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Journal ArticleDOI

Microstructure and Electrical Properties of La2O3-Doped ZnO-Bi2O3 Based Varistor Ceramics

01 Aug 2009-Advanced Materials Research (Trans Tech Publications Ltd)-pp 2007-2010
TL;DR: In this paper, the microstructure and electrical properties of the varistor ceramics were studied by a solid reaction route, and the results showed with addition of 0-1.00mol% La2O3 and 0.08mol% ZnO-based varistor Ceramics exhibit comparatively ideal comprehensive electrical properties such as the threshold voltage was 320V/mm, the nonlinear coefficient was 36.8 and the leakage current was 0.29μA.
Abstract: La2O3-doped ZnO-Bi2O3-based varistor ceramics were obtained by a solid reaction route, and the microstructure and electrical properties of the varistor ceramics were studied in this paper. The results showed with addition of 0-1.00mol% La2O3, La2O3-doped ZnO-based varistor ceramics were prepared in this paper with the voltage gradient of 77-503V/mm, the nonlinear coefficient of 2.4-36.8, and the leakage current of 0.09-494μA. The results also showed with addition of 0.08mol% La2O3, La2O3-doped ZnO-based varistor ceramics exhibit comparatively ideal comprehensive electrical properties. Such as the threshold voltage was 320V/mm, the nonlinear coefficient was 36.8 and the leakage current was 0.29μA. The doping of La2O3 affects the form and decomposition of the pyrochlore.
Citations
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Journal ArticleDOI
TL;DR: In this article, the dielectric and varistor properties of Zn-substituted CaCu 3 Ti 4 O 12 (CCZTO) were analyzed by a precision impedance analyzer and a varistor tester, respectively.

60 citations

Journal ArticleDOI
TL;DR: In this article, the microstructure and electrical properties of ZnO-Bi 2 O 3 -based varistor ceramics doped with different Sc 2O 3 content sintered at 1100°C were investigated.

57 citations

Journal ArticleDOI
TL;DR: Y(NO 3 ) 3 ·6H 2 O-doped ZnO-Bi 2 O 3 -based varistor ceramics were prepared using a solid reaction route as mentioned in this paper.

47 citations

Book
01 Jan 2009
TL;DR: In this paper, the authors present a collection of peer-reviewed papers on multi-functional materials and structures for various engineering applications, and make a valuable contribution to the literature on the subject.
Abstract: With the rapid development of science and technology, the functionalization of structural materials, and the structurization of functional materials are attracting increasing attention in the scientific and engineering fields. The development of multi-functional materials and structures (MFMS), at the micro- and nano-scale levels, has grown rapidly due to the requirement of increasing safety margins for all infrastructure, biomedical and engineering elements. Multi-functional material systems are capable of performing multiple 'primary' functions, simultaneously or sequentially in time, and are specially designed to improve system performance via a reduction in the redundancy between sub-system materials and functions. Materials having special structures can exhibit multi-functional properties. For example, shape-memory alloys can act as actuators as well as sensors, and the aim of composite materials is to exploit each aspect's advantages; plus their synergistic effect. The current collection of peer-reviewed papers focuses on multi-functional materials and structures for various engineering applications, and makes a valuable contribution to the literature on the subject.

45 citations

Journal ArticleDOI
TL;DR: In this article, the microstructures of the varistor ceramics samples were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM).

43 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the authors present a review of the history of SnO2-based voltage-dependent resistors, discusses the main characteristics of these polycrystalline semiconductor systems and includes a direct comparison with traditional ZnO-based resistor systems to establish the differences and similarities.
Abstract: The present review describes mainly the history of SnO2-based voltage-dependent resistors, discusses the main characteristics of these polycrystalline semiconductor systems and includes a direct comparison with traditional ZnO-based voltage-dependent resistor systems to establish the differences and similarities, giving details of the basic physical principles involved with the non-ohmic properties in both polycrystalline systems. As an overview, the text also undertakes the main difficulties involved in processing SnO2- and ZnO-based non-ohmic systems, with an evaluation of the contribution of the dopants to the electronic properties and to the final microstructure and consequently to the system’s non-ohmic behavior. However, since there are at least two review texts regarding ZnO-based systems [Levinson, L. M., and Philipp, H. R. Ceramic Bulletin 1985;64:639; Clarke, D. R. Journal of American Ceramic Society 1999;82:485], the main focus of the present text is dedicated to the SnO2-based varistor systems, although the basic physical principles described in the text are universally useful in the context of dense polycrystalline devices. However, the readers must be careful of how the microstructure heterogeneity and grain-boundary chemistry are capable to interfere in the global electrical response for particular systems. New perspectives for applications, commercialization and degradation studies involving SnO2-based polycrystalline non-ohmic systems are also outlined, including recent technological developments. Finally, at the end of this review a brief section is particularly dedicated to the presentation and discussions about others emerging non-ohmic polycrystalline ceramic devices (particularly based on perovskite ceramics) which must be deeply studied in the years to come, specially because some of these systems present combined high dielectric and non-ohmic properties. From both scientific and technological point of view these perovskite systems are quite interesting.

