Microstructure and electrical properties of (Ta, Co, Pr) doped TiO2 based electroceramics

The addition of different dopants affects the densification, mean grain size and electrical properties of TiO₂-based varistor ceramics. This paper discusses the microstructural and electrical properties of (Ta, Co, Pr) doped TiO₂ systems, demonstrating that some of these systems display electrical properties that allow for their use as low voltage varistor. Dopants such as Ta₂O₅ play a special role in the formation of barriers at the grain boundary and in the nonlinear behavior in TiO₂-based systems. The higher values of nonlinear coefficient and breakdown electric field were obtained in the system just doped with Ta₂O₅ and CoO.     

Synthesis and characterization of Co-doped nano-TiO<Subscript>2</Subscript> through co-precipitation method for photocatalytic activity

The aim of this work was synthesis and investigation of various properties of Co-doped titanium dioxide nanostructures. Synthesis was conducted by the co-precipitation method using cobalt nitrate and titanium isopropoxide as a precursor, followed by thermal treatment at a temperature of 500 °C. The materials were fully characterized using several techniques (X-ray diffraction XRD, SEM, FTIR, TGA/DTA, UV–Vis diffuse reflectance DRS and photoluminescence). However, dopant has no effect on XRD pattern of the host but it can influence on the various characteristics of host such as optical and electrical properties. The scanning electron microscopy was used to detect the morphology of synthesized nanoparticles which sizes changed with the altitude in the doping concentration to 6%. FTIR spectra exhibit broad peaks where anatase phases of TiO₂ demonstrate very sharp UV–Vis band gap results showed the reduction in band gap from from 3.21 eV, for undoped TiO₂, to 2.74 eV, for Co doped 6% TiO₂. The photocatalytic activity of the samples were studied based on the degradation of methyl orange as a model compound, where the results showed that Co doped 6% TiO₂ a good photocatalytic activity.     

Influence of samarium doping on structural and dielectric properties of strontium bismuth tantalate ceramics derived by molten salt synthesis route

Layered Sr(Bi_1?xSm_x)₂Ta₂O₉ ceramics with x ranging from 0 to 0.10 (10 mol%) were fabricated by the low temperature molten salt synthesis route. X-ray powder diffraction studies revealed that the single phase orthorhombic layered perovskite structure is retained in all these compositions. Scanning electron microscopic studies on these ceramics confirmed the presence of well packed equiaxed plate shaped grains. The dielectric and electrical conductivity properties were studied in the 100 Hz–1 MHz frequency range at 300 K. Interestingly, the 10 mol% samarium doped SrBi₂Ta₂O₉ ceramics exhibited high dielectric constant (ε_r = 155) and low dielectric loss (0.00298) compared to those of other compositions. The electrical conductivity of undoped and samarium doped ceramics increased linearly with increase in frequency.     

Thin metallic oxides as transparent conductors

Films of tin oxide doped with fluorine or of indium oxide doped with tin (i.e. indium tin oxide (ITO)) can be obtained by standard procedures such as thermal evaporation or sputtering, or by other methods such as the hydrolysis of metallic chlorides (spraying) or the pyrolysis of organometallic compounds (chemical vapour deposition). The optical and electrical properties of these layers are very similar: for thicknesses in the range of a few hundred nanometers, a resistivity ? of the order of 4 × 10^?4 Ω cm and a transparency T of 80%–90% in the visible range of the spectrum are obtained. These layers are commonly used as transparent heating systems and in the field of digital display and light-emitting devices. More recently, some large-scale uses have been envisaged in the field of solar energy. Solar cells with a conversion efficiency of 12% have been obtained for ITO/Si or SnO₂/Si structures. Stack filters such as glass/SnO₂:F/(black molybdenum)/SnO₂:F have shown excellent properties as photothermal converters.     

Metal-metal distances in vanadium,scandium, and aluminum doped Ti2O3 and their implications for the role of vanadium in (Ti1−xVx)2O3

Single crystal x-ray structure determinations of a series of V, Sc, and Al doped Ti₂O₃ samples have shown that the metal-metal distance along the 3-fold axis in all of these corundum-like systems increases with increasing concentration of dopant. However, the effect of V is at least twice that of a corresponding amount of Al or Sc. The metal-metal distance in the basal plane decreases with increasing V and Al concentration and increases with increasing Sc concentration. These structural changes have been correlated with the electrical behavior of the doped systems and a cluster model has been proposed for the behavior of vanadium in Ti₂O₃.     

