A recent discovery of high-performance Mg3Sb2 has ignited tremendous research activities in searching for novel Zintl-phase compounds as promising thermoelectric materials. Herein, a series of planar Zintl-phase XCuSb (X = Ca, Sr, Ba) thermoelectric materials are developed by vacuum induction melting. All these compounds exhibit high carrier mobilities and intrinsic low lattice thermal conductivities (below 1 W·m−1·K−1 at 1010 K), resulting in peak p-type zT values of 0.14, 0.30, and 0.48 for CaCuSb, SrCuSb, and BaCuSb, respectively. By using BaCuSb as a prototypical example, the origins of low lattice thermal conductivity are attributed to the strong interlayer vibrational anharmonicity of Cu—Sb honeycomb sublattice. Moreover, the first-principles calculations reveal that n-type BaCuSb can achieve superior thermoelectric performance with the peak zT beyond 1.1 because of larger conducting band degeneracy. This work sheds light on the high-temperature thermoelectric potential of planar Zintl compounds, thereby stimulating intense interest in the investigation of this unexplored material family for higher zT values.

Multiple-band degeneracy has been widely recognized to be beneficial for high thermoelectric performance. Here, we discover that the p-type Dirac bands with lower degeneracy synergistically produce a higher Seebeck coefficient and electrical conductivity in topological semimetal BaAgBi. The anomalous transport phenomenon intrinsically originated from the asymmetric electronic structures: (i) complete p-type Dirac bands near the Fermi level facilitate high and strong energy-dependent hole relaxation time; (ii) the presence of additional parabolic conduction valleys allows for a large density of states to accept scattered electrons, leading to an enlarged hole–electron relaxation time ratio and, thus, weakened bipolar effect. In combination with the strong lattice anharmonicity, an exceptional p-type average ZT of 0.42 is achieved from 300 to 600 K, which can be dramatically enhanced to 1.38 via breaking the C 3v symmetry. This work uncovers the underlying mechanisms governing the abnormal transport behavior in Dirac semimetal BaAgBi and highlights the asymmetric electronic structures as target features to discover/design high-performance thermoelectric materials.

Quasi‐2D semiconductors have garnered immense research interest for next‐generation electronics and thermoelectrics due to their unique structural, mechanical, and transport properties. However, most quasi‐2D semiconductors experimentally synthesized so far have relatively low carrier mobility, preventing the achievement of exceptional power output. To break through this obstacle, a route is proposed based on the crystal symmetry arguments to facilitate the charge transport of quasi‐2D semiconductors, in which the horizontal mirror symmetry is found to vanish the electron–phonon coupling strength mediated by phonons with purely out‐of‐plane vibrational vectors. This is demonstrated in ZrBeSi‐type quasi‐2D systems, where the representative sample Ba1.01AgSb shows a high room‐temperature hole mobility of 344 cm2 V−1 S−1, a record value among quasi‐2D polycrystalline thermoelectrics. Accompanied by intrinsically low thermal conductivity, an excellent p‐type zT of ≈1.3 is reached at 1012 K, which is the highest value in ZrBeSi‐type compounds. This work uncovers the relation between electron–phonon coupling and crystal symmetry in quasi‐2D systems, which broadens the horizon to develop high mobility semiconductors for electronic and energy conversion applications.

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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.