Structure and Chemical Bonding of the Li-Doped Polar Intermetallic RE2In1−xLixGe2 (RE = La, Nd, Sm, Gd; x = 0.13, 0.28, 0.43, 0.53) System

Abstract

Four polar intermetallic compounds belonging to the RE2In1−xLixGe2 (RE = La, Nd, Sm, Gd; x = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system have been synthesized by the traditional solid-state reaction method, and their crystal structures have been characterized by single-crystal X-ray diffraction (SXRD) analyses. The isotypic crystal structures of four title compounds adopt the Mo2FeB2-type structure having the tetragonal space group P4/mbm (Z = 2, Pearson code tP40) with three crystallographically independent atomic sites and can be simply described as a pile of the identical 2-dimensioanl (2D) RE2In1-xLixGe2 slabs stacked along the c-axis direction. The substituting Li atom shows a particular site preference for replacing In at the Wyckoff 2a site rather than Ge at the Wyckoff 4g in this crystal structure. As the size of a used rare-earth metal decreases from La3+ to Gd3+ throughout the title system, the Ge-Ge and Ge-In/Li bond distances, both of which consist of the 2D anionic Ge2(In/Li) layer, gradually decrease resulting in the reduction of a unit cell volume. A series of theoretical investigations has been performed using a hypothetical structure model Gd2In0.5Li0.5Ge2 by tight-binding linear muffin-tin orbital (TB-LMTO) method. The resultant densities of states (DOS) value at the Fermi level (EF) suggests a metallic conductivity for this particular composition, and this calculation result is in a good agreement with the formal charge distribution assigning two extra valence electrons for a metal-metal bond in the conduction band. The thorough analyses of six crystal orbital Hamilton population (COHP) curves representing various interatomic interactions and an electron localization function (ELF) diagram indicating the locations of paired-electron densities are also provided in this article.

Chemical Driving Force for Phase-Transition in the Ca2–xRExCdSb2 (RE = Yb, Eu; 0.11(1) ≤ x ≤ 1.36(2)) System

“…This type of site-preference is not as largely noticeable as that between Ca 2+ and Eu 2+ in our Ca 2– x Eu x CdSb 2 system due to the relatively smaller size difference between Ca 2+ ( r = 1.00 Å) and Yb 2+ ( r = 1.02 Å, both for the 6-coordinates). The atomic site-preference is normally understood either by the electronic-factor or by the size-factor criteria as previously reported in various Zintl phases including the Ca 11– x Yb x Sb 10– y Ge z (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3), RE 11 Ge 4 In 6– x M x (RE = La, Ce; M = Li, Ge; x = 1, 1.96), Ca 5– x Yb x Al 2 Sb 6– y Ge y ( x = 0.2, 0.5, 0.7), and RE 2 In 1– x Li x Ge 2 (RE = La, Nd, Sm, Gd; x = 0.13, 0.28, 0.43, 0.53) . For the title Ca 2– x Eu x CdSb 2 system, we believe that the site-preference should be strongly affected by the size-factor criterion given the large size difference between Ca 2+ and Eu 2+ ( r (Eu 2+ ) = 1.17 Å for the 6-coordinates) resulting in the predominant Eu 2+ occupation at the M1-site.…”

p-Type to n-Type Conversion through the “Bypass” Phase Transition in the Zintl-Phase Thermoelectric Materials

“…Finding a sustainable clean energy source is an enduring issue for humankind in modern society. Despite our continuous efforts to discover and develop various energy sources, we easily overlook the fact that about 67% of the energy we use is wasted in the form of heat. , Since thermoelectric (TE) materials can directly convert wasted heat sources into electricity, these materials and devices adapting TE materials have been considered as one of the smartest solutions for energy-recycling purposes. − Among the numerous candidates for this TE application, the Zintl phase is considered an excellent candidate with respect to its intrinsically semiconducting property and complex crystal structure, both of which are required for good TE candidates. − In particular, the Zintl-phase A 5 M 2 Pn 6 (A = Ca, Sr, Eu, and Yb; M = Al, Ga, and In; Pn = As, Sb, and Bi) series has been extensively investigated by worldwide researchers for TE applications. − Our recent studies for the Zintl-phase Ca 5– x Yb x Al 2 Sb 6 (1.0 ≤ x ≤ 5.0) system revealed that some Yb-rich compounds having a particular range of composition initially adopted the Ca 5 Al 2 Bi 6 -type phase, but they underwent a phase transition to the Ca 5 Ga 2 As 6 -type phase through the annealing process . Moreover, their electrical transport properties were also shifted from metallic to semiconducting during this phase transition.…”

Special Issue: Advances in Zintl Phases

“…New compounds and new synthetic approaches are the topic of four of the papers. Lithium-containing solid solutions of the polar intermetallic of RE 2 InGe 2 (RE = La, Nd, Sm, Gd) were investigated by You et al [3]. These new intermetallics crystallize in the Mo 2 FeB 2 structure type with Li substituting for In.…”