Enhanced Thermoelectric Performance in SmMg₂Bi₂ via Ca-Alloying and Ge-Doping

Abstract

Zintl phase compounds with a CaAl 2 Si 2 structure are promising thermoelectric materials. In this paper, enhanced thermoelectric performance was achieved in SmMg 2 Bi 2 , a new member of AB 2 X 2 compounds, via Ca-alloying and Ge-doping. The introduction of point defects by alloying Ca on the Sm site significantly reduces the lattice thermal conductivity, and the lowest value was achieved when the Sm/Ca molar ratio is 1:1. Doping Ge on the Bi site increases the hole concentration of the material, which successfully suppresses the bipolar effect and significantly improves the power factor (PF) in the whole temperature range. Due to the decrease of thermal conductivity and the increase of PF over 323−873 K, the peak zT value of Sm 0.5 Ca 0.5 Mg 2.15 Bi 1.99 Ge 0.01 reached 0.71 at 873 K and the zT ave approached 0.44, about 51 and 47% enhancement compared with the pristine sample, respectively. This work provides a thermoelectric performance optimization strategy that can be used for other AB 2 X 2 compounds.

Modeling Temperature-Dependent Thermoelectric Performance of Magnesium-Based Compounds for Energy Conversion Efficiency Enhancement Using Intelligent Computational Methods

“…The thermoelectric figure of merit (TFM) for magnesium-based compounds is modeled using intelligent algorithms with ionic radii of elemental constituents, operating temperature and elemental concentration descriptors. The experimental values of thirty different thermoelectric figures of merit for magnesium-based thermoelectric compounds employed for modeling are extracted from the literature [4,6,8,9,13,15,17,[54][55][56][57][58][59][60][61]. The modified chemical formula for thermoelectric magnesium-based material is shown in Equation (14).…”

Recent advances of 2D conductive metal–organic frameworks in thermoelectrics

“…[37][38][39][40][41][42][43][44][45][46] Big progress has been achieved in inorganic TE materials in the past years. [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] He et al enhanced the ZT to 2.7 at 750 K in germanium telluride-based high-entropy materials and realized a high experimental conversion efficiency of 13.3% by highentropy concept tuning electron and phonon decoupling. 53 Zhao and coworkers developed a lattice plainication strategy for defect engineering to weaken defect scattering and boost carrier mobility, leading to a ZT of ∼1.5 at 300 K. 54 However, traditional inorganic TE materials are oen composed of transition metals, such as Pb, Te, Bi, etc., which are heavy, brittle and toxic.…”

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

“…23,45,46 However, the single valence valley with low carrier mobility at the Brillouin center results in a low power factor of the hole-doped Mg 3 Sb 2 , making it a poor P-type TE material despite its low lattice thermal conductivity. 47 Fortunately, the P-type α-MgAgSb exhibits phonon glass electron crystal behavior, and a peak ZT value of 1.2 has been obtained by enhancing the phase purity of the hole-doped sample. 48 The complex lattice structure of α-MgAgSb consists of a distorted Mg−Sb rock salt lattice rotated by 45°along the c axis and silver atoms inside the polyhedrons as shown in Figure 1c.…”

“…By incorporation metallic inclusions such as Nb or Ta into the Mg 3 (Sb,Bi) 2 -based matrix, the electrical conductivity was enhanced and the lattice thermal conductivity was reduced, leading to a record-high average ZT > 1.5 with a maximum value of 2.04 at 798 K . Other alloying elements like Y, Sc, Se, Te, Tm, and Nd have also been found to boost the ZT value to 1.8–1.9, especially at elevated temperatures, but are restricted by their scarcity. ,, However, the single valence valley with low carrier mobility at the Brillouin center results in a low power factor of the hole-doped Mg 3 Sb 2 , making it a poor P-type TE material despite its low lattice thermal conductivity …”