262 citations

Journal ArticleDOI
Dong Xu1, Liyi Shi1, Zhenhong Wu1, Qingdong Zhong1, Xinxin Wu1 
TL;DR: In this article, the effect of sintering processes on the microstructure and electrical properties of ZnO-Bi2O3-based varistor ceramics was investigated.
Abstract: The effect of sintering processes, such as open sintering, sintering inside a closed crucible, and sintering within a powder bed, on the microstructure and V–I characteristics of ZnO–Bi2O3-based varistor ceramics was investigated at sintering temperatures in the range 1000–1200 °C. The results from the experiments showed that the microstructure and electrical properties of the samples varied according to the sintering method and temperature. Optimal values for the electrical characteristics of the varistor ceramics by different sintering processes were obtained when the sintering was conducted at 1100 °C. At the same sintering temperature, the different processes affected the properties differently. At 1000 °C, the samples sintered within a powdered bed showed better electrical properties than those subjected to the other two processes, while at 1100 or 1200 °C, the samples sintered in an open crucible exhibited the best electrical properties.

118 citations

Journal ArticleDOI
TL;DR: The microstructural and electrical properties of ZnO-Bi 2 O 3-based varistor ceramics doped with Y 2O 3 in the range from 0 to 0.9 mol% have been investigated in this article.
Abstract: The microstructural and electrical characteristics of ZnO–Bi 2 O 3 -based varistor ceramics doped with Y 2 O 3 in the range from 0 to 0.9 mol% have been investigated. The addition of Y 2 O 3 resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase along the grain boundaries of the ZnO grains which inhibits the grain growth. The mean ZnO grain size decreased from 11.3 to 5.4 μm with increasing amounts of Y 2 O 3 . The threshold voltage ( V T ) of the ceramics increased from 150 to 274 V/mm, the non-linear coefficient α was not influenced and remained at approximately 40, and the leakage current also increased with the amount of Y 2 O 3 added. On the basis of the Mukae et al. (Mukae, K., Tsuda, K. and Nagasawa, I., Capacitance-vs-voltage characteristics of ZnO varistors. J. Appl. Phys ., 1979, 50 , 4475–4476) Schottky barrier model of ZnO varistors, the addition of Y 2 O 3 resulted in a slight increase in the density of interface states ( N S ) and a more pronounced increase in the donor density ( N D ), causing a decrease of the barrier height ( Φ B ) and the depletion layer width (t). The increase of the leakage current ( I L ) with higher amounts of Y 2 O 3 added can be ascribed to the increase in donor density (N D ) as well as to the increased amount of Y 2 O 3 -containing phase at the grain boundaries of ZnO.

75 citations

Journal ArticleDOI
TL;DR: In this article, the influence of Al2O3 doping in the range 0.00-0.83% on the microstructure and currentvoltage characteristics of ZnO-based varistor ceramics sintered at 1200°C for 2h was studied.
Abstract: The influence of Al2O3 doping in the range 0.00–0.83 mol% on the microstructure and current–voltage characteristics of ZnO-based varistor ceramics sintered at 1200 °C for 2 h was studied. The threshold voltage VT (V/mm) increased up to a dopant level of about 0.08 mol% Al2O3; the nonlinear coefficient α was significantly increased by additions of up to 0.04 mol% Al2O3, although larger additions of Al2O3 caused it to decrease; and the leakage current increased sharply with increasing amounts of Al2O3. Doping with Al2O3 up to about 0.12 mol% Al2O3 resulted in a significantly decreased ZnO grain size, which is mainly responsible for the significantly increased threshold voltage, VT. No ZnAl2O4 spinel phase was detected in any of the samples, and EDXS and WDXS analyses showed that most of the added Al2O3 distributed between the Zn7Sb2O12 spinel phase and the ZnO phase, while only trace amounts were detected in the Bi2O3-rich phase. The spinel phase incorporates an appropriate amount of Al2O3; however, with an increasing amount of added Al2O3, more of it remains outside the spinel phase in the Bi2O3-rich liquid, where it can incorporate into the growing ZnO grains at the sintering temperature. The amount of Al in the ZnO grains was determined. A mechanism for the grain growth inhibition resulting from the small amounts of Al2O3 in the Bi2O3-rich liquid phase is also proposed.

63 citations

Journal ArticleDOI
TL;DR: In this paper, X-ray fluorescence analysis is performed to describe the Bi 2 O 3 vaporization profile as a function of distance to the outer surface, taking into account its influence on microstructural evolution.
Abstract: Bi 2 O 3 -doped ZnO ceramic varistors are usually sintered at temperatures near to 1200 °C in the presence of a Bi-rich liquid phase, which is partially vaporized during the sintering process Volatilization of bismuth oxide depends on the total surface area in direct contact to the reaction atmosphere and this in turn is related to the area/volume ratio of the ceramic compact This loss of Bi 2 O 3 has a significant role on the development of the varistor microstructure and more specifically ZnO grain growth, which is strongly enhanced by the presence of the liquid phase, should be particularly affected In the present paper, X-ray fluorescence analysis is performed to describe the Bi 2 O 3 vaporization profile as a function of distance to the outer surface, taking into account its influence on microstructural evolution

63 citations