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The microstructure, oxidation state and thermoelectric transport properties of Mg and Pb co-doped p -type Bi 1–2 x Mg x Pb x CuSeO oxyselenides have been investigated. Pure single BiCuSeO phase are obtained for all the samples without preferential growth in the crystallites. X-ray photoelectron spectroscopy (XPS) results indicate that both Mg and Pb dopants are in the 2+ oxidation state whereas other than the expected Bi 3+ , higher-oxidation-state Bi ions also exist in both the pristine and doped BiCuSeO compounds. The Mg and Pb co-doping yields a remarkable enhancement in the electrical conductivity coupled with a moderate Seebeck coefficient. A pronounced increment in power factor is achieved from 2.54 μW cm −1 K −2 for the pristine BiCuSeO to 11.1 μW cm −1 K −2 for Bi 0.88 Mg 0.06 Pb 0.06 CuSeO at 750 K. In addition to increasing the power factor, Mg and Pb co-doping reduces the lattice thermal conductivity owing to the dopant-induced point defect scattering of phonon. The combination of optimized power factor and intrinsically low lattice thermal conductivity results in a high Z T of 1.19 at 750 K for Bi 0.88 Mg 0.06 Pb 0.06 CuSeO, which is about 3.1 times as large as that for the pristine BiCuSeO. [ABSTRACT FROM AUTHOR]

The thermoelectric properties and electronic structures were investigated on p -type BiCu 1- x Ag x SeO ( x =0, 0.02, 0.05, 0.08) ceramics prepared using a two-step solid state reaction followed by inductively hot pressing. All the samples consist of single BiCuSeO phase with lamella structure and no preferential orientation exists in the crystallites. Upon replacing Cu + by Ag + , maximum values of electrical conductivity of 36.6 S cm −1 and Seebeck coefficient of 350 μV K −1 are obtained in BiCu 0.98 Ag 0.02 SeO and BiCu 0.92 Ag 0.08 SeO, respectively. Nevertheless, a maximum power factor of 3.67 μW cm −1 K −2 is achieved for BiCu 0.95 Ag 0.05 SeO at 750 K owing to the moderate electrical conductivity and Seebeck coefficient. Simultaneously, this oxyselenide exhibits a thermal conductivity as low as 0.38 W m −1 K −1 and a high ZT value of 0.72 at 750 K, which is nearly 1.85 times as large as that of the pristine BiCuSeO. The enhancement of thermoelectric performance is mainly attributed to the increased density of states near the Fermi level as indicated by the calculated results. [ABSTRACT FROM AUTHOR]

Although natural silk fibers have excellent strengthand flexibility,the regenerated silk materials generally become brittle in the drystate. How to reconstruct the flexibility for silk fibroin has bewilderedscientists for many years. In the present study, the flexible regeneratedsilk fibroin films were achieved by simulating the natural formingand spinning process. Silk fibroin films composed of silk I structurewere first prepared by slow drying process. Then, the silk fibroinfilms were stretched in the wet state, following the structural transitionfrom silk I to silk II. The difference between the flexible film anddifferent brittle regenerated films was investigated to reveal thecritical factors in regulating the flexibility of regenerated silkmaterials. Compared with the methanol-treated silk films, althoughhaving similar silk II structure and water content, the flexible silkfilms contained more bound water rather than free water, implyingthe great influence of bound water on the flexibility. Then, furtherstudies revealed that the distribution of bound water was also a criticalfactor in improving silk flexibility in the dry state, which couldbe regulated by the nanoassembly of silk fibroin. Importantly, theresults further elucidate the relation between mechanical propertiesand silk fibroin structures, pointing to a new mode of generatingnew types of silk materials with enhanced mechanical properties inthe dry state, which would facilitate the fabrication and applicationof regenerated silk fibroin materials in different fields. [ABSTRACT FROM AUTHOR]