Enhanced Thermoelectric Performance of GeTe-Based Composites Incorporated with Fe Nanoparticles

Chemical modulation and defect engineering in high-performance GeTe-based thermoelectrics

Thermoelectric technology plays an important role in developing sustainable clean energy and reducing carbon emissions, offering new opportunities to alleviate current energy and environmental crises. Nowadays, GeTe has emerged as a highly promising thermoelectric candidate for mid-temperature applications, due to its remarkable thermoelectric figure of merit (ZT) of 2.7. This review presents a thorough overview of the advancements in GeTe thermoelectric materials, meticulously detailing the crystal structure, chemical bonding characteristics, band structure, and phonon dynamics to elucidate the underlying mechanisms that contribute to their exceptional performance. Moreover, the phase transition in GeTe introduces unique degrees of freedom that enable multiple pathways for property optimization. In terms of electrical properties, noticeable enhancement can be realized through strategies such as band structure modulation, carrier concentration engineering, and vacancy engineering. For phonon transport properties, by incorporating defect structures with varying dimensions and constructing multi-scale hierarchical architectures, phonons can be effectively scattered across different wavelengths. Additionally, we provide a summary of current research on devices and modules of GeTe. This review encapsulates historical progress while projecting future development trends that will facilitate the practical application of GeTe in alignment with environmentally sustainable objectives.

Effect of Magnetic Moment on Carrier Effective Mass and Transport in Magnetic Nd2Fe14B Composite Bi2Te3 Films

A composite of magnetic and thermoelectric (TE) materials is one of the most popular methods to improve TE properties. However, the influential mechanism of the magnetic property on the carrier has not been clarified. In this study, Nd2Fe14B cylinders are used as the magnetic phase to regulate carrier behaviors in Bi2Te3 films. Roaming state Fe atoms in Nd2Fe14B provide some carriers. The VTe at the composite interface also provides carriers. These lead to the increase of carrier concentration and conductivity of the composite film. Meanwhile, the Lorentz force generated by the magnetic moment of Nd2Fe14B provides the carriers with a stronger energy, which results in the increase of carrier effective mass and thereby increases the Seebeck coefficient. Thus, the power factor of the magnetic composite film is improved by 366% compared with that of the pure Bi2Te3 film.

The Latest Advances in Ink-Based Nanogenerators: From Materials to Applications

Nanogenerators possess the capability to harvest faint energy from the environment. Among them, thermoelectric (TE), triboelectric, piezoelectric (PE), and moisture-enabled nanogenerators represent promising approaches to micro-nano energy collection. These nanogenerators have seen considerable progress in material optimization and structural design. Printing technology has facilitated the large-scale manufacturing of nanogenerators. Although inks can be compatible with most traditional functional materials, this inevitably leads to a decrease in the electrical performance of the materials, necessitating control over the rheological properties of the inks. Furthermore, printing technology offers increased structural design flexibility. This review provides a comprehensive framework for ink-based nanogenerators, encompassing ink material optimization and device structural design, including improvements in ink performance, control of rheological properties, and efficient energy harvesting structures. Additionally, it highlights ink-based nanogenerators that incorporate textile technology and hybrid energy technologies, reviewing their latest advancements in energy collection and self-powered sensing. The discussion also addresses the main challenges faced and future directions for development.

Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration

Metal-semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe2) nanophase within the nanocrystalline ternary skutterudite (Co(Ge1.22Sb0.22)Te1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase's role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ∼ 1.30) is attained with CGST-7 wt. % CoTe2 nanocomposite film at 655 K compared to that of pristine CGST.

Magnetism Modulation for Cryogenic Thermoelectric Enhancements in Fe3O4 Nanoparticle-Incorporated Bi0.85Sb0.15 Nanocomposites

The internal magnetism introduced by the magnetic nanoparticles combined with the external magnetic field can provide an effective way to modulate the thermoelectric (TE) properties of materials. Herein, we comparably investigate the effect of magnetism of Fe₃O₄ nanoparticles (Fe₃O₄-NPs) and the external magnetic field on the cryogenic thermoelectric properties of Fe₃O₄-NP/Bi_0.85Sb_0.15 nanocomposites. With the ferromagnetism-superparamagnetism transition, the Fe₃O₄-NPs in the superparamagnetic state exhibit a stronger magneto-trapped carrier effect, where the electron concentration at high temperature is evidently reduced. With the simultaneous increase of S and reduction of electronic thermal conductivity, a high ZT value of 0.33 at 180 K is obtained for 0.05 wt % Fe₃O₄/Bi_0.85Sb_0.15. Meanwhile, under the external magnetic field, the magnetoresistance of the composites is suppressed by Fe₃O₄-NPs, which results in a remarkable enhancement of the electronic transport performance. Consequently, the highest ZT value of 0.48 at 220 K under 1 T is achieved for 0.1 wt % Fe₃O₄-NPs/Bi_0.85Sb_0.15, increased by 55% compared with that of the matrix. A single-leg device is prepared using 0.1 wt % Fe₃O₄-NP/Bi_0.85Sb_0.15 nanocomposites. Its cooling temperature difference at 180 K reaches 1.3 and 3.2 K under 0 and 1 T when applying 300 mA current, increased by 20 and 46% compared with that of the matrix, respectively. This work suggests that magnetism modulation with introducing magnetic nanoparticles will enhance the TE and magneto-TE performance of composite materials.

Magnetically Enhanced Thermoelectric Performance of Ti0.75NiSb+x mol % Fe (x = 0-5) Nanocomposites

Ti_0.75NiSb is a half-Heusler compound with low lattice thermal conductivity due to a large number of cation vacancies. However, the higher carrier concentration limits the improvement of its thermoelectric performance. In this paper, magnetic Fe nanoparticles with a size of 30 nm are composited into Ti_0.75NiSb in the form of the second phase. The charge transfer between Fe nanoparticles and Ti_0.75NiSb leads to a decrease in carrier concentration. The strong interaction between the magnetic moment and carriers enhances the electron scattering, so that the scattering factor increases and the mobility decreases. The combined effect results in an increase of about 10% in the Seebeck coefficient and a decrease by about 14% in the electronic thermal conductivity at 873 K for the composite Ti_0.75NiSb+2 mol % Fe. Meanwhile, the magnetic Fe nanoparticles provide additional scattering centers, leading to a decrease in lattice thermal conductivity. As a result, a zT value of 0.4 at 873 K is achieved for the composite Ti_0.75NiSb+2 mol % Fe, which is 21% higher than that of Ti_0.75NiSb. This work demonstrates that the compositing magnetic nanoparticles Fe can enhance the thermoelectric performance of Ti_0.75NiSb.