Papers by Author: Xi Yao

Abstract: The mass sensitivity of a piezoelectric diaphragm biosensor has been investigated. The piezoelectric diaphragm utilizing a flexural vibration mode is an acoustic wave device which can be immobilized with a bio-molecular recognition layer on its surface. The mass sensitivity of the sensor was analyzed by the approximately theoretical and FEM methods, respectively. The sensitivity formula expressed by the structural parameters and the material parameter was educed for easy computing. The procedure utilizing Rayleigh method for the analytic solution of the sensitivity was introduced. The expression was verified by using a commercial FEM software package, ANSYS. The simulations are well consistent with the theory.

Abstract: Conductive LaNiO₃(LNO) thin films are grown on Si(100) substrates by a sol-gel method and their application as the bottom electrode for the growth of sol-gel derived Pb(Zr,Ti)O₃(PZT) thin films are studied. Morphology and electrical properties of the multilayer films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), electrical measurements. Experiment results show LNO thin films get highly (110)-oriented perovskite-type structure. Smooth and dense surfaces are observed on LNO thin films. The dielectric properties of PZT films show that PZT/LNO films exhibit worse dielectric properties than those of the PZT/Pt thin films. And LNO thin films prepared by sol-gel methods are not suitable as bottom electrode to deposit PZT thin films. On the other hand, FTIR spectrum and pyroelectric results of LNO thin films reveal that LNO can be used as absorber layer of PT thin films infrared detector with multi-layer thin film thermal insulation structure. At 10Hz, the detectivity (D*) and the voltage response (R_v) of PT thin films are 1.11×10⁷cm·Hz^1/2/W, 1.46×10³V/W respectively.

Abstract: (x)CoFe2O4-(1-x) BaTiO3 thick film with x=0.2 was prepared by electrophoretic deposition technique using BaTiO3 and CoFe2O4 nanopowders. X-ray diffraction indicated the film was consisted of single spinel CoFe2O4 and perovskite BaTiO3 phase. The thick film exhibited good ferromagnetic and ferroelectric property. The dielectric properties were influenced by ferromagnetic phase, especially at low frequency and high temperature, which was attributed to space charge effects and Maxwell-Wagner relaxation.

Abstract: xMnCO3–(1–x)[70wt% (10wt% MgO–90wt% Ba0.4Sr0.6TiO3)–30wt% MgAl2O4] (where x=0.0, 0.5, 1.0, 2.0, 5.0 and 10.0wt%) composite ceramics have been prepared through the solid-state reactions. Three phases, corresponding to the Ba0.4Sr0.6TiO3(BST), MgAl2O4(MA) and MgO phases, are clearly visible in the composite ceramics. The permittivity peak is initially enhanced and shifted toward a higher temperature and then suppressed, shifted toward a lower temperature. Meanwhile, the tunability (calculated by [ε(E0)−ε(E)]/ε(E0)) is also initially improved and then decreased by doping MnCO3.

Abstract: The effect of 9Bi2O3-CuO mixed oxides as sintering agent on sintering behaviors and dielectric properties of Ba0.6Sr0.4TiO3 (BST) ceramics were investigated. It was found that 9Bi2O3-CuO mixed oxides lowered the sintering temperature about 300°C and that highly denser BST ceramic pellets were obtained by sintering at 975oC with addition of 5.0-10.0wt% mixed oxides. For BST ceramics with 5.0wt% CB content sintered at 975°C, had a moderate dielectric constant (ε=1315), low dielectric loss (0.0067) and high tunability (36%) at dc electric field of 20kV/cm and at room temperature and at 10kHz.