Study On The Phase Diagrams Of Al-La-Sb And On The Cystal Structures And Properties Of Several New Compounds

Partial phase relations in the Al-La-Sb ternary system at 773K have been investigated in this work. The crystal structures and properties of several new compounds Al_0．33ErGe₂,Al₂ErGe₂,Dy₅Co₆Sn₁₈,Mg₂₁Ga₅Hg₃have also been studied. The main contents were as follows:1 The isothermal section of Al-La-Sb ternary system at 773KThe partial phase relationship in the Al-La-Sb ternary system at 773k has been studied mainly by means of X-ray powder diffraction with the aid of differential thermal analysis and optical microscope. There are 12 three-phase regions, 25 two-phase regions and 14 single-phase regions in this ternary system at 773k. A new binary compound AlLa₂ was found and the existence of Al₄La₅ was confirmed.2 Crystal structure and properties of several new compoundsThe crystal structure of the Al_0.32ErGe₂ has been studied by X-ray powder diffraction technique and refined by Rietveld profile fitting method. The compound has an orthorhombic with the defect CeNiSi₂ structure type (space group Cmcm, (No.63) a=0.40701(2)nm, b=1.60401(9)nm, c=0.39240(2)nm, z=4 and D_calc=8.326g/cm³ ). The Rietveld refinement result was R_p=10.6% and R_wp=14.7%. we also studied the lattice thermal expansion coefficients using X-ray powder diffraction technique. The avreage thermal expansion coefficients areα_a=1．72×10^-5K^-1,α_b=1．11×10^-5K^-1,α_c=1．52×10^-5 K^-1,α_v=4．35×10^-5K^-1, respectively. Electrical resistivity of Al_0.32ErGe₂ was measured between 5 and 300K, it shows a metallic-like character in the whole investigated temperature range.The crystal structure of the compound Al₂ErGe₂ was refined by using Rietveld method. The compound Al₂ErGe₂ crystallizes in a hexagonal Al₂CaSi₂-type structure (space group P3m1 (No. 164) a=0.41781(9)nm, c=0.66698(1)nm, z=1, and D_calc=6.032g/cm³). The Rietveld refinement result was R_p=9.97% and R_wp=13.74%. Lattice thermal expansion studies on the compound were carried out in the temperature range from 298 to 913K. The avreage thermal expansion coefficients areα_a=0.90×10^-5K^-1,α_c= 1.25×10^-5 K^-1,α_v3.03×10^-5K^-1, respectively.The crystal structure of the Dy₅Co₆Sn₁₈ has been studied by X-ray powder diffraction technique and refined by Rietveld profile fitting method. The compound has a tetragonal with the Tb₅Rh₆Sn₁₈ structure type (space group I4₁/acd(No.142) a=1.35598(3)nm, c=2.71470(5)nm, z=8 , and D_calc=8.789g/cm³ ) The Rietveld refinement result was R_p=5.42% and R_wp=8.07%. Electrical resistivity of Dy₅Co₆Sn₁₈ was measured between 5 and 300K, it shows a metallic-like character in the whole investigated temperature range. The magnetic susceptibility fitted to a modified Curie-weiss law, the effective magnetic momentμ_eff=10.61μ_B and the paramagnetic Curie temperatureθ_p=-15.7K.The crystal structure of the newly discovered compound Mg₂₁Ga₅Hg₃ was determined from X-ray powder diffraction data using Rietveld and trial-and-error methods. The compound crystallizes in the tetragonal, space group I4₁/a(No.88), with lattice parameters a=1.45391(5)nm, c=1.15955(4)nm, Z=4, D_calc=4.004g/cm³ and Ge₈Pd₂₁ structure type. The Rietveld refinement result was R_p=6.37% and R_wp=8.25%. Lattice thermal expansion studies on the compound were carried out in the temperature range from 298 to 693K. The avreage thermal expansion coefficients are α_a=2．6×10^-5K^-1.,α_c=2．02×10^-5K^-1,α_v=7．25×10^-5K^-1.Electrical resistivity ofMg₂₁Ga₅Hg₃ was measured between 5 and 300K, it shows a metallic-like character in the whole investigated temperature range.