iron-rich intermetallic Nd3(Fe1-xTix)29 phase, previously reported as Nd2(Fe1-xTix)19, has been carried out by means of powder X-ray diffraction on a Nd3(Fe0.955Ti0.0045)29 sample. The structure is monoclinic with the space group P2(1)/c (No.14). There are two Nd sites, namely 2a and 4e, and fifteen Fe(Ti) sites in the structure, one 2d and fourteen 4e sites. The refined lattice parameters are a = 10.641(1) angstrom, b = 8.5913(8) angstrom, c = 9.748(1) angstrom and beta = 96.928(6)-degrees, and Z = 2. The structure is a new intermediate structure between the well known rhombohedral Th2Zn17 and tetragonal ThMn12 structures. All these three structures are derived by the replacement of a fraction of the Ca(Tb or Nd) atoms in the CaCu5 structure by a pair of Cu(Zn, Fe(Ti) or Mn) atoms (dumb-bells) along the c-axis of the CaCu5 structure. The relationship between these three structures will be discussed in terms of the dumbbell substitution sequence in the hexagonal CaCu5 structure. The fractions of dumbbell replacement are 1/3, 2/5 and 1/2 for the Th2Zn17, Nd3(Fe1-xTix)29 and ThMn12 structures, respectively. It has been shown that only light rare-earths and Gd form the new Nd3(Fe1-xTix)29 phase, while for heavy rare-earths beyond Tb there should exist another new structure type.