Jun Zhao

Grain-oriented sodium bismuth titanate-based lead-free piezoelectric ceramics prepared using the pulsed strong magnetic field and template grain growth

In this paper, 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNBT6) lead-free piezoelectric ceramics have been prepared using the gelcasting technology. The dielectric and piezoelectric properties of these ceramics have been investigated. The specimens were sintered at 1100–1200 °C after grain-oriented under the pulsed strong magnetic field during the solidification of the green bodies. Compared with the BNBT6 samples without applying magnetic field, the ceramics textured by applying 5 T pulsed magnetic field has a coercive field with reduction of 400 V/mm, which makes the polarization process easier. Meanwhile, it is noted that the orientation degree increases with increasing sintering temperature, whereas the piezoelectric constant and electromechanical coupling coefficients are improved. If SrTiO3 seed grain is introduced, the orientation degree can reach 0.70 and the relative density of the sintered ceramics is up to 96%. The dielectric properties are anisotropic in directions vertical and parallel to the applied ma...

Preparation and effects of glass-coatings on BaTiO3-based PTC thermistors

AbstractGlasses in the Na2O–K2O–K2SiF6–ZnO–Al2O3–B2O3–SiO2 system were investigated as potential intermediate temperature sealing materials to protect BaTiO3-based positive temperature coefficient (PTC) thermistors. The influence of compositional changes on the crystallization tendency and sintering behavior of the glass was reported. Additionally, the electrical properties of PTC thermistors with glass-coatings were compared with those without glass-coatings. The results showed that the formulation (in wt%), 3.1Na2O–9.4K2O–10.6K2SiF6–4.3ZnO–4.3Al2O3–20.3B2O3–48SiO2 (G2), performed better on thermal properties, had a good glass formability within a relatively wide range of sintering temperature and was compatible with the PTC thermistors (no cracks or pinholes). Furthermore, the glass layer did not affect the characteristics of the PTC thermistors too much.

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.

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.

Fabrication of Lead-Free and High Tc Positive Temperature Coefficient of Resistivity Ceramics Sintered in Air

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.

Microwave Dielectric Properties of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ Ceramics with Ba2+ Substitution at A-Site

The microwave properties of (Ca1-xBax)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ(0.0≤x≤0.2, CBLNZ) ceramics were investigated. A single phase with orthorhombic perovskite structure was obtained at x = 0.0 − 0.025. Both the εr and Qf value firstly increased with increasing Ba2+ content, and then began to decrease at x = 0.025. The τf value increased from −9.4 ppm/°C at x=0.0 to 18ppm/°C at x=0.2, which could be explained by the decrease of B-site bond valence in perovskite structure.

Phase Development and Microwave Dielectric Properties of Ba4(Sm1−yNdy)9.33Ti18O54

In order to study the effect of coexistence of Nd2O3 and Sm2O3 on phase development in Ba4 (Sm0.7Nd0.3)9.33Ti18O54 ceramics, the calcination process was applied in one-step and two-step way. From the XRD patterns of one-step calcinated powders, the solid-state reactions were deduced. And the results indicated the coexistence of Nd2O3 and Sm2O3 would be helpful to form secondary phase Nd2Ti2O7, which would worsen the properties. The final tested results of sintered samples confirmed the advantages of two-step calcination. The εr was improved from 72.1 to 82.4 and Q.f was improved from 7200 GHz to 8300 GHz, while τf was still near zero.