Many samples with differents nonlinear currentvoltage characteristics according to the specific chemical. Article pdf available in american ceramic society bulletin 654. The microstructure of a zno varistor material springerlink. A zno ptfe nanocomposite is formed from a cold sintering process with volume fractions of ptfe up to 40 vol%. Pdf electrical degradation of doubleschottky barrier in. The purpose of this thesis is to study and explore the advantages of zno based tfts deposited by metalorganic chemical vapor deposition mocvd. In this paper a detailed nature of the electrical potential barriers in zno based varistors are presented. Pdf advances in the synthesis of zno nanomaterials for. Selfassembled arrays of zno nanoparticles and their. The relationship between the electrical parameters and the intrinsic material parameters of zno. Effect of impurities and temperature on electrical. Characteristics of sno2doped znobased varistor ceramics. Response surface methodology for optimization of sintering process for preparation of zno low.
Electrical degradation of doubleschottky barrier in zno varistors jinliang he, chenlu cheng, and jun hu citation. Binesti, phd thesis, university of bordeaux i, bordeaux. The starting composition z12 has the following composition written in mol%. Recent advances in study of zno materials by atomicscale firstprinciples calculations are partly included and discussed, which brings to our attention distinct cognition on the native. Pdf zno varistors with high voltage gradient and low leakage.
Rareearth re doping can greatly enhance the voltage gradient of zno based varistors, and their nonlinear coefficient, leakage current, energy absorption capability, throughcurrent capability and residual voltage can also be improved to certain extent. Modern methods for the microscopic characterization of zno. The microstructure of these varistors consists of zno grains surrounded by thin insulating metal oxide barriers. A systematic study of the defects in zno has been performed. The exceptional nonlinear current voltage iv characteristics and energyabsorption capabilities of zno based varistors are strongly related to their microstructure, which develops during the process of firing zno with small additions of bi 2 o 3, sb 2 o 3, co 3 o 4, mn 3 o 4, cr 2 o 3, nio and other oxides. Begum, shahida 1996 powder processing parameters and their influence on the electrical performance of zno varistor. Typical vi characteristic of a zno varistor the relationship between voltage and current of a varistor can be approximated to. Completely uptodate, this is the first comprehensive monograph on metal oxide varistors with a focus on microstructure, conduction mechanisms, device failures, ageing, additive impacts and future varistor systems. The main focus of this work was to develop novel industrially viable procedures, based on sol gel technology, for the preparation of nanosize doped zno materials for varistor applications. Zno varistor system is a multiphase one being the zno grains as predominant phase and several secondary phases as the spinel phase zn 7 sb 2 o 12, pyrochlore phase zn 2 bi 3 sb 3 o 14 and a polymorphic phase of bismuth oxide.
Besides these established applications, zno and its ternary alloys are now also being considered as potential materials for. This class of material has been characterised with special emphasis on the functional microstructure and the development of the microstructure during sintering. By this method a peak for the interface states of zno varistors was detected at higher temperatures for the first time. Pdf metal oxide znobased varistor ceramics researchgate. Typical currentvoltage characteristics for zno varistors 2. By careful control of the microstructure, through nanostructuring by chemical routes, it should be possible to produce varistors with high breakd. Department of science and technology itn, campus norrkoping, linkoping university, se601 74 norrkoping, sweden. The sintering process of metal matrix composites and ceramic varistors has been studied in this project. They protect electrical equipment from damage by limiting overvoltages and dissipating the associated energy.
Computer simulation of zno varistors failures unt digital. Unpublished msc thesis, school of mate rials engineering, northern malaysia. The obtained phases were used for preparation of varistor mixtures with phase compositions listed in tab. It is very clear from the above figures that the major reflections between 30 and 40 2. It involves coating zno nanoparticles with sio2 through the hydrolysis of tetraethyl orthosilicate teos and the subsequent coating of additives on the core of the sio2coated zn.
The full sintering process of doped zno powder granules was studied insitu in the environmental sem. A new interpretation for the degradation phenomenon of zno varistors. Stability of zinc oxide varistors a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical sciences 2014 poonsuk poosimma school of materials. When rareearth oxide additives are added into zno varistors, the growing speed is slowed down due to the. The most famous type of varistor is metal oxide varistor mov, which is also called as zno varistor. Microstructure and electric properties of a sno2 based. The quality of our products is oneup in china, its residual voltage ratio is little and ageing performance is excellent. Abstract of thesis presented to the senate of universiti putra malaysia in fulfillment of the requirement for the degree of master of science. The minor constituents segregate to the grain boundaries to help.
