Wenyu Zhao

The thermoelectric optimization of metallic heavy-fermion systems, such as the YbAl3 Kondo lattice, is fundamentally constrained by an excessively high electronic thermal conductivity (κE) that stems from an inherently high carrier concentration. Herein, we propose an approach to decouple electrothermal transport in YbAl3 by incorporating the soft magnetic alloy LaFe10.4Co0.8Si1.8 (LFS) as a functional second phase. Our results demonstrate that itinerant-electron magnetic fluctuations arising from the LFS phase near its Curie temperature (TC ≈ 292.5 K) act as a dynamic regulator of the Kondo environment. The incorporation of LFS elevates the Kondo temperature and enhances the Kondo interaction while simultaneously reducing the carrier concentration, resulting in a suppression of electrical conductivity. Crucially, this regulation results in a significant reduction in total thermal conductivity (κ), where the decline in κE accounts for 61% of the κ reduction, highlighting the dominance of electronic transport management in metallic TE systems. Simultaneously, magnetoresistance modeling confirms that strong spin–phonon coupling further curtails the phonon mean free path and reduces the lattice thermal conductivity by 34.9% at 300 K. Consequently, a peak zT of 0.38 is achieved at 300 K for the 0.3 wt % LFS composite, representing a 26.7% improvement over pristine YbAl3. This work provides profound insights into leveraging itinerant-electron magnetic degrees of freedom to transcend the metallic transport bottleneck in advanced heavy-fermion thermoelectric materials.

Integrating functional nanoparticles into thermoelectric matrices is a widely used strategy for performance optimization. However, the thermodynamic instability of such inclusions during high-temperature sintering frequently triggers interfacial reactions that degrade expected functionality. Traditionally, these reactions are regarded as detrimental and are suppressed through complex surface modification processes. This work breaks through this convention by proposing a reaction-assisted nanocompositing strategy, in which the in situ chemical reaction between GdCo₂ nanoparticles and p-type BiSbTe matrix is utilized as a spontaneous route for hierarchical microstructure construction. Instead of maintaining the initial magnetic phase, GdCo₂ precursors undergo decomposition during spark plasma sintering, playing a dual role: released Co atoms intercalate into the van der Waals gaps of BiSbTe to finely tune carrier concentration, while residual species self-assemble into nanoscale CoTe₂ precipitates and Gd-rich clusters. These reaction-induced structures act as efficient multiscale phonon scattering centers, reducing lattice thermal conductivity by ∼16.3% while preserving high carrier mobility. As a result, the optimized composite with 0.35 wt % GdCo₂ achieves a peak zT value of ∼1.30 at 350 K. This study provides a universal and reliable design principle for improving thermoelectric performance by converting interfacial instability from a disadvantage into an effective regulation strategy for thermoelectric performance enhancement.

The durability of thermoelectric devices (TEDs) has been a critical concern since they need to sustain frequent current or temperature shocks during operation. Herein, a shape memory alloy NiTi thin film is developed as a potential barrier layer to significantly enhance the durability of Bi₂Te₃-based TEDs. Atomic-resolution microscopy analysis confirms that the sputtered NiTi thin-film barrier layers coexist with B2 austenite and B19′ martensitic phases, which form NiTi/Bi₂Te₃ joints exhibiting excellent superelasticity and strain recovery ability. Among these, the NiTi barrier layer at the equimolar ratio possesses the highest η_e and η_d (52.1% and 59.3%, respectively), exhibiting unique superelasticity. The NiTi/Bi₂Te₃ jointed TEDs achieve a maximum cooling power density of 3.55 W·cm^–2, much higher than other reported TEDs. Importantly, after 10,000 aging cycles of pulsed current, the decay of maximum cooling temperature difference for the NiTi/Bi₂Te₃ jointed device is only half of that for the traditional Ni/Bi₂Te₃ jointed one, exhibiting remarkably enhanced durability. This work reveals that the superelastic NiTi barrier layer as an outstanding stress buffer provides insight for realizing high-performance and high-durability TEDs.

