No abstract

The effects on transition critical temperature, lattice parameters, critical current density, and flux pinning of doping MgB2 with carbon nanoparticles, were studied for bulk, wire and tape under a wide range of processing conditions. Under the optimum conditions, magnetic Jc was enhanced by two orders of magnitude at 5 K for a field of 8 T, and by a factor of 33 at 20 K for a field of 5 T for bulk samples, whereas enhancement by a factor of 5.7 was observed in the transport Ic at 12 T and 4.2 K for a wire sample. Samples sintered at high temperature (900 and 1000 °C) exhibited excellent Jc, approximately 10 000 A cm−2 in fields up to 8 T at 5 K. This result indicates that flux pinning was enhanced by the carbon substitution for B with increasing sintering temperature. Highly dispersed nanoparticles are believed to enhance the flux pinning directly, in addition to the introduction of pinning centres by carbon substitution. Nano-C is proposed to be one of the most promising dopants besides SiC and CNT for the enhancement of flux pinning for MgB2 in high fields.

hollow nano-micro hierarchical microspheres (NCM-HS) are synthesized using MnCO 3 both as a self-template and Mn source. The hollow microspheres with diameters of about 1 mm have walls about 250 nm thick, which are composed of approximately 100 nm primary nanoparticles. NCM-HS cathodes have an initial discharge capacity of 212 mA h g À1 at 0.1 C between 2.5 and 4.5 V. After 40 charge-discharge cycles, the capacity retention at 0.1 C is 85.1%. At higher rates, the reversible capacities of the NCM-HS cathodes are 208.9 (0.5 C), 204.8 (1 C), 180.7 (2 C), 155.7 (5 C) and 135.9 mA h g À1 (10 C). The high performances can be attributed to the distinctive hollow microspherical structures with the 100 nm building blocks, which could effectively reduce the path of Li ion diffusion, increase the contact area between electrodes and electrolyte and buffer the volume changes during the Li ion intercalation/deintercalation processes. † Electronic supplementary information (ESI) available: SEM images and XRD proles of MnCO 3 and MnO 2 microspheres, XPS prole of NCM-HS, SEM image of NCM-bulk, one more TEM image of NCM-HS, the rst ve cyclic voltammetry (CV) curves of NCM-HS cathode. See

Two-dimensional (2D) multicomponent transition-metal oxide nanosheets are the most promising candidate in low-cost and eco-friendly energy storage/conversion applications. Their surface-enhanced properties and synergic effects are fascinating, yet still underdeveloped. Here, we first report the highquality ultrathin 2D nanosheets of ZnCo 2 O 4 synthesized on a large scale via microwave-assisted liquidphase growth coupled with a post annealing procedure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness, suggesting a high surface atom ratio with an unique surface and electronic structure, thus facilitating the charge transfer to enhance the overall performances in electrochemical reaction. When used as anode materials for lithium ion batteries, the ultrathin ZnCo 2 O 4 nanosheets exhibit a high reversible lithium storage capacity of 930-980 mA h g À1 at 200 mA g À1 current density in 200 cycles with an excellent cycling stability and good high-rate capability. Even more importantly, we have extended the facile method for the formation of other analogue nanosheets including binary and ternary transition metal oxides (NiO, Co 3 O 4 , NiCo 2 O 4 , and CuCo 2 O 4 ) and make a possibility in exploring more unique properties and promising commercial applications.

We have synthesized antiperovskite manganese nitrides Mn3(Cu0.6SixGe0.4−x)N, (x=0–0.2) and investigated their negative thermal expansion (NTE) in the temperature range of 80–300 K. We found that the transition temperature of NTE moves toward lower temperature region and as well the NTE operation-temperature window (ΔT) becomes broader with increasing Si content. Typically, the giant low-temperature NTE coefficient identified in Mn3(Cu0.6Si0.15Ge0.25)N reaches as large as −16×10−6 K−1, and its ΔT reaches as wide as 100 K. The magnetic properties of these compounds were measured and correlated with the broadened NTE operation-temperature window. The present discovery highlights the potential applications of NTE materials in cryogenic engineering.