The emphasis is given to the fabrication of dense, uniform and defectfree zno layers for the memristive application by. Preparation and characterization of zinc oxide 69 figure 3. Electrical properties of zno varistors prepared by direct. Such ceramics contain conductive grains of doped zno with highly resistive nearsurface. This class of material has been characterised with special emphasis on the functional. Firstly, the effects of zno nanoparticles, ph value of chemical solution, angel. Novel znobased ternary oxides for optoelectronic applications. University of wollongong thesis collection university of wollongong thesis collections 20 synthesis and characterizations of highly crystalline zno nanocrystals grown on silicon substrate using a novel method xuchuan wang university of wollongong research online is the open access institutional repository for the university of wollongong. Heuer american ceramic society, columbus, ohio, 1983 p. The effect of the starting powders particle size on the. The microemulsionb table 2 comparative study of electrical properties for zno varistor synthesized using microemulsion a and microemulsion b properties of zno particles leakage method of synthesis grain size critical voltage current ocmax m kvcm znaotethanolisooctane. Synthesis of zno nanoparticles for varistor application using. Solgel chemical method was used to develop the uniform zno nanoparticles, in a folic acid template at room temperature and ph 7.
Synthesis and characterisation of nanocrystalline zno for. Electrical barriers in the zno varistor grain boundaries. A zno varistor from metal oxide diffusion figure 1. The results showed that in the case of using zno nano powder, sintering time. Stability of zinc oxide varistors research explorer. We performed a comparative study of electrical and thermal properties of zno. Exploration of zno and znmgozno thin film transistors. Much of the research on zno varistors has concentrated on the explanation of their dc currentvoltage characteristics.
It is found that the sintering temperature of v2o5added zno will be lower down to about 600oc. Chemical preparation and properties of highfield zinc oxide varistors volume 1 issue 1 r. It was preserved for the fabrication of varistor discs. These varistors are used to protect circuits against excessive voltages. Temperature dependence of zinc oxide grain resistivity in. This is to certify that the thesis entitled synthesis and characterization of zno nanoparticles is submitted by mr. The currentvoltage iv nonlinearity of the varistor is a. Wortai electric has manufactured the metal oxide varistor, mov blocks, zno varistor, zinc oxide varistor for more than 20 years. Thesis submitted to the school of graduate studies, universiti putra malaysia, in fulfillment of the. Zno passes away in manufacturing of simpler zno devices like ceramic varistors, piezoelectric transducers etc. We present experimental evidence to show that the highly nonlinear currentvoltage characteristics, with. Jayanta kumar behera, roll no 407ph102 to this institute in partial fulfillment of the requirement for the award of the degree of master of science in department physics, is a bonafied record of the work carried out under my. Bi2o3, and spinel, synthesis of varistor ceramics from powder mixtures of constituent phases.
Ambient oxygen gas suppressed increases in the leakage current during ac biasing, while it rejuvenated degraded samples. Grain boundaries in model zno bi 2 o 3 and zno bi 2 o 3 coo varistors and a commercial multicomponent varistor have been characterized by high. The elemental distribution of zno based ceramics was analysed with an electron microprobe jeol jcxa733. Onedimensional zno nanostructures have great potential applications in the fields of optoelectronic and sensor devices. Metal matrix composites of a1a1203 and al6061sic and ceramic zno varistors were manufactured through compaction and sintering process. The work presented in this thesis is concerned with the microstructure of zinc oxide varistor materials used in surge protecting devices. Preparation of zno varistors by the dmcp method proceeded in two steps.
These grain boundaries in the microstructure results in a few device. Today, the majority of varistors produced commercially are based on zno with minor additions 2 of typically bi 2 o 3, sb 2 o 3, coo, mno 2 and cr 2 o 3. Unpublished msc thesis, school of materials engineering, northern malaysia. Zno based varistors are widely used for overvoltage protection in many electrical and electronic circuits, at voltages ranging from a few to over a million volts.
