Papers by Author: Ji Zhou

Abstract: Dense NiCuZn ferrites consisting of fine grains were prepared by spark plasma sintering (SPS) at 750°C for 3 min under a uniaxial pressure of 15 MPa. The powders were densified to >95% of theoretical density by the SPS process, and the average grain size of the prepared NiCuZn ferrite was < 1 /m. The saturation magnetization of prepared specimens (without further annealing treatment) was approximate 50.54 emu/g, which was slightly smaller than that of 52.21 emu/g for specimens prepared by conventional sintering at 980°C for 4 h. Phase identifications indicated that prepared NiCuZn ferrite existed impurity phase (Cu2O), and Cu2O would gradually transform to CuO when annealing temperature increased.

Abstract: The effect of Co-substitution on the complex permeability of LiZn ferrite was studied. The polycrystalline ferrite samples with a composition of ((Li0.5Fe0.5)0.8Zn0.2)1-xCoxFe2.05O4, where x varies from 0 to 0.08, were prepared by solid-reaction method. The sintered samples were annealed at 490oC for 96 h to produce perminvar effect. The complex permeability was measured in the frequency range from 1 MHz to 2 GHz. The Co-substitution can enhance the real part of complex permeability (μ’). The maximum μ’ appears when x=0.02. The Co-substituted LiZn samples, especially for x=0.02 and 0.04, present resonance-type magnetic spectra obviously. The μ’ of the sample for x=0.02 increases because the damping of domain wall movement decreases after the annealing treatment. The resonance character of the annealed sample becomes even more remarkable due to its domain wall stabilization.

Abstract: Cofiring behavior of composites consisting of ferroelectric PMZNT and ferromagnetic NiCuZn ferrite was investigated via X-ray diffractometer (XRD), thermomechanical analysis (TMA) and scanning electron microscopy (SEM). Mismatch of sintered camber consisting of two layered structure of ferroelectric PMZNT and NiCuZn ferrite was observed. Mismatched sintering behavior was modified by adopting PMZNT and NiCuZn powders to form composite materials. The temperature of appearance pyrochlore phase in prepared composite materials is lower than that of sintering pure PMZNT material. The grain size of PMZNT and NiCuZn in prepared composites is smaller than that of sintering pure PMZNT and NiCuZn ferrite, respectively.

Abstract: Electromagnetic meta-materials are artificial and periodical materials which both the permittivity and permeability are simultaneously negative. Electromagnetic meta-materials represent a new concept where composite materials are designed to display particular properties. The work which we had finished includes theoretical design and numerical simulation of the structure, fabrication of the samples and measurement of the properties. We designed electromagnetic meta-materials which composed by periodic split ring resonators (SRR) based on ceramics and then researched the influence by microwave guide. It is showed that the resonance frequency of meta-materials can be adjusted by dielectric constant and thickness of ceramic substrate.

Abstract: The lithium ions doped red-emitting phosphors of (Ca,Eu)WO4 and (Ca,Eu)MoO4 were synthesized by solid-state reaction method, and their luminescent properties were investigated. The XRD patterns show that the phosphors are isostructural and share a tetragonal scheelite structure, even some lithium ions are doped. The excitation spectra consist of broad charge transfer bands in the short-wave UV region of W6+→O2- and Eu3+→O2- with three sharp lines around 395, 465 and 535 nm of the Eu3+ 4f excitation transitions. The characteristic emissions of WO4 2- and MoO4 2- are quenched absolutely and red light emission of Eu3+ exhibits predominate peak around 615 nm due to the electric dipole energy transition of 5D0→7F2. Excited with 395 nm, the evident enhanced emission of the phosphors were observed when Li+ doped in the host, which implies that the addition of some Li+ is beneficial for the energy transfer from WO4 2- or MoO4 2- to Eu3+.

Abstract: Surfactant-zirconium phosphate composites were prepared by surfactant cetyltrimethylammonium bromide intercalating to α-zirconium phosphate. The interlayer spacing of the lamellar structure was greatly expanded to 39.6 Å, as compared to 7.6 Å of α-zirconium phosphate. The molar ratio of surfactant to α-zirconium phosphate in the composites was found to be 1/1.46. The expanded interlayer separation is beneficial for complicated guest molecules intercalating to the galleries of the composites.

Abstract: Sulfide nanowire arrays have been synthesized by DC electrodeposition from an electrolyte containing S in DMSO. The AAO membrane with the barrier layer has been directly used as template in electrodeposition. The as-synthesized products are characterized by SEM, TEM and resonance Raman spectroscopy. CdS and ZnS nanowires have been obtained, respectively.

Abstract: This paper studied the dielectric performances and microstructure of the Ba-Ti-B-Si-O glass-ceramics fabricated with different methods. The experimental results showed that the pre-calcined method was an effective way to decrease the sintering temperature in glass-ceramic fabricating process, and the dielectric properties of the LTCC materials were εr ≈10, tanδ ≤ 2×10-3 (@1MHz). This study provided a composite method to fabricate LTCC for different applications that was composed of pre-calcined powders and molten powders with different ratios; Moreover, the dielectric constant and sintering performance of composite LTCC were adjustable by changing the ratio of pre-calcined powders and molten powders.

Abstract: A series of novel composites with the composition of xNiCuZn-(1-x)PZT (NiCuZn: Ni0.2Cu0.2Zn0.6Fe2O4; PZT: PbZr0.52Ti0.48O3.) were prepared by solid-state reaction methods. The presence of ferromagnetic NiCuZn ferrite phase and ferroelectric PZT phase was confirmed by XRD analysis. It was revealed that composite materials exhibit typical ferromagnetic hysteresis behaviors. With the increase of phase fraction of NiCuZn ferrite, the permeability of composites increases and the natural resonance peak appears. Meanwhile, the maximum of quality factors shifts to the lower frequency.