ZnO Elements Research Articles

Electronic structure and optical properties ofrare earth element (Y,La) doped in ZnO

The geometrical structures,band structures,density of states(DOS) and optical properties of undoped and doped rare earth elements(Y,La) in ZnO have been calculated from the first principles of plane wave ultra-soft pseudo-potential method based on density functional theory. After doping,the stability of structures are enhanced and the band gap becomes wider. When doped with Y(La), the Fermi energy of the system goes into the conduction band,the system shows metallicity and transforms into degenerate semiconductor. Furthermore, the change of optical properties after doping have been analyzed.

Magnetic Resonance of Impurities, Intrinsic Defects and Dopants in ZnO

In the last years an increasing technological interest in the wide band gap semiconductor ZnO has widely stimulated research on this material. The electrical and optical properties of ZnO are strongly affected by the presence of defects and dopant. For instance, to obtain p-type conductivity it requires not only to find a suitable doping element but also to suppress counteracting intrinsic defects. Magnetic resonance experiments can contribute considerable knowledge to this subject. We review the current knowledge on impurities, intrinsic defects and doping elements in ZnO as obtained by magnetic resonance experiments in this paper.

The Creative, Originative, and Useful Progress of Surge Arresters and Insulation Coordination for AC 66–1100 kV Power Systems Described in the IEEJ Technical Report No. 1132

AbstractIt is essential to prove that the technology of metal (zinc) oxide surge arresters born in Japan is very creative, originative, and useful to insulation coordination for power systems. Surge arresters investigating R&D Committee of Japan have summarized ‘power technology of Japan through the experience of developments and applications of surge arresters—AC 3.3–1100 kV and HVDC 125–600 kV power systems’. This technical report No. 1132 describes lightning phenomena, manufacturing of ZnO elements, surge arresters and insulation coordination for AC 3.3–550 kV, 800 kV, 1100 kV substations, 22–500 kV transmission lines, power cables, HVDC 125–DC 600 kV systems, 6.6–33 kV distribution lines, 100–200 V surge protective devices, and maintenance methods. This paper describes that the creative, originative and useful progress of metal (zinc) oxide surge arresters contributes drastically to the insulation coordination for AC 66–1100 kV power systems. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Interaction between Na and Li in ZnO

The interaction between group-Ia elements in ZnO have been studied by implanting Na into hydrothermally grown ZnO samples containing ∼4×1017 Li/cm3 and employing secondary ion mass spectrometry for sample analysis. Postimplantation annealing above 500 °C results in a diffusion of Na and concurrently Li is efficiently depleted from the regions occupied by Na. The data show unambiguously that Na and Li compete for the same trapping site and the results provide strong experimental evidence for that the formation energies of Na on Zn site together with that of interstitial Li are lower than those of Li on Zn site and interstitial Na in highly resistive ZnO. This conclusion is also supported by recent theoretical estimates of the formation energies of these species as a function of the Fermi-level position in ZnO.

Vacancy-assisted diffusion mechanism of group-III elements in ZnO: An ab initio study

Based on ab initio total energy calculations, the diffusion mechanisms of group-III elements (B, Al, Ga, and In) in ZnO are investigated. The activation energy of vacancy-assisted mechanism consists of formation energy of Zn vacancy (VZn), binding energy between the dopants and VZn, as well as effective diffusion energy barrier of the dopants in ZnO. The effective diffusion energy barriers of B, Al, Ga, and In are estimated to be 1.12, 1.76, 1.45, and 1.06 eV for in-plane diffusion, and 1.12, 2.19, 1.80, and 1.06 eV for out-of-plane diffusion, respectively. The binding energies are estimated to be −0.66, −0.52, −0.48, and −0.43 eV for B-, Al-, Ga-, and In-VZn pairs, showing a size decreasing behavior.

Development of 1100 kV a.c. high‐performance GIS‐arrester and its verification tests

AbstractFor the purpose of realizing 1100 kV a.c. power transmission system to meet the demands for electricity in future Japan, the 1100 kV a.c. high performance gas‐insulated metal enclosed arrester (GIS‐arrester) was developed and its high reliability was confirmed by a long‐term performance verification test. The high‐peformance GIS‐arrester is a key component to determine the insulation level of 1100 kV a.c. power transmission systems and substation equipments. As part of a series of activities started around 1975 by the Special Committee on 1100 kV a.c. Power‐Transmission system, the high‐performance GIS‐arrester with the superior protective performance of the world highest level was developed by applying the ZnO elements developed and commercialized in Japan.This paper introduces the application effects, duties, specifications, progress of development, and results of verification tests for the high‐performance GIS‐arresters for 1100 kV a.c. power transmission system. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Local Structures of Zn1-xTMxO (TM = Co, Mn, and Cu) Nanoparticles Studied by X-ray Absorption Fine Structure Spectroscopy and Multiple Scattering Calculations

