Microchemistry of ZnO Varistors

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.

Fabrication of High Performance Multilayer ZnO Varistors with Chemically Synthesized Doped Zinc Oxide Powder

2007 ◽  
Vol 336-338 ◽  
pp. 739-742 ◽  
Author(s):  
Lan Yi Wang ◽  
Cheng Xiang Lu ◽  
Guo Yi Tang
Keyword(s):  
Electrical Properties ◽  
Mixed Oxide ◽  
High Performance ◽  
Nonlinear Coefficient ◽  
Oxide Powder ◽  
Homogeneous Distribution ◽  
Dopant Distribution ◽  
Fine Grain ◽  
Zno Varistors ◽  
Zno Powder

Two types of multilayer ZnO varistors are prepared by the chemically synthesized (CS) powder and the mixed oxide (MO) powder. The ceramic microstructure analysis shows that the multilayer variestor (MLV) ceramic prepared by the CS powder has the fine grain, the homogeneous distribution of grain size and the uniform dopant distribution. The CS powder prepared multilayer ZnO varistors display better electrical properties, including higher nonlinear coefficient, higher breakdown voltage, higher peak current, lower leakage current and lower clamping voltage, than those made by the mixed oxide powder. All these superior electrical properties are attributed to the CS powder, which makes more uniform dopant distribution throughout the multilayer ZnO varistors. The homogeneous distribution for the various dopants in the varistor ceramic has been achieved by the chemically synthesized doped ZnO powder. Therefore, the chemically synthesized powder can be used in the manufacture of high performance multilayer ZnO varistors.

Origin of Leakage Currents in ZnO Based Varistor Ceramics with Al(NO3)3 Dopant

2010 ◽  
Vol 434-435 ◽  
pp. 386-388 ◽  
Author(s):  
Jun Hu ◽  
Wang Chen Long ◽  
Jin Liang He ◽  
Jun Liu ◽  
Feng Chao Luo
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Electrical Properties ◽  
Grain Boundaries ◽  
The Other ◽  
Leakage Currents ◽  
Donor Density ◽  
Zno Varistor ◽  
Zno Varistors ◽  
Simulation Results

The additive of Al(NO3)3 has been doped into ZnO varistors in order to reduce their residual voltages. However, the leakage currents of samples always increase at the same time. Generally, it is recognized that some of doped Al3+ ions enter the ZnO grains and reduce their resistivity, which results in lower residual voltages of varistor samples. On the other hand, the remnant Al3+ ions appear in the grain boundaries and also reduce their resistivity, which results in larger leakage currents. In this paper, the electrical properties of ZnO varistor samples with various amounts of Al(NO3)3 dopant were measured. The experimental data are compared with the numerical simulation results, which reveals that the increased leakage currents of ZnO varistors with Al(NO3)3 dopant are not only due to the decreased resistivity of grain boundaries, but also the increased donor density of ZnO grains.

SIMS studies of Ca and Mg distributions in sintered Al2O3

1992 ◽  
Vol 50 (2) ◽  
pp. 1772-1773
Author(s):  
K. K. Soni ◽  
A. M. Thompson ◽  
M. P. Harmer ◽  
D. B. Williams ◽  
J. M. Chabala ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Analytical Techniques ◽  
Solute Drag ◽  
Ion Microprobe ◽  
Grain Boundary Mobility ◽  
High Lateral Resolution ◽  
Significant Research ◽  
The University

The addition of MgO to α-Al2O3 has been practiced for over 30 years in order to improve greatly the properties of the sintered material. However, a complete understanding of the role of MgO has not been achieved despite significant research efforts by various groups. The most difficult obstacle is microchemical characterization of MgO doped Al2O3. Surface analytical techniques, primarily AES and XPS, have been employed by past researchers in order to analyze the grain boundaries on fractured surfaces of sintered Al2O3. This prior work has met with limited success due to poor sensitivity and spatial resolution. MgO is believed to segregate to the grain boundaries and to retard the grain boundary mobility via a solute drag mechanism; this hypothesis has not been verified experimentally.In this study, the distribution of Ca and Mg was characterized by a high lateral resolution scanning ion microprobe (SIM) developed at The University of Chicago (UC).

Effect of Sb Addition on the Electrical Characteristics of Bi-Based ZnO Varistors Containing Zr and Y

2013 ◽  
Vol 566 ◽  
pp. 223-226
Author(s):  
Takayuki Watanabe ◽  
Yosuke Tokoro ◽  
Yuuki Sato ◽  
Shinzo Yoshikado
Keyword(s):  
Grain Boundaries ◽  
Leakage Current ◽  
High Resistance ◽  
Electrical Characteristics ◽  
Zno Varistor ◽  
Low Leakage ◽  
Electrical Degradation ◽  
Low Leakage Current ◽  
Zno Varistors

The effects of adding Sb to a BiMnCoSiCrNiYZr-added ZnO varistor (with the same composition as a commercial varistor) on the varistor voltage, leakage current, and resistance to electrical degradation were investigated. Bi is incorporated in spinel particles, and δ-Bi2O3eventually disappears with the addition of small amounts of Bi, especially as the amount of Sb2O3added increased. Reduction in both the nonlinearity index and the amount of δ-Bi2O3for small amounts of added Bi with the addition of more than approximately 1.25 mol% Sb2O3demonstrates that Sb inhibits Bi2O3from forming deep interfacial impurity levels at the grain boundaries. The sample containing 1.2 mol% Bi2O3, 1.0 mol% ZrO2, 1.0 mol% Y2O3, and 1.5 mol% Sb2O3added exhibits a high varistor voltage (approximately 630 V/mm), high resistance to electrical degradation and low leakage current.

