Sr₉Mg_4.45(1)Bi₉ and Sr₉Mg_4.42(1)Sb₉: Mg-Containing Zintl Phases with Low Thermal Conductivity

Abstract

Zintl phases with nominal 9−4−9 formulas are very interesting for their potential applications as thermoelectric materials. However, the formation of such phases usually requires divalent transition metals, for example, Zn, Mn, and Cd, which are covalently bonded to the pnictogen atoms. In this report, for the first time, two Mgcontaining compounds with such structures as Sr 9 Mg 4.45(1) Bi 9 and Sr 9 Mg 4.42(1) Sb 9 were synthesized and their structures were determined by the single-crystal X-ray diffraction method. Both title compounds crystallize in the orthorhombic space group Pnma and are isostructural with Ca 9 Mn 4.41(1) Sb 9 , which features complex polyanion structures compared to the classical 9−4−9 phases. For Sr 9 Mg 4.45(1) Bi 9 , its low thermal conductivity, combined with its high electrical conductivity and moderate Seebeck coefficient, leads to a decent figure of merit of 0.57 at 773 K, which obviously prevails in the unoptimized 9− 4−9 phases. The discovery of such Mg-containing 9−4−9 phases is very significant, as the discovery not only enriches the structure map of the well-known 9−4−9 family but also provides very valuable thermoelectric candidates surely deserving of more in-depth investigation.

Exploring structural, mechanical, and thermoelectric properties of half-Heusler compounds RhBiX (X = Ti, Zr, Hf): A first-principles investigation

“…7 Therefore, novel thermoelectric materials with high performance and a wide range of elements must be explored. [8][9][10][11][12] We observed that thermoelectric materials can be employed in daily life to meet the growing demand for energy. Highly efficient TE devices can generate electricity from heat waste.…”

LiAlTt (Tt = Si, Ge): Experimental and Theoretical Reinvestigation on the Thermoelectric Properties of 8-Valence-Electron Half-Heusler Compounds

“…However, substantial waste heat exists as low-grade energy near ambient temperature, and unfortunately, current commercial Bi 2 Te 3 -based thermoelectric materials, which are suitable to work in such a temperature range, are of low efficiency and high cost and severely limit massive applications . Therefore, exploration of new candidates, which are of high performance and composed of earth-abundant elements, will be especially meaningful. − …”

Cation Substitution and Size Effects in Ca2ZnSb2 and Yb2MnSb2: Crystal and Electronic Structures and Thermoelectric Properties

“…Take Ca 1.84(1) Li 0.16(1) Zn 0.84(1) Sb 2 for example (Figure b), [ZnSb] layers are the basic unit of the anionic framework of the structure, propagating along the c -axial, wherein Ca 2+ (Li + ) are sandwiched between those layers. Notably, the Zn atom, which has a 4f site, is split by the (001) mirror plane, resulting in a disorder with a statistical site occupancy of ∼21%, similar to those interstitial sites in Sr 9 Mg 4+ x Pn 9 (Pn = Sb and Bi) and Ca 9 Mn 4+ x Sb 9 . , This structure can be regarded as a derivative of LiGaGe-type structure. The growth of high-quality single crystals of Ca 2 ZnSb 2 and Yb 2 MnSb 2 failed due to poor structural stability; yet, the successful preparation of Ca 1.84(1) Li 0.16(1) Zn 0.84(1) Sb 2 and Yb 1.82(1) Li 0.18(1) Mn 0.96(1) Sb 2 phases indicated the improved stability.…”