Site-Preference among Three Anions in the Quaternary BaAl₄-Type Structure: Experimental and Computational Investigations for BaLi_1.09(1)In_0.91Ge₂

Abstract

Zintl phases and polar intermetallics including lithium atoms can offer not only a good opportunity to investigate the correlation among crystal structure, chemical bonding, and physical properties given the unique role of lithium acting as a "zwitter" ion, 1-3 but be considered as electrode materials for Li-ion batteries and as thermoelectric materials.4,5 Since a lithium atom can play a role as either a cation or an anion, various tetrelide phases containing lithium substitution or insertions have been synthesized, and their characteristics have been investigated using both experimental and theoretical approaches. 1-9During our recent research activities to investigate the influence of lithium substitution or intercalation for components in the polar intermetallic AE/RE-In-Ge (AE = alkalineearth metals, RE = rare-earth metals) system, we have serendipitously synthesized a quaternary compound BaLi 1.09(1) -In 0.91 Ge 2 adopting the BaAl 4 -type structure.9,10 The given crystal structure type is one of the most prominent structure types observed among binary MTr 4 (M = alkali-earth metals, rare-earth metals; Tr = tetrels) compounds and has already been studied elsewheres.11,12 Moreover, numerous ternary phases with different substitutions for anionic elements have also been successfully synthesized, 13-21 and the site-preference of anions within the 3-dimensional (3D) frameworks has been thoroughly studied in terms of geometric-as well as electronic-perspectives. 11,13,14,21 However, the researches for the quaternary BaAl 4 -type phases containing an additional anion substitution in the polyanionic frameworks have been limited mostly for transition-metal 22-24 containing compounds due to the allowable range of electron counts between 12-14 to form the BaAl 4 -type structure. In addition, the site-preference rules established based on numerous ternary compounds have not been applied to the cases of quaternary compounds including a lithium substitution.In this report, therefore, we focus more on the site-preference of three anions forming the 3D-polyanionic frameworks. For this purpose, we start from the parental binary structure BaIn 4 , 25 then two steps of anion substitutions by Ge and Li will be considered subsequently in terms of geometricand electronic-factors. Theoretical studies using tight-binding muffin-tin (TB-LMTO) method were also performed. Crystal orbital Hamilton population (COHP) curves as well as density of states (DOS) were interrogated in depth to understand the observed site-preference of anions and chemical bonding. ExperimentalEach element in the stoichiometric ratio of 1:2:2:2 for Ba:Li:In:Ge was loaded in an one end-sealed Nb-tubing inside an argon-filled glove box. The other end of Nb-tubing was sealed by arc-welding under a partial argon atmosphere, then the tubing was subsequently sealed in a fused-silica jacket under vacuum to avoid any contact with oxygen during the reaction at the elevated temperature. The mixture of reactants was initially heated up to 950 °C by 200 °C/h, kept at th...

Effect of Rare-Earth Metals Substitution for Ca on the Crystal Structure and Thermoelectric Properties of the Ca11–xRExSb10–y System

“…There are some examples, in which the electronic-factor criterion using QVAL successfully explains the observed site preference. These include the EuZn­In 4– x ( x = 1.1–1.2), RE 4 Li­Ge 4 (RE = La, Ce, Pr, and Sm), Gd 5– x ­Y x Ge 4 (0 ≤ x ≤ 5), Ca 11– x ­Yb x ­Sb 10– y ­Ge z (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) systems, and BaLi 1.09(1) ­In 0.91 ­Ge 2 …”

Cationic Site-Preference in the Yb14-xCaxAlSb11 (4.81 ≤ x ≤ 10.57) Series: Theoretical and Experimental Studies

“…In the past several years, numerous observed site preferences between components in Zintl phases and polar intermetallic compounds have been nicely explained by this QVAL value criterion. Some examples include the EuZn x In 4- x ( x = 1.1~1.2) [32], the RE 4 LiGe 4 ( RE = La, Ce, Pr and Sm) [33], the RE 11 Ge 4 In 6- x M x ( RE = La, Ce; M = Li, Ge; x = 1, 1.96) series [17] and BaLi 1.09(1) In 0.91 Ge 2 [34]. …”

Ce11Ge3.73(2)In6.27: Solid-state synthesis, crystal structure and site-preference

“…Therefore, the relatively larger In atom (r In ¼1.50 Å, r Ge ¼ 1.22 Å: covalent values) [31] surely prefer to occupy the more spacious anionic sites. Based upon the comparison of the site-volume, we could conclude that if the electronic-aspect and the size-aspect conflict each other in terms of the atomic site-preference in the Ho 11 Ge 10 -type phase [6], the size-aspect related to the site-volume criterion wins over the electronic-aspect [32][33][34]. This site-preference of In atoms based upon the size-aspect will be further discussed by the theoretical perspective in the subsequent section.…”