High Thermoelectric Performance in Earth-Abundant Cu3SbS4 by Promoting Doping Efficiency via Rational Vacancy Design

Sulfides are well investigated as thermoelectric materials but their performance is typically limited by low electrical conductivity. High electrical performance in Cu₃SbS₄ is reported by creating high valence vacancies, which efficiently provides multiple carriers. It is revealed from the perspective of a chemical bond by calculations that Al can serve as vacancy stabilizer as its entry into the lattice forms intensified bonds with neighboring atoms and lowers the vacancy formation energy. As a result, the average power factor of Cu₃SbS₄ with 9 wt% CuAlS₂ reaches 16.1 µW cm⁻¹ K⁻². Finally, by further addition of AgAlS₂, a peak zT of 1.3 and an average zT of 0.77 are obtained due to the reduced thermal conductivity. The attained average power factor and average zT are superior to other low-toxic thermoelectric sulfides. The findings shed light on the new strategy for creating favorable vacancies to realize high-efficiency doping in thermoelectric materials.     

LBL法制备Cu3SbS4薄膜

针对水溶液化学沉积法沉积过程复杂且难于控制的缺点,利用LBL(layer-by-layer)法,在玻璃基片上制备出了Cu3SbS4薄膜。即首先在玻璃基片上沉积Sb2S3薄膜,然后再在其上制备CuS薄膜,最后进行退火处理。探讨了薄膜的制备机理、生长速度、结构特性和光学特性。制备的薄膜为多晶Cu3SbS4(四方晶系)结构,厚度为344nm,直接光学带隙约为0.47eV。     

Thermoelectric Properties of Mn-Doped Cu2SnSe3

We report the thermoelectric properties of Mn-doped Cu₂Mn _x Sn_1?x Se₃ compound, with x ranging from 0.005 to 0.1 at temperature ranging from 80?K to 723?K. All samples maintain cubic zincblende-like structure, and no impurity phase was detected. The electrical resistivity decreases rapidly when Mn⁴⁺ replaces Sn²⁺ in the matrix. The excess Mn impurities in the x?=?0.05 and x?=?0.1 samples also affect the Seebeck coefficient. The total thermal conductivity is increased for Mn-doped samples except for the x?=?0.005 sample. In all, both power factor and figure of merit are improved by Mn doping over the entire temperature range. The ZT value of the x?=?0.02 sample reaches 0.035 at 300?K, and for x?=?0.01 reaches 0.41 at 716?K, which are comparable to the best thermoelectric performance for ternary Cu-based compounds.     

Thermoelectric Properties of Cu2HgSnSe4-Cu2HgSnTe4 Solid Solution

Copper-based semiconductors from the family Cu₂-II-IV-VI₄ have recently attracted a great deal of attention because of their promising thermoelectric (TE) properties. Polycrystalline samples from the Cu₂HgSnSe _x Te_4â?’x (x = 0, 0.8, 2, 3.2, 4) solid solution were prepared and structurally characterized by powder x-ray diffraction. The samples from this solid solution crystallize in the stannite structure (space group \(I\bar{4}2m\) ). Transport, TE, and thermal properties of hot-pressed samples are reported. About a 20 % reduction in calculated lattice thermal conductivities, compared to the lattice thermal conductivities of pure components of the alloys (i.e. Cu₂HgSnSe₄ and Cu₂HgSnTe₄), was observed for Cu₂HgSnSe₂Te₂ alloy. The maximum ZT of the Cu₂HgSnSe₂Te₂ sample reaches 0.6 at 575 K.     

Effect of Indium Substitution on the Thermoelectric Properties of Orthorhombic Cu4SnS4

We report the thermoelectric properties of Cu₄In _x Sn_1?x S₄ (x = 0–0.02), which undergoes a first-order structural phase transition at ~230 K. Substitution of In³⁺ for Sn⁴⁺ suppresses the phase transition temperature (T _t). Indium substitution reduces the electrical resistivity, and degenerate conduction by the orthorhombic phase is observed. The Seebeck coefficient increases over the whole temperature range and a maximum value occurs in the monoclinic phase as a result of indium substitution. Thermal conductivity decreases as x increases, which enhances the dimensionless figure of merit, ZT. We therefore expect optimization of the chemical composition of indium-doped Cu₄SnS₄ to result in an even larger ZT value.     

