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Electrical Properties (electrical + property)
Kinds of Electrical Properties Selected AbstractsInfluence of Al-Containing Interfacial Coatings on Carbon-Fiber/Bakelite Composite Thermal and Electrical Properties,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Zeljko Pajkic Polymer-matrix (Bakelite®) composites were produced with coated short carbon fibers as a filler material and characterized in terms of their thermal, electrical, and mechanical properties. The influence of thin, Al-containing ceramic coatings on the composite material's macroscopic properties is discussed, as the composites with interfacial coatings show improvements in some properties, as compared to the ones with uncoated fibers. [source] Atomic Structure and Electrical Properties of In(Te) Nanocontacts on CdZnTe(110) by Scanning Probe MicroscopyADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Gili Cohen-Taguri Abstract Understanding complex correlations between the macroscopic device performance (largely dependent on the character of the metal,semiconductor contact) and the metallurgy of contact formation on the atomic level in cadmium zinc telluride (CdZnTe) radiation detectors remains a formidable challenge. In this work, an effort towards bridging that macro,nano knowledge gap is made by conducting a series of controlled experiments aimed at correlating electrical properties of the In contact to n-type CdZnTe(110) surface with the step-by-step process of contact formation. This can only be achieved by using high spatial resolution techniques, capable of conducting highly localized measurements on the nano- and sub-nanoscale, such as scanning probe microscopy. Scanning tunneling microscopy is used in situ to monitor the behavior of various In atom coverages on an atomically flat and ordered CdZnTe surface under well-controlled molecular beam epitaxial conditions in ultra-high vacuum. Electrical derivatives of atomic force microscopy are used to measure the electrical contact properties, such as contact potential difference and spreading resistance in torsion resonance tunneling mode. It is concluded that In atoms preferentially reacted with Te atomic-rows already at room temperature, forming nanometric patches of indium,telluride Schottky-type contacts. The methods developed in this study, in terms of both nanocontact fabrication and characterization (especially in terms of electrical properties) should benefit basic and applied research of any metal,semiconductor system. [source] Synthesis, Structure and Electrical Properties of Mo-doped CeO2,Materials for SOFCsFUEL CELLS, Issue 5 2009Q. Li Abstract In this paper, we report the synthesis, structure and electrical conductivity of Mo-doped compounds with a nominal chemical formula of Ce1,xMoxO2+, (x,=,0.05, 0.07, 0.1) (CMO). The formation of fluorite-like structure with a small amount of Ce8Mo12O49 impurity (JCPDS Card No. 31-0330) was confirmed using a powder X-ray diffraction (PXRD). The fluoride-type structure was retained under wet H2 and CH4 atmospheres at 700 and 800,°C, while diffraction peaks due to metal Mo were observed in dry H2 under the same condition. AC impedance measurements showed that the total conductivity increases with increasing Mo content in CMO, and among the investigated samples, Ce0.9Mo0.1O2+, exhibited the highest electrical conductivity with a value of 2.8,×,10,4 and 5.08,×,10,2 S cm,1 at 550,°C in air and wet H2, respectively. The electrical conductivity was found to be nearly the same, especially at high temperatures, in air, O2 and N2. Chemical compatibility of Ce0.9Mo0.1O2+, with 10,mol-% Y2O3 stabilised ZrO2 (YSZ) and Ce0.9Gd0.1O1.95 (CGO) oxide ion electrolytes in wet H2 was evaluated at 800,1,000,°C, using PXRD and EDX analyses. PXRD showed that CMO was found to react with YSZ electrolyte at 1,000,°C. The area specific polarisation resistance (ASPR) of Ce0.9Mo0.1O2+, on YSZ was found to be 8.58,ohm,cm2 at 800,°C in wet H2. [source] Silicon Nanowires: A Review on Aspects of their Growth and their Electrical PropertiesADVANCED MATERIALS, Issue 25-26 2009Volker Schmidt Abstract This paper summarizes some of the essential aspects of silicon-nanowire growth and of their electrical properties. In the first part, a brief description of the different growth techniques is given, though the general focus of this work is on chemical vapor deposition of silicon nanowires. The advantages and disadvantages of the different catalyst materials for silicon-wire growth are discussed at length. Thereafter, in the second part, three thermodynamic aspects of silicon-wire growth via the vapor,liquid,solid mechanism are presented and discussed. These are the expansion of the base of epitaxially