Jin Hai-Bo

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.

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.

Microwave Absorption Properties of Ni-Foped SiC Powders in the 2?18 GHz Frequency Range

Ni-doped SiC powder with improved dielectric and microwave absorption properties was prepared by self-propagating high-temperature synthesis (SHS). The XRD analysis of the as-synthesized powders suggests that Ni is accommodated in the sites of Si in the lattice of SiC, which shrinks in the presence of Ni. The experimental results show an improvement in the dielectric properties of the Ni-doped SiC powder in the frequency range of 2–18 GHz. The bandwidth of the reflection loss below −10 dB is broadened from 3.04 (for pure SiC) to 4.56 GHz (for Ni-doped SiC), as well as the maximum reflection loss of produced powders from 13.34 to 22.57 dB, indicating that Ni-doped SiC could be used as an effective microwave absorption material.

Deposition Behavior and Mechanism of Ni Nanoparticles on Surface of SiC Particles in Solution Systems

Ni-deposited SiC particles are prepared successfully by a facile chemical reaction approach. The structure and morphology analyses demonstrate the Ni nanoparticles have been deposited on the surface of SiC particles. The deposition behavior of Ni on the surface of SiC particles is investigated. Pd-Sn catalytic nuclei formed in the pretreatment process promote the redox reaction and lead to the reduction of Ni2+ to metal nickel. Moreover, the kinetic mechanism of the reaction process of Ni2+ and H2PO?2 has also been discussed in detail. Kinetic models have been established.

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

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.

First Principle Study of the Electronic Properties of 3C-SiC Doped with Different Amounts of Ni

The electronic properties of 3C-SiC doped with different contents of Ni are investigated by using first-principles calculations. It is observed that the non-filled impurity energy levels in the band-gap region increase with increasing Ni content, which subsequently results in an enhancement of electrical conductivity of 3C-SiC. This enhancement in conductivity is verified by the conductivity spectrum in which new peaks appear in the middle-infrared region, visible region, and middle-ultraviolet region. It is further observed that the width and intensity of these newly appeared peaks increase with the increase of Ni content. The electronic density of states exhibits the peaks crossing the Fermi level, which favors the electronic transitions and proves Ni-doped 3C-SiC to be a half-metallic semiconductor. Through the analysis of electron density difference and Mulliken overlap population, it is found that the covalent bonds are formed between Ni and near-by C atoms. These features confirm that the Ni-doped 3C-SiC semiconductor is a promising material for device applications in modern day electronics.

Different Roles of a Boron Substitute for Carbon and Silicon in β-SiC

The first-principles numerical simulation is employed to calculate the effect of replacement of carbon and silicon with boron on the electronic structure and optical properties of β-SiC. Mulliken analysis shows that the B impurity bond lengths shrink in the case of BSi, while they expand with reference to BC. In addition, BSi contains C—C, Si—Si and B—Si bonds. The calculated results show that the two systems of BC and BSi apply different dispersion. BC is in accordance with the Lorentz dispersion theory while BSi follows the Drude dispersion theory. Theoretic analysis and quantitative calculation are used for conductivity spectra in the infrared region.

Effects of Oxygen Vacancy on Optical and Electrical Properties of ZnO Bulks and Nanowires

Based on the generalized gradient approximation (GGA) in density functional theory (DFT) and using the first-principle plane wave ultrasoft pseudopotential method, we construct and optimize the structures of intrinsic and oxygen vacancy (VO) ZnO bulks and nanowires (NWs) in the Castep module. Moreover, the calculation of band structures and the optical properties are carried out. The calculated results exhibit that the oxygen vacancy exerts a more significant influence on the electronic structures of the ZnO bulks instead of the NWs. What is more, the influences of the VO on the optical properties are mainly embodied in the ultraviolet region, and the main optical parameters of ZnO bulks and NWs with VO are anisotropic.

Structures and electrical properties of pure and vacancy-included ZnO NWs of different sizes*

The structures and electronic properties of ZnO nanowires (NWs) of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy (VO) exerts a more evident influence on the band gap of the ZnO NWs. However, the effect will be weakened with the increase of the diameter. In addition, the energy band shifts downward due to the existence of VO and the offset decreases with the reduction of the VO concentration. As the concentration of surface Zn atoms decreases, the conduction band shifts downward, while 2p electrons are lost in the oxygen vacancy, resulting in the split of valence band and the formation of an impurity level. Our findings agree well with the previous observations and will be of great importance for theoretical research based on ZnO NWs.

Effects of N doping on photoelectric properties of along different directions of ZnO bulk and nanotube

The electronic structures and optical properties of N-doped ZnO bulks and nanotubes are investigated using the first-principles density functional method. The calculated results show that the main optical parameters of ZnO bulks are isotropic (especially in the high frequency region), while ZnO nanotubes exhibit anisotropic optical properties. N doping results show that ZnO bulks and nanotubes present more obvious anisotropies in the low-frequency region. Thereinto, the optical parameters of N-doped ZnO bulks along the [100] direction are greater than those along the [001] direction, while for N-doped nanotubes, the variable quantities of optical parameters along the [100] direction are less than those along the [001] direction. In addition, refractive indexes, electrical conductivities, dielectric constants, and absorption coefficients of ZnO bulks and nanotubes each contain an obvious spectral band in the deep ultraviolet (UV) (100 nm ~ 300 nm). For each of N-doped ZnO bulks and nanotubes, a spectral peak appears in the UV and visible light region, showing that N doping can broaden the application scope of the optical properties of ZnO.