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This study prepared Bi2Te3 single crystals and investigated the thermoelectric properties of Bi2Te3 based on the electronic structure and formation energy of point defects which are calculated by density functional theory.

Environmentally friendly BiFeO3 capacitors have a great potential for applications in pulsed-discharge and power conditioning electronic systems because of its excellent intensity of spontaneous polarization (Ps). Herein, (0.7-x)BiFeO3-0.3BaTiO3-xNaTaO3+0.3wt%MnO2 (abbreviated as...

Cu 1.8 S-based thermoelectric (TE) materials have garnered considerable interest due to their pollution-free, lowcost, and superior performance characteristics. However, high Cu vacancy and Cu migration inhibit their performance and electrical stability improvement. Through mechanical alloying and spark plasma sintering, a series of Cu 1.8 S and Mn x Cu 1.8 -S 0.5 Se 0.5 (0.01 ≤ x ≤ 0.06) bulk samples were prepared in this study. With Se alloying and Mn doping, the configuration entropy of Mn x Cu 1.8 S 0.5 Se 0.5 increases from low-entropy 0.4R * for pristine Cu 1.8 S to medium-entropy 1.2R * for Mn x Cu 1.8 S 0.5 -Se 0.5 . Mn x Cu 1.8 S 0.5 Se 0.5 subsequently crystallized in a cubic phase with enhanced symmetry and Mn solid solubility. High solubility enables the filling of excessive Cu vacancies, the reduction of carrier concentration, the adjustment of band structure, the enhancement of the Cu migration energy barrier, and the inhibition of Cu migration. Even at current densities exceeding 25 A cm −2 at 750 K, the resistance of Mn 0.03 Cu 1.8 S 0.5 Se 0.5 remained hardly changed, indicating a vastly improved electrical stability. In addition, the ultralow thermal conductivity of the lattice is achieved by decreasing the sound velocity and softening the lattice. At 773 K, the bulk ZT of Mn 0.06 Cu 1.8 S 0.5 Se 0.5 reaches a maximum of 0.79, which is twice that of pure Cu 1.8 S. The results indicate that combining entropy engineering and Cu vacancy engineering is an effective strategy for developing high-performance Cu 1.8 S TE materials.

Copper sulfides (Cu2–x S) have become potential thermoelectric (TE) materials because of their high element abundance, low toxicity, and high performance. A series of Cu1.8–2x Bi2x S1–3x Se3x (0 ≤ x ≤ 0.03) bulks were fabricated using mechanical alloying and spark plasma sintering. The main Cu1.8S phase was obtained in all compositions of 0 ≤ x ≤ 0.03, and marginal Cu1.96S and Cu2S phases were detected at 0.02 ≤ x ≤ 0.03, which is attributed to the volatilization of sulfur and selenium. Benefiting from the introduced extra electronics by Bi3+ doping, the carrier concentration was optimized in 2.31×1021 cm–3. Multiscale defects introduced by Bi–Se co-doping, including secondary phases, micropores, and point defects (BiCu ••, SeS ×, and VS ••), strongly scattered the phonons, leading to a drastically decreased thermal conductivity from 2.71 W m–1 K–1 for Cu1.8S at 773 K to 0.80 Wm–1 K–1 for Cu1.74Bi0.06S0.91Se0.09. A maximum ZT of 0.78 was achieved for Cu1.74Bi0.06S0.91Se0.09 at 773 K, which is 144% higher than that of Cu1.8S (0.32). The current stress test confirms that Bi doping could improve the stability of Cu1.8S by suppressing the Cu ion migration. Our work demonstrates that Bi–Se co-doping is an effective way to enhance the TE properties for Cu1.8S.