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This study focuses on the effect of Cu doping on the thermoelectric properties of BiSbTe3 (BST) alloys. Firstly, we successfully prepared high-quality BST alloys using the KCl solvent method and selected the most promising BST(KCl)3.5 sample from them, followed by Cu doping experiments. The experimental results show that Cu doping significantly improves the crystal quality and density of the alloy, thereby increasing the material's mobility and reducing the resistivity, leading to an improvement in the power factor. However, Cu doping also introduces a large number of dislocations and lattice distortions. Additionally, the highly doped samples contain Cu2Te and BST superlattice structures, which further enhance the scattering of heat transfer phonons, significantly reducing the lattice thermal conductivity. In the experiment, Cu-doped samples exhibited extremely low lattice thermal conductivity, as low as 0.32 W m−1 K−1 at 300 K. These improvements in structure and performance have greatly enhanced the thermoelectric efficiency of Cu-doped samples, leading to a significant increase in their ZT values. Particularly, in samples with a Cu doping level of x = 0.01, the maximum ZT value was 1.47 at 400 K, and the average ZT value reached 1.28 in the temperature range of 300 K to 450 K. These findings underscore the wide-ranging application potential of Cu-doped BiSbTe3 alloys in room temperature refrigeration and power generation. The study provides crucial insights into the characteristics of Cu-doped BiSbTe3 alloys, while also contributing to the optimization of thermoelectric material design and the advancement of sustainable energy conversion technologies. [ABSTRACT FROM AUTHOR]

In this study, Bi2Se3 thermoelectric materials with high density, low thermal conductivity, and excellent thermoelectric performance are prepared using a Se slow-release method. It was found that the number of Se defects in the material could be effectively reduced by changing the content of NaCl solvent, and a certain number of Na atoms are introduced into the Bi2Se3 matrix. The carrier concentration of Bi2Se3 is greatly optimized due to the synergistic effect of the two, leading to a gradual increase in the Seebeck coefficient from −94 to −122 μV K−1 at room temperature. Simultaneously, we conducted an in-depth investigation into the effects of Na doping and Se vacancies on the electronic structure of the materials. Our findings indicate that the presence of these two defects gives rise to resonance energy levels and sharpens the density of state peaks near the Fermi level. This discovery further underscores the potential for enhancing thermoelectric performance. Finally, the Bi2Se3(NaCl)10 sample achieved the maximum ZT value of 0.69 at 550 K, and the average ZT within the temperature detection range reached 0.36, increasing the thermoelectric performance of the material. [ABSTRACT FROM AUTHOR]

Rhombohedral β-Zn4Sb3 is a promising thermoelectric material in the medium-temperature range due to its excellent properties. In this paper, Na/Mg co-doped β-Zn4Sb3 crystals with high thermoelectric performance are researched. The acquired crystals exhibit p-type conduction with carrier concentration changes from 18.6 × 1019 cm−3 to 9.6 × 1019 cm−3, and the carrier mobility varies from 22.3 cm2 V–1 s–1 to 19.7 cm2 V–1 s–1 at room temperature. Compared with the sample without Mg-doping, the sample with x = 0.1 shows a high Seebeck coefficient. The thermal conductivity is as low as 0.78 W m–1 K–1 at 630 K. Ultimately, the maximum dimensionless figure-of-merit value obtained is ~ 1.58 at 630 K, 12% higher than the peak value (~ 1.41 at 690 K) of the Na-doped sample. The results provide an efficient approach to improving thermoelectric performance through other diatomic doping, and it could also be applied to other thermoelectric materials. [ABSTRACT FROM AUTHOR]

In this study, based on the stoichiometric ratio of Sm: Ba: Ga: Sn = x: 8 − x: 16: 50 (x = 0, 0.25, 0.5, 0.75, 1, 1.5, 2), Sm-doped type-VIII single-crystalline clathrate SmxBa8−xGa16Sn30 thermoelectric material was successfully prepared via Sn-flux method. The electrical properties were investigated by the measurement of conductivity, Seebeck coefficient and Hall coefficient. The results show that the solubility of Sm in type-VIII Ba8Ga16Sn30 is very low, and the lattice constant of the samples containing Sm decreases compared with type-VIII Ba8Ga16Sn30. However, for all samples containing Sm, the lattice constant increases with the increase of the initial content of Sm. Sm plays a "modulation" framework atoms ratio role in the cage compound. Moreover, the carrier mobility of the sample is greatly improved by Sm doping. The related electrical properties exhibit irregular changes with the increase of the initial content of Sm. The sample with x = 0.75 consistently shows high Seebeck coefficient and conductivity in the 300-600 K test temperature range. The maximum power factor is 2.25 × 10−3 W/mK2 near 442 K, indicating that the energy band structure is optimized, while the conductivity is improved. The ZT value is estimated to be 1.31 at 457 K. [ABSTRACT FROM AUTHOR]

