Exaggerated Grain Growth of ZnO in Low Voltage ZnO Varistor.

A novel fabricated technique, by feeding two sets of different ZnO formulations powder in a die by parts, molded only once to produce layered structure(including layer A and layer B) low-voltage ZnO varistor. The samples are examined by using energy dispersive X-ray spectroscopy (EDS), electron probe microanalysis (EPMA), scanning electron microscope (SEM) and DC electrical measurements. EDS and EPMA data indicate that doped elements only exists in layer A, The results of SEM indicate that secondary phases are formed at grain boundaries in layer A, not found in layer B. It is found that the electrical properties of low-voltage varistor are improved without reducing thickness and changing energy absorption capabilities. The higher nonlinearity coefficients, lower breakdown fields and leakage currents of layered structure low-voltage ZnO varistor, as compared to those of ZnO varistor fabricated from the conventional route. The improved current-voltage properties are attributed to the band structure difference in both sides grains, due to the different ion concentration and species in both sides of grain boundary. Layered structure varistor also has more simpler prepared technology than multilayer chip varistor.

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The control of abnormal grain growth in low-voltage SnO2 varistors by microseed addition

Ceramics International ◽

10.1016/j.ceramint.2017.11.129 ◽

2018 ◽

Vol 44 (3) ◽

pp. 3388-3393 ◽

Cited By ~ 9

Author(s):

Mohammad Maleki Shahraki ◽

Mohammad Golmohammad ◽

Iman Safaee ◽

Mehdi Delshad Chermahini

Keyword(s):

Grain Growth ◽

Low Voltage ◽

Abnormal Grain Growth

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Cracks in Nano-Ceramic thin Layers Produced by Laser Treatments

MRS Proceedings ◽

10.1557/proc-539-189 ◽

1998 ◽

Vol 539 ◽

Author(s):

J.Th.M. De Hosson ◽

D.H.J. Teeuw

Keyword(s):

Grain Growth ◽

Low Voltage ◽

Sol Gel ◽

Thin Layers ◽

Resolving Power ◽

Laser Treatments ◽

Laser Curing ◽

The Magnetic Field ◽

Voltage Scanning ◽

Scanning Electron

AbstractSol-gel derived thin nano-ceramic layers of TiO2 and Al2O3 are studied using scanning electron microscopy to reveal the microstructure and morphologies of the layers. The low-voltage scanning electron microscope with a field emission gun is equipped with an especially designed lens, where the specimen is placed at the location where the magnetic field is the largest. In such a way a maximum resolving power could be attained of 1.5 nm at 3kV accelerating voltage. The melt-spun layers were treated differently afterwards, i.e. by furnace and by laser curing. These heat treatments appeared to dictate the final morphologies of the layers to a large extent. Grain growth is observed for the furnace as well as the laser cured layers. The activation energy for grain growth of these layers is determined. Homogeneous dense layers may be obtained if the parameters in the curing process are selected adequately. If the parameters are chosen incorrectly, severely debonded layers may be obtained. Pre-heating the layers resulted in less blister formation. The mechanisms which may cause the layers to fail were examined in more detail.

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High Barrier Effects of (0001)|(0001) Zinc Oxide Bicrystals: Implication for Varistor Ceramics with Inversion Boundaries

Journal of Materials Research ◽

10.1557/jmr.2005.0243 ◽

2005 ◽

Vol 20 (8) ◽

pp. 2101-2109 ◽

Cited By ~ 8

Author(s):

Jong-Sook Lee ◽

Joachim Maier

Keyword(s):

Zinc Oxide ◽

Grain Boundaries ◽

Grain Growth ◽

Growth Behavior ◽

Impurity Effects ◽

Barrier Effects ◽

Zno Varistor ◽

Grain Growth Behavior ◽

Superior Property ◽

Strong Barrier

Inversion boundaries (IBs) of a head-to-head or (0001)|(0001) (C+|C+) configuration bisect virtually every grain in typical commercial ZnO varistor ceramics. They are most often considered electrically inactive, and the effect on the grain growth behavior has been recently addressed. In this work, various configurations of ZnO bicrystals were prepared using different source crystals and strong barrier effects were observed in some (0001)|(0001) (C−|C−) bicrystals using crystals with higher impurity contents. The crystallographic polarity and impurity effects were systematically examined by doping C+|C+ and C−|C− bicrystals with single and double additives of Mn, Co, Ni, and Bi. Varying degrees of barrier effects including varistor-like behaviors were observed in C−|C− bicrystals depending on dopants, while C+|C+ bicrystals consistently exhibited negligible effects. Because the IBs in ZnO varistor ceramics preferentially expose C− surfaces in the grain boundaries, the superior property of commercial ZnO varistor ceramics is suggested to be assisted by the presence of IBs.

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Interface states and MWS polarization contributions to the dielectric response of low voltage ZnO varistor

Ceramics International ◽

10.1016/j.ceramint.2010.08.036 ◽

2011 ◽

Vol 37 (1) ◽

pp. 207-214 ◽

Cited By ~ 16

Author(s):

C. Tsonos ◽

A. Kanapitsas ◽

D. Triantis ◽

C. Anastasiadis ◽

I. Stavrakas ◽

...

Keyword(s):

Dielectric Response ◽

Low Voltage ◽

Interface States ◽

Zno Varistor

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Micro-Degradation Characteristics and Mechanism of ZnO Varistors under Multi-Pulse Lightning Strike

Energies ◽

10.3390/en13102620 ◽

2020 ◽

Vol 13 (10) ◽

pp. 2620

Author(s):

Chunlong Zhang ◽

Hongyan Xing ◽

Chunying Li ◽

Ran Cai ◽

Dongbo Lv

Keyword(s):

Boundary Layer ◽

Grain Boundary ◽

Distribution Systems ◽

Pulse Current ◽

Low Voltage ◽

Grain Structure ◽

Lightning Strike ◽

Time Interval ◽

Zno Varistor ◽

Zno Varistors

In view of the problem that ZnO varistors are often subjected to thermal breakdown and deterioration due to lightning strikes in low-voltage power distribution systems, this article used a 8/20 µs multi-pulse surge current with a pulse time interval of 50 ms to perform shock experiments on ZnO varistors. SEM scanning electron microscope and an XRD diffractometer were used to analyze the structure of the grain boundary layer and the change of the crystalline phase material of ZnO varistor under the action of a multi-pulse current. The damage mechanism of ZnO varistor under the multi-pulse current was studied at the micro level. The results show that the average impact life of different types of ZnO varistor is significantly different. It was found that the types of trace elements and grain size in the grain boundary layer will affect the ability of ZnO varistor to withstand multi-pulse current. As the number of impulses increases, the grain structure of the ZnO varistor continues to degenerate. The unevenness of internal ion migration and the nonuniformity of the micro-grain boundary layer cause the local energy density to be too large and cause the local temperature rise to be too high, which eventually causes the internal grain boundary to melt through, and the local high temperature may cause the Bi element in the ZnO varistor to change in different crystal phases.

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