Crystal structure and phase relationships in the pseudobinary system RE 5Si 4–RE 5Ge 4 (RE=Nd and Pr) at 1273 K

Abstract

High-temperature (1273 K) phase relationships in the pseudobinary system RE 5Si 4–RE 5Ge 4 (RE=Nd and Pr) were studied by X-ray powder diffraction (XRD). Three structurally distinct phase regions exist in the Nd 5Si 4− x Ge x system: the Nd 5Si 4-based solid solution crystallizing in the tetragonal Zr 5Si 4-type structure with space group P4 12 12, the Nd 5Ge 4-based solid solution crystallizing in the orthorhombic Gd 5Ge 4-type structure with space group Pnma and a ternary intermediate phase crystallizing in the monoclinic Gd 5Si 2Ge 2-type structure with space group P112 1/ a. In the Pr 5Si 4− x Ge x system, there are only two structurally distinct phase regions: the Pr 5Si 4-based solid solution crystallizing in the tetragonal Zr 5Si 4-type structure with space group P4 12 12 and the Pr 5Ge 4-based solid solution crystallizing in the orthorhombic Gd 5Ge 4-type structure with space group Pnma. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structures. The lattice parameters, atomic positions and interatomic distances in the high-temperature Nd 5Si 2.8Ge 1.2, Nd 5Si 2Ge 2 and Pr 5Si 2Ge 2 compounds were derived.