Electrical properties and microstructure of ZnO-based varistor ceramics doped with rare earth

Other Title(s)

الخواص الكهربائية و التركيب الدقيق لمقاوم أوكسيد الخارصين السيراميكي المتغير المطعم بالأتربة النادرة

Dissertant

Kazim, Adil Ismail

Thesis advisor

Mahdi, Abd al-Hamid Rahim
Ibrahim, Aysar Jumah

University

University of Baghdad

Faculty

College of Education for Puresciences-IBN al-Haitham

Department

Department of Physics

University Country

Iraq

Degree

Ph.D.

Degree Date

2015

English Abstract

ZnO is a ceramic material which tends to intrinsically form as an n-type semiconductor material, which plays an important role in a wide range of industrial processes and commercial products.

One of most important usages is a Surge protection device which used to protect power and electronic equipment from the destructive transient overvoltage which arises from lightning or other large-magnitude surge, this device is called metal oxide varistor (MOV).

Varistors are voltage dependent, non-ohmic devices whose electrical characteristics are almost similar to back-to-back Zener diodes.

Improvement ZnO varistor performance accomplished by doping it by some metal oxides, Bi2O3, Sb2O3, Co3O4, Cr2O3, and MnO2, where they were testing their effect alone first, and second was added rare earth oxides (M2O3) with oxides mentioned above and test their effect on varistor, where (M = Dy, La, Y) and molar concentrations (10-3, 5*10-3, 10*10-3 The preparation process starts from mixing ZnO with additives, calcination at 600℃ in a furnace to remove the gases and the humidity from the powders.

) Then the calcined powders uniaxially pressed into discs (pellets) of 15 ???? in diameter and 2 ???? in thickness under a pressure equals to 25????.

After pressing the green pellets sintered under different temperatures (1050, 1100, 1150℃) and a fixed time to accomplish the final shapes and reach the desired properties of the samples.

Then the densities of the samples were measured by using Archimedes Principle with mercury liquid to calculate the relative density and the porosity of each sample, and to study the effect of the sintering temperature and REO concentration, which already be obvious the effect of them.

The microstructure test of the material prepared gave a clear vision for the diffusion and grain growth, although the results of XRD test showed that the crystal structure is an orthorhombic, and the values of (a, b, c) and the size of a the unit cell has been increased with increase the sintering temperature and ratios of the concentration of oxides added and kind.

Micro and nano grains within the present research showed a significant effect on the studied electrical characteristics, which designed a tool in the laboratory for it and to measure the nonlinear coefficient, the amount breakdown voltage, leakage current, the potential gradient, the energy absorption capability, and the voltage per grain boundary.

It was found that the nonlinear coefficient increases with the increasing of REO concentration added and increasing sintering temperature and then starts decreased after degree (1100℃ ) due to volatilization and evaporation of bismuth oxide and spinel phase (Zn7Sb2O12 The amount of breakdown voltage, potential gradient, energy absorption capability decreased with rising the sintering temperature, while the leakage current has been increased with increasing the sintering temperature, as well as the voltage per grain boundary has been increased with increasing of the sintering temperature.

Main Subjects

Physics

No. of Pages

108

Table of Contents

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Language

English

Data Type

Arab Theses

Record ID

BIM-735838