Showing papers by "Mao-Sheng Cao published in 2012"

Ferroferric Oxide/Multiwalled Carbon Nanotube vs Polyaniline/Ferroferric Oxide/Multiwalled Carbon Nanotube Multiheterostructures for Highly Effective Microwave Absorption

Abstract: Light-weight nanocomposites filled with carbon nanotubes (CNTs) are developed for their significant potentials in electromagnetic shielding and attenuation for wide applications in electronics, communication devices, and specific parts in aircrafts and vehicles. Specifically, the introduction of a second phase into/onto CNTs for achieving CNT-based heterostructures has been widely pursued due to the enhancement in either dielectric loss or magnetic loss. In this work, ferroferric oxide (Fe(3)O(4)) was selected as the phase in multiwalled carbon nanotube (MWCNT)-based composites for enhancing magnetic properties to obtain improved electromagnetic attenuation. A direct comparison between the two-phase heterostructures (Fe(3)O(4)/MWCNTs) and polyaniline (PANI) coated Fe(3)O(4)/MWCNTs, namely, three-phase heterostructures (PANI/Fe(3)O(4)/MWCNTs), was made to investigate the interface influences of Fe(3)O(4) and PANI on the complex permittivity and permeability separately. Compared to PANI/Fe(3)O(4)/MWCNTs, Fe(3)O(4)/MWCNTs exhibited enhanced magnetic properties coupled with increased dielectric properties. Interfaces between MWCNTs and heterostructures were found to play a role in the corresponding properties. The evaluation of microwave absorption of their wax composites was carried out, and the comparison between Fe(3)O(4)/MWCNTs and PANI/Fe(3)O(4)/MWCNTs with respect to highly efficient microwave absorption and effective absorption bandwidth was discussed.

Graphene/polyaniline nanorod arrays: synthesis and excellent electromagnetic absorption properties

Abstract: In the paper, we find that graphene has a strong dielectric loss, but exhibits very weak attenuation properties to electromagnetic waves due to its high conductivity. As polyaniline nanorods are perpendicularly grown on the surface of graphene by an in situ polymerization process, the electromagnetic absorption properties of the nanocomposite are significantly enhanced. The maximum reflection loss reaches −45.1 dB with a thickness of the absorber of only 2.5 mm. Theoretical simulation in terms of the Cole–Cole dispersion law shows that the Debye relaxation processes in graphene/polyaniline nanorod arrays are improved compared to polyaniline nanorods. The enhanced electromagnetic absorption properties are attributed to the unique structural characteristics and the charge transfer between graphene and polyaniline nanorods. Our results demonstrate that the deposition of other dielectric nanostructures on the surface of graphene sheets is an efficient way to fabricate lightweight materials for strong electromagnetic wave absorbents.

Quaternary Nanocomposites Consisting of Graphene, Fe3O4@Fe Core@Shell, and ZnO Nanoparticles: Synthesis and Excellent Electromagnetic Absorption Properties

Abstract: This paper presents for the first time a successful synthesis of quaternary nanocomposites consisting of graphene, Fe3O4@Fe core/shell nanopariticles, and ZnO nanoparticles. Transmission electron microscopy measurements show that the diameter of the Fe3O4@Fe core/shell nanoparitcles is about 18 nm, the Fe3O4 shell’s thickness is about 5 nm, and the diameter of ZnO nanoparticles is in range of 2–10 nm. The measured electromagnetic parameters show that the absorption bandwidth with reflection loss less than −20 dB is up to 7.3 GHz, and in the band range more than 99% of electromagnetic wave energy is attenuated. Moreover, the addition amount of the nanocomposites in the matrix is only 20 wt %. Therefore, the excellent electromagnetic absorption properties with lightweight and wide absorption frequency band are realized by the nanocomposites.

