Chunlei Wan

Electrical and dielectric behaviors of Ti3SiC2∕hydroxyapatite composites

Ti3SiC2∕Hydroxyapatite composites were prepared by spark plasma sintering. The effective dc conductivity and dielectric behavior of the composites were studied. The percolation theory was applied to demonstrate the dielectric behavior of the composites. The experimental results showed that the dielectric constant increased greatly with the Ti3SiC2 concentration, and can reach as high as 700 when the Ti3SiC2 concentration was close to the percolation threshold.

Indium-doped SnO2 nanobelts for high-performance transparent and flexible photosensors by a facile assembly

Flexible and transparent electronics is the emerging future technology for optoelectronic devices. Recently, it has attracted considerable attention from the research community due to its prodigious commercial applications. Herein, we report highly flexible and transparent ultraviolet photosensors based on indium-doped tin oxide nanobelts with enhanced simultaneous photosensitivity and recovery speed, compared to pure SnO2 nanobelts. Optoelectronic properties of the nanobelt photosensors have been found to be strongly related to the indium doping concentration and grain size of the nanobelts. A facile assembly method has been used to prepare the well-aligned nanobelt device for UV photosensors. Excellent flexible properties of the nanobelts have been explored, which show a superior response during bending tests and almost maintain their properties after 300 bending cycles. The enhanced photosensitivity of about 70 times that of undoped SnO2 nanobelts along with a highly enhanced recovery speed of less than 1.75 s have been achieved by the precise doping of In3+ into SnO2 lattice nanobelts. All these results show that our prepared photosensors demonstrate superior mechanical, electrical, and optical properties for their use in flexible and transparent electronics.

High photodetectivity of low-voltage flexible photodetectors assembled with hybrid aligned nanowire arrays

One-dimensional (1-D) hybrid nanostructures with high opto-electronic performance, flexible features, and a rationally designed device assembly have an exponentially growing demand for their use in transparent and flexible photodetectors. To meet these requirements, a cost effective and facile processing route is mandatory for their fabrication and integration into the device assembly. Herein, we have successfully assembled photodetectors from high quality well-oriented uniaxially aligned hybrid ZnO–ZnGa2O4 nanofibers. Our prepared flexible devices demonstrate outstanding performance in terms of large responsivity (1.73 × 102 A W−1), high photodetectivity (∼1.02 × 1012 Jones), and external quantum efficiency (7.10 × 104%) along with fast rise and recovery times of less than 400 and 500 ms, respectively. In addition, the prepared photodetectors have shown outstanding flexibility and stability with more than 70% retention in photosensitivity at a very small bending radius of 2 mm. The synthesized hybrid nanofibers have also shown more than 80% transparency in the visible range (400–700 nm). The assembled hybrid photodetectors indicate that ZnO–ZnGa2O4 nanofibers are highly valuable for optoelectronic devices. It is also worth emphasizing that our assembled flexible photodetectors based on hybrid nanofibers with high surface-to-volume ratio have promising applications in soft electronics and invisible optoelectronic devices.

Enhanced thermoelectric performance of Bi2Te3 through uniform dispersion of single wall carbon nanotubes

The advancement in nanostructured powder processing has attracted great interest as a cost effective and scalable strategy for high performance thermoelectric bulk materials. However, the level of technical breakthrough realized in quantum dot supperlattices/wires has not yet been demonstrated in these materials. Here, we report the first ever study on the uniform dispersion of single wall carbon nanotubes (SWCNTs) in nanostructured Bi2Te3 bulk, and their effect on thermoelectric parameters above room temperature. The Bi2Te3 based SWCNT composites were prepared through controlled powder processing, and their thermoelectric properties were finely tuned at the nanoscale by regulating various (0.5, 0.75, 1.0 and 1.5) vol% of SWCNTs in the matrix. The flexible ropes of SWCNT, making an interconnected network through the inter/trans granular positions of Bi2Te3, thus substantially change the transport properties of the composites. The perfect one-dimensional (1D) conducting structure of SWCNTs acts as a source of electrical transport through a percolating network, with significantly suppressed lattice thermal conductivity, via intensified boundary scattering. The remarkable increase in power factor is ascribed to energy filtering effects and excellent electrical transport of 1D SWCNTs in the composites. Consequently, with a considerable reduction in thermal conductivity, the figure of merit culminates in a several-fold improvement, at 0.5 vol% of SWCNTs, over pristine bulk Bi2Te3.

Effect of Uniform Dispersion of Single-Wall Carbon Nanotubes on the Thermoelectric Properties of BiSbTe-Based Nanocomposites

Thermoelectric properties of BiSbTe-based bulk nanocomposites by incorporation of single-wall carbon nanotubes (SWCNTs) in different (0.0, 0.5, 1.0 and 1.5) vol.% were investigated from 300 K to 500 K. SWCNTs were uniformly dispersed in BiSbTe via a combination of ultra-sonication, magnetic stirring and mild ball milling. Fine BiSbTe powder was formed by crushing and ball milling the lumps in an inert environment. The composites demonstrate grain boundary structures exhibiting a three-dimensional network of one-dimensional flexible SWCNTs in BiSbTe bulks. The homogenous distribution of SWCNTs in BiSbTe drastically changes the transport properties of the composites. At 0.5 vol.% of SWCNTs, the effective thermal conductivity decreases suggesting the increased phonon scattering. Meanwhile, at 1.0 vol.% and 1.5 vol.%, the conductivities of the composites somehow increases attributed to homogenous distribution of SWCNTs in the BiSbTe matrix. The increased electrical resistivity with the addition of SWCNTs implies the enhanced scattering of carriers at the grain boundaries and SWCNTs/BiSbTe interfaces. The dimensionless figure of merit somewhat decreases with the addition of 0.5 vol.% SWCNTs. The results suggest that the figure of merit can be improved by optimizing the SWCNT composition below 0.5 vol.% by adequately tailoring the thermoelectric transport.

Anisotropy of mechanical and thermal properties of perovskite LaYbO3: first-principles calculations

ABSTRACT LaYbO3 ceramic material with a perovskite structure has the advantages of a high melting point, sintering resistance and high-temperature phase stability. It is a promising candidate for a structurally and functionally integrated material. However, the anisotropy of physical properties of LaYbO3 has rarely been studied. Herein, the anisotropy of the mechanical and thermal properties of LaYbO3 was studied by first-principles calculations. The elastic coefficients, Young’s modulus, Poisson’s ratio and minimum thermal conductivity of LaYbO3 were found to exhibit anisotropic characteristics. In particular, the sound velocity of the longitudinal wave was nearly twice that of the transverse wave. Especially, the minimum thermal conductivity of LaYbO3 at high temperature was found to be as low as 0.88 W/m K, indicating that the compound has potential for use in thermal insulation applications.