Cobalt‐Doped Nickel Phosphite for High Performance of Electrochemical Energy Storage

Compared to single metallic Ni or Co phosphides, bimetallic Ni–Co phosphides own ameliorative properties, such as high electrical conductivity, remarkable rate capability, upper specific capacity, and excellent cycle performance. Here, a simple one‐step solvothermal process is proposed for the synthesis of bouquet‐like cobalt‐doped nickel phosphite (Ni₁₁(HPO₃)₈(OH)₆), and the effect of the structure on the pseudocapacitive performance is investigated via a series of electrochemical measurements. It is found that when the cobalt content is low, the glycol/deionized water ratio is 1, and the reaction is under 200 °C for 20 h, the morphology of the sample is uniform and has the highest specific surface area. The cobalt‐doped Ni₁₁(HPO₃)₈(OH)₆ electrode presents a maximum specific capacitance of 714.8 F g^?1. More significantly, aqueous and solid‐state flexible electrochemical energy storage devices are successfully assembled. The aqueous device shows a high energy density of 15.48 mWh cm^?2 at the power density of 0.6 KW cm^?2. The solid‐state device shows a high energy density of 14.72 mWh cm^?2 at the power density of 0.6 KW cm^?2. These excellent performances confirm that the cobalt‐doped Ni₁₁(HPO₃)₈(OH)₆ are promising materials for applications in electrochemical energy storage devices.     

Localization of uranium ions in synthetically grown CaF2.U single crystals

Single crystals of CaF₂ doped with 0.1% wt. uranium were grown by the Czochralski-Kyropoulos method. The localization of uranium ions was investigated by optical and transmission electron microscopy, optical absorption and electron spin resonance. These studies revealed not only the presence of isolated uranium ions but also of UO₂ agglomerates which can play an important role in understanding the properties of such systems.     

Influence of high heat capacity substances doping on quench currents of fast ramped superconducting oval windings

The effect of high heat capacity substances doping on superconducting magnets ramp rate induced quench currents has been investigated for three oval windings. The windings were wound from Rutherford type cable (1.44 × 4.64 mm²), made of 10 multifilamentary NbTi strands 0.85 mm dia. Before application of electrical insulation and winding the cable was covered with epoxy resin with three different fillers: BN (boron nitride—a standard filler for preventing of epoxy cracking at low temperatures), and two rare-earth intermetallic compounds (HoCu₂ and CeCu₆). The specific heat of these compounds at liquid helium temperatures is extremely high. The volumetric fraction of these compounds was 2.9% of the total winding volume, corresponding to 4.5 times increase of averaged winding heat capacity for HoCu₂ and to 1.5 times increase for CeCu₆. At high ramp rates (∼4 kA/s, or ∼6.5 T/s) quench current of HoCu₂ doped winding was 35% higher than that for the BN doped one, while for CeCu₆ doped winding the quench current increase was 12%. Measured quench currents match values calculated with our theoretical model, in which whole doping substances enthalphy was taking into account. It indicates that the enhanced enthalphy is fully utilized in the used range of dB/dt.     

Electrical and microstructural properties of CaTiO3-doped K1/2Na1/2NbO3-lead free ceramics

Microstructure, electrical properties and dielectric behaviour of K_1/2Na_1/2NbO₃ (KNN) and CaTiO₃-modified K_1/2Na_1/2NbO₃ (CTO-KNN) systems, were investigated. Discs doped with 0 to 0·55% mol of CaTiO₃ (CTO) were sintered at 1125°C for 2 h. Although minority phases were found in doped samples, CaTiO₃ was not detected. It was also observed that CTO changed the microstructure and grain size of KNN drastically. Also, the Curie temperature and permittivity values decreased. Addition of CTO between 0·15 and 0·45 mol% decreases the density and dielectric values. Samples prepared with higher content of CTO than 0·45 mol% showed better electrical properties.     