Phase diagram and properties of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 polycrystalline ceramics

Abstract: yPb(In1/2Nb1/2)O3–(1 − x − y)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (yPIN–(1 − x − y)PMN–xPT) polycrystalline ceramics with morphotropic phase boundary (MPB) compositions were synthesized using columbite precursor method. X-ray diffraction results indicated that the MPB of PIN–PMN–PT was located around PT = 0.33–0.36, confirmed by their respective dielectric, piezoelectric and electromechanical properties. The optimum properties were found for the MPB composition 0.36PIN–0.30PMN–0.34PT, with dielectric permittivity ɛr of 2970, piezoelectric coefficient d33 of 450 pC/N, planar electromechanical coupling kp of 49%, remanent polarization Pr of 31.6 μC/cm2 and TC of 245 °C. According to the results of dielectric and pyroelectric measurements, the Curie temperature TC and rhombohedral to tetragonal phase transition temperature TR–T were obtained, and the “flat” MPB for PIN–PMN–PT was achieved, indicating that the strongly curved MPB in PMN–PT system was improved by adding PIN component, offering the possibility to grow single crystals with high electromechanical properties and expanded temperature usage range (limited by TR–T).

Polymer/carbon nanocomposites for enhanced thermal transport properties – carbon nanotubes versus graphene sheets as nanoscale fillers

Abstract: Light-weight composite materials of superior thermal transport properties are important to thermal management and other applications. Carbon nanomaterials with their high thermal conductivities have been widely pursued for such a purpose. Specifically, carbon nanotubes have been shown both theoretically and experimentally to possess extraordinarily high thermal conductivities at the individual nanotube level, and thus are logically considered as ideal fillers for highly thermally conductive polymeric nanocomposites. However, the predicted dramatically enhanced thermal transport in polymers upon the incorporation of carbon nanotubes has not yet materialized. Recently, graphene research has brought new opportunities to the development of polymer/carbon nanocomposites of high thermal conductivities, with already some successful uses of exfoliated graphite sheets as nanoscale fillers. In this work poly(vinyl alcohol) (PVA) was selected as the polymer matrix for the dispersion of single-walled carbon nanotubes (seamlessly with PVA functionalization and solubilization) vs. few-layer graphene sheets as nanoscale carbon fillers for a more direct comparison on the thermal transport performance in the resulting nanocomposites. The effect of aligning the nanotubes embedded in the nanocomposite films via mechanical stretching was also evaluated. Implications of the comparison between the nanotubes and nanosheets with respect to their potentials in thermally conductive polymeric nanocomposites are discussed.

Investigation of Ternary System PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 with Morphotropic Phase Boundary Compositions

Abstract: (1 − x )Pb(Sn 1− y Ti y )O 3 – x Pb(Mg 1/3 Nb 2/3 )O 3 ( x = 0.1–0.4, y = 0.45–0.65) ternary system was prepared using two-step columbite precursor method. Phase structure of the synthesized ceramics was studied by using X-ray powder diffraction and the morphotropic phase boundary (MPB) curve of the ternary system was confirmed. The isothermal map of Curie temperature ( T C ) in the phase diagram was obtained based on the dielectric–temperature measurements. The coercive field E C and internal bias field E i were found to increase with increasing PT content, while decrease with increasing PMN content. The optimum properties were achieved in the MPB composition 0.8Pb(Sn 0.45 Ti 0.55 )O 3 –0.2Pb(Mg 1/3 Nb 2/3 )O 3 , with dielectric permittivity ɛ r , piezoelectric coefficient d 33 , planar electromechanical coupling k p , mechanical quality factor Q m and T C of being on the order of 3040, 530pC/N, 55.5%, 320 and 190 °C, respectively, exhibiting potential usage for high power application.

Piezoelectric properties of PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics

Abstract: (1 – x)Pb(Hf1–yTiy)O3–x Pb(Mg1/3Nb2/3)O3 (x = 01 ∼ 025, y = 0555) ternary piezoelectric ceramics were prepared using the two-step precursor method Morphotropic phase boundary (MPB) compositions, located at x = 018 ∼ 022, were confirmed using X-ray diffraction and by their dielectric, piezoelectric and ferroelectric properties The optimum dielectric and piezoelectric properties were achieved for the MPB composition 08Pb(Hf0445Ti0555)O3–02Pb(Mg1/3Nb2/3)O3, with dielectric permittivity er, piezoelectric coefficient d33, planar electromechanical coupling kp and Curie temperature TC being on the order of 2800, 680 pC/N, 70% and 276 °C, respectively Of particular significance is that the new ternary ceramics exhibit comparable piezoelectric and electromechanical properties to commercial PZT5H ceramics, but with much improved TC, showing a potential for applications at elevated temperature (© 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

