No abstract

No abstract

Mg 2 X-based (X = Si, Ge, Sn) phases are promising for thermoelectric applications due to their nontoxicity, low cost, and high performance. Substantial experimental work has already been carried out based on the polycrystalline samples; however, studies on related single-crystal growth and corresponding properties are still very limited owing to the high volatility and reactivity of Mg, which makes it very challenging to obtain highquality single crystals with big sizes. In this report, for the first time, the Bridgman method was successfully applied in the single-crystal growth of the Bi-doped Mg 2 Sn materials. The crystals are of high quality and related anisotropic thermoelectric properties were systematically investigated. The Bi-doped Mg 2 Sn 0.99 Bi 0.01 single crystal exhibited a maximum zT value of 0.58 along the [111] orientation at 623 K, which is about 30 times that of the pristine Mg 2 Sn single crystal.

Zintl compounds often feature complex structural fragments and small band gaps, favoring promising thermoelectric properties. In this work, a new phase Ca 2 ZnSb 2 is synthesized and characterized to be a LiGaGe-type structure. It is isotypic to Yb 2 MnSb 2 with half vacancies at transition metal sites and undergoes a phase transition to Ca 9 Zn 4+x Sb 9 after annealing. Interestingly, Ca 2 ZnSb 2 and Yb 2 MnSb 2 are amenable to diverse doping mechanisms at different sites. Here, by substituting smaller Li on cation sites, two novel layered compounds 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 with the P6 3 /mmc space group are discovered, which can be viewed as derivatives of LiGaGe type. Despite having lower occupancy, the structural stability is improved compared with the prototype compounds owing to the reduced interlayered distances. Besides, the band structure analyses demonstrate that the bands near the Fermi level are mainly governed by the interlayered interaction. Due to the highly disordered structure, Yb 1.82 Li 0.18 Mn 0.96 Sb 2 features ultralow thermal conductivity from 0.79 to 0.47 W•m −1 •K −1 among the testing range; in addition, a remarkable Seebeck coefficient of 270.77 μV•K −1 at 723 K is observed. The discovery of the Ca 2 ZnSb 2 phase enriches the 2-1-2 map, and the size effect induced by cations provides new ideas for material designing.