Experimental and Theoretical Study on the Nonmagnetic Li/Mg Cosubstitution in the Gd_5–x(Li/Mg)_xGe₄ (x = 1.04, 1.17, 1.53) System

Abstract

Three Li- and Mg-cosubstituted compounds in the Gd5–x (Li/Mg) x Ge4 (x = 1.04(2), 1.17(2), 1.53(2)) system have been successfully prepared by conventional high-temperature reactions. According to powder and single-crystal X-ray diffraction analyses, all three compounds adopt a Gd5Si4-type phase with the orthorhombic Pnma space group (Pearson code oP16, Z = 4) and six crystallographically independent atomic sites. The crystal structure can be described as a combination of two-dimensional Mo2FeB2-type ∞ 2[Gd2(Li/Mg)­Ge2] layers and [Ge2] dimers. Interestingly, as 64% of Li and 26% of Gd at the RE3 and RE2 sites, respectively, were exclusively substituted by Mg in Gd3.47(1)Li0.36(2)Mg1.17(3)Ge4, the lattice parameter b was selectively shortened as a result of the RE3–Ge1 bond shrinkage in comparison to that in Gd4LiGe4, while lattice parameters a and c remained nearly intact. A series of theoretical calculations using the tight-binding linear muffin-tin orbital (TB-LMTO) method indicated that the reduction of the particular RE3–Ge1 bond distance in the title compounds could also be explained by an optimization of bonding based on the corresponding RE3–Ge1 crystal orbital Hamilton population (COHP) curve. Moreover, the specific site preference of Mg for the RE3 site was supported by both size-factor as well as electronic-factor criteria on the basis of the smallest atomic size and the highest electronegativity of Mg among the three cations. Therefore, the overall electronic structure was further interrogated by a density of states (DOS) analysis. The influence of nonmagnetic Li/Mg cosubstitution for the magnetic Gd atoms in the title Gd5–x (Li/Mg) x Ge4 system on the magnetic characteristics was also thoroughly studied by isofield magnetization at 100 Oe and 10 kOe and isothermal magnetization measurements at 4 K using two of the title compounds: Gd3.83(1)Li0.48Mg0.69(3)Ge4 and Gd3.47(1)Li0.36(2)Mg1.17(3)Ge4.

Role of Eu-Doping in the Electron Transport Behavior in the Zintl Thermoelectric Ca5–x–yYbxEuyAl2Sb6 System

“…150 K without any noticeable magnetic ordering down to 15 K. The effective magnetic moment of this compound can be calculated from the linear fit of the inverse magnetic susceptibility versus temperature. 40 The obtained value of 7.11 μ B per Eu atom is somewhat lower than that of the theoretically expected effective magnetic moment of 7.94 μ B for a free Eu 2+ ion. 41 This kind of magnetic moment reduction should be attributed to the trace amounts of Eu 2 O 3 impurity existing in the large batch of Eu-containing products as observed in our earlier work for the Eu 3.13(2) Ca 5.87 In 8 Ge 8 .…”

“…Ca 4.37(2) Eu 0.63 Al 2 Sb 6 shows the typical Curie–Weiss behavior in the paramagnetic region above ca. 150 K without any noticeable magnetic ordering down to 15 K. The effective magnetic moment of this compound can be calculated from the linear fit of the inverse magnetic susceptibility versus temperature . The obtained value of 7.11 μ B per Eu atom is somewhat lower than that of the theoretically expected effective magnetic moment of 7.94 μ B for a free Eu 2+ ion .…”