Papers by Keyword: PTCR

Abstract: Barium strontium titanate (BST), Ba_0.8Sr_0.2TiO₃ ceramic prepared using conventional solid-state reaction method has achieved a single phase at 1400 °C. The Ba_0.8Sr_0.2TiO₃ ceramic shows the highest dielectric constant and capacitance at 65°C about 4001 (10 Hz) and 2.92765 x10^-9 F, respectively. The conductivity of Ba_0.8Sr_0.2TiO₃ ceramic is in between the range of semi-insulator and insulator materials, and this composition also has exhibited the positive temperature coefficient resistivity (PTCR) properties jump of one order of magnitude from 2.06202 x 10⁷ Ω.cm to 3.00958 x 10^8­ Ω.cm measured at 1 kHz.

Abstract: Conditions for the formation of (1-x)BaTiO₃–xLi_0.5Bi_0.5TiO₃ (0 ≤ x ≤0.6) solid solutions with positive temperature coefficient of resistance (PTCR) effect were studied. Solid solutions were prepared by solid state reaction technique. Samples were sintered under reducing atmosphere N₂/H₂ in the temperature range 1200–1450 °C with subsequent oxidation in air. The phase composition was investigated by X-ray powder diffraction method. It was found that samples of (1-x)BaTiO₃–xLi_0.5Bi_0.5TiO₃ (0 ≤ x ≤0.6) solid solutions at room temperature exhibit perovskite structure. Unit cell parameters of unstable at the room temperature compound Li_0.5Bi_0.5TiO₃ were determined by extrapolation of concentration dependence of the unit cell parameters in the (1-x)BaTiO₃–xLi_0.5Bi_0.5TiO₃ system. It was shown that minimum value of resistivity ρ_min rises with increase in x value. Complex impedance method shown that ceramic grains of (1-x)BaTiO₃–xLi_0.5Bi_0.5TiO₃ materials consist of three areas with different electrical properties. Boundary and outerlayer region of grains make the main contribution to the PTCR effect in lithium-containing solid solutions. It was shown that magnitude of the potential barrier's decreases with increasing x.

Abstract: Porous Sb-doped barium titanate (Sb-BaTiO3) ceramics were fabricated by adding various amounts of graphite powders. The density, structure, microstructure, porosity and electrical resistivity of the porous Sb-BaTiO3 ceramics produced without and with graphite were investigated. All the sintered ceramics showed a tetragonal perovskite structure, irrespective of the amount of graphite added. The porosity of the ceramics increased and the grain size decreased with increasing graphite addition which mainly due to the exothermic reactions of the graphite and oxygen molecules in the ceramics. The prepared porous Sb-BaTiO3 ceramics exhibit PTCR behavior where the PTCR jump of the ceramics with graphite was about 103 which is higher than that of the ceramics without graphite. The increasing in the PTCR jump with increasing graphite addition was attributed mainly due to the increase in the electrical barrier height of grain boundaries and the porosity. It was found that the graphite is an effective pore forming agent for fabricating porous BaTiO3-based ceramics.

Abstract: In the firing process of ceramic products, the sintering conditions vary from firing phase to firing phase. In different firing phases, flame texture changes obviously, so it can be used as a important parameter of burning zone identification for ceramic roller kiln. In this paper, both flame image recognition of simulating artificial-look-fire and multi-point temperature detection technology are used to detect burning zone working conditions of ceramic roller kiln so as to greatly improve detection accuracy. The key data fusion algorithm of PTCR-based point detection temperature and flame image recognition–based detection method of burning zone working condition for ceramic roller kiln are proposed. The temperature measurement experiment system scheme of ceramic roller kiln burning zone is also given. The system can fuse the key process data with flame image characteristics so as to get the comprehensive database used to judge burning zone working conditions and temperatures. In the end, The testing experiment was carried out. The experimental results show that the method proposed above is feasible and effective.

Abstract: The conductive properties of donor doped BaTiO₃ semiconductor ceramic was studied with a quantitative model in this paper. Considering the influence of acceptor grain boundary segregation, a differential equation of electron level was established. According to a four order Runge-Kutta formula, the energy level of the grain boundary barrier was obtained at different temperatures numerically. Further, the PTCR effect of BaTiO₃ semiconductive ceramics was calculated.

