Cao Mao-Sheng

Structural and Electrical Properties of PZT/PVDF Piezoelectric Nanocomposites Prepared by Cold-Press and Hot-Press Routes

The 0-3 PZT/PVDF piezoelectric composites are prepared separately by hot-press and cold-press processes. The effects of the PZT content and the shaping-process on the composites are studied. The experimental results indicate that composites with 70% PZT nanopowders prepared by the hot-press method exhibit excellent piezoelectric and dielectric properties. The maxima of dss and e of the composites prepared by hot-press method are about 30% and 65% higher than those prepared by the cold-press method, respectively. This is mainly attributed to the favourable coupling of the two materials in the process of the hot press and the formation of the β-type PVDF, which possesses better electric properties.

Structural and electrical properties of Nd ion modified lead zirconate titanate nanopowders and ceramics

A modified sol-gel method is used for synthesizing Nd ion doped lead zirconate titanate nanopowders Pb1–3x/2NdxZr0.52Ti0.48O3 (PNZT) in an ethylene glycol system with zirconium nitrate as zirconium source. The results show that it is critical to add lead acetate after the reaction of zirconium nitrate with tetrabutyl titanate in the ethylene glycol system for preparing PNZT with an exact fraction of titanium content. It has been observed that the dopant of excess Nd ions can effectively improve the sintered densification and activity of the PNZT ceramics. Piezoelectric, dielectric and ferroelectric properties of the PNZT ceramics are remarkably enhanced as compared with those of monolithic lead zirconate titanate (PZT). Especially, the supreme values of piezoelectric constant (d33) and dielectric constant () for the PNZT are both about two times that of the monolithic PZT and moreover, the remnant polarization (Pr) also increases by 30%. According to the analysis of the structures and properties, we attribute the improvement in electrical properties to the lead vacancies caused by the doping of Nd ions.

Enhanced Ferromagnetism and Microwave Dielectric Properties of Bi0.95Y0.05FeO3 Nanocrystals

Bi0.95Y0.05FeO3 nanocrystals are synthesized by a hydrothermal method, and are crystallized in a rhombohedrally distorted perovskite BiFeO3 structure in the R3c space, with compressive lattice distortion induced by the Y substitution at Bi sites from XRD study. Compared with BiFeO3 gained under similar conditions, the magnetic properties are greatly enhanced, with saturate magnetization of 2.3emu/g at room temperature. Microwave dielectric properties of Bi0.95Y0.05FeO3 nanocrystals are investigated in the range of 2–18 GHz. The Y substitution results in the increase of permeability and decrease of permittivity, which are attributed to the enhanced spin relaxation of domain wall motion and the weakened electron-relaxation caused by decreasing Fe2+, respectively. The changes for microwave dielectric response could lead to the excellent microwave absorption due to the improvement of the impedance match between BiFeO3 and air.

Modification of Band Gap of β-SiC by N-Doping

The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1−xNx (x = 0, 1/32, 1/16, 1/8, 1/4) with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity.

Mechanical Reinforcement and Piezoelectric Properties of PZT Ceramics Embedded with Nano-Crystalline

The double-scale lead zirconate titanate (PZT) piezoelectric ceramics were prepared by the solid state processing with PZT nano-crystalline and micro-powder. The microstructures, electrical and mechanical properties of the double-scale PZT are investigated. All the sintered ceramics exhibit a single perovskite structure and the grain size of the double-scale PZT reduces due to the incorporation of PZT nano-crystalline. Compared to normal PZT, the mechanical properties increase significantly and the piezoelectric properties decrease slightly. Mechanisms responsible for the reinforcement of the double-scale PZT are discussed.

Dynamic Tensile Behavior and Fracture Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Nanowhiskers

Dynamic tensile properties of glass-fiber polymer composites embedded with ZnO nanowhiskers are investigated by a split Hopkinson tensile bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by the macroscopic and microscopic observation of fractured specimens. The strain rate effect on the mechanical behavior is discussed and a constitutive model is derived by simulating the experimental data. The experimental results show that the materials have an obvious non-linear constitutive relation and strain rate strengthening effect. The composites with ZnO nanowhiskers under dynamic loading have various failure modes and better mechanical properties.

High-Temperature Dielectric Response and Multiscale Mechanism of SiO2/Si3N4 Nanocomposites

The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300°C at 9.0 GHz are measured by the resonant cavity method. The SiO2/Si3N4 nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO2/Si3N4 on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures.

Preparation and Dielectric Properties of Nanostructured ZnO Whiskers

By a novel controlled combustion synthesis method, a large number of nanostructured ZnO whiskers with different morphologies, such as tetra-needles, long-leg tetra-needles and multi-needles, are prepared without any additive in open air at high temperature. The morphologies and crystalline structures of the as-prepared ZnO nanostructured whiskers are investigated by SEM and XRD. The possible growth mechanism on the nanostructured ZnO whiskers is proposed. The experimental results indicate that the dielectric constants and losses of the nanostructured ZnO whiskers are very low, demonstrating that the nanostructured ZnO whiskers are low-loss materials for microwave absorption in X-band. However, obvious microwave absorption in nanostructured ZnO whiskers is observed. The quasi-microantenna model may be attributed to the microwave absorption of the ZnO whiskers.

Preparation and Ferroelectric Properties of Double-Scale PZT Composite Piezoelectric Thick Film

Dense and crack-free double-scale lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT) composite piezoelectric thick films have been successfully fabricated on Au/Cr/SiO2/Si substrates by a modified sol-gel method. The XRD analysis indicates that the thick film possesses a single-phase perovskite-type structure. The SEM micrograph shows that the surface is crack-free and the cross section is dense and clear. The thickness of the PZT thick film is about 4 μm. It also exhibits good ferroelectric properties, and has high direct current compression resistant properties. At the test frequency of 1kHz, the film has the coercive field of 50 kV/cm, the saturation polarization of 54 μC/cm2 and the remnant polarization of 30 μC/cm2.

Electrical Properties of Lead Zirconate Titanate Thick Film Containing Micro- and Nano-Crystalline Particles

We report the ferroelectric, dielectric and piezoelectric properties of a dense and crack-free lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT) thick film containing micro- and nano-crystalline particles. The results show that these electrical properties are dependent strongly on the annealing temperature and film thickness. For the different-annealing-temperature and different-thickness films, the higher-annealing-temperature thicker ones show the larger remnant polarization and smaller coercive field. The dielectric results show that relative dielectric constant achieves the largest value at annealing temperature of 700°C, and increases with the increasing film thickness. For the piezoelectric properties, the longitudinal piezoelectric coefficient increases linearly with the film thickness increasing and the 4-μm-thick PZT film shows the largest value of about 200.65 pC/N. Therefore, the PZT thick films present good electric properties and enlarged potential in MEMS applications.