The high lattice thermal conductivity of half-Heuslers (HHs) restricts the further enhancement of their thermoelectric figure-of-merit (ZT). In this study, multiscale scattering centers, such as point defects, dislocations, and nanoprecipitates, are synchronously introduced in a n-type ZrNiSn-based HH matrix through Nb doping and Hf substitution. The lattice thermal conductivity is substantially decreased from 4.55 (for the pristine ZrNiSn) to 1.8 W·m⁻¹·K⁻¹ at 1123 K via phonon scattering over a broad wavelength range through the adjustment of multiscale defects. This value is close to the theoretically estimated lowest thermal conductivity. The power factor (PF) is enhanced from 3.25 (for the pristine ZrNiSn) to 5.01 mW·m⁻¹·K⁻² for Zr_0.66Hf_0.30Nb_0.04NiSn at 1123 K owing to the donor doping and band regulation via Nb doping and Hf substitution. This can be ascribed to the synergistic interaction between the lowering of the lattice thermal conductivity and retention of the high PF. Consequently, a ZT value of as high as 1.06 is achieved for Zr_0.66Hf_0.30Nb_0.04NiSn at 1123 K. This work demonstrates that these actions are effective in jointly manipulating the transport of electrons and phonons, thereby improving the thermoelectric performance through defect engineering.

The thermoelectric (TE) performance of p-type ZrCoSb-based half-Heusler (HH) alloys has been improved tremendously in recent years; however, it remains challenging to find suitable n-type ZrCoSb-based HH alloys due to their high lattice thermal conductivity (κ_L). In this work, n-type Zr_1-xTa_xCo_1-xNi_xSb HH alloys were firstly designed by multisite alloying. The evolution of the Raman peak proved that alloy scattering, phonon softening, anharmonicity, entropy-driven disorder, and precipitates had a combined effect on decreasing κ_L by 46.7% compared to that of pristine ZrCoSb. Subsequently, Hf_0.75Zr_0.25NiSn_0.99Sb_0.01 was introduced into Zr_0.88Ta_0.12Co_0.88Ni_0.12Sb to further suppress κ_L. Remarkably, the grain size of the biphasic HH alloys was refined by at least one order of magnitude. A biphasic high-entropy HH alloy with y = 0.2 exhibited the minimum κ_L of ~2.44 W/(m·K) at 923 K, reducing by 67.7% compared to that of ZrCoSb. Consequently, (Zr_0.88Ta_0.12Co_0.88Ni_0.12Sb)_0.9(Hf_0.75Zr_0.25NiSn_0.99Sb_0.01)_0.1 exhibited the highest TE figure of merit (~0.38) at 923 K. The cooperation between the entropy and biphasic microstructure resulted in multiscale defects, refined grains, and biphasic interfaces, which maximized the scattering of the multiwavelength phonons in HH alloys. This work provides a new strategy for further reducing the grain size and κ_L of medium- and high-entropy HH alloys.

Cu₂Te-based materials are a type of superionic conductor belonging to the class of phonon-liquid electron-crystal materials and have achieved high ZT values by doping and nanostructuring. However, it is easy to form copper vacancies in Cu₂Te which leads to an excessive carrier concentration and then results in a low Seebeck coefficient. Hence, controlling copper ion migration and optimizing carrier concentration is essential to improve the thermoelectric performance of Cu₂Te. This paper reports high-performance Cu₂Te–Ag₂Te composite with high application value in the low-middle temperature region, which is achieved by fine tuning the carrier concentration using Fe addition and non-stoichiometric Te, as well as controlling the thermal conductivity of composite. A high ZT of ~1.2 is obtained in AgCu_0.97Fe_0.03Te_0.96 at a low temperature of 573 K. Meanwhile, the phase transition mechanism of Cu₂Te–Ag₂Te and its effect on the thermoelectric transport performance are revealed that go beyond nanostructuring and single-doping, which provides a strong theoretical basis for research and performance improvement of thermoelectric materials in this system.