Crystal Structure, Phase Relationships And Physical Properties In RE₅Si₄-RE₅Ge₄ Pseudobinary System

Crystal structure, phase relationships and physical properties of Pr5Si₄-Pr5Ge₄, Nd₅Si₄-Nd₅Ge₄ and Gd₅Ge₄-La5Ge₄ systems are systematically investigated in present thesis. The main results are summarized as follows:X-ray powder diffraction (XRD) investigation of the Pr5Si₄-xGex pseudobinary system reveals that three structurally distinct phase regions exist in the system at ambient temperature. The Pr5Si₄ based solid solution crystallizes in the Zr5Si₄-type tetragonal structure with space group P41212 and extends between 0≤x≤1.35. The Pr5Ge₄ based solid solution crystallizes in the Sm5Ge₄-type orthorhombic structure with space group Pnma and extends between 2.9≤x≤4.0. A ternary intermediate phase, which exists for 1.65≤x≤2.6, crystallizes in the Gd₅Si2Ge2-type monoclinic structure with space group P1121/a. Only two structurally distinct phase regions exist in this system at 1273K: the Pr5Si₄ based solid solution and the Pr5Ge₄ based solid solution. The ternary intermediate phase, which crystallizes in the monoclinic Gd₅Si2Ge2-type structure with space group P1121/a at ambient temperature, crystallizes in the tetragonal Zr5Si₄-type structure with space group P41212 at 1273K. Based on the Rietveld powder diffraction profile fitting of the XRD patterns, the detailed structural information about some compounds is reported.The M-T curves of all Pr5(Si₄-xGex) compounds show an irreversibility between the zero field cooling (ZFC) and field cooling (FC) magnetization curves, which may be induced by the magnetocrystalline anisotropy of the Pr ions and spin canting. The magnetic properties and their structure dependence of the Pr5Si₄-xGex compounds are elucidated by the RKKY model. A large magnetoresistance (about 25%) is found in Pr5Ge₄ compound, which is associated with the transformation of the magnetic structure due to the application of magnetic field.Unlike Pr5Si₄-xGex system, there are four structurally distinct phase regions exist in Nd₅Si₄-xGex system at ambient temperature. The Nd₅Si₄ based solid solution crystallizes in the tetragonal Zr5Si₄-type structure with space group P41212 and extends in the range 0≤x≤0.7. The Nd₅Ge₄ based solid solution crystallizes in the orthorhombic Gd₅Ge₄-type structure with space group Pnma and extends in the range 2.9≤x≤4.0. There are two ternary intermediate phases, which crystallize in the orthorhombic Gd₅Si₄-type structure with...