High-Performance Ceramics IV

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Authors: Witold Mielcarek, Slavko Bernik, Krystyna Prociów
Abstract: Because of their unusual properties – non-ohmic behavior and the ability to absorb a lot of energy – metal-oxide varistors are widely used for the protection of electrical and electronic devices against over-voltages. ZnO ceramics have varistor properties because of their metal-oxide additives and the microstructures developed during sintering. The value of the varistor voltage depends largely on the number of conducting ZnO grains between the electrodes; this can be set by controlling the thickness of the device or the size of the grains. The desired grain size can be achieved by altering the composition of the metal-oxide additives and the sintering conditions. In this work the grain growth was controlled by combining two ZnO powders of differing sinterability in the starting material. Also, the use of BaBiO2.77 as a precursor for Bi2O3 is an innovation in varistor technology that makes it possible to reduce the amount of added metal oxides. As a result, a variety of varistors with good varistor properties and a wide range of working parameters were produced.
Authors: Tomasz Janiczek, Dorota Nowak, Witold Mielcarek, Krystyna Prociów
Abstract: Metal oxide modified Bi2O3 finds the application in metal oxide varistors and as ionic conductors. Electrical properties of MeO-modified Bi2O3 change with MeO modifier and sintering temperature. In this paper we report how to predict Bi2O3 electrical properties using simulation model. Measurements of the electrical response of the modified Bi2O3 oxides were carried out using the impedance spectroscopic technique. As a result an equivalent model of electrical behaviour of modified Bi2O3, described by fractional derivates was proposed. To test the model, the series of simulation were run on computer, and after subjecting the results to verification the equivalent parameters of electrical circuit were determined. Model was elaborated with the view of facilitating the research on metal oxide ionic conductors and varistors.
Authors: Jing Nan Cai, Yuan Hua Lin, Rong Juan Zhao, Ce Wen Nan, Jin Liang He
Abstract: ZnO-Pr6O11-Dy2O3-based varistor ceramics doped with 0~1.5 mol% La2O3 were fabricated by a conventional ceramic method. All the samples were sintered at 1350 oCfor 2 h. The phase composition and microstructure of the ceramic samples have been investigated by XRD, SEM and EDS. The results of SEM micrographs indicated that the La2O3 additives can promote ZnO grain’s growth, and the rare earth elements dispersed mainly in the intergranular phase observed by EDS. The electrical properties of the samples determined by the V-I curves revealed that the breakdown voltage of samples decreases from 508 V/mm to about 100 V/mm with the increase of La2O3, and the nonlinear exponent also decreases from 20.2 to 13.2. The typical leakage current is about 10.2 μA for the sample doped with 0.5 mol% La2O3.
Authors: Zhou Zhang, Hui Ming Ji, Yan Fei Gu, Xiao Dong Chen, Dao Yin Yu
Abstract: Pure and Cu2+-doped LaFeO3 thin films were prepared on Al2O3 substrate by polymer complex method using La(NO3)3⋅6H2O, FeCl3⋅6H2O and Cu(NO3)2⋅3H2O as raw materials, citric acid (CA) as chelating agent and ethylene glycol (EG) as cross-linking agent. As-growth thin films were well-crystallized and the grain size was about 40nm after being annealed at 650°C. The sensitivities of pure and Cu2+- doped LaFeO3 thin films to 80 ppm acetone gas measured at 350°C were 315 and 30, respectively. Partial substitution of Fe3+ in LaFeO3 with Cu2+ could widen testing temperature of the materials.
Authors: Zhi Dong Han, Li Min Dong, Ze Wu, Lian Wei Shan, Xian You Zhang
Abstract: BaFe12O19 and La-Mn substituted M-type Ba hexaferrites were synthesized by sol-gel method and characterized by XRD, SEM and FTIR. The results showed that citric acid played an important role in the forming process of BaFe12O19. BaFe12O19, synthesized under lower citric acid and presintered at 450°C, showed improved hexagonal crystal phase. BaLa0.5Fe11.5O19 and Ba(MnLa)0.5Fe11O19 showed similar crystal structure to BaFe12O19 while Ba0.5Mn0.5Fe12O19 and Ba0.5Mn0.5La0.5Fe11.5O19 showed changed crystal constant. FTIR analysis proved the formation of new mental-oxygen bond in substituted hexaferrites.
