Zhen Xing Yue

Electrical and magnetic studies of Ba3Co2Fe23−12xMn12xO41 Z-type hexaferrites

The electromagnetic and dielectric properties of Mn substituted Ba3Co2Fe23−12xMn12xO41 (Z-type) hexaferrites where 0≤x<0.1 were investigated in this study. The ferrite samples behaved as a semiconductor, and DC resistivity as well as activation energy for electronic conduction increased as the amount of Mn substituted for Fe increased, reaching maximum around x=0.02, and then decreased with further substitution. The behavior of dielectric constant was in an opposite manner to that of the activation energy and DC resistivity. Conduction is explained on hopping of electrons between Fe2+ and Fe3+. It was inferred that the initial permeability was sensitively controlled by the substitution of Mn because of magnetostriction compensation. Low-temperature sintered Co2Z hexaferrite with the substitution of Mn for Fe with low dielectric constant and high initial permeability is suitable for very high frequency (VHF; 300–800 MHz) multilayer chip inductors (MLCI) use.

Nonlinear magnetic properties of Mn-modified Ba/sub 3/Co/sub 2/Fe/sub 23/O/sub 41/ hexaferrite

We have investigated the structural and magnetic properties of a novel type of hexaferrite with composition of Ba/sub 3/M/sub 2/Fe/sub 23/O/sub 41/ (where M=Co and Mn) (Z hexaferrite) with tunable permeability. The material is promising for very high frequency (VHF) control when used in a voltage-controlled oscillator (VCO) as a tunable inductor. We substituted Mn for Co in the composition Ba/sub 3/Co/sub 2-x/Mn/sub x/Fe/sub 23/O/sub 41/ from x=0.0 to 1.2 to improve the inductance tunability and quality factor of the inductor material. Mn substitution had significant influence on the grain size of the sintered hexaferrites, and the coercivity was greatly reduced. The initial permeability and quality factor increased with increasing substitution of Mn for Co until x reached 0.5, an effect attributed to the decrease of the magnetocrystalline anisotropy constant of the hexaferrite and increase of average grain size. The tunability of the samples also increased with increasing Mn substitution, reaching a maximum at x=0.5, and then decreased with further substitution. This behavior is similar to that of the initial permeability and coercivity, and can be explained by the same mechanism.

Preparation of ZnNb2O6 Nano-Powders by Pechini Method

ZnNb2O6 ceramics with a columbite crystal structure, is a promising candidate for application in microwave devices. In this study, ZnNb2O6 nano-powders were prepared using Nb2O5 and Zn(NO3)2 as raw materials by Pechini method. The microstructure and crystal structure of ZnNb2O6 powders were investigated systematically using X-ray powder diffraction and SEM techniques. The effect of amount of citric and ethylene on the formation of sol-gel and the particle size of ZnNb2O6 powders were also investigated using orthogonal design. Finally, the optimum process parameters for synthesis ZnNb2O6 nano-powders were obtained in this study.

Microstructure and Microwave Dielectric Properties of Ba5(Nb1-xTax)4O15 (x = 0 ~ 0.5) Ceramics

The Ba5(Nb1-xTax)4O15 (x=0~0.5) solid-solution ceramics with hexagonal perovskite structure were prepared by solid-state oxide route. The phases and structure of the sintered ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of composition and sintering temperature on the bulk density, microstructure and microwave dielectric properties were also investigated. As the value of x increased from 0 to 0.5, the Q×f value increases from 36,049 to 49,493 GHz (at ~9GHz), whereas the dielectric constant (εr) decreases from 39.21 to 33.03 and the temperature coefficient of resonant frequency (τf ) decreases from 78.6 to 19.4 ppm/oC. The results indicate that the microwave dielectric properties of Ba5(Nb1-xTax)4O15 ceramics can be easily modified in a large range by changing the relative content of Ta to Nb.