grown Si wires, a stability criterion regarding the surface tension of the catalyst droplet, and the consequences of the Gibbs,Thomson effect for the silicon wire growth velocity. The third part is dedicated to the electrical properties of silicon nanowires. First, different silicon nanowire doping techniques are discussed. Attention is then focused on the diameter dependence of dopant ionization and the influence of interface trap states on the charge carrier density in silicon nanowires. It is concluded by a section on charge carrier mobility and mobility measurements. [source] Controlling Electrical Properties of Conjugated Polymers via a Solution-Based p-Type Doping,ADVANCED MATERIALS, Issue 17 2008Keng-Hoong Yim Tetrafluoro-tetracyano-quinodimethane (F4TCNQ) is used to p-dope conjugated polymers with a wide range of the HOMO levels via co-blending in a common organic solvent. Doping results in several orders of magnitude increase in the bulk conductivity and hole-current with reduced turn-on voltage. The effectiveness of doping increases as the HOMO level of the polymer becomes smaller. [source] Structure-Dependent Electrical Properties of Carbon Nanotube Fibers,ADVANCED MATERIALS, Issue 20 2007W. Li Improved electron transport along a carbon nanotube (CNT) fiber when it is spun from an array of longer nanotubes is reported. The effect of chemical post-treatments is also demonstrated. For example, the covalent bonding of gold nanoparticles to the CNT fibers remarkably improves conductivity (see figure), whereas annealing CNT fibers in a hydrogen-containing atmosphere leads to a dramatic decrease in conductivity. [source] The Variability of the Electrical Properties of the Pulmonary VeinsJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 9 2009AUGUSTUS O. GRANT M.B., Ch.B. [source] Ranolazine Exerts Potent Effects on Atrial Electrical Properties and Abbreviates Atrial Fibrillation Duration in the Intact Porcine HeartJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 7 2009KAPIL KUMAR M.D. Introduction: In vitro studies and ambulatory ECG recordings from the MERLIN TIMI-36 clinical trial suggest that the novel antianginal agent ranolazine may have the potential to suppress atrial arrhythmias. However, there are no reports of effects of ranolazine on atrial electrophysiologic properties in large intact animals. Methods and Results: In 12 closed-chest anesthetized pigs, effects of intravenous ranolazine (,9 ,M plasma concentration) on multisite atrial effective refractory period (ERP), conduction time (CT), and duration and inducibility of atrial fibrillation (AF) initiated by intrapericardial acetylcholine were investigated. Ranolazine increased ERP by a median of 45 ms (interquartile range 29,50 ms; P < 0.05, n = 6) in right and left atria compared to control at pacing cycle length (PCL) of 400 ms. However, ERP increased by only 28 (24,34) ms in right ventricle (P < 0.01, n = 6). Ranolazine increased atrial CT from 89 (71,109) ms to 98 (86,121) ms (P = 0.04, n = 6) at PCL of 400 ms. Ranolazine decreased AF duration from 894 (811,1220) seconds to 621 (549,761) seconds (P = 0.03, n = 6). AF was reinducible in 1 of 6 animals after termination with ranolazine compared with all 6 animals during control period (P = 0.07). Dominant frequency (DF) of AF was reduced by ranolazine in left atrium from 11.7 (10.7,20.5) Hz to 7.6 (2.9,8.8) Hz (P = 0.02, n = 6). Conclusions: Ranolazine, at therapeutic doses, increased atrial ERP to greater extent than ventricular ERP and prolonged atrial CT in a frequency-dependent manner in the porcine heart. AF duration and DF were also reduced by ranolazine. Potential role of ranolazine in AF management merits further investigation. [source] Electrical Properties of Gadolinium,Europium Zirconate CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Xiao-Liang Xia (Gd1,xEux)2Zr2O7 (0,x,1.0) ceramics are prepared via a solid-state reaction process at 1973 K for 10 h in air. (Gd1,xEux)2Zr2O7 (0.2,x,1.0) ceramics exhibit an ordered pyrochlore-type structure; however, Gd2Zr2O7 has a disordered defect fluorite-type structure. Raman spectroscopy analysis indicates that the degree of structural ordering increases with the increase of Eu content. The electrical properties of (Gd1,xEux)2Zr2O7 ceramics are investigated using complex impedance spectroscopy over a frequency range of 0.1 Hz to 20 MHz from 623 to 923 K. Electrical conductivity obeys the Arrhenius equation. Both the activation energy and the preexponential factor for grain conductivity decrease with increasing europium content from Gd2Zr2O7 (x=0) to Eu2Zr2O7 (x=1.0). The measured electrical conductivity of (Gd1,xEux)2Zr2O7 ceramics increases with increasing Eu content and temperature. Electrical