Yuanbing Mao

Polyaniline-tungsten oxide metacomposites with tunable electronic properties†

Polyaniline (PANI) nanocomposites reinforced with tungsten oxide (WO3) nanoparticles (NPs) and nanorods (NRs) are fabricated via a facile surface-initiated-polymerization (SIP) method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations reveal the uniform coating of polymer on the filler surface and a good dispersion of the nanofillers within the polymer matrix. Unique negative permittivity is observed in pure PANI and its nanocomposites. The switching frequency (frequency where real permittivity switches from negative to positive) can be easily tuned by changing the particle loading and filler morphology. Conductivity measurements are performed from 50∼290 K, and results show that the electron transportation in the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH well explains the dielectric response of the metacomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposites with the addition of nanofillers as compared to that of pure PANI.

Electrical and dielectric properties of polyaniline–Al2O3 nanocomposites derived from various Al2O3 nanostructures

Four Al2O3 nanostructures (i.e. nanofiber, nanoplatelet, nanorod and nanoflake) have been successfully synthesized via hydrothermal procedures followed by a dehydration process. Subsequently, polyaniline (PANI) nanocomposites incorporating these four Al2O3 nanostructures have been fabricated using a surface initialized polymerization (SIP) method. Both TEM and SEM are used to characterize the morphologies of the Al2O3 nanostructures and PANI/Al2O3 nanocomposites. X-Ray diffraction results reveal that the morphology of the nanofiller has a significant effect on the crystallization behavior of the PANI during polymerization. The electrical conductivity and dielectric permittivity of these nanocomposites are strongly related to both the morphology of the filler and the dispersion quality. Temperature-dependent-conductivity measurements from 50–290 K show that the electron transportation of the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH is well correlated to the dielectric response of these nanocomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results reveal an enhanced thermal stability of the PANI/Al2O3 nanocomposites as compared to that of pure PANI due to the strong interaction between the nanofillers and polymer matrix. The mechanism of the SIP method is also elaborated in this work.

Optical nanocrystallography with tip-enhanced phonon Raman spectroscopy

Conventional phonon Raman spectroscopy is a powerful experimental technique for the study of crystalline solids that allows crystallography, phase and domain identification on length scales down to approximately 1 microm. Here we demonstrate the extension of tip-enhanced Raman spectroscopy to optical crystallography on the nanoscale by identifying intrinsic ferroelectric domains of individual BaTiO(3) nanocrystals through selective probing of different transverse optical phonon modes in the system. The technique is generally applicable for most crystal classes, and for example, structural inhomogeneities, phase transitions, ferroic order and related finite-size effects occurring on nanometre length scales can be studied with simultaneous symmetry selectivity, nanoscale sensitivity and chemical specificity.

Three-dimensional ZnO@MnO2 core@shell nanostructures for electrochemical energy storage

Three-dimensional (3D) ZnO@MnO2 core@shell branched nanowire arrays exhibit five times higher areal capacitance, better rate performance and smaller inner resistance than their nanowire array counterparts. These novel 3D architectures offer promising designs for powering microelectronics and other autonomous devices on exceptionally small geometric scales.

Synthesis and characterization of submicron single-crystalline Bi2Fe4O9 cubes

Single-crystalline, submicron-sized Bi2Fe4O9 cubes of reproducible shape have been successfully prepared using a facile, large-scale solid-state reaction employing a molten salt technique in the presence of a nonionic surfactant. The role of surfactant as well as alterations in the molar ratio of Bi3+ to Fe3+ precursors have been examined under otherwise identical reaction conditions and correlated with the predictive formation of different shapes of Bi2Fe4O9 products. Extensive structural characterization of as-prepared samples has been performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), Mossbauer spectroscopy, and X-ray diffraction (XRD). Magnetic measurements were obtained using a superconducting quantum interference device (SQUID).

Shape control and spectroscopy of crystalline BaZrO3 perovskite particles

Rational control over the shape of perovskite metal oxides has been achieved for single-crystalline BaZrO3 particles through a convenient, simplistic, large-scale molten salt synthetic methodology. The evolution of particle morphology from predominantly cubes to a mixture of cubes and spheres and finally to solely spheres has been demonstrated by increasing annealing/reaction times at suitable annealing temperatures, all other parameters being equal. Rationally controlling the shape of perovskite oxides is of great importance due to their strongly structure-dependent physical properties. As-prepared, rare-earth ion-doped submicron-scale samples possess a noticeably higher photoluminescence (PL) efficiency as compared with bulk, and in particular, spheres evince a better PL signal as compared with cubes.

Synthesis of classes of ternary metal oxide nanostructures

Nanoscale structures, such as nanoparticles, nanorods, nanowires, nanocubes, and nanotubes, have attracted extensive synthetic attention as a result of their novel size-dependent properties. Ideally, the net result of nanoscale synthesis is the production of structures that achieve monodispersity, stability, and crystallinity with a predictable morphology. Many of the synthetic methods used to attain these goals have been based on principles derived from semiconductor technology, solid state chemistry, and molecular inorganic cluster chemistry. We describe a number of advances that have been made in the reproducible synthesis of various ternary oxide nanomaterials, including alkaline earth metal titanates, alkali metal titanates, bismuth ferrites, ABO(4)-type oxides, as well as miscellaneous classes of ternary metal oxides.

Synthesis and characterization of multiferroic BiFeO3 nanotubes.

Multiferroic bismuth ferrite (BiFeO(3)) nanotubes have been synthesized using a modified template methodology and characterized by a number of techniques, including XRD, SEM, TEM, HRTEM as well as EDX and SAED.

Fibrous cellulose membrane mass produced via forcespinning for lithium-ion battery separators

In this study, fibrous cellulose membranes were successfully mass produced by forcespinning® cellulose acetate, followed by alkaline hydrolysis treatment. Its performance as lithium-ion battery separator was evaluated. The cellulose membrane exhibits a randomly-oriented, fully-interconnected and highly porous three-dimensional fibrous network structure with a high porosity of 76xa0%. The developed membranes show good electrolyte wettability and high electrolyte uptake capability. Differential scanning calorimetry and thermal treatment show a superior thermal stability of the cellulose nonwoven membrane. Compared to commercially available polypropylene based separators, the developed fibrous cellulose membrane displays higher ionic conductivity, lower interfacial resistance and better electrochemical stability. Given its outstanding thermal characteristics and excellent electrochemical performance, this fibrous cellulose membrane has potential to be used as high-performance lithium-ion battery separator. This study provides a novel and feasible pathway for developing promising separators for high-performance lithium ion batteries.

Observation of Fano asymmetry in Raman spectra of SrTiO3 and CaxSr1−xTiO3 perovskite nanocubes

Bulk SrTiO3 is cubic and not expected to exhibit any first-order Raman scattering. However, nanocubes of SrTiO3 with an edge length of 80±10nm show strong first-order Raman scattering originating from the breaking of symmetry caused by frozen surface dipoles (local tetragonality) and the presence of nanoscopic polar domains (arising from incorporated impurities). Rapid polarization fluctuations within these nanoscopic ferroelectric regions interfere with a polar phonon, resulting in a Fano-like asymmetric line shape in these SrTiO3 nanocubes, as well as in Ca0.3Sr0.7TiO3 nanocubes.