Doping effect in Ca3Co4−xZnxOy ceramics

Ca₃Co_4?xZn_xO_y (x = 0.01, 0.03, and 0.05) polycrystalline thermoelectric ceramics have been prepared by the classical solid state method. XRD data have shown that Ca₃Co₄O₉ is the major phase, with small amounts of the Ca₃Co₂O₆ one. Moreover, it has been found that the Zn has been incorporated into these two phases. Slight Zn doping decreases electrical resistivity compared with the values obtained in undoped samples. The minimum values have been obtained for the 0.01-Ni doped samples, increasing for further Zn substitution. Seebeck coefficient does not appreciably change in all the measured temperature range, independently of Zn content. The improvement in electrical resistivity leads to higher power factor values for the 0.01 Zn-doped samples (about 30 %) than for the undoped ones. The maximum power factor at 800 °C, around 0.27 mW/K² m is significantly higher than the best results obtained in Zn doped samples reported in the literature.     

On the performance of a class‐4 partial response digital communication system

Abstract

The dark conductivity of phosphorus‐doped amorphous‐silicon alloys (a‐Si:H:F) prepared by the RF plasma decomposition of a gaseous mixture of SiF₄, H₂ and diluted PH₃ is extremely high; it exceeds 10 (O‐cm)^‐1 with only a small amount of PH₃ (～500 ppm) added in the gas phase. These doping characteristics represent a significant improvement over the doping characteristics of a‐Si:H alloys prepared by a glow‐discharge of SiH₄. The improvement was found to be due to the fact that P‐doped a‐Si:H:F contains microcrystallites which are embedded in an amorphous network. The percolation process in these two‐phase systems gives rise to high conductivity. We have used transmission electron microscopy (TEM) and diffraction (TED) to determine the critical surface fraction, ρ_c, of crystallinity at the onset of extended conduction. The measured ρ_c is approximately 0.46. This percolation limit provides a basis for the analysis of the electrical properties of P‐doped a‐Si:H:F.     

Current-voltage characteristics and grain growth of Li2CO3-doped tungsten trioxide ceramics

Ceramics samples of tungsten trioxide doped with lithium carbonate from 0.5 to 5 mol% were prepared by conventional electroceramic technique. The current-voltage characteristics of these ceramics were measured under various ambient temperatures. All of the I-V curves showed non-ohmic electrical properties with obvious negative-resistance characteristic at room temperature. It is found that there exists a direct correlation between the negative-resistance phenomenon in the I-V curves and the electrical history of these samples. The suitability of some models regarding the negative-resistance characteristics is discussed. X-ray diffraction (XRD) revealed coexistence of two phases of tungsten trioxide, which depends on the amount of lithium. Scanning electron microscope (SEM) showed great differences for both grain shape and size between the Li-doped and undoped WO₃ ceramics, and this indicates that Li₂CO₃ doped into WO₃ influences strongly the growing of WO₃ during sintering process.     

CdS thin films doped with metal-organic salts using chemical bath deposition

CdS thin films doped with metal-organic salts were grown on glass substrates at 90 °C by the chemical bath deposition technique. Metal-organic salts such as zinc acetate, chromium acetylacetonate, ammonium fluoride, aluminum nitrate, tin acetate and indium acetate were used. The chemical bath was prepared with cadmium acetate, ammonium acetate, thiourea and ammonium hydroxide. In the case of un-doped films, the S/Cd ratio was varied by changing the thiourea in the range 1-12. The best optical, structural and electrical properties were found for S/Cd = 2. The doped films were prepared by always keeping the ratio S/Cd constant at 2. The band gap (E_g) of doped and un-doped films was evaluated from transmittance spectra, where films with lower sulfur concentration exhibited higher E_g. X-ray analysis showed that both un-doped and doped films were polycrystalline with preferential orientation along the (111) direction and with the zincblende structure in all cases. The dark electrical results showed that CdS doped with Zn (1 at.%) exhibited the lowest resistivity values of 10 Ω cm.     