Transitional metal doped ZnO is a good candidate for dilute magnetic semiconductors possessing high Curie temperature ferromagnetism. The local atomic configuration of dopant elements in ZnO is an important issue for understanding their ferromagnetic mechanism. In this work Co, Mn, and Cu doped ZnO nanoparticles with particle size of about 5 nm were prepared by the coprecipitation method. X-ray absorption fine structure spectra were measured at doppant metal K-edges for the as-prepared and calcinated samples. The results show significantly different local structural evolutions for various dopant element doping and heat treatment. Co-doped nanoparticles are stable up to high temperature calcinations, while Mn and Cu in ZnO exhibit complex interatomic diffusion and reduction behavior activated by modest calcinations, and this is explained by either a charge transfer from ZnO to doppant element or the reduction induced by thermal decomposition products of surfactants. Multiple scattering calculations were pe...

Improvement on ZnO Element Performance by Optimizing the Amount of Spinel Particles

The performance of ZnO elements such as voltage-current characteristic, life performance under a continuous system voltage, energy absorption capability is strongly dependent on the performance of boundaries between ZnO grains formed during the sintering process. The performance of these boundaries is greatly influenced by spinel particles (Zn7Sb2O12) that are produced between ZnO grains and hence have a relation to the formation of boundaries.The authors studied the influence of reducing spinel particles on the performance of ZnO elements by experimentally manufacturing and evaluating the elements with various amounts of Sb2O3. As the result, some characteristics of the spinel-reduced elements were improved compared with that of normal ZnO elements: e.g. superior voltage-current characteristic, smaller micro-pores and larger capacitance. It was also found that the sintering temperature of the spinel-reduced elements could be decreased by more than 100°C than that of normal elements which the authors are currently manufacturing.

Storage of Oxygen Gas for ZnO Varistors

We have been studying the diagnostics (5)(7)(9)(11) and the degradation(3)(8)(10) of ZnO elements which were installed in 275kV surge arresters operated for 20 years. I have examined the leakage currents of ZnO elements as I have accomplished ageing tests. As the results of examinations, I found that migrated oxygen ions are evaporated by supplied voltages(2)(6), and again this oxygen gas evaporated is absorbed into ZnO elements in no voltage period(1)(4). The evaporation and the absorption are concerned with the Gibbs free energy and the diffusion energy of oxygen. When the Schottky barriers of ZnO elements are higher than 0.5RT; R is the gas constant and T is the absolute temperature, the evaporation and the absorption are stopped earlier. This reason is that the diffusion energy of oxygen becomes zero before the Gibbs free energy is reached to the balance.

On the role of group I elements in ZnO

Diffusion of Li, Na and K into single-crystal substrates of ZnO was performed. We compare the results with ZnO epitaxial films doped with the respective elements during growth. The diffused and in-situ doped layers were studied using mass spectroscopy and low temperature photoluminescence spectroscopy. Li and Na are known to produce deep acceptor centers which give rise to shallow donor to deep acceptor recombinations in the visible spectral region. We will demonstrate that shallow acceptors are also introduced, having binding energies around 300 meV. A donor–acceptor pair recombination (zero phonon line at 3.05 eV) with LO phonon replica is observed. We further investigated bulk ZnO crystals which contained the deep Li acceptor by thermal treatments under H2 atmospheres. With increasing annealing temperature shallow donors are introduced as monitored by EPR while the EPR signal of the neutral Li acceptors decreases. Quite unexpectedly, the shallow Li acceptor centre which is not present in the as-grown state is also created.

Withstand capability tests of transient voltage surge suppressors

This paper investigates the capability of some samples of transient surge suppressors (TVSSs), used in electrical submersible pump (ESP) installations, to withstand non-destructive standard impulse tests. Tests were performed on different ratings of the TVSS and with a voltage rating up to 2.5 kV, to fulfill the basic impulse withstand level (BIL) of the ESP motors. On the other hand, used and unused TVSS were also tested by the standard high-amplitude impulse currents to examine the degradation effect. Compared to the (old) TVSS, the used (new) TVSSs gave lower internal leakage current under AC and DC applications. A similar trend was also observed for the high discharge impulse current. This common trend reflects the effect of ageing “degradation” due to the modification of the microstructure of the ZnO elements.

Effects of Heat Sinks in Metal-Oxide Surge Arresters on ZnO Element Power Dissipation and Temperature Distribution

The cooling effect of heat sinks placed between the ZnO elements of a surge arrester is evaluated in the context of the IEC Type Test for thermal stability using transient nonlinear finite element analysis with coupled thermal and electric fields to simulate the entire operating duty type test sequence in IEC60099-4.

