Zhilun Gui

Synthesis of nanocrystalline NiCuZn ferrite powders by sol–gel auto-combustion method

Abstract A nitrate–citrate gel was prepared from metal nitrates and citric acid by sol–gel process, in order to synthesize Ni 0.25 Cu 0.25 Zn 0.50 Fe 2 O 4 ferrite. The thermal decomposition process was investigated by DTA-TG, IR and XRD techniques. The results revealed that the nitrate–citrate gel exhibits self-propagating combustion behavior. After combustion, the gel directly transformed into single-phase, nano-sized NiCuZn ferrite particles with spinel crystal structure. The synthesized powder can be densified at a temperature lower than 900°C. The sintered body possesses fine-grained microstructure, good frequency stability and high-quality factor compared to the sample prepared by conventional ceramic route.

Preparation and characterization of NiCuZn ferrite nanocrystalline powders by auto-combustion of nitrate–citrate gels

Abstract A novel nitrate–citrate gel process was used to synthesize NiCuZn ferrite powders. The thermal decomposition and combustion process of nitrate–citrate gels were investigated by using DTA-TG, IR spectra and XRD techniques. The results revealed that the nitrate–citrate gels exhibit self-propagating behavior after ignition in air at room temperature. NiCuZn ferrite powders with a particle size of 20–50 nm were directly formed after combustion. The ratio of metal nitrates to citric acid in the starting solution affects the combustion process, and then determines the particle size of the as-synthesized powder. The magnetic structure of powders was characterized using Mossbauer spectroscopy.

Ferroelectric characteristics of ytterbium-doped barium zirconium titanate ceramics

Abstract Ferroelectric characteristics of ytterbium-doped barium zirconium titanate (BZT in brief) ceramics have been investigated. It is found that ytterbium dopant greatly influences the dielectric properties of BZT ceramics. With the increase of ytterbium content, the Curie temperature is lowered by three apparent stages identified by the falling “rate”, and the relative permittivity maximum is enhanced and broadened enormously. The diffuseness of the ferroelectric phase transition for BZT is increased monotonously as well. The A/B ratio in perovskite structure plays another important role on the ferroelectric phase transition characteristics for ytterbium doped BZT. The alternation of the substitution preference of ytterbium ions for the host cations in perovskite lattice seems to account for these effects. Thanks to the modifications of ytterbium on BZT, we developed a novel Y5V dielectric material with the room temperature dielectric constant over 23,000, and the dielectric strength higher than 4.0 kV/mm under AC field, which can be used in manufacturing high voltage ceramic capacitors.

Thermally tuning of the photonic band gap of SiO2 colloid-crystal infilled with ferroelectric BaTiO3

SiO2 colloid crystal infilled with BaTiO3 was synthesized by a process of self-assembly in combination of a sol–gel technique. It is found that infilling of the fully crystallized BaTiO3 into the colloid assembly can enhance the photonic band gap significantly. In the vicinity of the ferroelectric phase transition point of BaTiO3 (100–150 °C), the photonic band gap of the assembly exhibits a strong temperature dependence. At the Curie point, the band gap has a 20 nm redshift, and the optical transmittance reaches its minimum. Such a temperature-tuning effect in the photonic band gap should be of high interest in device applications.

A simple way to prepare nanosized LaFeO3 powders at room temperature

Abstract Nanosized LaFeO 3 powders of 30 nm particle size were directly prepared by sol-gel auto-combustion at room temperature. The overall process involves three steps: formation of homogeneous sol; formation of dried gel; and combustion of the dried gel. Experiments revealed that LaFeO 3 dried gel derived from citrate and nitrate sol exhibits self-propagating combustion at room temperature once it is ignited in air. After auto-combustion, the gel directly transforms into nanosized LaFeO 3 particles. The auto-combustion was considered as a heat-induced exothermic oxidation–reduction reaction between nitrate ions and carboxyl group. Differential thermal analysis–thermogravimetry (DTA–TG) was used to study the decomposition of the precursor. The structure of the nanosized LaFeO 3 powders was characterized by X-ray diffraction (XRD).

