Xianfu Meng

The roles of Na doping in BiCuSeO oxyselenides as a thermoelectric material

The thermoelectric properties of the Bi1−xNaxCuSeO (0.0 ≤ x ≤ 0.02) system have been investigated in the temperature range 300–923 K. Na doping significantly increased the carrier concentration to ∼0.92 × 1020 cm−3 at the doping amount of x = 0.02. Furthermore, a relatively high carrier mobility and a slight Seebeck coefficient enhancement was seen, thus resulting in a high power factor of 8.0 μW cm−1 K−2 at room temperature. Coupled with a low thermal conductivity reduced by point defects scattering, this leads to a ZT of 0.91 at 923 K for Bi0.985Na0.015CuSeO which is nearly twice the value observed in pristine BiCuSeO.

Enhanced thermoelectric and mechanical properties of p-type skutterudites with in situ formed Fe3Si nanoprecipitate

In the present work, p-type skutterudites La0.8Ti0.1Ga0.1Fe3CoSb12 composite with n-type Fe3Si nanoprecipitate was fabricated via an in situ method. Both thermoelectric and mechanical properties of La0.8Ti0.1Ga0.1Fe3CoSb12/xFe3Si composites were thoroughly investigated. With the introduction of homogeneously dispersed nanosized Fe3Si in the matrix, the power factor is almost unchanged due to the counteraction between the decreased electrical conductivity and the significantly enhanced Seebeck coefficient. Simultaneously, the total thermal conductivity was decreased for samples with Fe3Si nanoprecipitate because of the reduced electronic thermal conductivity. As a result, a ZT value of about 1.2 at 700 K has been achieved for La0.8Ti0.1Ga0.1Fe3CoSb12/0.1Fe3Si sample, whose ZT value was slightly enhanced in comparison with the Fe3Si-freeLa0.8Ti0.1Ga0.1Fe3CoSb12 sample. Furthermore, the indentation fracture toughness of La0.8Ti0.1Ga0.1Fe3CoSb12/0.1Fe3Si was improved by nearly 30% compared to the Fe3Si-free skutterudites.

Contrasting the Role of Mg and Ba Doping on the Microstructure and Thermoelectric Properties of p-Type AgSbSe2

Microstructure has a critical influence on the mechanical and functional properties. For thermoelectric materials, deep understanding of the relationship of microstructure and thermoelectric properties will enable the rational optimization of the ZT value and efficiency. Herein, taking AgSbSe2 as an example, we first report a different role of alkaline-earth metal ions (Mg(2+) and Ba(2+)) doping in the microstructure and thermoelectric properties of p-type AgSbSe2. For Mg doping, it monotonously increases the carrier concentration and then reduces the electrical resistivity, leading to a substantially enhanced power factor in comparison to those of other dopant elements (Bi(3+), Pb(2+), Zn(2+), Na(+), and Cd(2+)) in the AgSbSe2 system. Meanwhile, the lattice thermal conductivity is gradually suppressed by point defects scattering. In contrast, the electrical resistivity first decreases and then slightly rises with the increased Ba-doping concentrations due to the presence of BaSe3 nanoprecipitates, exhibiting a different variation tendency compared with the corresponding Mg-doped samples. More significantly, the total thermal conductivity is obviously reduced with the increased Ba-doping concentrations partially because of the strong scattering of medium and long wavelength phonons via the nanoprecipitates, consistent with the theoretical calculation and analysis. Collectively, ZT value ∼1 at 673 K and calculated leg efficiency ∼8.5% with Tc = 300 K and Th = 673 K are obtained for both AgSb0.98Mg0.02Se2 and AgSb0.98Ba0.02Se2 samples.

Thermoelectric SnTe with Band Convergence, Dense Dislocations, and Interstitials through Sn Self-Compensation and Mn Alloying

SnTe is known as an eco-friendly analogue of PbTe without toxic elements. However, the application potentials of pure SnTe are limited because of its high hole carrier concentration derived from intrinsic Sn vacancies, which lead to a high electrical thermal conductivity and low Seebeck coefficient. In this study, Sn self-compensation and Mn alloying could significantly improve the Seebeck coefficients in the whole temperature range through simultaneous carrier concentration optimization and band engineering, thereby leading to a large improvement of the power factors. Combining precipitates and atomic-scale interstitials due to Mn alloying with dense dislocations induced by long time annealing, the lattice thermal conductivity is drastically reduced. As a result, an enhanced figure of merit (ZT) of 1.35 is achieved for the composition of Sn0.94 Mn0.09 Te at 873 K and the ZTave from 300 to 873 K is boosted to 0.78, which is of great significance for practical application. Hitherto, the ZTmax and ZTave of this work are the highest values among all single-element-doped SnTe systems.

High thermoelectric performance of p-type Cerium single-filled skutterudites by dislocation engineering

Filled skutterudites, possessing a high power factor and good mechanical properties, have attracted intensive attention for the intermediate-temperature power generation. Since n-type filled skutterudites can achieve a high peak ZT of over 1.5, it is imperative to develop their high-performance p-type counterparts for real applications. In this work, single phase p-type cerium (Ce)-filled skutterudites with dense dislocation arrays were first fabricated by the liquid phase compaction method. It was demonstrated that the dense dislocation arrays significantly reduced the lattice thermal conductivity via strain scattering. Simultaneously, there was almost no influence on the normal carrier transport process. As a result, a high peak ZT value of over 1.1 at 723 K has been obtained for the liquid phase compacted Ce0.8Fe3CoSb12 alloy, which is the record-high value among the single element-filled p-type skutterudites.