Papers by Author: Yuan Fang Qu

Abstract: Samples of La(TixMn1-x)O3 (0.1 ≤ x ≤ 0.7) were sintered at different temperatures. The experimental results showed that the resistivity-temperature curves of the samples match NTC characteristic. The crystal structure was analyzed using X-ray diffraction and the microstructure was observed by scanning electron microscope.

Abstract: Microstructure and dielectric properties of Ba0.62Sr0.38TiO3 ceramics doped with x mol% (x=0.2~0.6) Y2O3 were investigated. SEM showed that Y3+ can accelerate growth of the grains at first, then turn to inhabit growth of the grains with further addition of Y3+ above 0.8mol%. The experimental results showed that the dielectric constants were improved with the additive amount of Y3+ increasing, if the amount of Y3+ increased continuously, the dielectric constants will drop, whereas the dielectric losses of the samples descended rapidly in the beginning, then went up obviously with further addition of Y3+ above 1.0mol%, the optimal dielectric constant and dielectric loss could reach 6700 and 0.0015 in the room temperature, respectively.

Abstract: Ferroelectric properties of (Bi1/2Na1/2) TiO3-SrTiO3 were studied. The dielectric properties were measured at 1KHz. It was found that the dielectric constants are improved with the increase of additive amount of BNT. If the amount continues increasing, the properties become worse, the optimum dielectric constant of the samples can reach 4300. When the proportion of (Bi1/2Na1/2)TiO3: SrTiO3 is 65:35, with the increase of additive amount of MnCO3, the Curie temperature descends obviously. The dielectric constant increased at beginning and dropped sharply when the amount of MnCO3 exceeds 1.1wt%.

Abstract: For the nano-ZrO2 powders, it is difficult to disperse the particles in a highly concentrated electrolyte. Polymer MZN with composite structure was employed as a dispersant in this work. On the basis of having obtained the optimum quantity of dispersant MZN, the effects of process conditions on stability of Ni-ZrO2 composite electroplating bath were investigated via sedimentation experiments and SEM micrograph. The results showed that the charging sequence have a significant influence on the stability of composite electroplating bath, and the optimum process conditions is that the stable aqueous suspension of 2.5g nano-powders in 100 ml water should be prepared at first by milling for 3 hours, and then the electrolytes were added in it. The well-dispersed composite electroplating bath was obtained, which made sure that the nano-ZrO2 smaller than 30nm was found in the Ni matrix.

Abstract: Nickel/graphite/BaTiO3 PTC composites with lower room-temperature resistivity and higher resistance jump were fabricated by adding graphite and nickel powders into BaTiO3 PTC ceramics. Characteristics and conductive mechanism of the composites were discussed based on the experimental results.

Abstract: High-performance PTCR ceramics with low resistivity (8Ω.cm) at room temperature and around four orders magnitude of the PTCR jump were obtained by adding BaCO3 and Pb3O4(B-P) in BaTiO3. The influence of adding B-P on the sintering behavior, the microstructure and the electrical properties of BaTiO3-based PTCR was investigated. The phase constituent in the sintered ceramics was analyzed by XRD and it was shown that the metallic layered Ba3Pb2O7 phase was synthesized during the sintering. Analysis suggested that making the weak reduction atmosphere at the grain boundary may decrease the grain-boundary resistivity.

Abstract: The influence of grahtite and bakelite content of Graphite/Bakelite/BaTiO3-based PTC ceramic composite on their properties was studied. It was found that the composite's room- temperature resistivity was decreased and the PTC intensity was assured. This method offered a new way to solving the problem of high room-temperature resistivity of the BaTiO3-based PTC ceramic.

Abstract: Ni/BaTiO3 composite was prepared by decomposition of NiC2O4·2H2O/BaTiO3 precursor, which was prepared by precipitating of nickel in the form of oxalate into the BaTiO3 slurry. The composite must be sintered in reducing atmosphere. Otherwise NTC effect would be introduced. The prepared composite almost had no PTC effect. But PTC effect of the Ni/BaTiO3 composite can be effectively renewed by heat-treatment in air. Under a proper composition and method, the composite shows low room-temperature resistivity (ρRT=6.0 Ω·cm) and obvious PTC effect (ρmax/ρmin=102).

Abstract: The effects of glass additives on the sintering and properties of Ni/(Ba0.92Sr0.08)TiO3 composites were investigated. Due to the addition of glass additives, Ni/ceramic composites with low room-temperature resistivity and obvious PTC effect were obtained at a low sintering temperature. It was shown that glass-additives could form liquid phase that aided the solution and diffusion of solid atoms, acting as sintering aids to accelerate the sintering and lower the sintering temperature. The room-temperature resistivity decreased first and increased later with the increasing content of glassadditives, which was explained by two functions of glass-additives, decreasing interface contact resistance as sintering aids and adding volume resistance as insulators. Moreover, a suitable amount of glass-additives could enhance the PTC effect unexpectedly, which was attributed to the decrease of the contact resistance existing at the ceramic/ceramic interface.