Impacts of Cu-Doping and Mg-Deficiency on Mg2Sn Thin Films Thermoelectric Properties

Abstract

Two groups of Mg-Sn thin films were deposited by magnetron co-sputtering of Mg, Sn, and Cu targets. Group I was Mg-Sn films with [Mg]/[Sn] = 2 and group II with [Mg]/[Sn] = 1.75. The effect of Mg-deficiency and Cu-doping on the structure and thermoelectric properties was investigated. Both groups were doped by different Cu concentrations (0 at.%, 0.5 at.%, and 1.5 at.%). The structure and morphology of the thin films were investigated. The stable face-centered cubic structure was only observed for undoped film of group I, while a mixture of facecentered cubic and metastable orthorhombic structures coexisted for other samples whatever the Cu content. Carrier concentration and mobility were measured to explain the electronic transport behaviors of the films. The bandgap energy for both groups was estimated by the Kubelka-Munk's method. The influence of the Mg deficiency and Cu doping on the thermoelectric properties was discussed for a range of temperatures: 30-200°C. For both groups, the best figure-of-merit, ZT, was obtained at 200°C for samples doped with 0.5 at.% Cu with ZT = 0.07 for group I and ZT = 0.27 for group II.

Low-Cost Magnesium-Based Thermoelectric Materials: Progress, Challenges, and Enhancements

“…Thus, optimizing carrier concentration for maximal TE performance is vital, achievable through band structure engineering techniques such as doping the matrix with acceptor or donor elements to achieve band convergence, forming solid solutions, introducing point defects, and modifying the nanostructure to influence electrical conductivity and Seebeck coefficient. 23,33 Extensive interest and attention have been directed toward the development of the Mg 2 X-based TE materials. 34,35 Alloying Sn and Ge in Mg 2 Si can introduce point defects that induce short-wavelength photon scattering 23 and mass difference scattering due to the large mass difference between the elements Si and Sn, thereby reducing thermal conductivity.…”

“…17 Furthermore, other elements such as Cu, Ag, Ni, Zn, and In have been considered as acceptor dopants in Mg 2 Sn, albeit with limited success. 33 Further doping of Bi 37 and Sb 38 into the Mg 2 X alloy system increased the maximum ZT values to 1.4 and 1.5, respectively, at 800 K. 36 These advancements have spurred the development of another group of alloys based on Mg 3 Sb 2 /Mg 3 Bi 2 Zintl compounds and MgAgSb. Mg 3 Sb 2 compounds possess a typical cubic antibixbyite symmetry of the minerals, with dynamically stable Ia3̅ and P3̅ m1 phases at ambient conditions.…”

“…Mg 2 Si-based materials offer carrier controllability through impurity doping, providing design flexibility in adjusting thermal impedance. Thus, optimizing carrier concentration for maximal TE performance is vital, achievable through band structure engineering techniques such as doping the matrix with acceptor or donor elements to achieve band convergence, forming solid solutions, introducing point defects, and modifying the nanostructure to influence electrical conductivity and Seebeck coefficient. , …”

Enhanced thermoelectric performance of p-type Mg2Sn single crystals via multi-scale defect engineering

“…35,36 On the contrary, p-type Mg 2 Sn has inferior TE properties for practical applications. Various elements such as Ag, 5 Li, 19,20 Ga, 25 Cu, 29 and Na 30 were used to introduce hole carriers into Mg 2 Sn. Many efforts have been devoted to enhancing the TE performance of p-type Mg 2 Sn.…”

“…Among the considered materials, Mg 2 Sn and its derivatives Mg 2 (Si,Ge,Sn) are potential TE materials for operation at moderate temperatures between 400 K and 800 K. 5–34 Good TE performances ( zT ∼ 0.9 at 750 K) have been reported for n-type Mg 2 Sn utilizing point defects and carrier optimization. 26,27 Among the n-type Mg 2 Sn samples, undoped, B-doped, and Sb-doped Mg 2 Sn single crystals (SCs), 22–24,34 Bi-doped Mg 2 Sn polycrystals (PCs), 26 and Sb-doped Mg 2 Sn PCs 27 prepared by applying physical and chemical pressure were found to contain Mg vacancy (V Mg ) as a point defect.…”