Combined effect of preferential orientation and Zr/Ti atomic ratio on electrical properties of Pb(ZrxTi1−x)O3 thin films

Lead zirconate titanate [Pb(ZrxTi1−x)O3, PZT] thin films with various compositions, whose Zr/Ti ratio were varied as 40/60, 48/52, 47/53, and 60/40, were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel method. A seeding layer was introduced between the PZT layer and the bottom electrode to control the texture of overlaid PZT thin films. A single perovskite PZT thin film with absolute (100) texture was obtained, when lead oxide was used as the seeding crystal, whereas titanium dioxide resulted in highly [111]-oriented PZT films. The dielectric and ferroelectric properties of PZT films with different preferential orientations were evaluated systemically as a function of composition. The maximums of relative dielectric constant were obtained in the morphotropic phase boundary region for both (100)- and (111)-textured PZT films. The ferroelectric properties also greatly depend on films’ texture and composition. The intrinsic and extrinsic contributions to dielectric and ferroelectric properties were dis...

Preparation and magnetic properties of titanium-substituted LiZn ferrites via a sol-gel auto-combustion process

Abstract A series of nitrate–citrate gels were prepared from metal nitrates and citric acid via a sol-gel process, in order to synthesize titanium-substituted lithium zinc (LiZn) ferrites with composition of Li 0.5(0.4+ x ) Zn 0.6 Ti x Fe (2.2−1.5 x ) O 4 ( x ranging from 0.05 to 0.20). The thermal decomposition process was investigated by DTA-TGA, IR and XRD techniques. The dried gels can burn in a self-propagating combustion process in air to transform into single-phase, nano-crystalline ferrite particles. The low-temperature sintering was realized using the synthesized powders, and the sintered ferrites have fine-grained microstructures and excellent magnetic properties. Appropriate amounts of titanium substituted for Fe in LiZn ferrites can significantly increase the permeability value. The prepared LiZn ferrites are good materials for multilayer chip inductors.

Effect of copper on the electromagnetic properties of Mg–Zn–Cu ferrites prepared by sol–gel auto-combustion method

Abstract A novel gel auto-combustion method was used to synthesize Mg–Zn–Cu ferrite powders with compositions of (Mg 0.5− x Cu x Zn 0.5 )O(Fe 2 O 3 ) 0.98 (where x =0.20, 0.25, 0.30, 0.35, 0.40). X-ray diffraction results showed that the dried gels, synthesized from metal nitrites and citric acid, transformed directly into nano-sized ferrite particles after an auto-combustion process in air. The synthesized powders exhibited high-sintering activity, and can be sintered at temperature less than 950 °C. The low-temperature sintered Mg–Zn–Cu ferrites prepared possess good electromagnetic properties, as well as fine-grained microstructures, making them become good materials for multilayer chip inductors with high-performance and low-cost. Copper content has significant influence on the electromagnetic properties, such as initial permeability, quality factor, DC resistivity, dielectric constant and dielectric loss tangent as well as their frequency dispersion for Mg–Zn–Cu ferrites. The possible reasons that are responsible for the composition dependence of main electromagnetic properties were discussed.

Complex Y-type hexagonal ferrites: an ideal material for high-frequency chip magnetic components

Abstract The magnetic properties of complex Y-type hexaferrites series with Ba2Me2Fe12O22 (Me=Zn, Co, Cu) have been investigated. Y-type polycrystalline hexaferrite powders prepared by the solid-state reaction method were characterized by X-ray diffraction and vibrating sample magnetometer. Permeabilities of the samples were investigated using an impedance analyzer. Experimental results show that the substitution of Co for Zn leads to a decrease of saturation magnetization and an increase of magnetic anisotropy. At room temperature, saturation magnetization does not increase linearly as Zn content increases due to the effect of the thermal agitation. The saturation magnetization and magnetic anisotropy of the sample determine the variation of initial permeability. Cu additions can lower the sintering temperature distinctly as the magnetic properties debase slightly. It is shown that these materials should be promising for next generation of high-frequency chip magnetic components (including chip inductors and chip EMI filters).

Effect of Mn substitution on the magnetic properties of MgCuZn ferrites

Abstract A series of Mn substituted MgCuZn ferrites (Mg 0.2 Cu 0.2 Zn 0.6 O) (Fe 2− x Mn x O 3 ) 0.97 with x =0.00,0.01,0.03,0.05,0.07 were prepared with nanosized precursor powders synthesized by a sol–gel auto-combustion method. All the ceramic samples can be sintered at low temperature (930°C) (below the melt point of Ag (961°C)). The effect of Mn content on microstructures and magnetic properties were investigated. Experiment shows that low temperature sintered MgCuZn ferrites doped with Mn possess higher initial permeability and better grain structure than that of low temperature sintered NiCuZn ferrites prepared by the same method. Therefor, Mn doped MgCuZn ferrites should be ideal materials for high inductance multilayer chip inductor. It is thought that the variation of initial permeability of MgCuZn ferrites with the Mn substitution was attributed to the decrease of magnetostriction constant.