No abstract

Sb nano-precipitates, which serve to alter the vibrational frequency of localized phonon modes that facilitate inter-valley scattering, emerge in pristine InTe after addition of Sb. As a result, exponentially declined carrier mobility is promoted by nearly 50% at 723 K in InTe–Sb0.01, leading to enhanced thermoelectric performance.

the total thermal conductivity consisting of the lattice part (κ L ) and the electronic part (κ e ). [6] Some of these parameters (S, ρ, and κ e ), however, are mutually interdependent and strongly coupled by way of the carrier concentration, making it difficult to attain high TE performance (zT) without making some compromise. Fortunately, in the past decade, several general strategies have been developed to achieve high zT in various materials. [7,8] Lowering the lattice thermal conductivity (κ L ), which is relatively independent of other parameters, is a comparatively easy method. Other well-documented methods for enhancing phonon scattering include nanostructuring, [9][10][11] dislocations, [12,13] point defects, [14][15][16][17] and strong lattice anharmonicity. [18][19][20] Additional strategies to boost the power factor (S 2 ρ −1 ) include carrier concentration optimization, [21,22] band convergence, [23,24] and creating band resonance levels. [25] Typically, practical TE materials are polycrystalline structures with grain boundaries that help to maintain a low lattice thermal conductivity but inevitably also degrade the charge carrier mobility. Recently, bulk SnSe [26][27][28][29][30] and In 4 Se 3[31] single crystals have attracted increasing amounts of attention. The layered structure and strong lattice anharmonicity of these materials cause ultralow lattice thermal conductivity, independent of grain boundary phonon scattering. Therefore, such single crystalline compounds are expected to yield superior performance as both high mobility and low lattice thermal conductivity can be maintained simultaneously. For instance, the ultrahigh zT of Lead-free tin sulfide (SnS), with an analogous structure to SnSe, has attracted increasing attention because of its theoretically predicted high thermoelectric performance. In practice, however, polycrystalline SnS performs rather poorly as a result of its low power factor. In this work, bulk sodium (Na)-doped SnS single crystals are synthesized using a modified Bridgman method and a detailed transport evaluation is conducted. The highest zT value of ≈1.1 is reached at 870 K in a 2 at% Na-doped SnS single crystal along the b-axis direction, in which high power factors (2.0 mW m −1 K −2 at room temperature) are realized. These high power factors are attributed to the high mobility associated with the single crystalline nature of the samples as well as to the enhanced carrier concentration achieved through Na doping. An effective single parabolic band model coupled with first-principles calculations is used to provide theoretical insight into the electronic transport properties. This work demonstrates that SnS-based single crystals composed of earth-abundant, low-cost, and nontoxic chemical elements can exhibit high thermoelectric performance and thus hold potential for application in the area of waste heat recovery.

We present a 63Cu and 65Cu NMR study of Cu12Sb4S13, the basis for tetrahedrite thermoelectric materials. In addition to electronic changes observed at the T c = 88 K metal–insulator transition, we find that locally there are significant structural changes occurring as the temperature extends above T c, which we associate with Cu atom displacements away from symmetry positions. Spin-lattice relaxation rates (1/T 1) are dominated by a quadrupolar process indicating anharmonic vibrational dynamics both above and below T c. We used a quasiharmonic approximation for localized anharmonic oscillators to analyze the impact of Cu rattling. The results demonstrate that Cu-atom rattling dynamics extends unimpeded in the distorted structural configuration below T c and provide a direct measure of the anharmonic potential well.

No abstract

The development of new routes for the production of thermoelectric materials with low-cost and high-performance characteristics has been one of the long-term strategies for saving and harvesting thermal energy. Herein, we report a new approach for improving thermoelectric properties by employing the intrinsically low thermal conductivity of a quasi-one-dimensional (quasi-1D) crystal structure and optimizing the power factor with aliovalent ion doping. As an example, we demonstrated that SbCrSe 3 , in which two parallel chains of CrSe 6 octahedra are linked by antimony atoms, possesses a quasi-1D property that resulted in an ultra-low thermal conductivity of 0.56 W m − 1 K − 1 at 900 K. After maximizing the power factor by Pb doping, the peak ZT value of the optimized Pb-doped sample reached 0.46 at 900 K, which is an enhancement of 24 times that of the parent SbCrSe 3 structure. The mechanisms that lead to low thermal conductivity derive from anharmonic phonons with the presence of the lone-pair electrons of Sb atoms and weak bonds between the CrSe 6 double chains. These results shed new light on the design of new and high-performance thermoelectric materials.

In this study, the synthesis and thermoelectric performance of CuInTe 2 −In 2 Te 3 and Cu 0.85 Ag 0.15 InTe 2 − In 2 Te 3 solid solutions are reported. The experimental results associated with model fitting reveal that the cation vacancies generated by creating solid solutions with a compound with a smaller cation-to-anion ratio can strongly scatter phonons with high frequency, which remarkably decrease the total as well as lattice thermal conductivity of the CuInTe 2 system and finally realize an enhanced thermoelectric properties compared to the pristine sample. Furthermore, substitutional Ag/ Cu defects integrated with vacancies lead to a further reduction in lattice thermal conductivity. With the benefit from the rational defect design, a high figure of merit of 1.1 is gained at 840 K for the sample (Cu 0.85 Ag 0.15 InTe 2 ) 0.98 -(In 2 Te 3 ) 0.02 . In addition, a 188% improvement on average zT is obtained. This work provides an effective method for boosting thermoelectric performance of chalcopyrite compounds by defect engineering on multiple types of defects.

High thermal conductivity of CoSbS-based limited its own prospect application in thermoelectric energy conversion. Solid solution is an effective approach to optimize the performance of thermoelectric materials with high lattice thermal conductivity because of the enhanced phonons scattering from disorder atoms. In this paper, we have synthesized and measured the thermoelectric properties of solid solution CoSbSSe (x = 0, 0.05, 0.10, 0.15, 0.20, 0.30) series samples. The collaborative optimization (enhancing the power factors and reducing the thermal conductivities) to add zT values were realized via substitution of S atoms with the isoelectronic Se atoms in the matrix. Meanwhile, the lowest room temperature lattice thermal conductivity in CoSbS-based materials is obtained (4.72 W m K) at present. Benefiting from the results of synergistic strategy, a zT of 0.35 was achieved at 923 K for sample CoSbSSe, a 59% improvement as compared with that of the pristine CoSbS. Band calculation demonstrated that CoSbSSe present a similar band dispersion with CoSbS. The mechanism of point defect scattering for reducing the lattice thermal conductivity at room temperature, was also analyzed by the Callaway model. The contributions to decrease the room temperature lattice thermal conductivity from the mass and the strain fluctuation in the crystal are comparable. These results can also be extended to other high-efficiency thermoelectric materials with stiff bond and smaller Gruneisen parameters.