Yb14MgSb11 and Ca14MgSb11-New Mg-containing zintl compounds and their structures, bonding, and thermoelectric properties

Yufei Hu, Jian Wang, Airi Kawamura, Kirill Kovnir, Susan M. Kauzlarich

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46 Scopus citations

Abstract

Magnesium-containing Zintl phase compounds Yb14MgSb11 and Ca14MgSb11 have been prepared by annealing the mixture of the elements at 1075-1275 K. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I41/acd (Z = 8). Single-crystal X-ray data (90 K) were refined for Yb14MgSb11 [a = 16.625(9) Å, c = 22.24(2) Å, V = 6145(8) Å3, and R1/wR2 (0.0194/0.0398)] and Ca14MgSb11 [a = 16.693(2) Å, c = 22.577(5) Å, V = 6291(2) Å3, R1/wR2 (0.0394/0.0907)]. This structure type has been shown to be highly versatile with a large number of phases with the general formula A14MPn11 (A = Ca, Sr, Ba, Yb, Eu; M = Mn, Zn, Nb, Cd, Group 13 elements; Pn = Group 15 elements). The two compounds reported in this paper are the first Mg-containing analogs. Replacing M with Mg, which is divalent with no d-orbitals, probes electronic structure and properties of this structure type. Mg2+ is well-known to prefer tetrahedral geometry and allows for integration of the properties of a main group analog isoelectronic to the transition metal (Mn2+) containing compounds of this structure type. Thermoelectric properties of both compounds were measured from room temperature to 1075 K on fully dense pellets. Yb14MgSb11 shows metallic behavior, whereas Ca14MgSb11 is a semiconductor with a much larger electrical resistivity. The figure of merit reaches 0.32 for Ca14MgSb11 at 1075 K, and 1.02 at 1075 K for Yb14MgSb11, which is a 45% improvement over the reported zT1075K of Yb14MnSb11 prepared from Sn-flux. Density functional band structure calculations on Ca14MgSb11 yield p-type materials with a band gap of ∼0.6 eV and shows Ca and Sb 5p orbitals contributes to the top of valence band. The electron localization function calculations show that Mg and Sb are covalently bonded in MgSb4 9- and that the bonding of Sb3 7- can be considered as a hypervalent 3c-4e bond.

Original languageEnglish (US)
Pages (from-to)343-351
Number of pages9
JournalChemistry of Materials
Volume27
Issue number1
DOIs
StatePublished - Jan 13 2015

ASJC Scopus subject areas

  • Materials Chemistry
  • Chemical Engineering(all)
  • Chemistry(all)

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