Abstract: The Ginzburg-Landau theory on ferroelectrics with random field induced by dipole defects is
studied using Monte Carlo simulation in order to investigate the possible dipole clustering and freezing
behaviors as well as the dielectric relaxation of relaxor ferroelectrics. The dipole clustering above the
transition temperature and the cluster-freezing far below this temperature are identified. The intrinsic
correspondence between dipole-clustering/freezing and the multi-peaked time-domain distribution of
dielectric relaxation is established.
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: 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: A novel ceramic synthesis technique, microwave-assisted process was investigated for the
production of Barium Hexagonal ferrite (BaFe12O19) powders with improved physical properties.
Compared to conventional syntheticroute, the new method significantly shortened synthetic steps and
reaction time. This technique involves the reaction of stoichiometric amount of metal nitrates and
appropriate dosage of citric acid at microwave oven and the whole process took only 15 min. The powders
of BaFe12O19 were further investigated by X-ray diffractometer (XRD) and scanning electron microscopy
(SEM). The results showed that the formation temperature of M-type Ba hexaferrite is significant low,
compared to conventional furnace heating. The X-ray diffraction analysis demonstrates that the phase
purity of the microwave-processed samples were determined and compared with a conventionally
processed material. SEM observations indicate that the size of the synthesized BaFe12O19 powders is
small and uniform distribution. Thus, microwave irradiation is proved to be a novel, extremely facile,
timesaving and energy-efficient route to the synthesis of BaFe12O19 powders.
Abstract: Sodium-potassium Niobate (K0.4Na0.6NbO3, KNN) nanopowders were prepared by hydrothermal
synthesis at the temperature range of 140-180°C for 12-48h using Nb2O5, NaOH and KOH as
source materials. By means of XRD and SEM techniques, the effects of composition and hydrothermal
treatment process, such as the rate of [R]/[Nb], the concentration of the alkali, the hydrothermal treatment
temperature and the hydrothermal treatment time, on the microstructures and the crystallinity of alkali
metals niobate were investigated in details. Results show that K0.4Na0.6NbO3 powders could be achieved
by hydrothermal synthesis at the temperature range of 140-180°C with the alkalinity concentration of
2-8M. With the increase of hydrothermal reaction temperature and time, the crystallinity of KNN
particles was improved. The obtained K0.4Na0.6NbO3 polycrystalline particles have rhombic structure.
Abstract: Yttrium iron garnet (YIG) nanopowders were synthesized by sol-gel method using
Fe(NO3)3·9H2O, Y(NO3)3·6H2O as raw materials. The influence of heat treatment, the citric acid to metal
nitrates molar ratio (CA / MN) and PH value on the synthesized powders were investigated using
scanning electron microscopy (SEM), thermal analyses (DTA/TGA) and X-ray diffraction (XRD). YIG
powders with average grain size of 80~90nm were synthesized after calcining at 1000°C for 4h.
Abstract: xBST-(1-x)YIG composite ceramics with x=0~1 were prepared by solid-state reaction method.
The variations for phase compositions were determined by XRD, and the magnetic and dielectric
properties of the composites were studied in the frequency range of 100Hz~1GHz. The results showed
that the composites (x=0.1~0.9) are consisted of BST phase and YIG phase and no significant chemical
interaction occurs between these two phases. The composite materials exhibit excellent frequency
dependences of dielectric and magnetic properties. The resonance frequency and high frequency
characteristics of YIG are improved by additions of BST, and when x=0.3, xBST-(1-x)YIG has the best
dielectric and magnetic properties.
Abstract: Single phase YIG powders were synthesized successfully using Fe2O3 and Y2O3 as starting
materials by solid state reaction, and YIG ceramics were prepared by pressureless sintering. The influence
of synthesizing temperature and Fe2O3 content on the final production were studied The effect of Fe2O3
content on volume density and microstructure of the sintered YIG was also investigated. The results
showed that single phase YIG powders were synthesized by solid state reaction at 1400°C for 3h. When
Fe2O3 content was excessive 3 wt%, YIG ceramics with a density of 5.294g·cm-3 was fabricated by
sintering at 1480°C for 2.5h.
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: Nanocrystalline Ni1-xZnxFe2O4 ferrites with 0 ≤ x ≤ 1 were prepared by sprayingcoprecipitation
method. The microstructure was investigated by TG-DSC, XRD, SEM, TEM and BET.
Magnetic properties were measured with vibrating sample magnetometer at room temperature. The
results showed that uniform and fine nanocrystalline Ni1-xZnxFe2O4 ferrites are obtained. The grain size of
sample calcined at 600°C for 1.5h is about 30nm. There are a few agglomerates with average sizes below
100nm. The specific saturation magnetization, Ms, of the sample increases with increasing Zn2+ concent x
at room temperature, and the maximum Ms is 66.8 A·m2·kg-1 as the Zn2+ content x is around 0.5mol. As
calcining temperature increased from 400°C to 1050°C, the Ms of Ni0.5Zn0.5Fe2O4 ferrite increases from
40.2 A·m2·kg-1 to 75.6 A·m2·kg-1. The coercivity maximum is about 5.97 kA·m-1 as its critical grain size is
about 62.0nm. The relation between coercivity and grain size for nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite
may be explained based on random anisotropy theory.