Thermoelectric Properties of Dy-Doped SrTiO3 Ceramics

Sr_1?x Dy _x TiO₃ (x?=?0.02, 0.05, 0.10) ceramics were prepared by the reduced solid-state reaction method, and their thermoelectric properties were investigated from room temperature to 973?K. The resistivity increases with temperature, showing metallic behavior. The Seebeck coefficients tend to saturate at high temperatures, presenting narrow-band behavior, as proved by ab?initio calculations of the electronic structure. The magnitudes of the Seebeck coefficient and the electrical resistivity decrease with increasing Dy content. At the same time, the thermal conductivity decreases because the lattice thermal conductivity is reduced by Dy substitution. The maximum value of the figure of merit reaches 0.25 at 973?K for the Sr_0.9Dy_0.1TiO₃ sample.     

The Effect of Cu Addition on the System Stability and Thermoelectric Properties of Bi2Te3

Cu-doped Bi₂Te₃ nanopowders with nominal composition Cu _x Bi₂Te₃ (x = 0, 0.01, 0.025, and 0.05) were synthesized by a gas-induced-reduction method using TeO₂, Bi(NO₃)₃·5H₂O and Cu(NO₃)₂·3H₂O as raw materials and then hot-pressed into bulk materials. x-Ray diffraction (XRD) analysis indicates that, when x ≠ 0, pure Cu _x Bi₂Te₃ phase was obtained, and that when x = 0, Bi₂Te₃ mixed with a small amount of Bi₂TeO₅ was obtained. Field emission scanning electron microscopy observation reveals that Cu addition significantly reduces the grain sizes of the materials. First-principle calculations show that the order of the free energies of the materials is: Cu-doped Bi₂Te₃ (substitution of Cu for Bi) < Cu intercalated Bi₂Te₃ < Bi₂Te₃. The electrical and thermal conductivities decrease and the Seebeck coefficient increases with Cu addition. The maximum figure of merit, ZT, reaches 0.67 at 500 K for a Cu_0.05Bi₂Te₃ sample.     

Thermoelectric Properties of Ca3Co4O9/[Ca2(Co0.65Cu0.35)2O4]0.624CoO2 Composites

Ca₃Co₄O₉ is one of the most promising p-type thermoelectric materials because of its high dimensionless figure of merit ZT. However, polycrystalline Ca₃Co₄O₉ ceramics shows lower ZT value than that for single crystal Ca₃Co₄O₉ due to its higher electrical resistivity ρ. Mikami et al. have reported that the addition of Ag to Ca₃Co₄O₉ ceramics could successfully reduce ρ and enhance the power factor. On the other hand, Ohtaki et al. reported that a composite structure could be highly effective to reduce κ for ZnO dually doped with Al and Ga. In this work, we tried to enhance the power factor and reduce κ by forming Ca₃Co₄O₉/[Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ composite structure. As a result, the ZT value for Ca₃Co₄O₉/[Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ composites reached 0.164 at 700 °C, which was 40 % higher than the value for Ca₃Co₄O₉.     

Thermoelectric Properties of Rare Earth-Doped SrTiO3 Nanocubes

A giant Seebeck coefficient of ?890 μV/K at 500 °C has been observed in Y_0.2Sr_0.8TiO₃ prepared using nanocubes. Doping rare earth elements, RE, has revealed that small RE is effective to enhance the Seebeck coefficient. Through soft mode observations by Raman spectroscopy and structural calculations based on density functional theory, it has been found that the breakdown of inversion symmetry of the perovskite structure near the surface of nanocubes can be recovered by doping with small RE. Because the dielectric constant is strongly related to the surface structure in this compound, we suggest that RE doping modulates the potential barrier at the grain boundary, resulting in a pronounced energy filtering effect in Y doped SrTiO₃.     

Influence of the Sintering Temperature on the Thermoelectric Properties of the Bi1.9Gd0.1Te3 Compound

Semiconductors - The regularities of the influence of the sintering temperature (750, 780, 810, and 840 K) on the elemental composition, crystal-lattice parameters, electrical resistivity, Seebeck...     

Effect of Spark Plasma Sintering Temperature on Thermoelectric Properties of Grained Bi1.9Gd0.1Te3 Compound

Semiconductors - Patterns in changes of the microstructure (grain structure) and the thermoelectric properties of the n-type grained Bi1.9Gd0.1Te3 compound, spark-plasma-sintered at different...     

Grain-Size-Dependent Thermoelectric Properties of SrTiO3 3D Superlattice Ceramics

The thermoelectric (TE) performance of SrTiO₃ (STO) 3D superlattice ceramics with 2D electron gas grain boundaries (GBs) was theoretically investigated. The grain size dependence of the power factor, lattice thermal conductivity, and ZT value were calculated by using Boltzmann transport equations. It was found that nanostructured STO ceramics with smaller grain size have larger ZT value. This is because the quantum confinement effect, energy filtering effect, and interfacial phonon scattering at GBs all become stronger with decreasing grain size, resulting in higher power factor and lower lattice thermal conductivity. These findings will aid the design of nanostructured oxide ceramics with high TE performance.