Chuanxi Xiong

A three-phase magnetoelectric composite of piezoelectric ceramics, rare-earth iron alloys, and polymer

A class of multiferroic, three-phase particulate composites of Tb–Dy–Fe alloy, lead–zirconate–titanate (PZT), and polymer are investigated, in which a small volume fraction f of Tb–Dy–Fe alloy particles are dispersed in a PZT/polymer mixture. The measured dielectric, piezoelectric, and magnetoelectric properties demonstrate that a percolation transition occurs at f∼0.12 in the composites. When f is low (e.g., f<0.07), the composites exhibit piezoelectric and increasing magnetoelectric response. In the critical f range of 0.07<f<0.12, such piezo- and magnetoelectric responses sharply drop, and equal zero at the percolation threshold, above which the composite becomes a conductor and a magnetostrictive composite only.

Enhancement of dielectric constant and piezoelectric coefficient of ceramic-polymer composites by interface chelation

Ferroelectric ceramics (e.g., lead zirconate titanate, PZT) and polymers exhibit extraordinary dielectric and piezoelectric properties and processability, respectively. It is, however, difficult to retain the ideal dielectric constant (er) and piezoelectric coefficient (d33) in their composites. Here we show that an interfacial adhesion mechanism (afforded by the chelation technique) in PZT-polymer composites can lead to a dielectric constant that is, remarkably, seven times greater than what is usually found. At frequencies below 40 Hz, the dielectric constant of the composite is higher than in PZT alone (i.e., er > 1300), and this is the first achievement of the ceramic–polymer 0–3 composites as reported. Additionally, a super-high piezoelectric coefficient (d33 > 170) is also obtained owing to the interfacial mechanism. Our finding can lead to a novel way for preparing ceramic–polymer composites with an ultrahigh dielectric constant and ultrahigh piezoelectric coefficient, which are required in many modern electric systems and energy converters.

Controlled Viscoelastic Carbon Nanotube Fluids

It is generally assumed that some qualitative factors, including high organic fraction, size, density, and surface chemistry of the core etc., will dominate the liquid-like behavior of the hybrid nanofluids. For quasi one-dimensional PEG-functionalized carbon nanotubes (PEG-CNTs), this paradigm may be quite different. Our investigations show that controlling the functional density, CNT contents, and aspect ratio of the nanopipes will extremely change the rheological properties of the nanofluids. Namely, a highly viscous longer PEG-MCNT system exhibits a liquid-like behavior throughout all the temperature range of 20−80 °C, but a low viscous shorter PEG-MCNT behaves as an elastic solid and even can give a solid−liquid transition at 56.7 °C. As we model the response of the nanofluids with a deformation mechanism governed by viscous interaction, we have 1/Jx = K × exp(−Ea/RT) (or a/x = K‘ × exp(−Ea/RT)). Then we gain a quantitative understanding of the relationship between functional density, CNT volume frac...

Uniform Nickel Vanadate (Ni3V2O8) Nanowire Arrays Organized by Ultrathin Nanosheets with Enhanced Lithium Storage Properties.

Development of three-dimensional nano-architectures on current collectors has emerged as an effective strategy for enhancing rate capability and cycling stability of the electrodes. Herein, a novel type of Ni3V2O8 nanowires, organized by ultrathin hierarchical nanosheets (less than 5 nm) on Ti foil, has been obtained by a two-step hydrothermal synthesis method. Studies on structural and thermal properties of the as-prepared Ni3V2O8 nanowire arrays are carried out and their morphology has changed obviously in the following heat treatment at 300 and 500 °C. As an electrode material for lithium ion batteries, the unique configuration of Ni3V2O8 nanowires presents enhanced capacitance, satisfying rate capability and good cycling stability. The reversible capacity of the as-prepared Ni3V2O8 nanowire arrays reaches 969.72 mAh·g−1 with a coulombic efficiency over 99% at 500 mA·g−1 after 500 cycles.

Fluxible Nanoclusters of Fe3O4 Nanocrystal-Embedded Polyaniline by Macromolecule-Induced Self-Assembly

We have prepared Fe3O4 nanocrystal-embedded polyaniline hybrids with well-defined cluster-like morphology through macromolecule-induced self-assembly. These magnetic and electrically conductive composite nanoclusters show flowability at room temperature in the absence of any solvent, which offers great potential in applications such as microwave absorbents and electromagnetic shielding coatings. This macromolecule-induced self-assembly strategy can be readily applied on the fabrication of other ion oxide/conjugated polymer composites to achieve robust multifunctional materials.