The excellent nonlinear currentvoltage iv characteristic of these varistors is attributed to the potential barriers formed between the successive zno grains during the processing cycle. This thesis focuses on the synthesis, characterizations and specific applications of two undoped and doped metal oxide nanostructures like zno and iron oxide. The two commonly observed levels l1, l2, located at around 0. Microstructural analysis of znopr6o11nd2o3 varistor ceramic. Nanoscale characterisation of barriers to electron. Relative 0002 peak intensities show that the quality of. The work presented in this thesis is concerned with the microstructure of zinc oxide. The arrhenius plots of the emission rate gave the depths of the interface states of 1.
Characterization of zno nanoparticles grown in presence of. The filler is made of commercially available doped zno varistor powder. The deep level transient spectroscopy depth profiling technique is applied on multilayer. Details of the varistor preparation procedure using dmcp can be found elsewhere 6, 7. Synthesis of novel coreshell nanocomposites for fabricating. Chapter vi, which is the core part of this thesis work, is mainly devoted to the characterization study of znobased building blocks. During that period zno based ceramics with their highly nonlinear currentvoltage characteristics have accrued more than half of the varistor market in numbers and nearly 80% of the market in value as reported by okinaka and hata 2. Parameters on the microstructure and energy absorption characteristics of low voltage zno varistors by damian michael me ardle bsc, dis this thesis is submitted as fulfillment of the requirements for the award of master of engineering to dublin city university sponsoring establishment. The zno varistor was initially invented by matsuoka in. Microstructural control of zinc oxide varistor ceramics.
The cu2o addition deteriorates the electrical properties of zno varistors, which is a good agreement with similar findings on ag2o additions. Synthesis and optical properties of zno nanostructures. Lowvoltage zno varistor fabricated by the solutioncoating method. The effect of ambient gases on degradation and rejuvenation of zno varistors was investigated from the viewpoint of voltagecurrent characteristics. Varistors prepared from the nanoarray zno by sintering 1050 c with appropriate mixtures of metal oxides showed a breakdown voltage of 786 30 v mm. The polymer is distributed along grain boundaries and used to limit current from across adjacent grains, enabling this varistor response, with. Powder processing parameters and their influence on the electrical performance of zno varistor a thesis submitted to dublin city university in fulfilment of the requirements for the degree of doctor of philosophy by shahida begum, bsc eng name of supervisors prof m s j hashmi dr ramon puyane collaborating establishment harris corporation. Synthesis and characterization of zno nanostructures. Zinc oxide zno varistor, which is a kind of polycrystalline semiconductor ceramic composed of multiple. A novel varistor composite synthesis for the fabrication of high breakdown voltage zno varistors has been successfully developed.
A comparative study of thermal conductivity in zno. The electrical properties and impedance analysis of zno. Synthesis and characterization of solgel derived zno thin. A comparative study between the effects of magnetic and.
The influence of the defect structure of zno grains on the electrical properties of zno varistors, on sintering parameters and temperature of subsequent heat treatment, was studied. Ceramic varistors based on zno, bi2o3, sb2o3, mno and co3o4 were prepared by the mixed oxide route. Synthesis of zno based nanopowders via a nonhydrolytic. The thesis highlights the development of novel synthesis techniquesprocedures which are rapid, consume. Although both mn and al do not influence the wellknown peaks related to wurtzite structure of zno ceramics, some other unknown peaks could be formed at higher doping conte. Advances in the synthesis of zno nanomaterials for. The presented varistor composite materials show very low values for the breakdown field strength down to 200 v mm. The best fitted impedance analysis reveals that the cu2o addition increases grain resistance and lowers the grain boundary resistance, results in low nonlinearity and higher leakage current of zno varistors. The densification and grain growth processes were studied through the sintering cycle. Zinc oxide varistors are multicomponent ceramic devices produced by sintering zno powder together with small amounts of other oxides. Progress on rareearth doped znobased varistor materials.
Compositions of the starting phases were the following. The formation of a functional microstructure in zno varistor materials was found to depend strongly on the total pressure. Lowvoltage zno varistor fabricated by the solutioncoating. They have become more and more important during the past four decades due to their highly nonlinear electrical characteristics and their large energy absorption capacity. Hrem and stem of intergranular films at zinc oxide. The first type was a bottom gate tft made on a substrate of silicon. A model of znozno grain boundaries in a zinc oxide varistor. Pillai tcd thesis 6659 synthesis and characterisation. Nanoscale characterisation of barriers to electron conduction in zno varistor materials.