Dielectric Breakdown and Failure of Ferroelectric Films as the Dielectric for Electrowetting Systems

In this paper, we study the electrical properties and breakdown phenomena of PZT ferroelectric thin film in electrowetting systems. The experimental results indicate that irreversible charge trapping occurred with repeated voltage actuation, resulting in contact angle relaxation and reduction of the ferroelectric film breakdown strength. The breakdown voltage depends on DC voltage polarity, and this polarity dependence was found to be related to the thickness of the ferroelectric layer. When AC voltage was applied, the breakdown voltage increased directly with voltage frequency. These phenomena are interpreted in terms of electrochemical reactions at the liquid/solid interface, an empirical model was used to estimate the amount of trapped charge in the ferroelectric film.

Ceramic-Polymer Composites with Low Dielectric Loss for Microwave Antennas and Wireless Sensors

The low dielectric loss ceramic-polymer composites were prepared by extrusion processing technique with high density polyethylene (HDPE) as matrix and high permittivity ceramic powder in BaO-Nd2O3-TiO2 (BNT) system as filter. The dielectric response in microwave frequency range was characterized, and the experimentally observed dielectric properties were compared with the theoretical models. The relative permittivity of the composites is increased from 3 to 10 with the increase in the volume fraction of BNT filter from 10 to 40 vol%. The dielectric losses of composites are less than 0.001 for all compositions. For 40 vol% ceramic loaded HDPE, the relative permittivity of 10 and loss tangent of 0.0007 at 7 GHz were obtained. The BNT-HDPE composites are promising materials for microwave dielectric antenna applications.

Low Dielectric Loss Polymer-Ceramic Composites for Wireless Temperature Sensation

The low dielectric loss polymer-ceramic composites with high density polyethylene (HDPE) as matrix and BaO-Nd2O3-TiO2 (BNT) as filter for wireless temperature sensation were prepared by an extrusion processing technique. For 30vol % ceramic loaded HDPE, as the ambient temperature increases from 30 to 100 °C, the relative permittivity and loss tangent of the composite vary from 6.25 to 6.09 and from 0.004 to 0.011 respectively, and the temperature coefficient of relative permittivity is -370ppm/°C. By using this composite as the patch microstrip antenna substrate, a simple UHF RFID temperature sensor antenna is fabricated and measured. The experimental results show that a 2MHz/10°C frequency increment can be obtained at 900 MHz in the temperature range from 25 to 100°C.

Dielectric Behavior of (1-X)BaTiO3-XCaCu2.94Mn0.06Ti4O12 Composite Ceramics

(1-X)BaTiO3-XCaCu2.94Mn0.06Ti4O12 (BTO-CCMTO) composite ceramics with X =0.1 and 0.2 were prepared through solid state reaction route. X-ray diffraction (XRD) analyses showed that a co-existence structure of BTO and CCMTO phase can be realized when the sample was sintered at 950°C. Furthermore, influences of CCMTO on the dielectric behaviors of the BTO-CCMTO composite ceramics were investigated. The results showed that the dielectric permittivity of the BTO-CCMTO composite ceramics increases with increasing amounts of CCMTO and the Curie peak of the pure BTO ceramics is greatly suppressed due to the addition of CCMTO. The dielectric loss of the BTO-CCMTO composite ceramics can be kept in the same magnitude order as that of the BTO ceramics.

Ferromagnetic Properties of Ni0.2Cu0.2Zn0.6Fe2O4-PZT Composites

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.

Effects of Ag-Pd Powder on Ferroelectric and Mechanical Properties of PLZT Ceramics

The Ag-Pd/PLZT composites were prepared by the conventional electronic ceramics method. The electrical and mechanical properties of the composites were investigated. As the amount of doped Ag-Pd particles increased, the fatigue and mechanical properties of the composites were improved, and the dielectric and ferroelectric properties after electric fatigue dropped less. The results indicate that the fatigue process leaves less damage on the composites due to the Ag-Pd particles incorporation. It is proposed that the improvement of fatigue property may be attributed mainly to the improvement of mechanical property.