ChemInform Abstract: Synthesis, Structure and Charge Transport Properties of Yb₅Al₂Sb₆: A Zintl Phase with Incomplete Electron Transfer.

Abstract

Ytterbium I 4100Synthesis, Structure and Charge Transport Properties of Yb5Al2Sb6: A Zintl Phase with Incomplete Electron Transfer. -The title compound is obtained in high yields directly from the elements in the presence of a catalytic amount of Ge (950°C, 2 d) or by arc melting under an Ar atmosphere. The samples are characterized by single crystal XRD, charge transport measurements, and FLAPW electronic band structure calculations. Yb5Al2Sb6 and Sr0.85Yb4.15Al2Sb6 (obtained by partial replacement of Yb by Sr) crystallize in the orthorhombic space group Pbam with Z = 2. Yb 5 Al 2 Sb 6 has an anisotropic structure with infinite anionic double chains cross-linked by Yb 2+ ions. It shows a room temperature conductivity of about 1100 S/cm, a thermopower of 20 µV/K, and a thermal conductivity of 3.8 W/m·K. -(TODOROV, I.; CHUNG, D. Y.; YE, L.; FREEMAN, A. J.; KANATZIDIS*, M. G.; Inorg.

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

“…However, compounds 2 and 3 (Ca 5 Ga 2 Sb 6 type) obtained after the annealing process both show typical semiconducting behaviors, where σ increases as the temperature increases as a result of thermal excitation of carriers. These characteristics are in good agreement with two previous reports: metallic conduction of Yb 5 Al 2 Sb 6 adopting the Ba 5 Al 2 Bi 6 -type phase 24 and semiconducting behavior of Ca 5 Al 2 Sb 6 adopting the Ca 5 Ga 2 Sb 6type phase. 26 For comparison, we have added temperaturedependent σ data of Yb 5 Al 2 Sb 6 /0.5Ge 24 and Ca 5 Al 2 Sb 6 26 in Figure 8a.…”

“…These characteristics are in good agreement with two previous reports: metallic conduction of Yb 5 Al 2 Sb 6 adopting the Ba 5 Al 2 Bi 6 -type phase 24 and semiconducting behavior of Ca 5 Al 2 Sb 6 adopting the Ca 5 Ga 2 Sb 6type phase. 26 For comparison, we have added temperaturedependent σ data of Yb 5 Al 2 Sb 6 /0.5Ge 24 and Ca 5 Al 2 Sb 6 26 in Figure 8a. Therefore, such an interesting physical behavior reveals that the electrical transport properties of three title compounds are solely influenced by the structure type (Ca 5 Ga 2 Sb 6 -type vs Ba 5 Al 2 Bi 6 -type) rather than the chemical composition (Yb-rich vs Ca-rich).…”

“…3.8, 1.3, and 1.1 W/mK, respectively (see Figure S5b), indicating that the majority of the heat is transported by lattice vibrations in the form of phonons. For comparison, we have included the temperature-dependent κ latt data for Yb 5 Al 2 Sb 6 /0.5Ge, 24 Yb 5 Al 2 Sb 6 , 59 and Ca 5 Al 2 Sb 6 26 in Figure S5b as well. It is noticeable that there are certain variations of room-temperature κ latt values among the Ba 5 Al 2 Bi 6 -type compounds, including compound 1 (ca.…”

“…2,19−22 Recently, the A 5 M 2 Pn 6 series has been extensively investigated as Zintl-phase TE materials, 23−31 and two major structure types have been identified: the Yb 5 M 2 Sb 6 series (M = Al, Ga, In; Ba 5 Al 2 Bi 6 -type structure) 23−25 having metallic behavior and the A 5 M 2 Sb 6 series (A = Ca, Sr, Eu; M = Al, Ga, In; Ca 5 Ga 2 Sb 6 -type structure) 26,27,29−31 showing semiconducting behavior. In particular, p-type doping for A or M in the A 5 M 2 Sb 6 system (A = Ca, Eu; M = Al, Ga, In; Ca 5 Ga 2 Sb 6type) 32−37 has successfully enhanced the maximum ZT value, and the substitution of Sr for Yb in the Yb 5 Al 2 Sb 6 (Ba 5 Al 2 Bi 6type) system 24 has also been conducted. However, despite the possible ZT improvement via the Ca 2+ and Yb 2+ cation mixing, which had already been proven to increase phonon scattering by the mass contrast of cations in the Ca x Yb 1−x Zn 2 Sb 2 system 38 without sacrificing too much in σ and S, only a few attempts at cation-mixing reactions have been reported for the A 5 M 2 Sb 6 system.…”

“…However, despite the possible ZT improvement via the Ca 2+ and Yb 2+ cation mixing, which had already been proven to increase phonon scattering by the mass contrast of cations in the Ca x Yb 1−x Zn 2 Sb 2 system 38 without sacrificing too much in σ and S, only a few attempts at cation-mixing reactions have been reported for the A 5 M 2 Sb 6 system. 24 Our investigation starts from this basic idea of introducing the Ca 2+ and Yb 2+ mixed cations to produce the solid-solution Ca 5−x Yb x Al 2 Sb 6 system with a reduced κ latt and to study the correlation between the Ca/Yb ratio and the resultant crystal structure. Therefore, a total of 10 particular compositions with different Ca/Yb ratios were successfully synthesized by hightemperature reactions and crystallized in either one of two very similar but slightly different structure types, the Ba 5 Al 2 Bi 6 type 39 or the Ca 5 Ga 2 Sb 6 type, 39 despite the very similar sizes (r(Ca 2+ ) = 1.00 Å vs r(Yb 2+ ) = 1.02 Å) 40 and divalent states of the two cations.…”