No abstract

Bi2Te3-based compounds are important near room temperature thermoelectric materials with commercial applications in thermoelectric modules. However, new routes leading to improved thermoelectric performance are highly desirable. Incorporation of superparamagnetic nanoparticles was recently proposed as a means to promote the thermoelectric properties of materials, but its feasibility has rarely been examined in mainstream thermoelectric materials. In this study, high quality single-crystalline Bi2Te2.7Se0.3 nanoplates and Ni nanoparticles were successfully synthesized by solvothermal and thermal decomposition methods, respectively. Bulk nanocomposites consisting of Bi2Te2.7Se0.3 nanoplates and superparamagnetic Ni nanoparticles were prepared by spark plasma sintering. It was found that incorporation of Ni nanoparticles simultaneously increased the carrier concentration and provided additional scattering centers, which resulted in enlarged electric conductivities and Seebeck coefficients. The greatly improved ZT was achieved due to the increase in power factor. Spark plasma sintered bulk nanocomposites of Bi2Te2.7Se0.3 nanoplates incorporated by 0.4 mol %Ni nanoparticles (in molar ratio) showed a figure-of-merit ZT of 0.66 at 425 K, equivalent to 43% increase when compared to pure Bi2Te2.7Se0.3 nanoplates. The results revealed that incorporation of magnetic nanoparticles could be an effective approach for promoting the thermoelectric performance of conventional semiconductors.

Thermal-assistant is considered potentially as an effective approach to improve machinability of hard and brittle materials. Understanding the material removal and friction behaviour influenced by the purposely introduced heat is crucial to obtain high quality machined surface. This paper aims to reveal material removal and friction behaviours of RB-SiC ceramics scratched by a Vickers indenter at elevated temperatures. Material removal mode, scratching hardness, critical depth of ductile-brittle transition, scratching force and friction were discussed under different penetration depths. Size effect of scratching hardness was used to assess the plastic deformation at elevated temperature. A modified model was established to predict the critical depth at elevated temperatures by taking into account of the changes of mechanical properties. The results revealed that the material deformation and adhesive behaviour enhanced the material removal in ductile regime and the coefficient of friction at elevated temperatures.

Based on two syntactic dependency treebanks built with two different styles of Chinese, a statistical study is conducted regarding word-frequency and distributions. We extracted three grammatical words as the research objects and analyzed their network features, including all degree, out-degree, in-degree, all closeness, in-closeness, out-closeness and betweenness. Then these three nodes were removed from the networks. We recorded and compared the network features of the two original networks and the three networks from which one node is respectively removed, including the number of vertices, average degree, average path length, diameter, the number of isolated vertices, domain and density. The results show that all three function words are central nodes of the Chinese syntactic networks but have different status. Their influence to the overall structure is also quite different. The research not only provides a new method for the study about Chinese grammatical words but also provides a new way of thinking the node characteristics in the complex network.