Investigation on Defect Structure in ZnO Varistor Ceramics by Dielectric Spectra

In this paper, the dielectric properties of ZnO-Bi2O3 based varistor ceramics doped with Li are investigated by Novocontrol wide band dielectric spectrometer. It is found that Lithium is an amphoteric impurity. If the content of Lithium is very low, It will enters into the interstitials and Lithium interstitial is formed as a donor. While with the increase of Lithium content, Zn is replaced with Li and Lithium substitution for Zinc as a acceptor is formed. If the content of Lithium increases further, Lithium interstitial is formed again with the redundant Lithium. Therefore, the concentrations of intrinsic point defects of Zinc interstitial and oxygen vacancy varies with the content of Lithium, which leads to the increase of Schottky barrier at grainboundary with Lithium.

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Dielectric spectra of ZnO varistor ceramics

Acta Physica Sinica ◽

10.7498/aps.61.187302 ◽

2012 ◽

Vol 61 (18) ◽

pp. 187302

Author(s):

Cheng Peng-Fei ◽

Li Sheng-Tao ◽

Li Jian-Ying

Keyword(s):

Dielectric Spectra ◽

Zno Varistor

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Electron Microscope Observations of Mechanical Metamorphism in Iron Meteorites

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069430 ◽

1970 ◽

Vol 28 ◽

pp. 488-489

Author(s):

D. Faulkner ◽

G.W. Lorimer ◽

H.J. Axon

Keyword(s):

Electron Microscope ◽

Defect Structure ◽

Shock Loading ◽

List Type ◽

Iron Meteorites

It is now generally accepted that meteorites are fragments produced by the collision of parent bodies of asteroidal dimensions. Optical metallographic evidence suggests that there exists a group of iron meteorites which exhibit structures similar to those observed in explosively shock loaded iron. It seems likely that shock loading of meteorites could be produced by preterrestrial impact of their parent bodies as mentioned above.We have therefore looked at the defect structure of one of these meteorites (Trenton) and compared the results with those made on a) an unshocked ‘standard’ meteorite (Canyon Diablo)b) an artificially shocked ‘standard’ meteorite (Canyon Diablo) andc) an artificially shocked specimen of pure α-iron.

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A new type of defect structure in 124-superconducting oxide revealed by HREM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100089779 ◽

1991 ◽

Vol 49 ◽

pp. 1092-1093

Author(s):

R. Sharma ◽

B.L. Ramakrishna ◽

N.N. Thadhani ◽

D. Hianes ◽

Z. Iqbal

Keyword(s):

Shock Wave ◽

Defect Structure ◽

Neutron Radiation ◽

Weak Links ◽

Defect Structures ◽

New Materials ◽

New Type ◽

Current Densities ◽

Processing Techniques ◽

Microstructural Studies

After materials with superconducting temperatures higher than liquid nitrogen have been prepared, more emphasis has been on increasing the current densities (Jc) of high Tc superconductors than finding new materials with higher transition temperatures. Different processing techniques i.e thin films, shock wave processing, neutron radiation etc. have been applied in order to increase Jc. Microstructural studies of compounds thus prepared have shown either a decrease in gram boundaries that act as weak-links or increase in defect structure that act as flux-pinning centers. We have studied shock wave synthesized Tl-Ba-Cu-O and shock wave processed Y-123 superconductors with somewhat different properties compared to those prepared by solid-state reaction. Here we report the defect structures observed in the shock-processed Y-124 superconductors.

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Defects in ion implanted silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109070 ◽

1978 ◽

Vol 36 (1) ◽

pp. 386-387

Author(s):

J.A. Lambert ◽

P.S. Dobson

Keyword(s):

Defect Structure ◽

Dislocation Loops ◽

Frank Loop ◽

Burgers Vector ◽

Temperature Range ◽

Perfect Dislocation ◽

Contrast Analysis ◽

Image Position ◽

Ion Implanted

The defect structure of ion-implanted silicon, which has been annealed in the temperature range 800°C-1100°C, consists of extrinsic Frank faulted loops and perfect dislocation loops, together with‘rod like’ defects elongated along <110> directions. Various structures have been suggested for the elongated defects and it was argued that an extrinsically faulted Frank loop could undergo partial shear to yield an intrinsically faulted defect having a Burgers vector of 1/6 <411>.This defect has been observed in boron implanted silicon (1015 B+ cm-2 40KeV) and a detailed contrast analysis has confirmed the proposed structure.

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Microchemistry of ZnO Varistors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100133102 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1694-1695

Author(s):

K. K. Soni ◽

J. Hwang ◽

V. P. Dravid ◽

T. O. Mason ◽

R. Levi-Setti

Keyword(s):

Grain Boundaries ◽

Multiple Roles ◽

Grain Boundary Engineering ◽

Ion Microprobe ◽

Dopant Distribution ◽

Important Ingredient ◽

Zno Varistor ◽

Zno Varistors ◽

Zno Powder ◽

The University

ZnO varistors are made by mixing semiconducting ZnO powder with powders of other metal oxides e.g. Bi2O3, Sb2O3, CoO, MnO2, NiO, Cr2O3, SiO2 etc., followed by conventional pressing and sintering. The non-linear I-V characteristics of ZnO varistors result from the unique properties that the grain boundaries acquire as a result of dopant distribution. Each dopant plays important and sometimes multiple roles in improving the properties. However, the chemical nature of interfaces in this material is formidable mainly because often trace amounts of dopants are involved. A knowledge of the interface microchemistry is an essential component in the ‘grain boundary engineering’ of materials. The most important ingredient in this varistor is Bi2O3 which envelopes the ZnO grains and imparts high resistance to the grain boundaries. The solubility of Bi in ZnO is very small but has not been experimentally determined as a function of temperature.In this study, the dopant distribution in a commercial ZnO varistor was characterized by a scanning ion microprobe (SIM) developed at The University of Chicago (UC) which offers adequate sensitivity and spatial resolution.

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A crystallographic analysis of the CoSi/Si(111) interface using Transmission Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176009 ◽

1990 ◽

Vol 48 (4) ◽

pp. 574-575

Author(s):

A.C. Daykin ◽

C.J. Kiely ◽

R.C. Pond ◽

J.L. Batstone

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Defect Structure ◽

Room Temperature ◽

Theoretical Method ◽

Crystallographic Analysis ◽

Si Substrate ◽

Transmission Electron ◽

Theoretical Predictions

When CoSi2 is grown onto a Si(111) surface it can form in two distinct orientations. A-type CoSi2 has the same orientation as the Si substrate and B-type is rotated by 180° degrees about the [111] surface normal.One method of producing epitaxial CoSi2 is to deposit Co at room temperature and anneal to 650°C.If greater than 10Å of Co is deposited then both A and B-type CoSi2 form via a number of intermediate silicides .The literature suggests that the co-existence of A and B-type CoSi2 is in some way linked to these intermediate silicides analogous to the NiSi2/Si(111) system. The phase which forms prior to complete CoSi2 formation is CoSi. This paper is a crystallographic analysis of the CoSi2/Si(l11) bicrystal using a theoretical method developed by Pond. Transmission electron microscopy (TEM) has been used to verify the theoretical predictions and to characterise the defect structure at the interface.

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