Tianhua Zou

Simultaneous enhancement in thermoelectric power factor and phonon blocking in hierarchical nanostructured β-Zn4Sb3-Cu3SbSe4

In Pb and Te-free β-Zn4Sb3 based composites incorporated with nanophase Cu3SbSe4 (∼200 nm), we concurrently realize ∼30% increase in thermoelectric power factor (PF) through an energy filtering effect caused by carrier scattering at interface barriers, and around twofold reduction in lattice thermal conductivity due to interface scattering allowing the figure of merit (ZT) to reach 1.37 at 648 K in the composite system with 5 vol. % of Cu3SbSe4. Present results demonstrate that simultaneous enhancement of PF and phonon blocking can be achieved via proper design of a material-system and its microstructures, resulting in large increase in ZT of a material-system.

Enhanced thermoelectric performance of β-Zn4Sb3 based nanocomposites through combined effects of density of states resonance and carrier energy filtering

It is a major challenge to elevate the thermoelectric figure of merit ZT of materials through enhancing their power factor (PF) and reducing the thermal conductivity at the same time. Experience has shown that engineering of the electronic density of states (eDOS) and the energy filtering mechanism (EFM) are two different effective approaches to improve the PF. However, the successful combination of these two methods is elusive. Here we show that the PF of β-Zn4Sb3 can greatly benefit from both effects. Simultaneous resonant distortion in eDOS via Pb-doping and energy filtering via introduction of interface potentials result in a ~40% increase of PF and an approximately twofold reduction of the lattice thermal conductivity due to interface scattering. Accordingly, the ZT of β-Pb0.02Zn3.98Sb3 with 3 vol.% of Cu3SbSe4 nanoinclusions reaches a value of 1.4 at 648 K. The combination of eDOS engineering and EFM would potentially facilitate the development of high-performance thermoelectric materials.

Resonant distortion of electronic density of states and enhancement of thermoelectric properties of β-Zn4Sb3 by Pr doping

The thermoelectric properties of Pr-doped compounds β-(Zn1−xPrx)4Sb3 (x = 0, 0.001, 0.002, 0.003) were investigated at the temperatures from 300 K to 615 K. The results indicate that Pr doping causes the resonant distortion of density of states of β-Zn4Sb3, as manifested by almost 2-fold increase of the density of state effective mass md* of β-Zn4Sb3, which results in ∼50 μV/K increase of the thermopower for the doped samples with x = 0.002 and 0.003. The thermal conductivity decreases substantially upon Pr doping. As a result, the figure of merit, ZT, of β-(Zn0.008Pr0.002)4Sb3 is ∼23% larger than that of the un-doped one and reaches 0.65 at 615 K, suggesting that Pr doping is an effective approach to raise ZT of β-Zn4Sb3.

Enhanced thermoelectric performance of nanostructured topological insulator Bi2Se3

To enhance thermoelectric performance by utilizing topological properties of topological insulators has attracted increasing attention. Here, we show that as grain size decreases from microns to ∼80 nm in thickness, the electron mobility μ increases steeply from 12–15 cm2 V−1 s−1 to ∼600 cm2 V−1 s−1, owing to the contribution of increased topologically protected conducting surfaces. Simultaneously, its lattice thermal conductivity is lowered by ∼30%–50% due to enhanced phonon scattering from the increased grain boundaries. As a result, thermoelectric figure of merit, ZT, of all the fine-grained samples is improved. Specifically, a maximum value of ZT = ∼0.63 is achieved for Bi2Se3 at T = ∼570 K.

Enhancement of thermopower and thermoelectric performance through resonant distortion of electronic density of states of b-Zn4Sb3 doped with Sm

Thermoelectric properties of Sm-doped compounds β-(Zn1−xSmx)4Sb3 (x = 0, 0.001, 0.002, and 0.003) (at 300-615 K) were investigated. The results indicate that Sm doping causes the resonant distortion of density of states of β-Zn4Sb3, as manifested by almost 2-fold increase in effective mass md* of β-Zn4Sb3, which results in ∼40 μV/K increase of the thermopower for all the doped samples. Besides, thermal conductivity decreases substantially by Sm doping. As a result, figure of merit ZT of β-(Zn0.008Sm0.002)4Sb3 is ∼53% larger than that of the un-doped one and reaches 1.1 at 615 K, suggesting that Sm doping is an effective approach to improve ZT of β-Zn4Sb3.

Enhancement of thermoelectric performance of β-Zn4Sb3 through resonant distortion of electronic density of states doped with Gd

The thermoelectric properties of Gd-doped β-Zn4Sb3 are investigated. The results indicate that Gd-doping not only causes a 41 μV K−1 increase in thermopower owing to resonant distortion of DOS but also results in ∼15% reduction in thermal conductivity at a doping content of 0.2%. Consequently, a largest value of ZT = 1.2 is achieved at 655 K.

Enhanced thermoelectric figure of merit in p-type β-Zn4Sb3/Bi0.4Sb1.6Te3 nanocomposites

The thermoelectric properties of Bi0.4Sb1.6Te3-based composites incorporated with β-Zn4Sb3 nanoparticles are investigated in the temperature range from 300 K to 500 K. The results show that ∼5% increase in Seebeck coefficient and ∼32% reduction of lattice thermal conductivity at 443 K are concurrently realized in the nanocomposite system with 1.3 vol% of β-Zn4Sb3, which originates from energy filtering effect as well as enhanced phonon scattering at dispersed nanoparticles and phase boundaries, respectively. As a result, the largest figure of merit ZT = 1.43 is achieved at 443 K for the sample with 1.3 vol% of β-Zn4Sb3 nanoinclusions, which is ∼18% larger than that (=1.21) of the Bi0.4Sb1.6Te3 matrix.

Recent Developments inβ-Zn4Sb3Based Thermoelectric Compounds

Thermoelectricity has been recognized as an environmentally friendly energy conversion technology due to its ability to directly achieve conversion between heat and electricity for a long time. β- has attracted considerable interest as promising thermoelectric material in the moderate temperature range (500 K–900 K), which is the temperature range of most industrial waste heat sources. In this paper, first we present the structure of β- and the traditional doping strategy used to enhance its performance. Next, we review the details of some new methods utilized for improving the thermoelectric properties of β- and its thermal stability as well as reliability. Finally, the review finishes with highlighting some promising strategies for future research directions in the material.

Optimized thermoelectric properties of AgSbTe2 through adjustment of fabrication parameters

AgSbTe2 bulk sample is obtained by hot-pressing under different fabrication parameters, and their thermoelectric properties are investigated in the temperature range of 300 - 550 K. The highest ZT = 0.86 is achieved at 475 K for the sample hot-pressed at 423 K and 500MPa due to the lower thermal conductivity and higher power factor. The results indicate that the optimized thermoelectric properties can be obtained for AgSbTe2 compound at the sintering temperature of 423 K under the pressure of 500 MPa.

Recent Developments in β-Zn4Sb3 Based Thermoelectric Compounds

Thermoelectricity has been recognized as an environmentally friendly energy conversion technology due to its ability to directly achieve conversion between heat and electricity for a long time. β- has attracted considerable interest as promising thermoelectric material in the moderate temperature range (500 K–900 K), which is the temperature range of most industrial waste heat sources. In this paper, first we present the structure of β- and the traditional doping strategy used to enhance its performance. Next, we review the details of some new methods utilized for improving the thermoelectric properties of β- and its thermal stability as well as reliability. Finally, the review finishes with highlighting some promising strategies for future research directions in the material.