Light-weight nanocomposite materials with enhanced thermal transport properties

Abstract: Polymeric nanocomposite materials that are highly thermally conductive are important to a variety of applications, with examples ranging from fl exible radiators in space to high-performance aircrafts and vehicles and to cutting-edge electronics. Among widely used nanoscale fi llers in the development of these materials are carbon nanotubes and graphene sheets. As concluded in previous reviews, the performance of carbon nanotubes for imparting high thermal conductivity into polymeric matrices was generally poor. Here recent results associated with the effort on signifi cant performance improvements are reviewed as an update. By contrast, graphene sheets have emerged as effective nanoscale fi llers for polymeric nanocomposites of excellent thermal transport performance, reaching levels that are competitive to those achieved by metals. The signifi cant recent results on thermally conductive polymeric nanocomposites with graphene sheets are highlighted, and their potential applications and issues on their further performance improvements are discussed.

The Comprehensive Retrieval Method of Electromagnetic Parameters Using the Scattering Parameters of Metamaterials for Two Choices of Time-Dependent Factors

Abstract: The electromagnetic parameters (permittivity and permeability) method, retrieved from the reflection and transmission coefficients of a slab, is presented. Improvements over existing methods, including the determination of the permittivity, permeability and impedance of the slab, are expressed as explicit functions of the S parameters for both the time-dependent factors, eiωt and e−iωt (ω is the angular frequency of the incident electromagnetic wave), and the proper selection of the sign of impedance and the real part of the refractive index. Moreover, based on the retrieving method, the calculations of the electromagnetic parameters of the conventional-material teflon slab standard sample through the experimental data of the S parameters are performed, which confirm the validity of the technique for the retrieval of electromagnetic parameters.

Effects of Nb2O5 addition on the microstructure, electrical, and mechanical properties of PZT/ZnO nanowhisker piezoelectric composites

Abstract: Nb2O5-modified PZT/ZnO nanowhisker (denoted as PZT/ZnOw–Nb2O5) piezoelectric composites were prepared by a solid state sintering technique. Effects of Nb2O5 addition on the microstructure, electrical, and mechanical properties of the PZT/ZnOw composites were investigated. With increasing Nb2O5 content, the grain size of the composites was reduced and the fracture mode changed from intergranular to intragranular gradually. Compared with the PZT/ZnOw composites, the dielectric, piezoelectric, and ferroelectric properties of the PZT/ZnOw–Nb2O5 composites were improved significantly, while mechanical properties were enhanced slightly. The optimum electrical and mechanical properties were achieved for the PZT/ZnOw composites modified with 0.75 wt% Nb2O5 sintered at 1150 °C, with dielectric permittivity er, piezoelectric coefficient d 33, planar electromechanical coupling k p, remnant polarization P r, fracture toughness K IC, and flexural strength σf being on the order of 4930, 600 pC/N, 0.63, 29.2 μC/cm2, 1.56 MPa m1/2 and 130 MPa, respectively. The Nb2O5-modified PZT/ZnOw piezoelectric composites, with comparable electrical properties and improved mechanical properties than those of commercial PZT-5H ceramics, are promising candidates for further applications.

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

Abstract: We report the ferroelectric, dielectric and piezoelectric properties of a dense and crack-free lead zirconate titanate (Pb(Zr052Ti048)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 20065 pC/N Therefore, the PZT thick films present good electric properties and enlarged potential in MEMS applications

Electronic scattering leads to anomalous thermal conductivity of n-type cubic silicon carbide in the high-temperature region

Abstract: This study simulates thermal conductivity via a carrier scattering mechanism and the related parameters are obtained based on first principles for intrinsic and doped silicon carbide (SiC) over a temperature range of 300-1450 K. The theoretical analysis results show that the thermal conductivity decreases with increasing temperature along each orientation for both cubic SiC (3C-SiC) and doped SiC. Compared with traditional calculations, the thermal conductivity of doped SiC is larger than that of intrinsic SiC in the high-temperature region. In particular, the n-type thermal conductivity is higher than the p-type thermal conductivity because of the scattering probability between electrons and the ionization impurity increasing with the temperature. Our studies are important to a further understanding of thermal transportation.