conductivity of the pyrochlore-type materials is higher than that of the defect fluorite-type material in (Gd1,xEux)2Zr2O7 solid solution systems. The electrical conductivity of (Gd0.4Eu0.6)2Zr2O7 is almost independent of oxygen partial pressure from 1.0 × 10,4 to 1.0 atm. The high ionic transference number of (Gd0.4Eu0.6)2Zr2O7 ceramic at different temperatures proves that conduction is purely ionic with negligible electronic contribution. [source] Negative Thermal Expansion and Correlated Magnetic and Electrical Properties of Si-Doped Mn3GaN CompoundsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Ying Sun The negative thermal expansion (NTE) and correlated magnetic and electrical transport properties of Mn3GaxSi1,xN were investigated. For pure Mn3GaN, there is a large NTE effect corresponding to the antiferromagnetic to paramagnetic transition. Very interestingly, when partial Ga was replaced by Si, the NTE properties around the magnetic transition were changed. The NTE temperature range was broadened to ,T=148 K for Mn3Ga0.75Si0.25N and the linear thermal expansion coefficient was estimated as ,=,1.4 × 10,5 K,1 (272,420 K). Accordingly, the resistivity also showed a decrease from 327 to 395 K with temperature. With a further increasing Si content to x=0.5, the magnetic transition still occured, but the NTE effect did not appear. After careful observation, an anomaly was found at around 350 K in a,T, ,,T, and DSC curves of Mn3Ga0.5Si0.5N, respectively. This phenomenon strongly implies the close correlation among lattice, spin, and charge in this series materials. [source] Physical and Electrical Properties of Nanosized Mn- and Cr-Doped Strontium Y-Type Hexagonal FerritesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Muhammad Javed Iqbal Nanometer-sized crystallites of Y-type strontium hexaferrite, Sr2Ni2Fe12O22 and its Mn- and Cr-doped derivatives have been synthesized by the sol,gel method. Y-type phase formation was achieved at a considerably lower temperature of 950°C than is required in the traditional solid-state method (1200°C). The effect of doping of manganese at the tetrahedral site, Sr2Ni2,xMnx Fe12O22 (x=0.0,2.0), and chromium at octahedral site, Sr2Ni2 Fe12,yCryO22 (y=0.0,1.5), has been studied. The crystal structure remains unaffected by the substitutions. The crystallite size in the range of 13,45 nm is calculated from the X-ray diffraction data. The energy-dispersive X-ray fluorescence analysis shows that Y-type hexaferrites can be prepared with a base of strontium. The extent of doped Cr+3 ions at the octahedral site has been increased from the reported maximum value of y=1.5. Scanning electron micrographs of the samples showed a homogenous microstructure. The dc electrical resistivity studies show that these hexaferrites exhibit high resistivity at room temperature. Cr-doped samples have comparatively higher resistivity than Mn-doped samples. The doubly doped (Cr+Mn) samples possess high resistivity (7.37 × 109,-cm), a low dielectric constant (33.88 at 3000 Hz), and a high Curie temperature (>698 K). The dielectric energy losses are minimized by increasing the Mn and Cr contents of the synthesized samples. [source] The Influence of ZnF2 Doping on the Electrical Properties and Microstructure in Bi2O3,ZnO-Based VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Lihong Cheng ZnO varistors with different amounts of ZnF2 from 0.00 to 0.80 mol% were prepared using a solid-state reaction technique, to explore the potential application of ZnO. The F-doping effects on the microstructure and electrical properties of ZnO-based varistors were investigated. The average grain size of ZnO increased from 4.93 to 6.48 ,m as the ZnF2 content increased. Experimental results showed that as the ZnF2 content increased, the breakdown voltage decreased from 617 to 367 V/mm, and the nonlinear coefficient did not change much. However, a slight increase was observed in the leakage current. Besides, when the ZnF2 content increased, the donor concentration increased from 0.669 × 1018 to 8.720 × 1018 cm,3. The study indicated that ZnF2 played a similar role as sintering aids to promote grain growth and the substitutional F atoms in the bulk served as a donor to increase the donor concentration. [source] Effect of Donor, Acceptor, and Donor,Acceptor Codoping on the Electrical Properties of Ba0.6Sr0.4TiO3 Thin Films for Tunable Device ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Yuanyuan Zhang We have investigated the effects of donor, acceptor, and donor,acceptor codoping on both the dielectric properties and the leakage current behavior of Ba0.6Sr0.4TiO3 thin films prepared by the metalorganic solution deposition technique. La and Co were selected as donor and acceptor