Xiwei Qi

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).

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.

Investigation of magnetic properties of Ni0.2Cu0.2Zn0.6Fe1.96O4–BaTiO3 composites

Abstract Composite materials with a ferromagnetic Ni 0.2 Cu 0.2 Zn 06 Fe 1.96 O 4 phase and a ferroelectric BaTiO 3 phase, x BaTiO 3 –(1− x )Ni 0.2 Cu 0.2 Zn 0.6 Fe 1.96 O 4 , in which x varies from 0 to 1, have been prepared via standard ceramics method with nanosized precursor powders. With the variation of x , typical magnetic hysteresis loops of composites have been observed in the composites at the room temperature. When the content of ferroelectric BaTiO 3 phase increases, the saturation magnetization and initial permeability decrease. Meanwhile, the coercive force tends to increase. Additionally, the cut-off frequency and quality factor of composite materials shift toward higher frequency. The simultaneous presence of nonmagnetic BaTiO 3 in composites pinned the domain wall motion, which lead to the decrease of initial permeability and the increase of cut-off frequency. Microstructure observation shows that the composites possess very fine crystalline grains.

High-frequency magnetic properties of Co-Ti substituted barium ferrites prepared by modified chemical coprecipitation method

Co-Ti substituted barium ferrites were prepared by a modified chemical coprecipitation method. Microstructures and high-frequency magnetic properties were investigated by X-ray diffraction (XRD) transmission electron microscopy (TEM) scanning electron microscopy (SEM) and measurements of complex permeability spectra. Barium ferrites with Co-Ti substitution x=1.0 have the highest permeability μ′ and the lowest magnetic resonant frequency fros and fros can be changed continuously with changing Co-Ti substitution in the hyper-frequency region while μ′′ keeps its high value at the same time. A higher sintering temperature corresponds to higher μ′ and lower fros due to the grain growth. The d.c. electrical resistivity for all samples was above 108 Ω cm.