High-Temperature Permittivity and Data-Mining of Silicon Dioxide at GHz Band

Abstract: The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO2/SiO2) nano-composites is studied on the basis of the multi-scale theoretical model. We obtain the permittivity of the SiO2/SiO2 at high temperature, which is dependent on the temperature by data-mining. The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones. The high-temperature permittivity can be well predicted for SiO2/SiO2 by the as-proposed model and the data-mining method.

Radiative recombination model of degenerate semiconductor and photoluminescence properties of 3C-SiC by P and N doping

Abstract: Based on radiative recombination theory, we have established a recombination model that can be used to calculate photoluminescence (PL) intensity for degenerate semiconductors. Using this model and density functional theory, we calculated photoluminescence excitation (PLE) and PL spectra of intrinsic 3C-SiC, P-doped SiC and N-doped SiC. The violet or near ultraviolet PLE peaks were found to be observed in PLE spectra for Sin−1PCn and SinNCn−1 (n = 4, 8, 12, and 16). Compared to intrinsic 3C-SiC, doped 3C-SiC exhibits higher PL peaks which for P-doped SiC are in the indigo spectral region, near the 3C-SiC’s peak, and for N-doped SiC appear in the green. The phenomena are studied through analyses of band structure, carrier concentration, and absorption. For doped 3C-SiC, the PL properties are mainly improved by the band-gap transformation from indirect to direct and the increase in carrier concentration near the Fermi level.

Micro-Nanometer Parasitic Crystal Growth and Photoluminescence Property of Unique Screw-Cone Like Zn 2 GeO 4 -ZnO by Combustion Oxidization

Abstract: screw-cone-like Zn2GeO4-ZnO particles with a base diameter of approximately 400 nm and a height of 400–800 nm or so were successfully synthesised by combustion oxidation of zinc and germanium powder at 960°C. No catalyst or carrier gases were used. XRD and SEM analyses reveal that Zn2GeO4 and ZnO grew to parasitic crystals evenly in interaction with each other. EDS images exhibit the homogeneity of the distribution of Ge and Zn. The formation mechanism is discussed and attributed to the unique growth process of the screw-cone-like Zn2GeO4-ZnO particles and its vapour-solid (VS) growth mechanism. In addition, the Zn2GeO4-ZnO particles could tune the energy level structure of nano-tetrapod ZnO, which leads to the emission peak redshift from 376 nm to 435 nm and enhances the light emission intensity in the visible light region.

Preparing and Ferroelectrical Properties of PZT Nanoparticle Modified PZT Thick Film by Alternately Spinning Technique

Abstract: The present work focused on the study of preparing processes and the ferroelectric properties of a crack-free and PZT nanoparticle modified PZT thick film by alternately spinning technique. With the increase of the annealing temperature, Pr increased and Ec changed inconspicuously. When the thickness of PZT thick film increased, Ec decreased but Pr increased. For the 4μm-thick film, Ec and Pr were 23 kV/cm and 60 μC/cm2，respectively. The results also confirmed that the alternately spinning technique not only improved the film thickness, but also solved the membrane surface roughness problem of the thick film prepared by PZT 0-3 composite sol method.

Study on Preparation and Dielectric Properties of Nano Ni/SiC Composite Particles

Abstract: In order to alleviate the glomeration of nanometer (SiC)p and improve its compatibility and performance, the chemical plating method was applied to get high-quality surface modification, and achieve the Ni/SiC composite particles. The dielectric and absorbing properties of the Ni/SiC particles were studied. The results showed that the modified SiC particles is nearly spherical, homogeneous morphology, and has a distinct core and shell parts. The different contrast of the shell indicated that more Ni is deposited on the (SiC)p surface, and the silicon carbide-nickel core-shell structure is formed. The dielectric constant, dielectric loss and magnetic permeability of the Ni/SiC composite particles have significant improvements compared with those of the original one. The dielectric constant rises about 24%, and R reaches -25.15dB when magnetic permeability up to 16.11GHz.