dopants, respectively. The electrical properties depend strongly on the type of dopants. Compared with others, codoped BST films have a much lower loss tangent, higher figure of merit, and lower leakage current. The electronic conduction mechanisms of the three types of dopants are reported. [source] Effect of La Doping on the Phase Conversion, Microstructure Change, and Electrical Properties of Bi2Fe4O9 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Ju Hong Miao Undoped and La-doped Bi2Fe4O9 ceramics were synthesized using a soft chemical method. It is observed that in calcining La-doped Bi2Fe4O9, Bi(La)FeO3 phase rather than Bi2,xLaxFe4O9 gradually increases with increasing La doping content. The phase conversion from mullite-type structure of Bi2Fe4O9 to rhombohedrally distorted perovskite one of Bi(La)FeO3 with increasing La doping content indicates that La doping can stabilize the structure of BiFeO3. This is further evidenced that Bi2Fe4O9 can be directly converted to Bi(La)FeO3 by heating the mixtures of nominal composition of Bi2Fe4O9/xLa2O3. Furthermore, the microstructure changes and the room temperature hysteresis loops and leakage current for Bi2,xLaxFe4O9 with x=0 and 0.02 were characterized. [source] Preparation and Electrical Properties of New Oxide Ion Conductors Ce6,xGdxMoO15,, (0.0,x,1.8)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009Defeng Zhou A series of oxide ion conductors Ce6,xGdxMoO15,, (0.0,x,1.8) have been prepared by the sol,gel method. Their properties were characterized by differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), Raman, IR, X-ray photoelectron spectroscopy (XPS), and AC impedance spectroscopy. The XRD patterns showed that the materials were single phase with a cubic fluorite structure. The conductivity of Ce6,xGdxMoO15,, increases as x increases and reaches the maximum at x=0.15. The conductivity of Ce4.5Gd1.5MoO15,, is ,t=3.6 × 10,3 S/cm at 700°C, which is higher than that of Ce4.5/6Gd1.5/6O2,, (,t=2.6 × 10,3 S/cm), and the corresponding activation energy of Ce4.5Gd1.5MoO15,, (0.92 eV) is lower than that of Ce4.5/6Gd1.5/6O2,, (1.18 eV). [source] Magnetic and Electrical Properties of (Mn, La)-Codoped SrTiO3 Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Song-Yin Zhang Mn-doped SrTiO3 -based thin films have been prepared by a simple sol,gel spin-coating method on silicon substrate. X-ray diffraction and high-resolution transmission electron microscopy reveal that these thin films are composed of amorphous and crystalline SrTiO3 phases. Optical and electrical measurements indicate that La codoping can make the band gap of SrTiO3 narrow and cause the leakage current to increase. Ferromagnetic behavior can be observed in these Mn- and/or La-codoped SrTiO3 -based thin films at room temperature, which should be ascribed to the magnetic coupling between the induced free electrons and Mn 3d spins. [source] Enhancing Electrical Properties in NBT,KBT Lead-Free Piezoelectric Ceramics by Optimizing Sintering TemperatureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Ya-Ru Zhang Conventional sintering of (Na1,xKx)0.5Bi0.5TiO3 (abbreviated as NKBTx, x=18,22 mol%) lead-free piezoelectric ceramics was investigated to clarify the optimal sintering temperature for densification and electrical properties. Both sintered density and electrical properties were sensitive to sintering temperature; particularly, the piezoelectric properties deteriorated when the ceramics were sintered above the optimum temperature. The NKBT20 and NKBT22 ceramics synthesized at 1110°,1170°C showed a phase transition from tetragonal to rhombohedral symmetry, which was similar to the morphotropic phase boundary (MPB). Because of such MPB-like behavior, the highest piezoelectric constant (d33) of about 192 pC/N with a high electromechanical coupling factor (kp) of about 32% were obtained in the NKBT22 ceramics sintered at 1150°C. [source] Preparation and Electrical Properties of an Anodized Al2O3,BaTiO3 Composite FilmJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Xianfeng Du A highly stable, water-based barium titanate BaTiO3, BT, sol was synthesized using a sol,gel route through a chelate lactate technique. Dried BT precursor powders were measured by thermal gravimetry,differential thermal analysis and X-ray diffraction. It was found that BT powders first converted into barium carbonate BaCO3, Ti complex, and intermediate phase Ba2Ti2O5CO3, and then transformed into perovskite phase BaTiO3. The crystallization temperature was about 550°C. The low-voltage etched aluminum foils were covered with BT sol by dip coating, and then annealed at 600°C for 30 min in air. After that, the samples were anodized in a 15 wt% aqueous solution of ammonium adipate. The