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Previous reports about the thermal conductivities of VO showed various temperature dependences across metal-insulator transition (MIT) temperature. In this work, polycrystalline VO samples were fabricated by spark plasma sintering of VO powder. Temperature dependences of their thermal conductivities were investigated using laser flash technique, and the thermal conductivity showed a significant decrease trend from metal-phase to insulator phase. Electrical transport properties were investigated to confirm both carrier and lattice contribution to the thermal conductivity. It is found that the lattice thermal conductivity decreased significantly across MIT point, which may be caused by soft phonon mode in metal phase of VO. [ABSTRACT FROM AUTHOR]

Bioactive tricalcium silicate ceramics (CaSiO) were fabricated by spark plasma sintering (SPS), and their sinterability and mechanical properties were examined. The bioactivity and in vitro biocompatibility of CaSiO ceramics were evaluated. CaSiO ceramics show higher density and superior mechanical properties compared with those prepared by conventional pressureless sintering. In addition, hydroxyapatite was induced to form on the surface of CaSiO ceramics when soaked in simulated body fluid and bone marrow mesenchymal stem cells were attached and spread well on the ceramics. CaSiO ceramics fabricated by SPS possess excellent mechanical properties, bioactivity, and biocompatibility and are promising bone repaired materials. [ABSTRACT FROM AUTHOR]

A convenient top-down method for preparation of Bi2Se0.3Te2.7crystalline nano-particles has been demonstrated. It contains two steps: (1) lithium was intercalated between the van der Waals bonded quintuple-layers by electrochemical process inside lithium ion batteries with precisely controlled speed and amount; (2) subsequent alcohol exposure of LixBi2Se0.3Te2.7to make the intercalated Li atoms explode like atom-scaled bombs and exfoliate the original micro/macro scaled materials into nano-scaled single crystalline particles with sizes around 10 nm. The intercalation process does not cost external energy, and can be scaled up by amplification of the intercalation devices. [ABSTRACT FROM AUTHOR]

Lithium intercalation and de-intercalation processes have been used to fabricate bulk Bi2Se0.3Te2.7with internal nanostructures. The doped Li content can be precisely controlled through this method. It provides a chance to directly optimize electrical properties when preparing nano-structured materials, leading to the optimum carrier concentration for improved thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

Abstract: Composite glass coating was fabricated on thermoelectric (TE) skutterudite (SKD) materials by using the dispersion system of modified nano-silica aerogel and micro glass powder. The organosilane was used as the binder in the slurry-blade process and isolated pores in micrometer size are formed due to the decomposition of polymerization product derived from organosilane and nano-silica aerogel particles at high temperature. These pores can effectively decrease the thermal conductivity of coating layer. The composite glass coating shows good stability at 823K in air. However, significant microstructural changes in the coating were observed after aging at 923K, at which the isolated micro-sized pores grew to sub-millimeter pores while the continuous composite glass coating was still maintained. The glass coated skutterudite materials show good oxidation resistance, i. e. no oxides are observed even after heating at 923K in ambient air. The present glass-coating approach is expected to be applied in fabricating skutterudite-based thermoelectric devices. [Copyright &y& Elsevier]

Abstract: Silica-based composite coatings with dispersion of glass or alumina granular particles were fabricated on n-type Yb0.3Co4Sb12 and p-type CeFe3CoSb12 skutterudite (SKD) thermoelectric (TE) materials using hybrid silica sol as raw material which was synthesized through hydrolysis and condensation under acid condition process. The dispersion of either glass particles or alumina particles restrained the formation of micro-cracks during solidification due to relaxing tremendous cohesive stress in the gel. The high temperature stability for both the coating materials and the coated skutterudite matrix were investigated through thermal aging at 873K in vacuum. Inter-diffusion of Sn from glass toward SKDs and Sb from SKDs toward coating layer was observed in the glass particle dispersed silica composite coating, which resulted in the failure of protecting function of the coating layer. In the alumina particle dispersed silica coating, neither diffusion nor reaction between the coating and SKD materials was observed after thermal aging at 873K. The sublimation of antimony is suppressed in the SKDs overlaid by the alumina dispersed silica composite coating. [Copyright &y& Elsevier]

Abstract: Bioactive beta-dicalcium silicate ceramics (β-Ca2SiO4) were fabricated by spark plasma sintering (SPS). The relative density of as-prepared β-Ca2SiO4 ceramics reached 98.1% when sintered at 1150°C, leading to great improvement in bending strength (293MPa), almost 10 times higher than that of the specimen prepared by conventional pressureless sintering (PLS). High fracture toughness (3.0MPam1/2) and Vickers hardness (5.8GPa) of β-Ca2SiO4 ceramics were also achieved by SPS at 1150°C. The simulated body fluid (SBF) results showed that β-Ca2SiO4 ceramics had a good in vitro bioactivity to induce hydraxyapatite (HAp) formation on their surface, which suggests that β-Ca2SiO4 ceramics are promising candidates for load-bearing bone implant materials. [Copyright &y& Elsevier]

Abstract: n-type filled skutterudite Yb0.26Co4Sb12 composites in which p-type GaSb nanostructured inclusions (5–20nm) were dispersed were fabricated by an in situ method involving the introduction of metastable void-filling impurity Ga and enrichment of Sb in the synthesis procedure. With the homogeneously dispersed GaSb nanoinclusions, which probably result from the scattering of low-energy electrons by the GaSb-related boundary energy barriers, the power factor is enhanced due to the significant enhancement of the Seebeck coefficient. The total thermal conductivity was decreased with the depression of electronic thermal conductivity. As a result, the dimensionless thermoelectric figure of merit ZT value was improved over a wide working temperature range of 300–850K, and the expected optimal thermal-electric conversion efficiency ηopt 15.0% was obtained for the Yb0.26Co4Sb12/0.2GaSb nanocomposite. [Copyright &y& Elsevier]

Abstract: Fully dense graphene nanosheet(GNS)/Al2O3 composites with homogeneously distributed GNSs of thicknesses ranging from 2.5 to 20nm have been fabricated from ball milled expanded graphite and Al2O3 by spark plasma sintering. The percolation threshold of electrical conductivity of the as-prepared GNS/Al2O3 composites is around 3vol.%, and this new composite outperforms most of carbon nanotube/Al2O3 composites in electrical conductivity. The temperature dependence of electrical conductivity indicated that the as-prepared composites behaved as a semimetal in a temperature range from 2 to 300K. [Copyright &y& Elsevier]