Imaging of Al-Li-Cu alloys with a Scanning Ion Microprobe

1990 ◽  
Vol 48 (2) ◽  
pp. 314-315
Author(s):  
K.K. Soni ◽  
D.B. Williams ◽  
J.M. Chabala ◽  
R. Levi-Setti ◽  
D.E. Newbury
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Equilibrium Phase ◽  
Icosahedral Symmetry ◽  
Ion Microprobe ◽  
X Ray ◽  
Cu Alloys ◽  
Two Phases ◽  
The University ◽  
Secondary Ion

In contrast to the inability of x-ray microanalysis to detect Li, secondary ion mass spectrometry (SIMS) generates a very strong Li+ signal. The latter’s potential was recently exploited by Williams et al. in the study of binary Al-Li alloys. The present study of Al-Li-Cu was done using the high resolution scanning ion microprobe (SIM) at the University of Chicago (UC). The UC SIM employs a 40 keV, ∼70 nm diameter Ga+ probe extracted from a liquid Ga source, which is scanned over areas smaller than 160×160 μm2 using a 512×512 raster. During this experiment, the sample was held at 2 × 10-8 torr.In the Al-Li-Cu system, two phases of major importance are T1 and T2, with nominal compositions of Al2LiCu and Al6Li3Cu respectively. In commercial alloys, T1 develops a plate-like structure with a thickness <∼2 nm and is therefore inaccessible to conventional microanalytical techniques. T2 is the equilibrium phase with apparent icosahedral symmetry and its presence is undesirable in industrial alloys.

Fluidized Catalytic Cracking Catalyst Microstructure as Determined by A Scanning Ion Microprobe

1990 ◽  
Vol 48 (2) ◽  
pp. 302-303
Author(s):  
J.K. Lampert ◽  
G.S. Koermer ◽  
J.M. Macaoy ◽  
J.M. Chabala ◽  
R. Levi-Setti
Keyword(s):  
Catalytic Cracking ◽  
Secondary Ion Mass Spectrometry ◽  
Fuel Oil ◽  
Ion Microprobe ◽  
Fluidized Catalytic Cracking ◽  
Ion Probe ◽  
Silica Alumina ◽  
Resolution Imaging ◽  
The University ◽  
High Spatial Resolution Imaging

We have used high spatial resolution imaging secondary ion mass spectrometry (SIMS) to differentiate mineralogical phases and to investigate chemical segregations in fluidized catalytic cracking (FCC) catalyst particles. The oil industry relies on heterogeneous catalysis using these catalysts to convert heavy hydrocarbon fractions into high quality gasoline and fuel oil components. Catalyst performance is strongly influenced by catalyst microstructure and composition, with different chemical reactions occurring at specific types of sites within the particle. The zeolitic portions of the particle, where the majority of the oil conversion occurs, can be clearly distinguished from the surrounding silica-alumina matrix in analytical SIMS images.The University of Chicago scanning ion microprobe (SIM) employed in this study has been described previously. For these analyses, the instrument was operated with a 40 keV, 10 pA Ga+ primary ion probe focused to a 30 nm FWHM spot. Elemental SIMS maps were obtained from 10×10 μm2 areas in times not exceeding 524s.

scholarly journals Sensitive High Resolution Ion Microprobe (SHRIMP IIe/MC) of the Institute of Geosciences of the University of São Paulo, Brazil: analytical method and first results

2014 ◽  
Vol 14 (3) ◽  
pp. 3-18 ◽  
Author(s):  
Kei Sato ◽  
Colombo Celso Gaeta Tassinari ◽  
Miguel Angelo Stipp Basei ◽  
Oswaldo Siga Júnior ◽  
Artur Takashi Onoe ◽  
...  
Keyword(s):  
High Resolution ◽  
Analytical Method ◽  
Sao Paulo ◽  
São Paulo ◽  
Ion Microprobe ◽  
First Results ◽  
The University

Effect of Simultaneous Addition of Zr and Y on Electrical Characteristics of ZnO Varistors

2011 ◽  
Vol 485 ◽  
pp. 257-260 ◽  
Author(s):  
Takayuki Watanabe ◽  
Ai Fukumori ◽  
Yuji Akiyamna ◽  
Yuuki Sato ◽  
Shinzo Yoshikado
Keyword(s):  
Leakage Current ◽  
Nonlinear Coefficient ◽  
The Other ◽  
Electrical Characteristics ◽  
Simultaneous Addition ◽  
Zno Varistor ◽  
Low Leakage ◽  
Electrical Degradation ◽  
Low Leakage Current ◽  
Zno Varistors

The effect of simultaneously adding Zr and Y to Bi–Mn–Co–Sb–Si–Cr–Ni-added ZnO varistors (having the same composition as a commercial varistor) on the varistor voltage, leakage current, and resistance to electrical degradation were investigated. Varistor voltage increased with increasing amount of Y for addition of 0–2 mol % Zr. On the other hand, the nonlinear coefficient α prior to electrical degradation changed very little on the addition of both Y and Zr. With the addition of approximately 1 mol% Zr, the leakage current decreased with increasing amount of Y added. A ZnO varistor with a varistor voltage of approximately 600 V/m, a low leakage current, and excellent resistance to electrical degradation was fabricated by adding approximately 2 mol% Y and approximately 1 mol% Zr.

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