voltage,time variations during anodizing were monitored, and the electrical properties of the anodic oxide film were examined. It was shown that the specific capacitance, the product of specific capacitance and withstanding voltage, and leakage current of samples with a BT coating were about 48.93%, 38.50%, and 167% larger than that without a BT coating, respectively. [source] Electrical Properties of Textured Potassium Strontium Niobate (KSr2Nb5O15) Ceramics Fabricated by Reactive Templated Grain GrowthJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008Sedat Alkoy Highly [001] textured KSr2Nb5O15 (KSN) ceramics were fabricated by templated grain growth using acicular KSN template particles (5,15 wt%) and reactive matrix of SrNb2O6 and KNbO3. Excess Nb2O5 (1,1.5 wt%) was added as a liquid former. Increasing sintering temperature and time resulted in increased texture with a maximum texture fraction of 0.98. Dielectric, ferroelectric, and piezoelectric measurements indicate anisotropic properties that are close to single crystal values in the textured ceramics with the highest Pr,18 ,C/cm2, Ps,25 ,C/cm2, and d33=65 pC/N obtained in the c -axis direction. [source] Synthesis and Electrical Properties of Stabilized Manganese Dioxide (,-MnO2) Thin-Film ElectrodesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008Do-Kyun Kwon Manganese dioxide (,-MnO2) thin films have been explored as a cathode material for reliable glass capacitors. Conducting ,-MnO2 thin films were deposited on a borosilicate glass substrate by a chemical solution deposition technique. High carbon activities originated from manganese acetate precursor, (Mn(C2H3O2)2·4H2O) and acetic acid solvent (C2H4O2), which substantially reduced MnO2 phase stability, and resulted in Mn2O3 formation at pyrolysis temperature in air. The ,-MnO2 structure was stabilized by Ba2+ insertion into a (2 × 2) oxygen tunnel frame to form a hollandite structure. With 15,20 mol% Ba addition, a conducting ,-MnO2 thin film was obtained after annealing at 600,650°C, exhibiting low electrical resistivity (,1 ,·cm), which enables application as a cathode material for capacitors. The hollandite ,-MnO2 phase was stable at 850°C, and thermally reduced to the insulating bixbyte (Mn2O3) phase after annealing at 900°C. The phase transition temperature of Ba containing ,-MnO2 was substantially higher than the reported transition temperature for pure MnO2 (,500°C). [source] Structural and Electrical Properties of Er2O3 -Doped Na1/2Bi1/2TiO3 Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Mengjia Wu Sodium bismuth titanates Na1/2Bi1/2TiO3 (NBT) doped with 0,3 wt% Er2O3 were prepared by the conventional solid-state reaction method. The X-ray diffraction results revealed that the sintered Er-doped NBT ceramics exhibited a pure perovskite structure with Er3+ concentrations ranging from 0 to 1 wt%. At a low Er2O3 concentration, the Er-doped NBT ceramics showed enhanced electrical properties with dielectric constant ,33T/,0=636, a low dielectric dissipation factor (tan ,=3.3%), a low coercive field (Ec=4.56 kV/mm), and a high piezoelectric constant (d33=75 pC/N). The relationship between the composition and properties of Er-doped NBT ceramics has been discussed. [source] Electrical Properties of Superlattice-Structured Bi4Ti3O12,PbBi4Ti4O15 Single CrystalsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007M. Ikezaki Single crystals of superlattice-structured ferroelectrics composed of Bi4Ti3O12 and PbBi4Ti4O15 were grown and the properties of polarization hysteresis and leakage current along the a -axis were investigated. Oxidation treatment led to a marked increase in leakage current at room temperature, showing that electron hole acts as a detrimental carrier for electrical conduction. A well-developed polarization hysteresis with a remanent polarization of 41 ,C/cm2 was observed, which is suggested to originate from the peculiar ferroelectric displacement of Bi in the Bi2O2 layers. [source] Synthesis, Densification, and Phase Evolution Studies of Al2O3,Al2TiO5,TiO2 Nanocomposites and Measurement of Their Electrical PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007Vikas Somani Alumina,aluminum titanate,titania (Al2O3,Al2TiO5,TiO2) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as-synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al2O3,TiO2 nanocomposite, while at a higher temperature (1300°C) an Al2O3,Al2TiO5,TiO2 nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties. [source] Atomic Structures and Electrical Properties of ZnO Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007Yukio Sato Various properties of ceramics can be significantly influenced by the presence of grain boundaries. The influence on the properties is closely