Authors: Huan Liu, Min Li, Jiu Xiao Wan, Jun Zhao, Qiu Yun Fu, Shu Ping Gong, Shu Xi Wu, Yun Xiang Hu, Dong Xiang Zhou
Abstract: 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.
422
Authors: Dong Xiang Zhou, Lu Gan, Qiu Yun Fu, Shu Ping Gong, Huan Liu, Wei Luo, Jun Zhao
Abstract: 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.
121
Authors: Jun Zhao, Hai Bo Yang, Shu Ping Gong, Dong Xiang Zhou
Abstract: As a lead-free positive temperature coefficient of resistivity (PTCR) material, [Ba0.95-x (K0.5Bi0.5)0.05Cax]1-yNbyO3 system was prepared by the conventional solid-state reaction method. All samples sintered in air at 1300°C possess PTC characteristics as well as semi-conductivity characteristics, especially they show high Tc(130°C~160°C) value and the jump of the resistivity (maximum resistivity ρmax / minimum resistivity ρmin ) is four orders of magnitude. Samples with the composition of 0.3mol% Nb5+ have low room-temperature resistivity (ρ25°C) of ~103Ω.cm.
1005
Authors: Dong Xiang Zhou, Fei Shi, Shu Ping Gong, Qiu Yun Fu
Abstract: 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.
362
Authors: Xu Xin Cheng, Dong Xiang Zhou, Qiu Yun Fu, Shu Ping Gong
Abstract: Electrical properties, positive temperature coefficient of resistivity (PTCR), and microstructures of (Bam-0.007Sm0.007)TiO3 (BST) with different Ba-site/Ti-site (A/B) ratio sintered in a reducing atmosphere and reoxidized in air are investigated. The results reveal that the room temperature resistivity of the semiconducting BST ceramics first decreases and then increases with increasing of A/B ratio (m), particularly when m is equal to 1.006, the semiconducting BST ceramics which have been sintered in a reducing atmosphere and reoxidized at 800°C exhibit significant PTCR effect with a resistance jumping ratio of 3 orders magnitude, and achieve a lower room temperature resisitivity of 80.8 Ω∙cm, in addition, the grain size distribution of the Ti-excess specimens is much better than that of the Ba-excess ones.
1032
Authors: Chao Fang, Dong Xiang Zhou, Hu An Liu, Shu Ping Gong
Abstract: The positive temperature coefficient of resistivity (PTCR) behavior of semiconductive BaTiO3
ceramics is often explained by the Heywang model. However, Heywang model couldn’t explain some
experimental phenomena of jump range more than 106. This paper considered that the migration of
donors, electrons and holes has important influence on grain boundary effect. A differential equation
about Fermi level was established on the base of Heywang model. By solving the equation the jump range
can be calculated quantitatively. It was found that a potential well exists on the edge of grain due to the
donor ionization, and the experimental phenomena of PTC jump range more than 106 could be explained.
1692
Authors: Zhi Ping Zheng, Shu Ping Gong, Shu Fen Cheng, Dong Xiang Zhou, Yun Xiang Hu, Huan Liu
Abstract: 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.
469
Authors: Huan Liu, Shu Ping Gong, Dong Xiang Zhou, Chun Fang Cheng, Zhi Ping Zheng, Yun Xiang Hu
Abstract: Dense PTC ceramics were prepared with BaTiO3 nanopowders synthesized by hydrothermal
method. BaCO3 and Ti(OC4H9)4 were used as barium and titanium sources, and Y(NO)3·6H2O as the
donor dopant respectively. The average grain size of the powders obtained after hydrothermal treatment at
160°C for 9h was about 30nm with cubic structure. Mn(NO3)2 was introduced to the as-prepared
nanopowders in order to improve the PTC effect. After sintered at 1280°C, the PTC ceramic samples
exhibited sufficient resistance jump ratio(1.086×103) around Curie temperature, the density of which was
5.81g/cm3(96.5% of the theoretical density).
456
Authors: Jun Zhao, Shu Ping Gong, Chun Fang Cheng, Zhi Ping Zheng, Huan Liu, Dong Xiang Zhou
Abstract: 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.
453
Authors: Shu Ping Gong, Li Hua Huang, Huan Liu, Ming Li, Dong Xiang Zhou
Abstract: Nanocrystalline thick-film gas sensor was fabricated by screen printing method with
CuO-doped tin oxide powder synthesized by hydrothermal method. Average grain size of the CuO-doped
tin oxide powders was typically below 10 nanometers and the thick-films had a narrow grain size
distribution typically below 50 nanometers. Effect of the amount of CuO on the sensing properties was
investigated and the optimal value was found to be 3 wt%. The nanocrystalline CuO-SnO2 thick-film gas
sensors were more sensitive to H2S than those based on commercial micro SnO2 powders, which were
attractive to the detection of low concentrations of H2S gas at relative low temperatures.
521