Moving Frontiers in Transition Metal Catalysis: Synthesis,Characterization and Modeling

Nanosized transition metal particles are important materials in catalysis with a key role not only in academic research but also in many processes with industrial and societal relevance. Although small improvements in catalytic properties can lead to significant economic and environmental impacts, it is only now that knowledge‐based design of such materials is emerging, partly because the understanding of catalytic mechanisms on nanoparticle surfaces is increasingly improving. A knowledge‐based design requires bottom‐up synthesis of well‐defined model catalysts, an understanding of the catalytic nanomaterials “at work” (operando), and both a detailed understanding and a prediction by theoretical methods. This article reports on progress in colloidal synthesis of transition metal nanoparticles for preparation of model catalysts to close the materials gap between the discoveries of fundamental surface science and industrial application. The transition metal particles, however, often undergo extensive transformations when applied to the catalytic process and much progress has recently been achieved operando characterization techniques under relevant reaction conditions. They allow better understanding of size/structure–activity correlations in these systems. Moreover, the growth of computing power and the improvement of theoretical methods uncover mechanisms on nanoparticles and have recently predicted highly active particles for CO/CO₂ hydrogenation or direct H₂O₂ synthesis.     

Thermoelectric properties of Zn doped Cu2SnSe3

Zn doped ternary compounds Cu₂Zn_xSn_1−xSe₃ (x = 0, 0.025, 0.05, 0.075) were prepared by solid state synthesis. The undoped compound showed a monoclinic crystal structure as a major phase, while the doped compounds showed a cubic crystal structure confirmed by powder XRD (X-Ray Diffraction). The surface morphology and elemental composition analysis for all the samples were studied by SEM (Scanning Electron Microscopy) and EPMA (Electron Probe Micro Analyzer), respectively. SEM micrographs of the hot pressed samples showed the presence of continuous and homogeneous grains confirming sufficient densification. Elemental composition of all the samples revealed an off-stoichiometry, which was determined by EPMA. Transport properties were measured between 324 K and 773 K. The electrical resistivity decreased up to the samples with Zn content x = 0.05 in Cu₂Zn_xSn_1−xSe₃, and slightly increased in the sample Cu₂Zn_0.075Sn_0.925Se₃. This behavior is consistent with the changes in the carrier concentration confirmed by room temperature Hall coefficient data. Temperature dependent electrical resistivity of all samples showed heavily doped semiconductor behavior. All the samples exhibit positive Seebeck coefficient (S) and Hall coefficient indicating that the majority of the carriers are holes. A linear increase in Seebeck coefficient with increase in temperature indicates the degenerate semiconductor behavior. The total thermal conductivity of the doped samples increased with a higher amount of doping, due to the increase in the carrier contribution. The total and lattice thermal conductivity of all samples showed 1/T dependence, which points toward the dominance of phonon scattering at high temperatures. The maximum 1/TZT = 0.48 at 773 K was obtained for the sample Cu₂SnSe₃ due to a low thermal conductivity compared to the doped samples.     

Creation of a Field-Induced Co(II) Single-Ion Magnet by Doping into a Zn(II) Diamagnetic Metal–Organic Framework

The combination of single-ion magnets (SIMs) and metal–organic frameworks (MOFs) is expected to produce new quantum materials. The principal issue to be solved in this regard is the development of new strategies for the synthesis of SIM-MOFs. This work demonstrates a new simple strategy for the synthesis of SIM-MOFs where a diamagnetic MOF is used as the framework into which the SIM sites are doped. 1, 0.5, and 0.2 mol% of the Co(II) ions are doped into the Zn(II) sites of [CH₆N₃][Zn^II(HCOO)₃]. The doped Co(II) sites in the MOFs perform as SIM with a positive D term of zero-field splitting. The longest magnetic relaxation time is 150 ms (0.2 mol% Co) at 1.8 K under a static field of 0.1 T. Temperature dependency of the relaxation time suggests suppressing magnetic relaxation by reduction of spin–spin interaction upon doping in the rigid framework. Thus, this work represents a proof of concept for the creation of a single-ion doped magnet in the MOF. This simple synthetic strategy will be widely applied for the creation of quantum magnetic materials.     

