Papers by Author: Yu Zhen Zhao

Abstract: Large-scale silver nanoparticles with fine dispersion and narrow size distribution were synthesized by reducing silver nitrate with sodium borohydride and sodium citrate and using poly (vinylpyrrolidone) as an adsorption agent in the ethanol solution. The sintering behavior and electrical properties of silver nanoparticles treated with and without glutaric acid were studied. Morphology studies showed that the treated silver nanoparticles obviously agglomerated and began to sinter at 200 °C and the sintering temperature is higher at least 50 degrees than that of the untreated silver nanoparticles The treated silver nanoparticles as fillers of electronically conductive adhesives (ECAs) is more advantageous to the increase of the conductivity. Otherwise, only in the conditions of the appropriate sintering temperature and loading of silver nanoparticles, the high conductivity of the ECAs was obtained. The effect of the treated silver nanoparticles on the electrical properties contributes to the surface activation and sintering behavior.Keywords: Silver nanoparticle, Sintering Behavior, Surface treatment, Electrical property

Abstract: In this paper, silver nanostructures were synthesized via a solvothermal method by reducing silver nitrate with ethylene glycol in the presence of poly (vinylpyrrolidone) and using NaCl, MgCl₂, AlCl₃, FeCl₃, Fe₂(SO₄)₃ , NaOH, NaBr and Na₂S as reaction inhibitor, respectively. Characteristics of the as-prepared silver nanostructures were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible (UV-vis) absorption spectrum. It is found that the mixture of nanoparticles and nanorods and nanowires can be observed in the AlCl₃ and NaOH systems, the nanorods as main products can be obtained in the MgCl₂ and NaCl and Fe₂(SO₄)₃ systems, the large scale silver nanowires as main products can be obtained in the FeCl₃ and Na₂S systems, especially in the Na₂S system, silver nanowires are very long and curved. The results indicated the reasons of the effect of the reaction inhibitors on the morphologies of silver nanostructures depend on the solubility product constant of silver salt which formed with silver ion and inhibitor anion ion in the initial stage and the properties of metal cationic ion of inhibitor. The smaller solubility product constant of silver salt or the presence of Fe³⁺ or low valence metal ion greatly facilitate the formation of one-dimensional silver nanostructures, especially to nanowires.

Abstract: Barium-strontium titanate Ba_1-xSr_xTiO₃ [0≤x≤1] has been investigated for tunable microwave application due to their high permittivity, low losses and high tunability. The influence of MgF₂ additives on the dielectric performance of Ba_0.6Sr_0.4TiO₃ (BSTO) were investigated in this paper. MgF₂ doped BSTO ceramics were prepared using the conventional mixed oxide techniques. The phase structure, microstructure and dielectric properties of MgF₂ doped BSTO ceramics were studied. The XRD patterns showed that all the samples exhibit a perovskite phase. A secondary phase of MgO was observed with excessive MgF₂ additives. The grain size of MgF₂ doped BSTO ceramics was slightly increased with the increasing of MgF₂ additives, while the distributed porosity was concentrated to get larger. The relative permittivity, dielectric loss and tunability were decreased accordingly. The relative permittivity was reduced from 3717 (pure Ba_0.6Sr_0.4TiO₃) to 680 (6 wt % MgF₂ doped BSTO), while the tunability changed from 51.7 % to 6.5 %. The dielectric losses were decreased from 0.004 to less than 0.001. The Curie temperature of MgF₂ doped BSTO was first decreased with the additives of MgF₂ (x<2 wt %) then remain the same with the rise of MgF₂ (2≤x≤6) content.

Abstract: Ba_xSr_1-xTiO₃ [(BST), 0£x£1] is a solid solution ferroelectric material exhibiting a large dielectric constant non-linear change with an applied DC electric field. And Ba(Zr_xTi_1-x)O₃ solid solution also has received much attention because of the good tunbality. In this paper, Ba_0.6Sr_0.4(Zr_xTi_1-x)O₃ (x=0.15,0.20,0.25,0.30,) ceramic was obtained by traditional ceramic processing. The structural, surface morphological, dielectric properties, tunable properties of this material as well as the mechanism of their nonlinear dielectric constant under DC electric field were systematically examined. The Zr ions substitution of Ti ions has a strong effect on the grain sizes and the dielectric property. The results show that Ba_0.6Sr_0.4(Zr_xTi_1-x)O₃ (x = 0.2, 0.25,0.3) ceramic is a promising candidate for the DC electric field tunable materials for microwave electronics application, because they exhibit high relative tunability (44%, 48%, 35%, respectively) as the strength of electric field is up to 1.5 kV/mm, and low dielectric loss (0.0026, 0.00044, 0.0015, respectively) at 100 kHz at room temperature. X-ray diffraction analyses indicated that the samples present perovskite phase. Scanning electron microscopy micrograph of sample indicated that the grain size decreased and density increased with Zr concentration increasing.

Abstract: Lead-free K_0.5Na_0.5NbO₃-xwt% (0.4ZnO-0.6B₂O₃) ceramics were synthesized by conventional ceramics process. The co-doping of ZnO and B₂O₃ can decrease the sintering temperature of K_0.5Na_0.5NbO₃ ceramics to 1000°C, and the samples show high relative density around 96%. X-ray diffraction (XRD) reveals that Co-doping of ZnO and B₂O₃ induces lattice distortion. Liquid phase is observed by scanning electron microscopy (SEM), which is resulted from the addition of ZnO and B₂O₃. The ceramics show better piezoelectric and dielectric properties with planar electromechanical coupling factor k_p= 40.7%, piezoelectric constant d₃₃=117pC/N, dielectric constant ε^T₃₃/ε₀=318.6, and loss tangent tanδ=0.034.

Abstract: (1-x) (K_0.475Na_0.475Li_0.05)(Nb_0.975Sb_0.025)O₃-xmolBiFeO3 (x=0, 0.002, 0.004, 0.006, 0.008) doped with 0.8mol%CuO lead-free piezoelectric ceramics were prepared by the solid state reaction technique. X-ray diffraction patterns suggested that all the ceramics presented perovskite structure. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. The ceramic (x=0.002) near room temperature exhibited excellent electrical properties (piezoelectric constant d₃₃=172pC/N, planar electromechanical coupling factor k_p=0.43, and dielectric constant =418). A relatively high mechanical quality factor (Q_m=200) was also obtained in this particular composition. All these results revealed that this system might become a promising candidate for lead-free piezoelectric materials.