Advanced Materials Research Vols. 105-106

Abstract: The thick-film metallization of AlN has received considerable attention because of its potential applications in electronic packaging. Here we reported on the thick film metallization of AlN by reactive binders. The metallization paste of Ag was prepared with organic vehicle of castor oil, ethyl cellulose and beta-terpineol and reactive binders of TiB2 and Co3O4. The control of the paste viscosity was discussed by changing the dispersant content. Meanwhile effects of the components and sintering process on the thick film properties were investigated. The properties of metallization film were analyzed with XRD, SEM and electrical test. The adhesion strength and the electrical resistance of the film were 12.7MPa and 5.3mΩ/□ respectively when the paste composition of Ag, TiB2, Co3O4 and the organic vehicle was 72.8%, 1.5%, 0.7% and 25% and the film was sintered in air at 850°C for 15 minutes.

Abstract: In this paper the authors discribed the convergent synthesis of a novel hyperbranched polymer, tris(8-hydroxyquinoline) aluminum (Alq3) linked with ethylene glycol, and the indentification of the polymer by UV/vis spectra, photoluminescence spctra(PL),1H NMR spectra, element analysis (EA), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), thermal gravimetric analysis (TGA), Cyclic voltammetry (CV), etc.. By introducing Alq3 into the hyperbranched polymer, which was connected with alkoxy chain, the electron injection and transport properties were improved. The maximum absorption peak of the polymer is 58nm blue-shifted, but the emission peak of the polymer is 32nm red-shifted to Alq3 in chloroform soltion. The optical energy band-gap estimated from the absorption edges is 2.845eV. These optical characters of it indicated that the operation, connecting Alq3 with ethylene glycol, could increase the energy band-gap but make the photos easier to transfer between the HOMO and LUMO energy levels.

Abstract: The additive of Al(NO3)3 was doped into ZnO varistors in order to reduce their residual voltages. Some of doped Al3+ enter the ZnO grains and infill into the vacancies of Zn2+ ions in the crystal lattice. Then, the resistances of ZnO grains decrease, which finally results in lower residual voltages of varistor samples. However, when most of Zn2+ vacancies inside the ZnO crystal lattice are filled with Al3+, redundant Al3+ ions inside ZnO grains will increase the grains’ resistances contrarily. In this paper, ZnO and Al(NO3)3 binary ceramics sintered at 1300 °C for 2, 4 and 8 hours were studied. The J-E curves of the investigated samples exhibit weak non-linear characteristics which may be due to the formation of grain boundary. Moreover, The resistivity dependence of ZnO ceramics on Al addition behaves as a U-type curve and the lowest resistivity of ZnO ceramics is obtained with doping 0.25mol% Al3+.

Abstract: High voltage zinc varistors was synthesized by high energy milling with Pr6O11 doped ZnO-Bi2O3 system as raw materials. The effects of milling time and sintering temperature on the electrical properties were investigated. The results show that high-energy milling decreases the sintering temperature of the ZnO varistors. The material derived from high-energy milling exhibit high density and good electrical properties at the sintering temperature from 1080 to 1180°C. The samples sintered at 1100 °C have average crystalline grain size of about 5 µm with the optimum values of electrical properties, gradient voltage V1mA is 371 V/mm, leakage current IL is 0.62 µA, non linear coefficient α is 60.

Abstract: Influences of sintering temperature on microstructure and electrical properties of TiO2 varistor ceramics were investigated. Morphologies of TiO2 ceramics samples were characterized using scanning electron microscope. The phase composition and crystal structure were researched by X-ray diffraction. The frequency dependences of the samples capacitance were determined using LCR meter, the varistor voltage V1mA and nonlinear coefficient α were discussed by experimental method. The results showed that TiO2 ceramics sintered at 1350°C for 2 h possesses fine microstructure and optimal electrical properties. However, the electrical properties of samples will deteriorate as excessive sintering temperature.

Abstract: In this paper, the TiO2-based varistor ceramics added different donor additives were prepared and their propreties had been compared. The effects of added methods and added amounts of V2O5 (Nb2O5, or Ta2O5) on the microstructure, dielectric and varistor properties of TiO2 double functional ceramics were investigated. The ceramic phase and the microstructure of the disks were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The frequency dependences of the samples capacitance (C), the dielectric loss (tanδ) were determined on LCR meter, and the varistor voltage V1mA was measured by using FC-2G meter. It is found that the proper amount of V2O5, Nb2O5 or Ta2O5 additves can promote the growth of the crystal and the formation of the grain boundary layer at a different extent. Meanwhile, the proper addition amount can increases the nonlinear exponent and the dielectric constant, but decreases the breakdown voltage. It can also improve the sintering properties of the samples.

Abstract: The effects of sintering temperature on microstructure, micro-composition, barrier structure and electrical properties of TiO2 varistors ceramics were investigated. The microstructures and chemical compositions of grains in TiO2 ceramics were measured by SEM and EDS. Based on the thermo electronic emission theory, Grain boundaries barrier structure was calculated by analyzing electrical properties of samples. The sample sintered at 1350°C exhibits better microstructure and properties. The grains size of the TiO2 sample sintered at 1350°C is about 15m, and other electrical properties are as follows: solid solubility of donor doping Nb5+ cation solute in TiO2 grains of 1.49mol%, barriers height of 0.28ev, barriers width of 48nm, varistor voltages of 5.25V/mm, non-linear coefficient of 4.2 and relative dielectric constant of 1.1×104.

Abstract: Sr2CeO4 nanocrystallites were prepared by a sonochemical process with a later heat treatment using CeO2 and SrCO3 as source materials. The influence of processing factors on the phase composition and morphology of the crystallites were investigated. Results show that nano-Sr2CeO4 monophase could be prepared at the calcining temperature up to 800oC for 2h. Particle size of Sr2CeO4 crystallites decrease with the increase of ultrasonic irradiation power. Around 20-30nm Sr2CeO4 crystallites can be obtained at 800oC when ultrasonic irradiation power reaches 300W.

Abstract: SiC powders with nickel powders and sintering aids were prepared by pressureless sintering at 1500oC under a N2 atmosphere. XRD, TEM, SEM techniques were used to characterize the phases and microstructure of the specimens. The thermoelectric properties of SiC matrix composites were investigated by measuring the Seebeck coefficient and the electrical conductivity. The main phase of all samples was -SiC, the Ni2Si can be observed with adding nickel powders. The largest electric conductivity was close to 3.5 m-1-1 at about 973K. The highest Seeback coefficient was up to 1800 V/K at 1073K. The transition from n-type to p-type was occurred.

Abstract: Pb- and La-substituted (Bi,Pb)2(Sr,La)2Co2Oy samples were prepared by solid-state reaction method and the effect of element substitution on the high-temperature thermoelectric properties was investigated. It was found that the presence of Pb and La elements improved the thermoelectric properties of the Bi2Sr2Co2Oy system owing to the simultaneous increase of conductivity and Seebeck coefficients. The optimal thermoelectric performance was obtained in Pb and La co-substituted samples and the power factor could reach 2.1×10-4Wm-1K-2 at 1000K.