PHASE-RELATIONSHIPS AND CRYSTALLOGRAPHY IN THE PSEUDOBINARY SYSTEM GD5SI4-GD5GE4

A study of phase relationships and crystallography in the pseudobinary system Gd-5(SixGe1-x)(4) revealed: (1) that both terminal binary comp ounds Gd5Si4 and Gd5Ge4 crystallize in the Sm5Ge4-type orthorhombic st ructure, and (2) the appearance of an intermediate (ternary) phase wit h a monoclinic crystal structure which is similar to both Gd5Si4 and G d5Ge4. The formation of the monoclinic phase at 0.24 less than or equa l to x less than or equal to 0.5 [between Gd-5(Si0.96Ge3.03)congruent to Gd-5(Si1Ge3) and Gd-5(Si2Ge2)] is probably due to the large differe nce in bonding characteristics of Si and Ge in the Gd5Si4-Gd5Ge4 pseud obinary system which limits the ability of the mutual substitution of Si for Ge and vice versa without a change of the crystal structure. Fo r the composition Gd-5(Si2Ge2) the lattice parameters of the monoclini c structure (space group P112(1)/a) are a=7.5808(5), b=14.802(1), c=7. 7799(5)Angstrom, gamma=93.190(4)degrees. A distinct difference in the magnetic behaviors of the alloys from three different phase regions in this system follows the distinct difference in the crystal structures observed for the alloys from the three phase regions. (C) 1997 Elsevi er Science S.A.