P-type Bi 2− x Sb x Te 3 compounds are crucial for thermoelectric applications at room temperature, with Bi 0.5 Sb 1.5 Te 3 demonstrating superior performance, attributed to its maximum density-of-states effective mass ( m *). However, the underlying electronic origin remains obscure, impeding further performance optimization. Herein, we synthesized high-quality Bi 2− x Sb x Te 3 (00 l ) films and performed comprehensive angle-resolved photoemission spectroscopy (ARPES) measurements and band structure calculations to shed light on the electronic structures. ARPES results directly evidenced that the band convergence along the Γ ¯ - M ¯ direction contributes to the maximum m * of Bi 0.5 Sb 1.5 Te 3 . Moreover, strategic manipulation of intrinsic defects optimized the hole density of Bi 0.5 Sb 1.5 Te 3 , allowing the extra valence band along Γ ¯ - K ¯ to contribute to the electrical transport. The synergy of the above two aspects documented the electronic origins of the Bi 0.5 Sb 1.5 Te 3 ’s superior performance that resulted in an extraordinary power factor of ~5.5 milliwatts per meter per square kelvin. The study offers valuable guidance for further performance optimization of p-type Bi 2− x Sb x Te 3 .

The device is based on the mechanism that the water flow will be divided into two streams with different pressure after flowing through the cylinder, and the two streams will be separated and developed, and the cycle will be repeated to form a Carmen vortex, and a bionic wedge-shaped pendulum chain structure will be placed behind the divided water flow. At the same time, the device uses the computer vision YOLO series algorithm to detect the target of scale in the pipe, and completes the scale detection in real time by capturing the screen with the camera in the head of the device to improve the scale detection and cleaning efficiency. There is also an impeller structure in the head of the device, which can run under the action of the drive module when encountering unexpected conditions, and the bionic fin part of the device will release acetic acid when the pipe is working to achieve the purpose of cleaning the scale in the pipe.

Forming solid solutions between two isostructural compounds is an important strategy of regulating thermal transport in solids and boosting thermoelectric performance of narrow gap semiconductors. However, its full potential is not reached in a large variety of systems because of the known miscibility gap. A typical example includes PbS-PbTe where a limited solubility is demonstrated for one in another. Here in this study we show that the miscibility gap between PbS and PbTe is well bridged by introducing 30 mol% PbSe. This considerably extends the solubility limit of PbTe from only ∼4 mol% in PbS to at least 16 mol% in PbS0.7Se0.3, thus remarkably reducing the lattice thermal conductivity from a solid solution point of view. More importantly, it is found that carrier mobility of PbS is negligibly affected by this heavy alloying process, which is against conventional knowledge that higher concentration of defects leads to stronger carrier scattering. Our electron localization functions (ELF) mapping calculation results suggest an increased overlap of the adjacent electron clouds and decreased periodic potential fluctuations when the miscibility gap between PbS and PbTe gets bridged by PbSe. Therefore, the strengthened chemical bond covalency of PbS upon PbSe/PbTe alloying is responsible for the well reserved carrier mobilities. The simultaneous optimization of electron and phonon transport enabled by miscibility gap engineering (also applicable to many other technologically important thermoelectric materials) greatly boosts the thermoelectric performance of n-type Ga-doped PbS, leading to an excellent peak ZT of ∼1.1 at ∼723 K together with a record high average ZT value of 0.73 (300-723 K) in the samples of Pb0.99Ga0.01S0.7-xSe0.3Tex (x ≥ 0.12).

Bi2Te3 films always exhibit n-type transport characteristics even under the Bi-rich condition, which, however, was not clarified clearly. Herein, by virtue of advanced techniques such as scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, scanning transmission electron microscopy, and x-ray photoelectron spectroscopy, we are able to identify the structural evolution on the atomic scale for Bi-rich Bi2Te3 films. The excess of Bi content will lead to the formation of p-type BiTe antisite defects; however, there is a doping limit for the excess of Bi to form BiTe antisites. Beyond this limit, the excess of Bi will form the n-type Bi2 planar defects in the van der Waals gap, the excellent electron donors, which can enhance the electron density by over one order of magnitude and up to the 1021 cm−3 range for Bi-rich Bi2Te3 films. Benefiting from the remarkable increase in the electron density and the suppression of carrier intrinsic excitations, Bi2Te3 films with Bi2 planar defects possess a much improved thermoelectric power factor, with a maximum value of 1.4 mW m−1 K−2 at 450 K, showing about 130% enhancement compared to that of the film without Bi2 intercalations. The discovery opens a new avenue to improve the thermoelectric properties of Bi2Te3 films utilizing the Bi2 planar defects.

In this study, the thermoelectric properties of group IIIA element (Al, Ga, In) doped PbS are systematically investigated. Al shows a low solubility limit (<1 mol %) in PbS, whereas Ga and In are soluble up to 2 mol %. Both experimental results and theoretical calculations suggest that Ga or In doping introduces strong gap states in PbS, which are the physical origins of enhanced effective mass and Seebeck coefficients. Meanwhile, a subtle simulation of carrier-concentration-dependent mobilities under single Kane band model clearly reveals that Ga doping significantly lowers the deformation potential of n-type PbS, whereas In does not. This lower deformation potential yields higher electrical conductivities at the same doping levels. The weakened electron phonon coupling phenomenon by Ga doping in PbS is further verified by our first-principles calculations. The rare combination of large effective mass and low deformation potential in Ga-doped PbS contributes to a high ZT value of ∼0.9 at 723 K, ∼50% higher than that of Cl-doped PbS control sample.