related to the grain-boundary atomic structures. As different grain boundaries have different atomic structure, different grain boundaries have different influence on the properties. It is difficult to examine the atomic structure and properties of individual grain boundaries in ceramics. In order to understand the atomic,structure,property relationships, well-defined single grain boundaries should be characterized. In the present paper, we review our recent results on the investigations of atomic structures and electrical properties of ZnO single grain boundaries. The relationships between the atomic structures and the electrical properties were investigated using ZnO bicrystals, whose grain-boundary orientation relationship and grain-boundary planes can be arbitrarily controlled. The discussion focuses on the microscopic origin of nonlinear current,voltage (I,V) characteristics across ZnO grain boundaries. High-resolution transmission electron microscopy (HRTEM) observations and lattice-statics calculations revealed the atomic structures of the undoped ZnO [0001] ,7 and ,49 grain boundaries, enabling a comparison between coincidence site lattice (CSL) boundaries with small and large periodicity. These grain boundaries contained the common structural units (SUs) featuring atoms with coordination numbers that are unusual in ZnO. The ,49 boundary was found to have characteristic arrangement of the SUs, where two kinds of the SUs are alternatively formed. It is considered that the characteristic arrangement was formed to effectively relax the local strain in the vicinity of the boundary. Such a relaxation of local strain is considered to be one of dominant factors to determine the SU arrangements along grain boundaries. I,V measurements of the undoped ZnO bicrystals showed linear I,V characteristics. Although the coordination and bond lengths of atoms in the grain boundaries differ from those in the bulk crystal, this does apparently not generate deep unoccupied states in the band gap. This indicates that atomic structures of undoped ZnO grain boundaries are not responsible for the nonlinear I,V characteristics of ZnO ceramics. On the other hand, the nonlinear I,V characteristic appeared when doping the boundaries with Pr. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Pr-doped boundaries revealed that Pr segregates to specific atomic columns, substituting Zn at the boundary. However, the Pr itself was not the direct origin of the nonlinear I,V characteristics, as the Pr existed in the three-plus state and would not produce acceptor states in the boundary. First-principles calculations revealed that Pr doping instead promotes the formations of acceptor-like native defects, such as Zn vacancies. We believe that such acceptor-like native defects are microscopic origin of the nonlinear I,V characteristics. Investigations of various types of grain boundaries in the Pr and Co-codoped ZnO bicrystals indicated that the amounts of Pr segregation and the nonlinear I,V characteristics significantly depend on the grain-boundary orientation relationship. Larger amount of Pr segregation and, as a result, higher nonlinearity in I,V characteristics was obtained for incoherent boundaries. This indicates that Pr doping to incoherent boundaries is one of the guidelines to design the single grain boundaries with highly nonlinear I,V characteristics. Finally, a Pr and Co-codoped bicrystal with an incoherent boundary was fabricated to demonstrate a highly nonlinear I,V characteristic. This result indicates that ZnO single-grain-boundary varistors can be designed by controlling grain-boundary atomic structures and fabrication processes. Summarizing, our work firstly enabled us to gain a deeper understanding for the atomic structure of ZnO grain boundaries. Secondly, we obtained important insight into the origin of nonlinear I,V characteristics across the ZnO grain boundaries. And, finally, based on these results, we demonstrated the potential of this knowledge for designing and fabricating ZnO single-grain-boundary varistors. [source] Normal Sintering of (K,Na)NbO3 -Based Ceramics: Influence of Sintering Temperature on Densification, Microstructure, and Electrical PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Yuhua Zhen Normal sintering of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO3,NaNbO3, KNN)-based ceramics was investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d33 value of 206 pC/N was obtained for the Li- and Ta-codoped KNN ceramics prepared at 1090°C. [source] Optical and Electrical Properties of Amorphous and Nanocrystalline (La0.8Sr0.2)0.9MnO3 Thin Films Prepared from Low-Temperature Processing TechniqueJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Toshio Suzuki