Abstract: Ceramic samples of (1 x)BaTiO_3–xNa_0.5Bi_0.5TiO₃ system were prepared by sintering in reducing atmosphere of N₂/H₂ and were subsequently reoxidized in air. The influence of reoxidation temperature firing on the PTCR effect of (1 x)BaTiO_3–xNa_0.5Bi_0.5TiO₃ ceramics was investigated. The effect of Na_0.5Bi_0.5TiO₃ concentration on resistivity and microstructure of the reoxidized samples was investigated by means of complex impedance spectroscopy and scanning electron microscopy. It has been found that the grain size decreases with the increase in Na_0.5Bi_0.5TiO₃ content. The values of minimum ρmin and maximum ρmax resistivities of the samples were observed to increase with the increase in reoxidation temperature in the 600 – 1000°C temperature range. It was shown that with increasing in reoxidation temperature of (1-x)BaTiO_3-xNa_0.5Bi_0.5TiO₃ solid solutions, potential barrier at grain boundaries increases.

Abstract: Donor doped BaTiO3 is a well known PTCR material. Many PTCR theories have been written but none of them can completely explain the PTCR property. In this work, BaTiO3 samples doped with Sb, La, Nb and Pb ions and compacted under various uniaxial pressures were examined. Results show that Sb and La-doped BaTiO3 have PTCR properties corresponding to Heywang and Jonker models to a greater degree than Nb-doped BaTiO3. Moreover, it was found that La and Nb-doped Ba1-xPbxTiO3 samples sintered at l000-1100°C have good PTCR properties while samples of the same composition sintered at 1150-1200°C have fair to poor PTCR properties. The PTCR properties in these materials do not correspond to Heywang and Jonker models. The resistivity change in these materials at Curie’s point is relatively lower than the resistivity change at other temperatures.

Abstract: (1-x)KNbO3-xBaGeO3 based PTCR ceramic materials are prepared using high purity K2CO3, Nb2O5, GeO2, Al2O3 and BaCO3 powders as starting materials, and the structural and electrical properties have been investigated. The results indicated that the samples doped with minute Ba as donor show excellent PTCR effect above the temperature of about 36°C. For the 0.40at% Ba-doped sample, the minimum resistance of 4.2×104Ω·cm, temperature coefficient (αk) of 24.37%/°C, PTCR anomaly lg(Rmax/Rmin) of 3.82 and transition temperature (Tmin) of 36°C are obtained.

Abstract: The barium-excessive BaTiO₃ ceramics with BN addition for laminated positive temperature coefficient (PTC)thermistors are fabricated. The tape casting technique and reduction/reoxidation process are employed into the fabricating procedure. The influences of BN additive on ceramic characteristics are discussed. The addition over 5% leads to rectangular and abnormal large grains. The 5% BN-doped ceramics shows a resistivity of 233 Ω•cm and PTC jump of 3.4 orders of magnitude. The charge carrier density in grain bulk and acceptor state density at grain boundaries are evaluated. The correlation of BN doping amount with room temperature resistivity, PTC jump, reoxidation effect as well as charge carrier and acceptor state density are investigated.

Abstract: In order to achieve cost-effective inner electrodes for the multilayer BaTiO₃-based ceramics having a positive temperature coefficient of resistivity (PTCR), we fabricated Ni paste based on Ni powder and investigated the effect of Ni electrode on the performance of semiconducting BaTiO₃ ceramics. We adjusted the particle size of Ni powder (0.2μm, 0.6μm and 1μm) and incorporated them as the electrodes into both single-layer and laminated BaTiO₃ PTCR devices. The device samples were sintered at 1200oC for 30min in reducing atmosphere consisting of N₂ and H₂ (97:3 by volume ratio), and went through a post-sintering in-air heat treatment at 700-900oC in air which is necessary for the PTCR effect. The results indicate that Ni powder with lager particle size are more stable against post-sintering heat treatment, and the heating temperature needs to be optimized to overcome the trade-off between ohmic behaviors of Ni electrodes and the PTCR effect of BaTiO₃-based semiconducting ceramics.