D. Li

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 Cu2Se/Bi0.4Sb1.6Te3 nanocomposites at elevated temperatures

Bi2Te3-based thermoelectric materials with large thermoelectric figure of merit, ZT, at elevated temperatures are advantageous in power generation by using the low-grade waste heat. Here, we show that incorporation of small proportion (0.3 vol. %) of nanophase Cu2Se into BiSbTe matrix causes an enhanced high-temperature thermopower due to elevated energy filtering of carriers and inhibition of minority transport besides enhanced phonon blocking from scattering at interfaces, which concurrently result in an ∼20% increase in the power factor and an ∼60% reduction in the lattice thermal conductivity at 488 K. As a result, ZT = 1.6 is achieved at 488 K in the composite system with 0.3 vol. % of Cu2Se. Significantly, its ZT is larger than unit in broad high-temperature range (e.g., ZT = 1.3 at 400 K and ZT = 1.6 at 488 K), which makes this material to be attractive for applications in energy harvesting from the low-grade waste heat.

Enhanced thermoelectric performance of BiSbTe-based composites incorporated with amorphous Si3N4 nanoparticles

Thermoelectric properties of BiSbTe-based composites dispersed with a small amount (<1 vol%) of amorphous Si3N4 (a-Si3N4) nanoparticles (∼25 nm) were investigated in the temperature range from 303 K to 483 K. The results indicate that with a-Si3N4 content increasing, the thermopower (S) of the a-Si3N4/BiSbTe composites increases substantially at T < ∼370 K, due to the decreased carrier concentrations and the enhanced energy-dependent scattering of the carrier at the heterojunction potential. Simultaneously, a-Si3N4 nanodispersion causes ∼20–30% reduction in thermal conductivity (κ) owing to phonon scattering of nanoparticles as well as phase boundaries. As a result, high dimensionless figure of merit (ZT) values of up to 1.20 (∼303 K) and 1.38 (∼383 K) are obtained in Bi0.4Sb1.6Te3 incorporated with only 0.44 vol% a-Si3N4 nanoparticles, demonstrating that the thermoelectric performance of the BiSbTe alloy can be improved effectively through incorporation of a-Si3N4 nanoparticles.

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.

Efficient perovskite solar cells via simple interfacial modification toward a mesoporous TiO2 electron transportation layer

Interfacial engineering toward the perovskite layer/electron transporting layer (ETL) interface has been demonstrated to be critical for achieving highly efficient perovskite solar cells (PSCs). In this work, PSCs with ETL/perovskite interfacial modification by benzoic acid derivatives are fabricated. No obvious influence of this interfacial modification on optical properties, crystal structure and surface morphology of perovskite films are found. Enhancement of the charge extracting ability of treated TiO2 and passivation toward trap states of the TiO2 surface are confirmed from transient PL spectra and EIS measurements. Besides, the effect of different groups on the para-position is also investigated. A PCE as high as 18.43% with a maximal steady-state output PCE of 17.19% has been achieved for the PSCs treated with para-Cl substituted benzoic acid.

Negative imaginary parts of complex permeability and microwave absorption performance of core double-shelled FeCo/C/Fe2.5Cr0.5Se4 nanocomposites

Cactus-shaped core double-shelled FeCo/C/Fe2.5Cr0.5Se4 nanostructures with a spiky surface were prepared by combining an arc-discharge process with a high-temperature solution chemical method, in which FeCo nanoparticles serve as the, while carbon and ferrimagnetic Fe2.5Cr0.5Se4 (FCS) are the inside and the outside shells, respectively. The magnetic properties, electromagnetic response, and microwave absorption properties of the (x)FeCo/C/FCS nanocomposites in the 1–18 GHz frequency range were investigated by changing the mass ratio x between FeCo/C and FCS. The frequency dependences of μ′′ (imaginary parts of complex permeability) and e′′ (imaginary parts of complex permittivity) of the (0 ≤ x ≤ 0.15)FeCo/C/FCS nanocomposites show distinct inverse trends of change in the high frequency ranges. Negative minimum values of μ′′ are found to be coupled with positive maxima of e′′ due to a phase lag. The bare FCS–paraffin composite starts with a minimum μ′′ of about −0.07, which shifts to −0.44 and −0.05 when the mass ratio x is increased to 0.1 and 0.15, respectively. As x increases to 0.2, all the μ′′ values of the nanocomposites become positive. The best absorption property with a reflection loss (RL) peak of −54.5 dB at 10 GHz is obtained in the (x = 0.1)FeCo/C/FCS–paraffin composite and RL exceeding −20 dB can be achieved within the 3–18 GHz frequency range by choosing an appropriate layer thickness between 1.4 and 6 mm. The contribution of the negative μ′′ response to the microwave absorption is discussed.

Magnetic Compression of Polyelectrolyte Microcapsules for Controlled Release

In this study, microcapsules with a magnetic particle as the core and polyelectrolyte multilayers as the shell were fabricated. The cavity of the microcapsules was created by etching the SiO2 layer, which was first coated on the magnetic core particle, and the size of the cavity can be adjusted by the thickness of the SiO2 layer. This magnetically responsive microcapsule deforms upon application of a constant magnetic field and results in the release of the core content, and the release velocity could be controlled by the strength of the magnetic field. This release mechanism is proactive and repeatable, combined with its localized and remote controllability; it can be a powerful tool for delivering medical agents on site.

Improved thermoelectric properties for solution grown Bi2Te3−xSex nanoplatelet composites

We herein report the large-scale synthesis of Bi2Te3−xSex (0.6 ≤ x ≤ 0.75) nanoplatelets through a hydrothermal method and subsequent spark plasma sintering. The effect of selenium alloying and the spark plasma sintering temperature on the thermoelectric properties of the Bi2Te3 nanostructured bulk materials were investigated. The results indicate that compared to samples fabricated in an autoclave, preparing Bi2Te3−xSex in glass beaker with suitable Se alloying and appropriate sintered temperature is an efficient way to reduce the lattice thermal conductivity due to a large number of Bi2TeO5 nanodots with sizes of around 10 nm. Meanwhile, a decrease in electrical resistivity due to increase in carrier mobility and an enhancement of the Seebeck coefficient attribute to decrease in carrier concentration were observed. As a result, the thermoelectric figure-of-merit, ZT, is significantly improved and the maximum value reaches 0.96 for Bi2Te2.25Se0.75 at 490 K.

Enhanced thermoelectric performance of SnSe based composites with carbon black nanoinclusions

Recently, a single crystalline SnSe and its sodium doped compound are reported to have an ultralow thermal conductivity and a high thermoelectric figure of merit. However, the highest thermoelectric figure of merit for polycrystalline SnSe-based materials is not larger than 1. In this study, we report a high thermoelectric figure of merit 1.21 at 903 K for poly-crystalline SnSe, realized by incorporating a proper proportion of carbon black as nano-inclusions. The exceptional performance arises from the enhanced power factor, coming from an increased electrical conductivity at high temperatures.

Modification of colloidal particles by unidirectional silica deposition for urchin-like morphologies

Through hydrolysis of silica precursor in an emulsion system, colloidal particles were modified by the unidirectional growth of silica rods on their surfaces, resulting in urchin-like morphologies. This strategy can be applied to various types of seed particles with different shapes and materials. The morphology of the silica rods can also be tuned.