Papers by Author: Ying Dai

Abstract: Single-crystalline BaTi₂O₅ nanowires were synthesized by a simple molten salt method, using BaC₂O₄•H₂O and TiO₂ powders as precursors. Electrical characterization was conducted with the as-synthesized BaTi₂O₅ nanowires. The current-time data of the nanowires obeyed the Curie-von Schweidler law. Steady-state I-V curve was obtained at room temperature from current-time data and it revealed that the leakage current of BaTi₂O₅ nanowires obeyed the ohmic law under low voltage, and obeyed the space-charge limited current (SCLC) law under higher voltage. The conductivity value of the BaTi₂O₅ nanowires is 2*10^-6 S/cm.

Abstract: Size controllable Barium titanate nanoparticles were synthesized in microemulsion consisting of water, OP-10, hexanol and cyclohexane under atmospheric pressure and low temperature, with Ba (OH)₂·8H₂O and tetrabutyl titanate used as starting reactants. Products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The results show that 65°C is the proper temperature for the synthesis. The particle size can be controlled by varying the reactants’ concentration, ω value (molar ratios of water to surfactant) and aging time.

Abstract: The complex perovskite compound Ca(Li_1/3Nb_2/3)O_3-δ(CLN) ceramics have received much attention due to the superior properties and relatively low sintering temperature 1150°C. In order to further low the sintering temperature of the CLN ceramics, enhance the Q · f values and other dielectric properties, the effects of the additive ZnO on the sinterability and dielectric properties of the CLN have been investigated. The CLN ceramics were prepared by conventional solid state ceramic route. With the addition of 1.0 wt% ZnO, the sintering temperature of Ca(Li_1/3Nb_2/3)O_3-δ(CLN) ceramics was effectively reduced from 1150 ^◦C to 1090 ^◦C，and the Q · f value was increased from 18920 to 20950 GHz (at 7.09 GHz). It also possesses compatible dielectric constant ε_r of 27.8 and τ_f value of -23.57 ppm/^◦C. While with the addition of 1.25 wt% ZnO, the Q · f value of Ca(Li_1/3 Nb_2/3)O_3-δ (CLN) ceramics sintered at 1150 ^◦C for 3 hours was increased significantly to 32150 GHz (at 7.09 GHz), ε_r of 28.3 and τ_f value of -18.55 ppm/^◦C. The relationship between microstructure and microwave dielectric characteristics was studied using X-ray diffractometer and Scanning electron microscope.

Abstract: Low-temperature sintered Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3-δ (CLNT) microwave dielectric ceramics with V₂O₅ and ZnO additives were prepared by the conventional solid state reaction method. The sintering behavior and microwave dielectric properties of CLNT ceramics were investigated. The main diffraction peaks of all the specimens sintered at the temperature under 1150^◦C split due to the coexistence of the non-stoichiometric phase and stoichiometric phase, which all possess CaTiO3-type perovskite structures. ZnO and V₂O₅ combined additives lowered the sintering temperature of CLNT ceramics from 1150^◦C to 1090^◦C. and the Qf values were improved from 18,210 GHz to 20,740 GHz. The CLNT ceramics with 4 wt% ZnO addition sintered at 1090^◦C showed good microwave dielectric properties with ε_r ~39.7, Qf ~20,740 GHz, τf ~8.6 ppm/^◦C. The relationship between dielectric properties and the sintering behavior was also discussed.

Abstract: Vanadium oxide nanotubes were synthesized via a rheological self-assembling process followed by a hydrothermal reaction. V2O5 gas sensors were fabricated from vanadium oxide nanotubess with an average diameter of around 90 nm and their gas-sensing properties were investigated. It was found that the sensors based on vanadium oxide nanotubes exhibit high responses ethanol gas at 270°C. The results indicate that vanadium oxide nanotube sensors will be promising candidates for practical detectors for ethanol.

Abstract: Large scale BaTiO3 nanorods were successfully synthesized by a template method based on a precipitation process. The templates used in our method are H2Ti8O17 nanorods, which can be synthesized from K2Ti4O9 fibers. The unique process of the synthesis is BaC2O4•0.5H2O shell was coated on the 1-dimensional H2Ti8O17 nanorods (the core). The as-prepared products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the BaTiO3 nanorods are ~100-300 nm in diameter and ~2-10 m in length. The process described provides a general route to fabricate this kind of perovskite 1-dimensional nanostructures, such as SrTiO3 and PbTiO3.

Abstract: Nanostructured flakes α-Ni(OH)2 microspheres were successfully synthesized by a facile solvothermal method using sodium dodecyl sulfate as a soft template and urea as a hydrolysis-controlling agent. The obtained products were characterized by Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Electrochemical properties studies were carried out using cyclic voltammetry, galvanostaitc charge/discharge method, respectively. The results exhibited that the α-Ni(OH)2 single electrode had high specific capacitance in KOH electrolyte. A maximum specific capacitance of the α-Ni(OH)2 single electrode was up to 2398F/g in 6M KOH electrolyte concentration with 0 to 0.4V potential at 4mA/cm2 current density. Furthermore, the effects of the heat treatment temperatures on the electrochemical capacitance of the α-Ni(OH)2 electrodes were investigated.

Abstract: Co3O4 microspheres were synthesized by hydrothermal-precipitation method using NH3•H2O, H2O2, n-butanol and polyethylene glycol as precipitator, oxidant, assistant solvent and dispersant respectively. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the Co3O4 electrode were performed by cyclic voltammetry (CV) and galvanostaitc charge/discharge methods. The results exhibited that the Co3O4 single electrode had excellent stability, cyclic performance and high specific capacitance in KOH electrolyte. The specific capacitance as a single electrode was up to 653.74 F/g in the 6mol/L KOH solution with 0-0.4V potential at 2mA/cm2 current density. The effects of electrolyte concentrations and current densities on its capacitive performance were investigated. The Co3O4 prepared material is potential candidate for the preparation of power source devices.

Abstract: Single-crystalline BaTiO3 nanoparticles and BaCO3 nanowires were synthesized respectively through the use of a reverse micelle as a medium in the same Oleic acid/n-octane/H2O system, by changing the H2O2 dosage. Both the phase composition and the morphology can be controled. The samples derived were characterized with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The formation mechanism has been fully discussed.

Abstract: Willemite ceramics (Zn2SiO4) possess excellent millimeter-wave dielectric properties, but it also has a high sintering temperature above 1300°C by traditional solid-state reaction and relatively large negative τf value. Zn2SiO4 nanoparticles synthesized by Sol–Gel method were used to improve the sintering and dielectric properties of the Zn2SiO4 ceramics. Using the nanoparticles, Zn2SiO4 ceramics can be sintered at a low temperature, 1150°C and exhibited improved microwave dielectric properties of εr =6.62, Q × f=24500 GHz, τf =-59ppm/°C. By adding TiO2 with high positive τf value (+450 ppm/°C) and CuO as sintering aid, near zero τf value and low sintering temperature can be achieved. With 11wt% of TiO2 and 5 wt% of CuO, an εr value of 9.3, a Q × f value of 12200GHz and a τf value of -11 ppm/°C were obtained at 1000°C, confirming the promising potential of the CuO-added TiO2-Zn2SiO4 ceramics as candidate materials for low–temperature cofired ceramic (LTCC) devices.