Jinle Lan

Remarkable Enhancement in Thermoelectric Performance of BiCuSeO by Cu Deficiencies

A significant enhancement of thermoelectric performance in layered oxyselenides BiCuSeO was achieved. The electrical conductivity and Seebeck coefficient of BiCu(1-x)SeO (x = 0-0.1) indicate that the carriers were introduced in the (Cu(2)Se(2))(2-) layer by Cu deficiencies. The maximum of electrical conductivity is 3 × 10(3) S m(-1) for Bicu(0.975)Seo at 650 °C, much larger than 470 S m(-1) for pristine BiCuSeO. Featured with very low thermal conductivity (∼0.5 W m(-1) K(-1)) and a large Seebeck coefficient (+273 μV K(-1)), ZT at 650 °C is significantly increased from 0.50 for pristine BiCuSeO to 0.81 for BiCu(0.975)SeO by introducing Cu deficiencies, which makes it a promising candidate for medium temperature thermoelectric applications.

Enhanced Thermoelectric Properties of Pb-doped BiCuSeO Ceramics

A high-performance thermoelectric oxyselenide BiCuSeO ceramic with ZT > 1.1 at 823 K and higher average ZT value (ZTave ≈0.8) is obtained. The heavy doping element and nanostructures can effectively tune its electronic structure, hole concentration, and thermal conductivity, resulting in substantially enhanced mobility, power factor, and thus ZT value. This work provides a path to high-performance thermoelectric ceramics.

High-temperature electrical transport behaviors in textured Ca3Co4O9-based polycrystalline ceramics

Highly (00l) oriented Ca3Co4O9-based ceramics were fabricated by spark plasma sintering combined with a dynamic forging process. The grain orientation is effective in lowering the electrical resistivity and enhancing the thermoelectric power factor but with little influence on the Seebeck coefficient. A metallic-to-semiconducting transition temperature can be observed and the activation energy is almost independent of the La-doping. All of the Ca3Co4O9-based ceramic samples exhibit large thermoelectric power, and the figure of merit for La-doped Ca3Co4O9 sample can reach 0.26 at 975 K, which can be a promising candidate of p-type material for high-temperature thermoelectric application.

Doping for higher thermoelectric properties in p-type BiCuSeO oxyselenide

The low power factor (PF) of BiCuSeO oxyselenide inhibits further improvement on thermoelectric figure of merit in the moderate temperature range. In this Letter, we show that the electron transport properties of doped BiCuSeO oxyselenide can be accurately described in acoustic phonon scattering assumption within the framework of single parabolic band model. It is further found that the doping elements alter the electron transport properties by tuning the effective mass and deformation potential. Based on these understandings, we argue that the higher power factor can be achieved by choosing the doping element based on reducing deformation potential coefficient and decreasing effective mass.

Enhanced thermoelectric performance of a BiCuSeO system via band gap tuning

Upon 20% Te substitution, the band gap decreases from 0.8 eV to 0.65 eV. Rising temperature promotes minority carrier jumps across the band gap, thereby improving electrical conductivity. With low thermal conductivity and large Seebeck coefficients, a remarkable ZT of 0.71 at 873 K is achieved for BiCuSe0.94Te0.06O.

Enhanced thermoelectric performance of La-doped BiCuSeO by tuning band structure

Bi1−xLaxCuSeO ceramic bulks have been prepared by the spark plasma sintering method. Our results indicate that La-doping can lead to an obvious change of the band structure evidenced by the absorption spectra and electric transportation behaviors (e.g., m* and Seebeck coefficient). The variation of band structure results in a great enhancement of carrier mobility caused by a decreased energy offset between the primary and secondary valence bands. A maximum ZT value of 0.74 can be obtained in 8% La-doped BiCuSeO sample at 923 K, which is 37% higher than that of the pure BiCuSeO bulk. Our results reveal that band engineering is an effective way to enhance the thermoelectric properties of BiCuSeO system.