In this study, β-Zn4Sb3 was prepared using the Zn-NaCl mixed-flux method based on the stoichiometric ratio of Zn/Sb/NaCl = (4−x):3:(7+x) (x = 0, 0.1, 0.2, 0.3). X-ray diffraction results showed that all samples were hexagonal rhombic crystal structures with the space group R 3 ¯ c . A second phase of ZnSb was detected in the samples with x = 0.2 and x = 0.3. In addition, the crystal-cell volume and lattice parameter of all samples increased for the larger ion radius of Na+ than Zn2+. The transmission electron microscopy image and corresponding area electron diffraction pattern demonstrated that the prepared samples had a complete crystal structure. All samples had hole conduction and exhibited p-type conduction behavior. The carrier concentration of the material increased with increased Na content and decreased Zn, ranging from 8.89 × 1019 cm−3 to 17.82 × 1019 cm−3. Moreover, the thermal conductivity (κ) of x = 0–0.2 samples decreased with increased Na content; however, the sample with x = 0.3 had a higher κ owing to the appearance of a ZnSb phase. Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point. Eventually, the sample with the nominal composition of β-Zn3.8Sb3NaCl7.2 achieved a ZT value of 1.43 at 690 K. [ABSTRACT FROM AUTHOR]

Cu2Se is a promising "phonon liquid–electron crystal" thermoelectric material with excellent thermoelectric performance. In this work, Cd-doped Cu2–xSeCdx (x = 0, 0.0075, 0.01, and 0.02) samples were prepared using NaCl flux method. The solubility of Cd in Cu2Se at room temperature was less than 6%, and a second phase of CdSe was found in the samples with large initial Cd content (x = 0.01 and 0.02). Field-emission scanning electron microscopic image showed that the arranged lamellae formed a large-scale layered structure with an average thickness of approximately 100 nm. Transmission electron microscopy demonstrated that doping of Cd atoms did not destroy the crystal integrity of Cu2Se. A small amount of Cd in Cu2Se could reduce the electrical and thermal conductivities of the material, thus significantly enhancing its thermoelectric performance. With the increase in Cd content in the sample, the carrier concentration decreased and the mobility increased gradually. Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point. Excessive Cd doping led to the emergence of the second phase of CdSe in the sample, thus significantly increasing the thermal conductivity of the material. A maximum ZT value of 1.67 at 700 K was obtained in the Cu1.9925SeCd0.0075 sample. [ABSTRACT FROM AUTHOR]

In this study, a nano-layered Cu2Se high-performance material is successfully grown using a NaCl-flux method based on the stoichiometric ratios of Cu2Se(NaCl)x (x = 1.5, 2, 2.5, 3, and 3.5). X-ray diffraction results show that samples possess an α-phase structure for 1.5 ≤ x ≤ 2.5, whereas samples consist of a mixture of β- and α-phase structures for x ≥ 3. Electron probe microanalysis results present that almost no Na or Cl atoms were found in all the samples. Meanwhile, the actual composition is close to the nominal composition of Cu2Se when 1.5 ≤ x ≤ 2.5, whereas it deviates from the nominal composition when x ≥ 3. The valence values of Cu and Se atoms are +1 and −2 in the sample, respectively. Transmission electron microscopy results prove that the crystals prepared using the NaCl-flux method have a good quality. The field emission scanning electron microscopy image shows that the samples prepared using the NaCl-flux method have a stacking nano-layered structure with an average thickness of approximately 110 nm. These thin lamellar crystals have several grain boundaries, which can effectively scatter the phonon and thus result in ultra-low lattice thermal conductivity. Cu2Se(NaCl)2.5 exhibits the best thermoelectric performance among all the samples because it has the lowest thermal conductivity. The maximum ZT value reaches 1.42 at 700 K, which is much higher than those prepared using fast melt-quenching (∼0.88 at 700 K), spark plasma sintering (∼0.8 at 700 K) and high-temperature and high-pressure synthesis (∼1.13 at 700 K). [ABSTRACT FROM AUTHOR]