Key Engineering Materials Vols. 434-435

Abstract: In this paper, the effect of gel-calcination on piezoelectric property in (1-x) BiScO3-xPbTiO3 with the composition of x=0.635 is investigated. According to previous work, the heating rate of 200°C/h and holding for 210min having been taken as the basic processing condition. The BSPT powders were obtained from the same sol solution but calcined at different temperatures, and then the powders were used to prepare BSPT ceramics. The result shows that for the bulk ceramics with higher relative density ( higher than 95%), with the increasing calcining temperature of the gel (from 420°C to 500°C), the piezoelectric coefficient d33 of ceramic specimens first increases to maximum of 636pC/N at 450°C, then shows a fluctuation. In this work how the powder activity and the grain size affect (which was leaded by powder particle size) piezoelectric properties of BSPT ceramics are discussed.

Abstract: Lead-free piezoelectric ceramics Na0.5Bi0.5TiO3+xmol%Co3+ (NBT-xC) were synthesized by conventional solid-state process. Effects of Co3+ addition on the phase structure, dielectric and piezo- electric properties of NBT-xC were investigated. The X-ray diffraction suggested that all specimens were rhombohedral perovskite structure. After a small addition of Co2O3, a dense microstructure with increased grains was developed. The doping with Co3+ enhanced mechanical quality factor Qm significantly, whereas piezoelectric constant d33 and electromechanical coupling factor kp decreased slightly with increasing amount of Co3+. For the ceramics with x=3, the electric properties become optimum, which are as follows: d33=~70pC/N, kp=~13%, Qm=~934, tanδ=~0.02 (1kHz), respectively. These results indicate that the Co3+ ion was considered to replace Ti4+ ion and present “hard doping” effect.

Abstract: Left-handed material (LHM), whose permittivity and permeability are both negative, has attracted much attention due to its exotic electromagnetic properties, such as negative refraction, backward wave propagation and evanescent wave amplification. The microwave left-handed property of a composite medium composed of ferrite cubes’ array and copper net was studied using the method of finite difference time domain in this paper. An obvious left-handed pass band emerged when ferrite cubes were combined with longitudinal copper wires, because the ferrite produced negative permeability by the ferromagnetic resonance and the copper wires produced negative permittivity by the plasma. With the addition of horizontal copper wires, the transmission intensity of the pass band was gradually weakened. It can be concluded that the horizontal wires played a negative role in realizing the composite LHM with ferrite cubes and copper net. This work gives an instructive direction to the fabrication of 3D LHMs.

Abstract: The effect of specific surface area on the growth and the porosity of oxide ceramic superconductor YBCO single domain are investigated. The enhancement of growth depth depends on the large specific surface area σ. When the specific surface area σ is more than the critical value 200mm2/g, the YBCO single domain is full-growth in the sample of size Ф20mm×18mm. It reveals that a large specific surface area providing an effective tunnel of oxygen diffusion for the crystal growth. On the other hand, this tunnel makes oxygen gas emitting out resulting in porosity diameter decreased. The mean porosity diameter is observed as 5μm in hole sample smaller than 80μm in plain sample. The porosity distribution is calculated as 1/(100μm)2 in plain sample and 8/(10μm)2 in hole sample.

Abstract: The magnetic hysteresis parameters like coercivity (Hc) and saturation magnetization (Ms), and dielectric parameters like dielectric constant (ε΄) and dielectric loss (ε΄΄/ε΄) of Ni0.5Zn0.5Fe2O4 prepared by “one-step synthesis” and conventional two-step synthesis methods, respectively, were comparatively investigated. It was observed that the saturation magnetization, dielectric constant and dielectric loss for samples prepared by “one-step synthesis” method are lower than those of ferrite samples prepared by conventional synthesis method. However, the coercivity of the former is higher due to its smaller grain size. The low dielectric loss makes these samples especially attractive for use at high frequencies.

Abstract: In this work, nano-composite of barium hexaferrite/magnetite was produced by partial reduction of barium hexaferrite with graphite via ball milling. Phase composition, morphology and magnetic properties of the samples were evaluated by XRD, SEM and VSM, respectively. XRD results revealed that after 15 hours milling, a nano-composite of BaFe12O19/Fe3O4 formed which mean crystallite size of BaFe12O19 was 17 nm. After milling for 20 and 40 hours, the peaks of BaFe12O19 were weakened and Fe3O4 was detected as a dominant phase. The coercivity decreased from 703 to 153 Oe when the milling time increased from 15 to 20 hours.

Abstract: Ferro-materials which possess both capacitance and inductance were sintered at low temperature using Bi2O3 as sintering additives. The composition of ferro-materials is 0.4PMZNT- 0.6NiCuZn. PMZNT relaxor ferroelectric is a solid solution that consists of Pb(Mg1/3Nb2/3)O3, Pb(Zn1/3Nb2/3)O3 and PbTiO3. NiCuZn ferrite with general formula is Ni0.2Cu0.2Zn0.6Fe2O4. Effects of the content of Bi2O3 and sintering temperature on the relative density of prepared ferro-materials have been studied. Dense ferro-materials were obtained at as low as 890°C with 2.0 wt% of Bi2O3. The X-ray diffractometer (XRD) identifications showed that ferro-materials consisted of distinct ferroelectric and ferromagnetic phases. Scanning electron microscopy (SEM) observations revealed that low temperature sintered ferro-materials possess high density and fine-grained microstructures. Prepared ferro-materials exhibit electromagnetic properties.

Abstract: Abstract. Hexagonal Co-containing Z-; Y- and M-type ferrites are used as soft magnetic materials for multilayer inductors for operating frequencies up to 3 GHz. Co2Z-type Ba3Co2Fe24O41, iron excess Ba3Co2-yFe24+yO41 (0  y  0.8) and Ba3Co2-CuxFe24O41 (0  x  1.0) ferrites have their stability intervals between 1260-1350°C. The permeability of a ferrite with y = 0.6 sintered at 1300°C is µ = 30 throughout the MHz. Addition of Bi2O3 shifts the maximum shrinkage down to 950°C. Their permeability is µ = 5 because of partial decomposition of the Co2Z phase. Y-type ferrite Ba2Co1.2-xZnxCu0.8Fe12O22 (x = 1.2) sintered at 1100°C shows a permeability of µ = 20. Sintering at 900°C reduces the permeability to µ = 10. M-type BaCo1.2Ti1.2Fe9.6O19 ferrites sintered at 970°C display a permeability of µ = 35.

Abstract: In this paper, the sol-gel process was used to synthesize a glass binder in thick-film paste for aluminum nitride (AlN) metallization. Some major factors that influenced the sol-gel process including PH value, quantity of water were discussed in detail. The xerogel was analyzed by means of TG-DSC in order to determine its optimum heat treatment process. Meanwhile, the sintering behavior of silver/glass composite thick film had been studied by varying the glass content. The results show that a glass powder of a low melting point and chemically compatible with AlN substrate can be obtained by sol-gel method when the composition (wt %) is CaO (40), B2O3 (15), SiO2 (35), BaO (10). During sintering, the glass becomes liquid and largely affects the microstructure development and square resistance of the thick film. When the glass content is optimum (10wt %), the film adhesion strength achieves maximum and the square resistance has a relatively low value.

Abstract: A new way to deposit oxide ceramic coating on the metal was prepared by Gel-casting and microwave assisted heating. The oxide ceramic coating was obtained by dipping the metal substrate whose surface carried positive charge through acid treatment to the gel slurry which was composited by oxide powder with negative charge, and then gelating, drying and heating by microwave. It was showed that it was feasible to realize coating of ceramics on metal surface through microwave heating.