High efficiency Bi2Te3-based thermoelectric materials and devices with energy conversion efficiencies of up to 6.0% under a temperature gradient of 217 K.

No abstract

Electrical and thermal transportation properties of a novel structured 3D CNT network have been systematically investigated. The 3D CNT net work maintains extremely low thermal conductivity of only 0.035 W/(m K) in standard atmosphere at room temperature, which is among the lowest compared with other reported CNT macrostructures. Its electrical transportation could be adjusted through a convenient gas-fuming doping process. By potassium (K) doping, the original p-type CNT network converted to n-type, whereas iodine (I(2)) doping enhanced its electrical conductivity. The self-sustainable homogeneous network structure of as-fabricated 3D CNT network made it a promising candidate as the template for polymer composition. By in situ nanoscaled composition of 3D CNT network with polyaniline (PANI), the thermoelectric performance of PANI was significantly improved, while the self-sustainable and flexible structure of the 3D CNT network has been retained. It is hoped that as-fabricated 3D CNT network will contribute to the development of low-cost organic thermoelectric area.

Polycrystalline SnSe was synthesized by a melting-annealing-sintering process. X-ray diffraction reveals the sample possesses pure phase and strong orientation along [h00] direction. The degree of the orientations was estimated and the anisotropic thermoelectric properties are characterized. The polycrystalline sample shows a low electrical conductivity and a positive and large Seebeck coefficient. The low thermal conductivity is also observed in polycrystalline sample, but slightly higher than that of single crystal. The minimum value of thermal conductivity was measured as 0.3 W/m·K at 790 K. With the increase of the orientation factor, both electrical and thermal conductivities decrease, but the thermopowers are unchanged. As a consequence, the zT values remain unchanged in the polycrystalline samples despite the large variation in the degree of orientation.

The crystal grain size can be quantitatively calculated by Scherrer equation according to the diffraction peak broadening in the XRD curves. Actually, the results calculated by the Scherrer equation are the thickness that perpendicular to the crystal planes. However, in the actual XRD measurements, the broadening of the diffraction peaks is not only because of the Micro‐level changes of crystal such as grain size and lattice distortion, but also due to the instrumental broadening. Thus, the Scherrer equation is less reliable if the full width at half maximum caused by the physical broadening is smaller than that caused by the instrumental broadening. In this paper, it is concluded that the applicable range of the Scherrer equation will increases with the increasing diffraction angle. As an example of Scherrer equation's application, the calculation result for the maximum applicable scope of Si(100) films is 137 nm.

Effective synthesis of rare-earth nickelates with various rare earth compositions enriches their thermistor functionality in addition to their metal to insulator transitions.

The discovery of hydrogen-induced electronic phase transitions in strongly correlated materials such as rare-earth nickelates has opened up a new paradigm in regulating materials’ properties for both fundamental study and technological applications. However, the microscopic understanding of how protons and electrons behave in the phase transition is lacking, mainly due to the difficulty in the characterization of the hydrogen doping level. Here, we demonstrate the quantification and trajectory of hydrogen in strain-regulated SmNiO3 by using nuclear reaction analysis. Introducing 2.4% of elastic strain in SmNiO3 reduces the incorporated hydrogen concentration from ~1021 cm−3 to ~1020 cm−3. Unexpectedly, despite a lower hydrogen concentration, a more significant modification in resistivity is observed for tensile-strained SmNiO3, substantially different from the previous understanding. We argue that this transition is explained by an intermediate metastable state occurring in the transient diffusion process of hydrogen, despite the absence of hydrogen at the post-transition stage.

For filled skutterudites, element Yb is one of the most common and important fillers. However, the optimal carrier concentration range in Y bxCo4Sb12 filled skutterudites has not been determined as a result of the low Yb filling fraction limit. In this study, a non-equilibrium fabrication process (MS-SPS process), consisting of a melt-spinning method and a spark plasma sintering technique, has been applied to prepare Y bxCo4Sb12 samples. The Yb filling fraction is successfully extended to 0.35, which provides the possibility to clarify the optimal carrier concentration range for Yb-filled skutterudites. High carrier concentrations, with a maximum of around 1 × 1021 cm−3, were achieved in the MS-SPS Y bxCo4Sb12 samples due to the significantly enhanced Yb filling fractions. The phase compositions, lattice parameters, electrical and thermal transport properties of the MS-SPS Y bxCo4Sb12 samples with high carrier concentrations were systematically investigated. An optimal carrier concentration range of around 5 ∼ 6 × 1020 cm−3, corresponding to the actual Yb filling fraction of around 0.21∼0.26, has been determined, which displays the highest thermoelectric performance in Y bxCo4Sb12 thermoelectric materials.