Authors: Xi Wei Qi, Zhi Yong Yu, Ming Ya Li, Ji Zhou, Zhen Xing Yue
Abstract: A series of novel composites with the composition of xNiCuZn-(1-x)PZT (NiCuZn: Ni0.2Cu0.2Zn0.6Fe2O4; PZT: PbZr0.52Ti0.48O3.) were prepared by solid-state reaction methods. The presence of ferromagnetic NiCuZn ferrite phase and ferroelectric PZT phase was confirmed by XRD analysis. It was revealed that composite materials exhibit typical ferromagnetic hysteresis behaviors. With the increase of phase fraction of NiCuZn ferrite, the permeability of composites increases and the natural resonance peak appears. Meanwhile, the maximum of quality factors shifts to the lower frequency.
Authors: Pei Bian, Dong Ying Ju
Abstract: Low temperature sintering NiCuZn ferrite was employed at most cases due to its co-firability with Ag (below 960°C). The purpose of this study is to fabricate NiCuZn ferrite sintered body with high-strength and high-frequency magnetic properties. Following is the procedure: firstly, NiCuZn ferrite powder was synthesized under CO2 atmosphere at 500°C from the mixed doxalate synthesized by liquid phase deposition method; then a small amount of boric acid [H3BO3] was added to the powder, and the NiCuZn ferrite powder compact was prepared with Newton press and CIP methods; finally, NiCuZn ferrite sintered body was fabricated by sintering at 900°C under CO2 atmosphere. By this method, NiCuZn ferrite sintered body with 0.5 mass% boric acid was obtained, which was additive with strength 340 MPa, high frequency applied scope below 20MHz and initial permeability 38.
Authors: S.A. Seyyed Ebrahimi, Z. Pishgahi Fard
Abstract: Manganese- Zinc ferrite is one of the most important spinel ferrites which is used in the electronics applications. These ferrites have an open lattice and can tolerate large amounts of the other metallic ions in their lattice. One of these divalent ions that can sit in the unit cell of Mn-Zn ferrites is Magnesium. Mn-Mg-Zn ferrites are new materials which is thought to be a good candidate for dielectric applications. In this work, a suitable relative values of raw materials for preparing pure Mn-Mg-Zn ferrite powder have been determined. It is carried out by using XRD experiments. The optimum temperature and time of calcination were also investigated by DTA/TGA, XRD and SEM techniques.
Authors: S.A. Seyyed Ebrahimi, H. Sepehri Amin, Y. Hormozan, P. Tabibzadeh
Abstract: Mn-Zn ferrites with chemical formula (Mn-Zn) Fe2O4 have widespread applications in the electrical and electronics industries. These ferrites are synthesized generally by conventional method. This method, which contains calcination of raw materials, is affected by several parameters such as composition and purity of the raw materials and temperature, time and atmosphere of the process. Optimization of these parameters is very important because these parameters affect the magnetic and electrical properties of the material. In this work, the ratio of the different Iranian routs of the raw materials for production of high Ms ferrite powder has been optimized and the effects of calcination conditions have been investigated using XRD, DTA/TGA techniques. The magnetic properties have also been measured.
Authors: Yan Ling Dong, Pi Yi Du, Wen Jian Weng, Gao Rong Han
Abstract: Ferroelectric/ferromagnetic multiphase powdered composites, consisting of PbTiO3 as ferroelectric phase and NiFe2O4 (PbFe12O19) as ferromagnetic phase, were successfully prepared in situ by sol-gel process. The phase structure, morphology and magnetism properties were observed. Biphase powdered ME composite consisting of PbTiO3 and NiFe2O4 is obtained at 700oC. Triphase composite consisting of PbTiO3, NiFe2O4 and PbFe12O19 is obtained above 750oC. With increasing heat-treatment temperature, the particles combine more tightly and the particle size decreases. The saturation magnetization (σs) and the initial permeability (μi) increase with the increase of NiFe2O4 content. The coercive force (Hc) increases with the increase of PbFe12O19 content.

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