The polycrystalline filler particles act as varistors due to their typical grainboundary structure. The degradation of the epoxy resincoated commercial zno varistors at. The microstructure of a zno varistor material has been investigated by a combination of xray diffractometry and analytical electron microscopy sem, tem, stem, edx. Requirements for the degree of doctor of philosophy. A comparative study between effects of mn and al on the properties of zno varistor sintered at 1200 is investigated by xrd, sem hardness, and iv measurements. Introducing a znoptfe polymer nanocomposite varistor.
V voltage c varistor voltage at 1 a i actual working current tangent of angle curve deviating from the horizontal examples when. Abstract the zinc oxide varistor with a low threshold voltage and large grain size was derived with zno crystalline seeds from a molten salt process the chemical composition and iv characteristics of single grains and single grain boundaries were determined by means of energy dispersive spectrum eds and microcontact measurement respectively. Ceramic materials based on zinc oxide zno with small additives of some other oxides exhibit highly nonlinear currentvoltage characteristic and, therefore, they have a wide application as varistors, devices for protection of electrical and electronic equipment against overvoltage. Elaboration of zno based varistors and the effect of the. The spinel is the product of the reaction between zno and sapphire. Electron holography study of active interfaces in zinc oxide varistor. In this study, v2o5 is added as the varistor forming oxide to lower down the sintering temperature of zno varistors for the further developing the chip varistor array by using the ag as the inner electrode. Synthesis and characterization of zno nanoparticles. The compressibility of a1a1203 was studied with respect to lubrication and volume fraction of. Volume 34, issue 7, september 2008, pages 16971701. The degradation of epoxy resincoated zno varistors. Powder processing parameters and their influence on the.
Electrical degradation of doubleschottky barrier in zno. Olsson, interfacial microstructure in zno varistor materials, ph. A zinc oxide zno varistor is an electronic ceramic material that possesses a nonlinear current i and voltage v characteristics with a symmetrical sharp. Pdf on sep 6, 2011, mohammad reza meshkatoddini and others. However, varistors also have unusual ac properties which can be technologically important, and must be described by any comprehensive model. Structural, electrical and optical properties of ptype zno epitaxial films by arnold l. Investigation of various models for metal oxide varistors. Microstructural control of zinc oxide varistor ceramics springerlink. Varistors 1 are materials with unique nonlinear, currentvoltage characteristics that allow them to be employed in voltage surge protection applications. Allenic a dissertation submitted in partial fulfillment of the requirements for the degree of doctor of philosophy materials science and engineering in the university of michigan 2008 doctoral committee. Highly nonlinear currentvoltage iv characteristics of zno varistors are used in electrical surge arresters. Modern methods for the microscopic characterization of zno varistor grain boundaries n. The effects of zinc oxide microstructure on the electrical characteristics of lowvoltage ceramic varistors kesan mikrostruktur zink oksida terhadap ciriciri elektrik varistor seramik voltan rendah by shahrom mahmud thesis submitted in fulfillment of the requirements for the degree of master of science january 2004.
The nanocomposite structure is verified to have polymer intergranular phase in a thickness range from 2 to. Synthesis of zno nanoparticles for varistor application using zn. Two types of transistors has been synthesized and characterized. Also the less intense peaks at 48, 57, 63 and 70 2. Ingredients zinc oxide varistors consist mainly of zinc oxide about 90 % by weight and small amounts of other metal oxides additives such as bismuth, cobalt, antimony and manganeseoxide. Modeling of electrical transport in zinc oxide varistors. Jul 12, 2012 zno nanoparticles grown in the template of folic acid are biologically useful, luminescent material. Ein varistor ist ein spannungsabhangiger widerstand. Zinc oxide zno has been used in a wide range of products for many years, including, among others, varistors, surface acoustic wave devices and cosmetics. The presence and characterization of zno and ag nps on bacterial cells were investigated by scanning electron microscopy sem, transmission electron microscopy tem, and energydispersive xray spectroscopy eds. Chapter vi, which is the core part of this thesis work, is mainly devoted to the characterization study of zno based building blocks. It has been nearly a quarter of a century since matsuoka 1 reported the nonohmic properties of zno ceramics.
Bavelis et al modeling of electrical transport in zno varistors 31 figure 3. Nanoscale characterisation of barriers to electron conduction. New varistor type polymer composites for lowvoltage application have been developed. The oxide reagentgrade powders were mixed in ball mill, calcinated, pressed and sintered in air at 0500c.
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