Thermoelectric Performance of n‑Type Magnetic Element Doped Bi₂S₃

Thermoelectric technology offers great potential for converting waste heat into electrical energy and is an emission-free technique for solid-state cooling. Conventional high-performance thermoelectric materials such as Bi2Te3 and PbTe use rare or toxic elements. Sulfur is an inexpensive and nontoxic alternative to tellurium. However, achieving high efficiencies with Bi2S3 is challenging due to its high electrical resistivity that reduces its power factor. Here, we report Bi2S3 codoped with Cr and Cl to enhance its thermoelectric properties. An enhanced conductivity was achieved due to an increase in the carrier concentration by the substitution of S with Cl. High values of the Seebeck coefficients were obtained despite high carrier concentrations; this is attributed to an increase in the effective mass, resulting from the magnetic drag introduced by the magnetic Cr dopant. A peak power factor of 566 μW m–1 K–2 was obtained for a cast sample of Bi2–x/3Crx/3S3–xClx with x = 0.01 at 320 K, as high as the highest values reported in the literature for sintered samples. These results support the success of codoping thermoelectric materials with isovalent magnetic and carrier concentration tuning elements to enhance the thermoelectric properties of eco-friendly materials

Simultaneous Increase in Dielectric Breakdown Strength and Thermal Conductivity of Oriented UHMWPE Containing Diamond Nanoparticles

In modern electronics and devices, the miniaturization, higher power, and higher frequency trends have led to an increase in heat generation, which has become a significant limiting factor. Polymer dielectrics with high thermal conductivity are highly desired to prevent thermal breakdown caused by accumulated heat, hence extending service life and reducing device size. Much effort has been devoted to enhancing the heat conduction of polymer dielectrics for the sake of efficient heat dissipation. The most common strategy is to introduce thermally conductive and electrically insulating fillers. However, the very high filler contents needed to achieve significant values of thermal conductivity typically impair other properties, especially dielectric breakdown strength. Herein, we demonstrate that it is possible to tackle this problem by the unique combination of high thermal conductivity (27 W·m–1·K–1) and high breakdown strength (627 MV·m–1) exhibited by oriented ultra-high-molecular-polyethylene nanocomposite films containing a small amount of nanodiamonds (0.5 wt % NDs). The influence of high thermal conductivity on reducing operating temperature is explored and quantified through finite element simulation. We demonstrated that a significant reduction in equilibrium temperature (>15 K) in a wound film capacitor can be obtained with our polymer dielectric films, with thermal conductivities in the region of 20 W·m–1·K–1, while maintaining other properties like breakdown strength without compromise

Terahertz Faraday Rotation of SrFe₁₂O₁₉ Hexaferrites Enhanced by Nb Doping

The magneto-optical and dielectric behavior of M-type hexaferrites as permanent magnets in the THz band is essential for potential applications like microwave absorbers and antennas, while are rarely reported in recent years. In this work, single-phase SrFe12–xNbxO19 hexaferrite ceramics were prepared by the conventional solid-state sintering method. Temperature dependence of dielectric parameters was investigated here to determine the relationship between dielectric response and magnetic phase transition. The saturated magnetization increases by nearly 12%, while the coercive field decreases by 30% in the x = 0.03 composition compared to that of the x = 0.00 sample. Besides, the Nb substitution improves the magneto-optical behavior in the THz band by comparing the Faraday rotation parameter from 0.75 (x = 0.00) to 1.30 (x = 0.03). The changes in the magnetic properties are explained by a composition-driven increase of the net magnetic moment and enhanced ferromagnetic exchange coupling. The substitution of the donor dopant Nb on the Fe site is a feasible way to obtain multifunctional M-type hexaferrites as preferred candidates for permanent magnets, sensors, and other electronic devices