The results of a study on the optical and electrical properties of (La0.8Sr0.2)0.9MnO3 (LSM) thin films obtained by a polymeric precursor spin coating technique were presented. This method allowed preparation of optical quality thin films at annealing temperatures around 800°C. Amorphous and crystalline LSM thin films were studied by optical and electrical conductivity measurements. The energy-dependent absorption coefficients for the crystalline specimen were calculated from optical spectra and extra absorption was observed in the range of 1.8,2.5 eV with the exchange-gap excitation behavior in the 3,5 eV range. In comparison to the amorphous specimens, the electrical conductivity of the nanocrystalline specimen increased two to three orders of magnitude with decreasing activation energy. The charge carrier absorption model suggested an increase of the carrier concentration in the nanocrystalline specimen which may be a reason for the change in the electrical conductivity. [source] Microstructural Morphology and Electrical Properties of Copper- and Niobium-Doped Tin Dioxide Polycrystalline VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Chun-Ming Wang The influence of a Nb2O5 additive on the densification, microstructural morphology, and nonlinear electrical properties of the CuO-doped SnO2 -based varistors was investigated. It was found that copper oxide significantly improves the densification of the SnO2 ceramics. The effects of Nb2O5 on tin dioxide varistors were analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and capacitance,voltage measurements, as well as impedance spectroscopy. Copper oxide segregates at the grain boundaries and precipitates at triple points, and niobium makes the tin dioxide grain semi-conductive. The copper oxide intergranular insulating layer separates two semi-conductive tin dioxide grains and forms the barriers. The reason for the nonlinearity of SnO2 -based ceramics was explained. [source] Geometry and Electrical Properties of Grain Boundaries in Manganese Zinc Ferrite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Jong-Sook Lee For large-grained manganese zinc (MnZn) ferrite ceramics, grain misorientation determined by electron backscatter diffractions and grain-boundary resistance measured using microcontact impedance spectroscopy have been correlated. The degree of oxidation of grain boundaries and, hence, the barrier height depends on the overall grain-boundary network as well as on the individual boundary structure; therefore, a statistical analysis has been performed based on several hundreds of local measurements. When the boundaries are divided into low- and high-resistance groups, statistically significant differences in rotation axis and angle distributions are found. The misorientation distribution of the low-resistance boundary group is suggested to reflect the low-energy configurations of boundary planes in MnZn ferrites. [source] Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: I, Electrical ConductivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Silvania Lanfredi The electrical behavior of NaNbO3 ceramic samples with different relative densities was investigated by ac impedance spectroscopy in a range of 13 MHz to 10,3 Hz between 400° and 800°C in dry air. Measurements were performed during heating and cooling cycles. The Nyquist impedance diagrams of dense sodium niobate exhibit only one semicircle representing the grain contribution with depression angles as small as 1°, indicating a high homogeneity of the specific electrical properties. In the case of porous samples, the data reveal an additional low-frequency semicircle related to microstructure. For all studied samples, the Arrhenius conductivity plots show a change in the activation energy around 640°C, attributed to the tetragonal-cubic phase transition. The electrical conductivity of porous samples appears to be higher than that of dense ones. [source] Electrical Properties of Cerium-Doped BaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Jin Hyun Hwang The high-temperature equilibrium electrical conductivity of Ce-doped BaTiO3 was studied in terms of oxygen partial pressure, P(O2), and composition. In (Ba1,xCex)TiO3, the conductivity follows the ,1/4 power dependence of P(O2) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P(O2) where electron compensation prevails at low P(O2). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO3, indicating the substitution of Ce as Ce4+ for Ti4+ in Ba(Ti1,yCey)O3. The Curie temperature (Tc) was systematically lowered when Ce3+ was incorporated into Ba2+ sites, whereas the substitution of Ce4+ for Ti4+ sites resulted in no change in this parameter. [source] | |||||||||||||||||||||||||||||||||||||||||||