High-temperature electrical transport behaviors of the layered Ca2Co2O5-based ceramics

Textured Bi-substituted Ca2Co2O5 ceramics have been prepared using a coprecipitation method combined with spark plasma sintering. The Bi substitution is effective in increasing the grain orientation of the Ca2Co2O5-based ceramics (from 0.46 to 0.85). Electrical conductivity increases obviously with partial substitution of Bi3+ for Ca2+ (from 113.9 to 142.4 S/cm at 973 K). The Ca1.92Bi0.08Co2O5 sample exhibits higher power factor (4.4×10−4 W m−1 K−2) than that of pure Ca2Co2O5 (3.2×10−4 W m−1 K−2) at 973 K, indicating that the Ca2Co2O5 system is another promising p-type material for high-temperature thermoelectric applications.

Enhanced thermoelectric performance of In2O3-based ceramics via Nanostructuring and Point Defect Engineering.

The issue of how to improve the thermoelectric figure of merit (ZT) in oxide semiconductors has been challenging for more than 20 years. In this work, we report an effective path to substantial reduction in thermal conductivity and increment in carrier concentration, and thus a remarkable enhancement in the ZT value is achieved. The ZT value of In2O3 system was enhanced 4-fold by nanostructuing (nano-grains and nano-inclusions) and point defect engineering. The introduction of point defects in In2O3 results in a glass-like thermal conductivity. The lattice thermal conductivity could be reduced by 60%, and extraordinary low lattice thermal conductivity (1.2 W m−1 K−1 @ 973 K) below the amorphous limit was achieved. Our work paves a path for enhancing the ZT in oxides by both the nanosturcturing and the point defect engineering for better phonon-glasses and electron-crystal (PGEC) materials.

Enhanced thermoelectric properties in Pb-doped BiCuSeO oxyselenides prepared by ultrafast synthesis

BiCuSeO oxyselenides have been successfully fabricated by self-propagating high-temperature synthesis (SHS). Compared with the SHS process of binary or ternary alloys, thermal analysis indicates the ignition temperature of quaternary layered BiCuSeO oxyselenides approaches the second lower melting point of the compound. The ZT value of SHS-synthesized BiCuSeO is almost 1.5 times larger than that of the solid state reaction (SSR) product at 873 K. This is attributed to the existing amorphous region, nano-pores, and optimized grain size. Furthermore, with the partial substitution of Pb2+ for Bi3+, ZT was enhanced through the optimization of charge carrier concentration and band gap narrowing. This achieved a ZT of 0.91 at 873 K for Bi1−xPbxCuSeO (x = 0.04). Combining with the Debye–Callaway model analysis, the ultralow lattice thermal conductivity of BiCuSeO can potentially be derived from the synergistic effect of intrinsic point defects, efficient grain boundaries and some other mechanisms.

Biomineralization on polymer-coated multi-walled carbon nanotubes with different surface functional groups

Substrate-controlled mineralization from simulated body fluid (SBF) has been studied as a model for biomineralization and for the synthesis of bioinspired hybrid materials. The mineralization procedure is complex and the features of final minerals are affected by many factors. Surface functional groups are among them and play important roles in inducing nucleation, crystal growth and transformation. In this study, multi-walled carbon nanotubes (MWCNTs) were surface-modified with poly(acrylic acid), polyacrylamide or poly(hydroxyethyl methylacrylate), and used as templates for biomineralization. The polymer coating was gained via photo-initiated polymerization of monomers and adsorption of polymer chains onto MWCNTs in solution. Then, the modified MWCNTs with different surface functional groups were incubated in 1.5 times SBF for different times to compare the effect of carboxyl, acylamino and hydroxyl group on calcium phosphate formation. The study involved various characterizations such as morphology observation, weight increase, chemical and crystal structures of deposited minerals at different soaking time points. In all cases, carbonated calcium-deficient hydroxyapatite (CDHA) was identified after 7 days immersion. The continuously growing mineral crystals would wrap MWCNTs into spherical composite particles ultimately. However, the rates of nucleation and crystal growth depended on the type of surface functional groups, in an order of COOH>CONH2>OH. And their different charge characteristics led to different Ca/P ratios in initially formed minerals. It revealed that acylamino group, which demonstrated the lowest Ca/P ratio in nucleation stage, was helpful to obtain c-axis preferentially oriented morphology resembling the HA structure in natural bone tissue.