Polypyrrole-encapsulated vanadium pentoxide nanowires on a conductive substrate for electrode in aqueous rechargeable lithium battery.

Precursors of ammonium vanadium bronze (NH4V4O10) nanowires assembled on a conductive substrate were prepared by a hydrothermal method. After calcination at 360°C, the NH4V4O10 precursor transformed to vanadium pentoxide (V2O5) nanowires, which presented a high initial capacity of 135.0mA h g(-1) at a current density of 50mA g(-1) in 5M LiNO3 aqueous solution; while the specific capacity faded quickly over 50 cycles. By coating the surface of V2O5 nanowires with water-insoluble polypyrrole (PPy), the formed nanocomposite electrode exhibited a specific discharge capacity of 89.9mA h g(-1) at 50mA g(-1) (after 100 cycles). A V2O5@PPy //LiMn2O4 rechargeable lithium battery exhibited an initial discharge capacity of 95.2mA h g(-1); and after 100 cycles, a specific discharge capacity of 81.5mA h g(-1) could retain at 100mA g(-1).

Self-assembled hairy ball-like V2O5 nanostructures for lithium ion batteries

Hairy ball-like nanostructures assembled from nanowires, are synthesized by a hydrothermal method. The reaction time has a significant effect on the morphologies of the products. After calcination at 360 °C, the precursor can be transformed to hairy ball-like V2O5 nanostructures, which present an excellent electrochemical performance for lithium ion batteries.

Three-Dimensional Porous Iron Vanadate Nanowire Arrays as a High-Performance Lithium-Ion Battery

Development of three-dimensional nanoarchitectures on current collectors has emerged as an effective strategy for enhancing rate capability and cycling stability of the electrodes. Herein, a new type of three-dimensional porous iron vanadate (Fe0.12V2O5) nanowire arrays on a Ti foil has been synthesized by a hydrothermal method. The as-prepared Fe0.12V2O5 nanowires are about 30 nm in diameter and several micrometers in length. The effect of reaction time on the resulting morphology is investigated and the mechanism for the nanowire formation is proposed. As an electrode material used in lithium-ion batteries, the unique configuration of the Fe0.12V2O5 nanowire arrays presents enhanced capacitance, satisfying rate capability and good cycling stability, as evaluated by cyclic voltammetry and galvanostatic discharge-charge cycling. It delivers a high discharge capacity of 293 mAh·g(-1) at 2.0-3.6 V or 382.2 mAh·g(-1) at 1.0-4.0 V after 50 cycles at 30 mA·g(-1).

Novel aligned sodium vanadate nanowire arrays for high-performance lithium-ion battery electrodes

Sodium vanadate (Na5V12O32 or Na1.25V3O8) nanowire arrays were successfully prepared using a facile hydrothermal method with subsequent calcination. The length of the Na5V12O32 nanowire arrays on titanium foil were about 10.5 μm. The unique architecture renders a high-rate transportation of lithium ions that is attributed to their nanosized structure, active materials connected to the current collector and the high specific surface area. The Na5V12O32 nanowire arrays on titanium foil annealed at 250 °C as electrodes for lithium-ion batteries exhibit a significant capacity stability with a capacity from 339.3 to 289.7 mA h g−1 in 50 cycles at 50 mA g−1. The superior electrochemical performance demonstrated that the Na5V12O32 nanowire arrays are promising electrodes for secondary organic lithium-ion batteries.

Particle Size Dependence of the Dielectric Properties of Polyvinyledene Fluoride/Silver Composites

The dependence of the dielectric properties of micro- (m-) and nano- (n-) silver (Ag)/poly(vinylidene fluoride) (PVDF) composites on the Ag particle size was determined. The magnitude of dielectric constant and conductivity for the PVDF/n-Ag composites was much higher than that of the PVDF/m-Ag composites at the same Ag volume loading. Our results suggest that the percolative behaviors were quite different for the m- and n-systems owing to the Ag particle size effect. The dielectric property depends on the synergistic effects of interfacial area, interparticle distance, and interfacial adhesion, all of which are highly dependent on the Ag particle size. The increased interfacial area, reduced interparticle distance, and improved interfacial adhesion contributed to the better dielectric properties of the PVDF/n-Ag composites.