Studies on micro-structural and electrical properties of spray-deposited fluorine-doped tin oxide thin films from low-cost precursor

Thin films of fluorine-doped tin oxide (SnO₂:F) on glass were prepared by spray pyrolysis technique using stannous chloride (SnCl₂) and ammonium fluoride (NH₄F) as precursors. The as-prepared films were characterized for their structural and electrical properties and are discussed in detail in this article. The surface morphology studies revealed that the films are grainy and the roughness of undoped films has been reduced on fluorine doping. X-ray diffraction (XRD) studies revealed that the films are polycrystalline. It further revealed that the undoped films grow along the preferred orientation of (211), whereas all the doped films grow along (200). The minimum sheet resistance 1.75 Ω/□ achieved in the present study for the films doped with 15 wt.% F is the lowest among the reported values for these materials prepared using SnCl₂ precursor. The electrical transport phenomenon has been analyzed in order to find out the possible scattering mechanism that limiting the mobility of charge carriers.     

Characterization and electrical conductivity of La<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>CrO<Subscript>3</Subscript> NTC ceramics

The La_1?xSr_xCrO₃ (x?=?0–0.1) negative temperature coefficient (NTC) ceramics have been prepared by the traditional solid state reaction method. X-ray diffraction (XRD) analysis has revealed that the as-sintered ceramics crystallize in a single perovskite structure. Scanning Electron Microscope (SEM) images show that the doped Sr²⁺ contributes to in the decrease in porosity. X-ray photoelectron spectroscopy (XPS) analysis indicates the existence of Cr³⁺ and Cr⁶⁺ ions on lattice sites, which result in hopping conduction. The presence of the Cr⁶⁺ is one of the key factors that affect the electrical conductivity of La_1?xSr_xCrO₃. Resistance–temperature characteristics were studied in the range of ?80 to 10?°C for the ceramic samples, the electrical characterizations show that the electrical resistivity and material constant B decrease with the increase of the strontium content.     

An alternative fluorine precursor for the synthesis of SnO2:F by spray pyrolysis

An alternative, non-toxic precursor was employed for the synthesis of SnO₂:F transparent conducting oxide. The performance of benzenesulfonyl fluoride (BSF) as F source for spray pyrolysis was investigated. Its decomposition and the actual incorporation of fluorine in the tin oxide matrix were confirmed by X-ray photoelectron spectroscopy while its effect on the electrical properties was investigated by resistance and Hall measurements. Results were compared with respect to samples grown using a common fluorine source (NH₄F), a commercial available sample and a sample grown by spray pyrolysis at an independent laboratory. We show that BSF leads to actively doped conductive SnO₂ with good carrier mobility, though the fluorine incorporation rate and hence overall conductivity of the films is lower than for fluorine precursors commonly used in spray pyrolysis.     

Electrical Conductivity and Thermodynamic Properties of Some Alkaline Earth-Doped Lanthanum Chromites

Alkaline-earth doped lanthanum chromites are currently the interconnecting materials of choice for solid oxide fuel cells (SOFCs). Since these materials in SOFC operating conditions are under a large oxygen potential gradient and at high temperature (1273 K), a thorough knowledge of their physical and thermochemical properties is very important. In the present study, the alkaline-earth doped lanthanum chromites La_1-xSr_xCrO₃ (x=0–0.3) and La_0.7Ca_0.3CrO₃ were prepared from complex precursors isolated from the La(NO₃)₃–Cr(NO₃)₃–urea system. The oxide powders were characterized by means of X-ray diffraction (XRD). The DC electrical conductivities of the samples were measured in the temperature range of 295–1273 K in air. The thermodynamic properties represented by the relative partial molar free energies, enthalpies, and entropies of oxygen dissolution in the perovskite phase, as well as the partial pressures of oxygen, have been investigated by the solid electrolyte galvanic cells method coupled with the solid-state coulometric titration technique, within the temperature range of 1073–1273 K and in a reducing atmosphere (10^–5 Pa). The variation of the electrical conductivities and thermodynamic properties with changing oxygen stoichiometry is discussed. The study demonstrates new correlations existing between the structural, electrical, and thermodynamic properties in the doped lanthanum chromites.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.