Narrow-bandgap full-Heusler Fe₂VAl-based alloys have received increasing attention for thermoelectric applications due to their favorable electrical transport behavior, high mechanical strength, and Earth-abundant constituent elements. However, the significant enhancement of the figure of merit is severely hindered by the low Seebeck coefficient due to the near-linear band structure and intrinsically high lattice thermal conductivity caused by the strong bonding. Here, employing first-principles calculations, we find that substituting 1/16 Fe atoms with Cu atoms can induce a strong localization of the 3d e_g orbital electrons of Fe and V atoms around the impurity atoms. This leads to the coexistence of dispersive bands and flat bands near the Fermi level, significantly boosting the Seebeck coefficient while maintaining high electrical conductivity, yielding a power factor of 5.8 mW m⁻¹ K⁻² at room temperature. Meanwhile, the Cu atoms with large atomic displacement form weak bonds with surrounding V atoms, strengthening low-frequency phonon scattering. Furthermore, the introduction of Cu atoms enhances the crystal anharmonicity, triggering a further decrease in the lattice thermal conductivity to 4.57 W m⁻¹ K⁻¹ at 300 K. Consequently, promising zT values of 0.36 and 2.3 are achieved at 300 K and 700 K, respectively. Our work demonstrates that Cu substitution in Fe sites may successfully decouple electrical and thermal transport of Fe₂VAl, offering an effective and scalable strategy for designing high-performance Fe₂VAl-based thermoelectric materials.

In-plane thermoelectric thin-film cooling devices are considered a promising solution for thermal management in electronic systems. However, the actual cooling performance is far below that of regular bulk cooling devices, making the design of thin-film devices much more difficult. In this work, a numerical analysis of the cooling performance of single-leg thin-film devices and multi-stage cascaded thin-film devices was conducted to understand the depressed cooling performance. The effects of input current, operating environment, substrate, and contact resistance on cooling performance were investigated and compared with the experimental data. The results show that under ideal conditions, including vacuum environment, absence of substrate, and no contact resistance, the maximum cooling temperature difference simulated by the finite element method (105.4 K) closely matches the theoretical value estimated from the ZT-based calculation (96.6 K). Under practical conditions, such as within atmosphere and with substrate and contact resistance, the simulated maximum temperature difference (2.1 K) fits well with the experimental value (1.1 K). These findings demonstrate that substrate effects, contact resistance, and operating environment can significantly impair the cooling performance of in-plane film thermoelectric devices, although high-performance thermoelectric materials were used. This study provides a guidance for the design and parameter optimization of thermoelectric thin-film cooling modules.

The low electrical transport performance of flexible thermoelectric (TE) films is the bottleneck that restricts the development of in-plane heat dissipation technology based on the Peltier effect. The architectonics of magnetic units in TE materials have been proven to be an effective method to improve the efficiency of TE conversion. In this study, a series of Bi_0.5Sb_1.5Te₃ (BST)/Fe/BST thermoelectromagnetic (TEM) films were successfully prepared by ordered architectonics of ferromagnetic Fe nanoparticles (Fe-NPs) as magnetic units with different distribution shapes between two layers of BST/epoxy films through screen-printing combined with hot-pressing curing. The study focused on the effects of the architectonic shapes of Fe magnetic units on the microstructure and electrothermal transport properties of TEM films. The ordered architectonics of magnetic units could optimize the carrier transport pathways and reduce carrier scattering due to the altered carrier trajectories induced by the magnetic field generated by the Fe magnetic unit, which has been confirmed by the magnetoresistance test, thus effectively enhancing σ. The introduction of the Fe magnetic unit preserved a large α through magnetic scattering and spin entropy contributions. The TEM film with Fe magnetic units patterned as rhombic shapes (BST-RhoFe-BST film) realized a 36.5% enhancement in the maximum power factor (PF), attributing to the largest negative magnetoresistance. The cooling temperature difference of the single-leg film device fabricated by the BST-RhoFe-BST film reached 1.8 K, 125% higher than that of the device fabricated by the BST-BST film. Furthermore, the cascade device based on the TEM film realized a temperature drop of 2.8 K and exhibited excellent in-plane heat dissipation capability. This work reveals that the ordered architectonic shapes of magnetic units could effectively regulate the electrothermal conversion performance of TE films, and the magnetoresistance theory can reveal the scattering mechanism of charge carriers in TEM films.