Shu Ping Gong

Fabrication of BaTiO3-Based Semiconducting Ceramic Thick Films by Aqueous Tape Casting

Semiconducting barium titanate powderss with an average particle size less than 40 nm were used for tape casting. Green tapes with a thickness of 100-500 μm were tape-cast from aqueous slurry of barium titanate powders using polyvinyl alcohol (PVA) as binder and polyelectrolyte ammonium salt as dispersant. The solid loading, viscosity and rheological properties of the ceramic slurries were investigated. Slurries with low viscosity were obtained when the concentration of dispersant was 1.5-2.0 wt% (based on ceramic powders weight) with fixed 75 wt% solid loading. The highest solid loading and optimum dispersion were determined through the proper viscosity to cast. Microstructure and PTC effect of the ceramic chips were studied as a function of firing temperature. Yttrium ions were homogeneously diffused into barium lattices at a low temperature of 1240 °C, and fine-grained PTC ceramics with grain size of 1-2 μm were developed successfully. These results can be explained by the higher rate of reactivity of finer powders and stable behavior of the suspension.

Nanopowder and Fine-Grained Ceramics for Multilayer PTCR Elements

BaTiO3 nanopowders prepared by sol-gel process were used for multilayer PTCR ceramics in order to utilize grain boundary effect and lower sintering temperature. The precursor gel was calcined at different temperatures and the powders were characterized by XRD and TEM. The average grain size was about 26nm when calcined at 800°C for 2h. Effects of acceptor/donor concentration and sintering temperature on PTCR ceramics were also investigated. The optimal concentration of the donor was found to be 0.6mol with the acceptor concentration being 1/8 of the donor. Multilayer PTCR elements were fabricated by tape-casting technique. The jump ratio of PTCR chips sintered at 1240°C was above 103 with the average grain size smaller than 1~2 μm, which is suitable for the multilayer PTCR elements.

Research on Sintering Dynamics and Microwave Dielectric Properties of Bi and Mn Doped Lead-Based Ceramics

The sintering dynamics, microstructures and microwave dielectric properties of Bi2O3 and MnO2 co-doped [(Pb,Ca) La](Fe,Nb)O3 (PCLFN) ceramics were investigated. Bi2O3 and MnO2 dopants effectively enhanced bulk densities and reduced sintering temperatures by about 100~140°C. Sintering procedure had significant effect on grain size and porosities of ceramics. Investigation of microstructures revealed that the grain growth was controlled by either volume diffusion or second-order interface mechanism in present ceramics. The potential microwave dielectric properties of εr=91.1,Qf=4870GHz and τf=18.5ppm/°C could be obtained when the mass ratio of Bi2O3/MnO2 (k) was 1, the doping content w=1wt% and sintered at 1050°C for 4h.

High Piezoelectric Property and Low Dielectric Constant PZN-PZT Ceramics

The influences of the substitution of (Zn1/3Nb2/3) group for Ti as well as addition of Fe2O3 and K2CO3 on d33, kp, εr, and tgδ of the Pb[Zr0.46Ti0.54-x(Zn1/3Nb2/3)x]O3 + y mol%Fe2O3+z mol%K2CO3 (PZNPZT) (0 ≤ x ≤ 0.20, 0 ≤ y ≤ 0.10, 0 ≤ z ≤ 0.20) ceramics were investigated. The experimental results demonstrated that when x increases in Pb[Zr0.46Ti0.54-x(Zn1/3Nb2/3)x]O3+0.3 mol%Fe2O3+0.5mol%K2CO3 ceramics, the d33, kp, εr, and tgδ increase and approach to their maximum values, then eventually decrease. XRD analysis revealed that the perovskite structure of the materials transfers from tetragonal phase to rhombohedral phase. The relative dielectric constant (εr) decreases dramatically in the rhombohedral phase area near the MPB; the d33 and εr decrease with the small amount of added Fe2O3 and K2CO3, which also contributes to densification of the PZN-PZT ceramics. The optimized piezoelectric performances through the experiment were obtained as d33=280 pC/N, kp=0.62, εr=900, tgδ=0.003.

Liquid Desiccant Drying Method for Gelcasting PTC Ceramics Based on BaTiO3

In this work, aqueous gel-casting (AGC) method was used for preparing PTC (positive temperature coefficient) ceramic green body based on BaTiO3. We studied on modeling of liquid desiccant drying method for gelcasting ceramic bodies, and compared with the conventional drying methods.