Group I elements in ZnO

ABSTRACTDiffusion of Li, Na and K into single-crystal substrates of ZnO were performed. We compare the results with ZnO epitaxial films doped with the respective elements during growth. The diffused and in-situ doped layers were studied using mass spectroscopy, low temperature photoluminescence and Raman spectroscopy. Li and Na are known to produce deep acceptor centers which give rise to shallow donor to deep acceptor recombinations in the visible spectral region. We will demonstrate that also shallow acceptors are introduced having binding energies around 300 meV. A donor-acceptor pair recombination (zero phonon line at 3.05 eV) with LO phonon replica is observed analogous to the “edge” emission in other II-VI compounds.

Characterization of Thermoelectric Metal Oxide Elements Prepared by the Pulse Electric‐Current Sintering Method

Thermoelectric elements consisting of the layered polycrystalline materials of Al‐doped ZnO and NaCo2O4 were prepared using the pulse electric‐current sintering (PECS) method at 900°C for 3 min. Direct contact between the polycrystalline Al‐doped ZnO and the NaCo2O4 was obtained in a single‐step process for the stacked powders. The electrical conductivities of the polycrystalline materials prepared by PECS were higher than those of materials prepared by conventional sintering, despite their porous structure. The thermoelectric voltage of the 1‐mol%‐Al‐doped ZnO and NaCo2O4 polycrystalline element (measuring ∼6 mm × 3 mm × 15 mm) was 83 mV at dT= 500 K, when the junction of the elements was at 800°C.

A Statistical Approach to Prediction of ZnO Arrester Element Characteristics

ZnO arrester elements consist of ZnO grains with dimensions in the range of 10 to 100 μm, the boundaries between which form double Shottky junctions with conduction voltages in the range of 3.5 V. A fraction of the grains contain no conducting boundaries with other grains, which results in the percolation path for current across the ZnO element being a statistical parameter that is a function of the fraction of nonconducting grains, which also affects the nonlinear properties of the element. In this paper, we use a simple statistical approach to predict the effect of the fraction of nonconducting grains on the nonlinear properties of the element. This computationally simple approach gives results that are comparable to far more complex approaches, which require solving a network of nonlinear resistive elements.

A statistical approach to prediction of ZnO arrester element characteristics

ZnO arrester elements consist of ZnO grains with dimensions in the range of 10 to 100 /spl mu/m, the boundaries between which form double Shottky junctions with conduction voltages in the range of 3.5 V. A fraction of the grains contain no conducting boundaries with other grains, which results in the percolation path for current across the ZnO element being a statistical parameter which is a function of the fraction of nonconducting grains, which also affects the nonlinear properties of the element. In this paper, we use a simple statistical approach to predict the effect of the fraction of nonconducting grains on the nonlinear properties of the element. This computationally simple approach gives results which are comparable to far more complex approaches which require solving a network of nonlinear resistive elements.

Increased energy absorption in ZnO arrester elements through control of electrode edge margin

ZnO nonlinear dielectric has a small temperature coefficient of conductivity up to about 550 C, and above 550 C the temperature coefficient of conductivity becomes substantially positive, which tends to result in thermal runaway through condensation of the current density into filaments which melt their way through the ceramic. Thus to obtain maximum energy absorption in a ZnO element, it is important to avoid hot spots so that the element will heat quite uniformly to its maximum stable operating temperature in the range of 550 C. The current density at the electrode edge is enhanced by spreading of the current into the ZnO at radii larger than the electrode. This causes an enhanced temperature at the electrode edge which results in the melting punctures commonly observed. Using transient, nonlinear finite element analysis with coupled thermal and electric fields, the authors have quantified the temperature enhancement as a function of edge margin and optimized the electrode topology.

配電用避雷器の繰り返し多数回動作による漏れ電流へのZnO素子内蔵水分の影響

配電用避雷器の繰り返し多数回動作による漏れ電流へのZnO素子内蔵水分の影響

避雷器用ZnO素子におけるエネルギー耐量の向上

避雷器用ZnO素子におけるエネルギー耐量の向上

Prospective method of lightning protection schemes in distribution system

Grounding wires and enclosed ZnO elements have been incorporated generally in 6.6-kV distribution systems by TEPCO for the reduction of lightning overvoltages. At present, the reliability to lightning surges is tolerably good. However, the facility of grounding wires is not inexpensive and its maintenance is hard due to corrosion and disconnection in some areas. A typical model simulating TEPCO field adopting enclosed ZnO elements has been developed and we have evaluated relative failure risks systematically according to conditions with and without grounding wires against lightning overvoltages. Two kinds of failures discussed in the paper are the flashover of insulation and the overduty of ZnO elements, and two kinds of induced and direct lightning overvoltages are studied in flashover. The greatest problem with no grounding wire is the increase of ZnO elements' duty, but it was demonstrated that a short partial grounding wire around ZnO elements or the selection of heavier ZnO elements provides a solution. The main objectives of this study are to clarify the relative failure risks systematically according to realistic field conditions, the risk of small stroke currents having long duration to ZnO elements' duty, and countermeasures against ZnO elements' overduty. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 1–10, 1999