Key Engineering Materials Vols. 368-372

Abstract: A novel nebulizer used in near dry machining systems for supplying cutting fluids and cooling air is presented. The nebulizer includes double-layer micro-nebulizers, each adopting piezoelectric transducer as the actuator, generating pressure in the chamber and ejecting liquid or air out of it. The mixture of cooling air and micro-partical spraying into cutting area has both the cooling and lubricating action. The design of the piezoelectric actuator and cavity structure, including the selection of the piezoelectric actuator type and materials is studied. The vibration modes are obtained by means of FEM.

Abstract: A sol-gel technology to fabricate PZT thick film for cantilever beam was investigated. In this process, PZT nano-powder is dispersed into a PZT sol solution, which is identical with the powder in composition, and then the PZT suspension and clean PZT sol solution were deposited alternately on an Au/Cr/SiO2/Si substrate using spin-coating route. Above process was repeated in order to deposit the desired thickness. The results showed that the perovskite PZT thick film with thickness of about 4 μm was obtained after annealing at 650 °C for 2 h and it has the saturation polarization of 54 μC/cm2, the remnant polarization of 30 μC/cm2 and the coercive field of 50 kV/cm.

Abstract: The magnitude versus frequency performance for a vibration acceleration sensor based on metal-ceramic piezocomposite transducer (cymbal) was studied in this paper. The results showed that the voltage sensitivity of this new sensor is as a function of not only the effective piezoelectric coefficient, d33 e, elastic coefficient, ky, and the resonance frequency, f0, of the cymbal transducer, but also the relative damping coefficient, ξ, of this new sensor. The relative damping coefficient, ξ, is also as a function of the capacitance, C0, of the cymbal transducer and a function of the mass, m, of the sensor, which is used as a prestressing force. The magnitude versus frequency plot for this vibration acceleration sensor was constructed. The results showed that the magnitude versus frequency performance of this new sensor changes as the relative damping coefficient, ξ, varies. The magnitude versus frequency performance is not dependent on the relative damping coefficient, ξ, when the ratio of operation frequency to the nature frequency, ω /ω0, is less than 0.2.

Abstract: BiFeO3 films were prepared by chemical solution method on Pt/Ti/SiO2/Si substrates. The ferroelectric properties of Pt/BiFeO3/Pt capacitors were investigated, and the effect of recovery annealing applied after Pt top electrode deposition was discussed. The pure phase film with recovery annealing exhibits lower leakage current and higher remanent polarization than those without post-annealing. The leakage current is reduced by three orders of magnitude, the remanent polarization increases from 2.59μC/cm2 to 3.44μC/cm2. The recovery anneals applied after top electrode deposition may optimize the ferroelectric performance by removing the effect of structural defects formed by sputtering.

Abstract: The high Dit is the major problem of III-V compound semiconductor MOSFET, which causes the pinning of the surface Fermi level near the middle of the energy gap. The GaAs with (NH4)2Sx treatment (S-GaAs) can remove the native oxides on GaAs and prevent it from oxidizing. The electrical characteristics of fluorinated polycrystalline TiO2 films deposited on p-type(100) S-GaAs were investigated. The fluorine from liquid phase deposition solution can passivate the grain boundary of polycrystalline TiO2 prepared by MOCVD. The leakage current through the grain boundaries was suppressed. The leakage current of MOCVD-TiO2/S-GaAs can be improved from 6.8 x 10-6 and 0.2 A/cm2 to 3.41 x 10-7 and 1.13 x 10-6A/cm2 under positive and negative electric fields at 1.5 MV/cm, respectively. Dit and k can be improved from 1.44 x 1012 cm-2eV-1 to 4.6 x 1011 cm-2eV-1 and 52 to 65, respectively. The effective oxide charges can be improved from 2.5 x 1012 C/cm-2 to 9.3 x 1011 C/cm-2.

Abstract: SiC-based boundary layer capacitors were prepared by hot pressing. XRD, TEM and the high-resolution TEM techniques were used to characterize the sintered samples. It was found that the width of the grain boundary within the SiC-based boundary capacitors was about 200 nm. Extremely high dielectric constant of >2,400,000 appeared in a wide temperature range from 590oC to 730oC, with the maximum of >2,900,000. The critical temperature was about 500oC. Space charge polarization was detected as the temperature increased. Nano grains in the boundary phase were observed, which might enhance the space charge behavior.

Abstract: Microwave sintering behaviors of four different compositions of YSZ electrolyte materials were investigated. The samples were sintered in 2.45GHz microwave furnace. For comparison, conventional sintering was performed at 1821K.The densities of sintered samples showed considerable enhancement in the densification process under the influence of microwave fields. The samples with lower Y2O3 content are easy to sinter. The influence of the composition and sintering methods on the final phase composition and microstructure were investigated by X-ray diffraction and scanning electron microcopy. Finer and more uniform microstructures were observed in the microwave sintered samples comparing to the conventionally sintered samples.

Abstract: With the YSZ nano-powders as raw materials, the thin electrolyte film was prepared by tape calendaring, then fired by a three-step sintering method. The YSZ film sintered at 1250°C is dense with a grain size of 0.4~3μm.The electrical conductivity, up to 0.2s/cm at 1000°C, and active energy, 0.99~1ev, are nearly the same for the samples sintered at 1250°C for 10, 15 and 20 h.

Abstract: Ceria oxygen-ion conductors doped with M2O3 (M=La, Nd, Sm and/or Ga) were prepared by a wet chemical method. Phases were analyzed by X-ray diffraction method and conductivities were measured by using AC impedance analyzer. The results showed that Ga2O3-CeO2 solid solution with 17 nm grains and pure fluorite phase had been obtained even at calcination temperature of 800 °C for 5 hs. Conductivities of Ga2O3-La2O3 co-doped CeO2 were higher than that of Sm2O3-doped CeO2, which was reported having the highest conductivity among CeO2-based oxides.

Abstract: A citrate gel method was applied to synthesize Ce0.8Sm0.2O1.9 powders by using cerium and samarium nitrates as raw materials and citric acid as complexing agent. It was shown that Ce0.8Sm0.2O1.9 phase was formed when the decomposition of the dried gel completed at 500 °C. The crystallite size of the synthesized powders calcined at 500 °C for 2 h is 5-10 nm. The powders can be easily sintered in air to yield over 97 % relative density at 1250 °C, which is significantly lower than sintering temperature of over 1500°C required by the doped ceria powders prepared via conventional ceramic techniques.