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Sustained thermoelectric efforts have concentrated on the enhancement of conversion efficiency of power generators, while simultaneously achieving high output power continues to lag. Specifically, the highest output power density of emerging Mg‐based modules reported so far is only half of that of commercial Bi2Te3‐based, mainly due to the low power factor of MgAgSb. Herein, homogenously distributed MgCuSb in situ nanoprecipitates in the MgAgSb matrix effectively optimized carrier concentration due to the effect of carrier injection from the metal–semiconductor Ohmic contact. As a result, a record‐high average power factor of 27.2 µW cm−1 K−2 is obtained in MgCu0.1Ag0.87Sb0.99 composite within the temperature range of 300–550 K, which is much higher than ever reported values of MgAgSb system. Benefiting from the combination of the optimized average power factor of p‐leg and low interface resistivity, a fabricated eight‐pair MgCu0.1Ag0.87Sb0.99/Mg3.2Bi1.5Sb0.5 module demonstrates an unprecedently high output power density of 2.9 W cm−2 under a temperature difference of 300 K, outperforming all low‐temperature advanced thermoelectric modules. Meanwhile, a competitive conversion efficiency of 7.65% is obtained simultaneously. The work significantly advances high‐power thermoelectric applications of Mg‐based modules in the field of low‐temperature sustainable energy harvesting. [ABSTRACT FROM AUTHOR]

Zintl compounds such as n‐type Mg3(Sb,Bi)2 show promising thermoelectric applications benefiting from their high valley degeneracy and low lattice thermal conductivity. However, the heavier p‐type AMg2X2 (A = Ca, and Yb; X = Bi and Sb) Zintl counterparts even exhibit a higher κlat due to strong chemical bonding. Reducing κlat of AMg2X2 is an important route for improving thermoelectric performance. Herein, it is found that Cd doping at the Mg site in CaMg2Bi2 can weaken intralayer covalent bonds and soften acoustic phonons, as well as fill the optical phonon gap. These effects result in large atomic displacement, low phonon group velocity, and strong lattice vibration anharmonicity. Doping 10% Cd leads to a reduction of 56% in the κlat of CaMg2Bi2. Moreover, Cd doping promotes orbital alignment and thus increases the density‐of‐states effective mass and Seebeck coefficient. Eventually, in conjunction with carrier concentration optimization by Na doping and band structure engineering by Ba doping, a high ZT of ≈1.3 at 873 K in (Ca0.85Ba0.15)0.995Na0.005Mg1.85Cd0.15Bi2 sample is realized. This work highlights the significant role of manipulating chemical bonding in suppressing phonon propagation of semiconductors. [ABSTRACT FROM AUTHOR]

AgBiSe2 undergoes two structural transitions in its service temperature range. Increasing entropy by alloying is considered an effective solution for modulating phase transition, but the efficacy of increasing entropy is limited by solubility and the selection of alloying components depends on trial and error. This study first confirmes that trigonal AgBiSe2 is metavalently bonded and searches metavalent PbTe as the alloying material based on the 2D map spanned by quantitative chemical bonding descriptors of electrons transferred (ET) and electrons shared (ES). The large solubility can be explained by the same bonding mechanism. PbTe alloying successfully stabilizes cubic AgBiSe2 to room temperature. Further, by optimizing the carrier concentration, the average ZT value from 300 to 773 K of (AgBiSe2)0.7(PbTe)0.3Cu0.02 reaches 0.42, which is 40% higher than that of pristine AgBiSe2. Simultaneously, heavy alloying leads to solid solution strengthening with enhanced hardness. This study not only paves the way for practical applications of AgBiSe2‐based materials but also provides an effective strategy for screening potential alloying candidates to solve the structure‐transition issue from the viewpoint of chemical bonding. [ABSTRACT FROM AUTHOR]