Synthesis of (1-x) Ca0.4Sm0.4TiO3 – xLi0.5Nd0.5TiO3 Ceramic Powders via Citric Acid Precursor

Using citric acid (CA) as a chelating agent, (1-x)Ca0.4Sm0.4TiO3 –xLi0.5Nd0.5TiO3 (CSLNT) (x = 0.3) ceramic powders were synthesized by the Pechini method. The CSLNT precursor and derived oxide powders were characterized by differential thermal analysis, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. Only perovskite CSLNT (x=0.3) phase appeared when the CSLNT precursor was calcined at 1050°C for 3 h. Compared with the conventional solid-state reaction method, microwave dielectric ceramics with better properties could be prepared by the Pechini method at lower sintering temperature.

Preparation and Characterization of Semi-Conducting (Ba,Sr)TiO3 Powders by a Wet Chemical Route

Ultrafine (Ba,Sr)TiO3-based powders used for making positive temperature coefficient of resistance (PTCR) were synthesized by two chemical steps: polyacrylamide gel process and liquid phase coating process. First, donor doped (Ba,Sr)TiO3 powders were synthesized by polyacrylamide gel process at rather low temperature, and the physical and chemical characteristics of the gels and the precursorpowders were investigated by DSC, TG, XRD and TEM. Secondly, acceptor and sintering aid were coated by an aqueous solution containing acceptor (Mn) and additive (Si). The characterization and sintering behavior of the semi-conducting powders and the PTC effect of ceramic samples prepared by the as-obtained powders were investigated.

Gas Sensing Performance of Macroporous SnO2 Thin Film Prepared by Using Carbonaceous Polysaccharide Microspheres as Pore-Forming Agent

The macroporous SnO2 thin film has been successfully prepared on alumina substrate with printed Ag interdigital electrodes by sol-gel dip-coating method. The carbonaceous polysaccharide microspheres synthesized by hydrothermal method were used as pore-forming agent. The SnO2 thin film prepared without using carbon microspheres was also synthesized for comparison. X-ray diffraction and scanning electron microscopy were taken to study the micro-characteristics of samples. The influences of operating temperature, gas concentration and structure feature on the H2S sensing performance of SnO2 thin film samples were systematically studied. Compared with SnO2 thin film prepared without using carbon microspheres, the macroporous SnO2 thin film showed a considerably reduced recovery time and good response-recovery properties.

Aerosol-Assisted CVD of SnO2 Thin Films for the Room-Temperature Detection of Hydrogen Sulfide

High-quality SnO2 thin-film materials capable of detecting H2S gas of low concentrations at room temperature was demonstrated in this paper. We employed aerosol-assisted chemical vapor deposition process for the deposition of SnO2 thin films on alumina substrates with pre-patterned electrodes. The gas-sensing performances of the films prepared under different deposition conditions were systematically compared and analyzed. When SnCl2·2H2O was used as the precursor, a response sensitivity of 98.4 toward 50 ppm of H2S at room temperature was achieved. At room temperatures, the resistance upon the H2S gas exposure could recover to 90% of the initial resistance of the sensor when the H2S gas flow was turned off.

Synthesis and Stabilization of BaTiO3/CoFe2O4 Ferrocolloids

In this article, nanocomposites of BaTiO3/CoFe2O4 have been prepared by sol-gel technique. The samples have been calcined at various temperatures ranging from 500 to 900 °C and then the microstructure of the composite nano-particles was studied. XRD, SEM analysis showed the powders can form the two phase composite system of BaTiO3 and CoFe2O4 and the average particle size of the crystalline phases is 50nm at sintering temperature of 800 °C. In addition, we have studied the effects of different solvents and mixed solvents on the stability of the nanocomposites suspensions. Results of sediment volumes and conductivity showed under ultrasonic agitation for at least 25 min, suspensions of the BaTiO3/CoFe2O4 in ethanol-acetylacetone (1:1 in volume) were most stable (the sediment volumes is 0.6cm3/0.4g, the conductivity is 9μS/cm). Electrophoretic deposition (EPD) was utilized for preparation of magnetoelectric (ME) composite films, the impact of deposition time and deposition voltage on electrophoretic deposition process was investigated. The obtained ME composite films exhibited good ferroelectric and ferromagnetic properties, which can meet the demand of ME devices.