ChemInform Abstract: Combined Effect of Chemical Pressure and Valence Electron Concentration Through the Electron‐Deficient Li Substitution on the RE₄LiGe₄ (RE: La, Ce, Pr, and Sm) System.

Abstract

System. -The title compounds are synthesized from the elements (Nb tube, 1075°C, 5 h, followed by annealing at 750°C for 2 d). The products are characterized by powder and single crystal XRD, magnetic measurements, and TB-LMTO electronic structure calculations. They crystallize in the orthorhombic space group Pnma with Z = 4 (Gd5Si4-type structure). The structure contains two-dimensional Ln2LiGe2 slabs (Ln: La, Ce, Pr, and Sm) and Ge2 dimers bridging two neighboring slabs. Li substitution for rare-earth elements in the title system leads to a combined effect of increasing chemical pressure and decreasing valence electron concentration, which results in the structure transformation from the binary parental Sm 5 Ge 4 -type structure to the Gd 5 Si 4 -type structure. The non-magnetic Li substitution leads to a ferromagnetic-like ground state for Ce 4 LiGe 4 and the coexistence of antiferromagnetic and ferromagnetic ground states for Sm4LiGe4. -(NAM, G.; JEON, J.; KIM, Y.; KANG, S. K.; AHN, K.; YOU*, T.-S.; J. Solid State Chem. 205 (2013) 10-20, http://dx.

Anionic Doping and Cationic Site Preference in CaYb4Al2Sb6–xGex (x = 0.2, 0.5, 0.7): Origin of the Enhanced Seebeck Coefficient and the Structural Transformation

“…Quite interestingly, two title phases clearly display two distinctive site-preference of Ca 2+ and Yb 2+ at the three cationic sites, respectively, as can be seen in Table 2. Normally, any particular site-preference 26,27 of an atom should be elucidated either by the size-factor based on the size match between a site volume and a central atom 37 or by the electronic-factor based on the correlation between an electronegativity of an atom and the QVAL at the site. 28 In our title compounds, a cationic site-preference observed in M = Al, Ga, In) series, 11,13,35,36,38−40 we revealed a significant influence of the cationic site-preference to the observed structural transformation and eventually to the electrical transport property of each structure type.…”

“…First, this type of site-preference can be elucidated by the size-factor criterion. 37 The M1 and M3 sites show quite similar coordination environments, where six Sb or the Sb1/Ge mixed-sites form the distorted octahedra as shown in Figure 3. However, according to the bond distances between M and Sb(Sb1/Ge) as well as the inner angles of ∠Sb−M−Sb, the M3 site can provide a relatively more symmetric coordinate environment than the M1 site.…”

Influence of Thermally Activated Solid-State Crystal-to-Crystal Structural Transformation on the Thermoelectric Properties of the Ca5–xYbxAl2Sb6 (1.0 ≤ x ≤ 5.0) System

“…One simple way of understanding this type of site preference 55,56 is to consider the size factor criterion, which is based on the size match between a central cation and the surrounding local coordination environment. 57,58 As illustrated in Figure 4, the Ca 5 Ga 2 Sb 6 -type phase contains three different types of cationic sites. Both the M1 and M3 sites are surrounded by six Sb atoms forming two slightly distorted octahedra, whereas the M2 site is coordinated by seven Sb atoms building a two-edge-capped square pyramid.…”

Effect of MultiSubstitution on the Thermoelectric Performance of the Ca11−xYbxSb10−yGez (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) System: Experimental and Theoretical Studies

“…Given that each QVAL value is evaluated by the summation of integrated electron densities inside each corresponding WS sphere, we should expect the element having the higher electronegativity to occupy the atomic site with the higher QVAL value. Some other successful examples include the EuZn x In 4−x (x = 1.1−1.2) system, 47 the RE 4 LiGe 4 (RE = La, Ce, Pr, and Sm) system, 48 the Gd 5−x Y x Ge 4 (0 ≤ x ≤ 5) system, 49 and Ba-Li 1.09(1) In 0.91 Ge 2 . 50 According to QVAL values evaluated for binary compound Ca 11 Sb 10 (Table 4), the Sb3 site (Wyckoff 8h) displays the smallest value among five anionic sites.…”