High Temperature Electrical Conductivity Research Articles

Sol–gel synthesis, structural and electrical properties of Li2CoSiO4 cathode material

Polyanionic cathode materials for lithium-ion batteries start to be considered as potential alternative for layered oxide materials. Among them, Li 2 CoSiO 4, characterized by outstanding capacity and working voltage, seems to be an interesting substitute for LiFePO 4 and related systems. In this work, structural and electrical investigations of Li 2 CoSiO 4 obtained by sol–gel synthesis were presented. Thermal decomposition of gel precursor was studied using EGA (FTIR)-TGA method. Chemical composition of the obtained material was confirmed using X-ray diffraction and energy-dispersive X-ray spectroscopy. The morphology of β- Li 2 CoSiO 4 was studied using transmission electron microscopy. High temperature electrical conductivity of Li 2 CoSiO 4 was measured for the first time. Activation energies of the electrical conductivity of two Li 2 CoSiO 4 polymorphs (β and γ) were determined. The room temperature electrical conductivity of those materials was estimated as well.

Experimental Investigation of Copper-Tungsten Electrode Wear in EDM

Copper-tungsten alloy which is widely used in the field of EDM has high melting temperature and excellent electrical and thermal conductivity. Copper tungsten electrodes for electrical discharge dressing of metal-bond wheel were studied, and experiments were conducted to observe their wear performance in this paper. Orthogonal experiment was designed to explore the wear at the edge of and the bottom of electrode with the machining of holes. Thickness of the carbon layer, micro topography and experimental results were analyzed. Low current and big pulse duration can reduce the electrode wear rate. Although carbon on the electrode surface can be wiped out easily, wear rate of copper-tungsten electrode decreases with the increasing in thickness of the carbon at the initial phase. There are fewer cracks and residue presented on the machined surface by microscope.

High temperature electrical conductivity in hydrothermally grown ZnO

AbstractResults of measurements of high temperature electrical conductivity (HTEC) in undoped hydrothermally grown ZnO single crystal are presented. HTEC measurements were made under the Zn component vapor pressure (up to 1 atm) and in the temperature range from 873 K to 1273 K. Reliable thermodynamic equilibrium in the ZnO crystal for HTEC measurements of isotherms and isobars was obtained at the temperatures higher than 873 K. Surprisingly slow chemical diffusion prolonged the high temperature measurement cycles continuously for several weeks. In our experiments the absolute value of HTEC in undoped hydrothermally grown ZnO was several orders of magnitude higher than HTEC in undoped ZnS. Slopes of HTEC isotherms varied with component vapor pressure and changed in the range from 0.2 to 0.4. For HTEC isobar in the temperature range from 1173 K to 1273 K it was found activation energy value 0.3‐0.4 eV at zinc vapour pressure 0.092 atm. Defect model for explanation of this high temperature experiment is discussed in connection with impurities. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of alumina nanofiller on the viscosity and electrical conductivity of glass-based seals for solid oxide fuel cells

Use of alumina nanofiller to strengthen the structure of the sealing glass used for solid oxide fuel cells (SOFCs) has been investigated by measurement of fracture strength, viscosity, and electrical conductivity at elevated temperatures. The electrical conductivity and viscosity of two glass-based seals for SOFCs were compared. Measurement of electrical conductivity and viscosity of the glass-based seals over the temperature range 400–600 °C showed that addition of 10 % nano-sized alumina powder to the sealing glass increased both the high-temperature electrical conductivity and viscosity of the sintered glass matrix. The higher conductivity and viscosity of glass composites containing alumina nanofiller were attributed to formation of bonds with bridging oxygen by partial dissolution of the alumina nanofiller in the sealing glass. Infrared spectroscopy and X-ray diffraction analysis were conducted to confirm this conclusion. Strengthening of the sealing glass structure to improve long-term durability may be possible by using glass composites containing alumina nanofiller.

Electrical Properties of Alkali/Alkaline-Earth Borosilicate Glass Composite Sealants for Solid Oxide Fuel Cells

Development of a reliable sealant or sealing system remains one of the top priorities in planar solid oxide fuel cells (SOFCs) technology. Recently, a compliant glass seal such as an alkali silicate glass was proposed for SOFCs. In contrast to the conventional glass–ceramic sealant which develops a rigid or semi-rigid microstructure after sealing, the compliant glass shows so called “self-healing” behavior and will remain vitreous without substantial crystallization after sealing and during operation at elevated temperatures. The objective of this study was to investigate the relationship between sealant structure and high temperature electrical conductivities of glass composite sealants for SOFCs. Alkali/alkaline-earth borosilicate glass-based sealants, both with and without Al2O3 or ZrO2 fillers, were heat treated at various temperatures for periods of up to 48 h. The effects of filler type, densification of glass and alkali/alkali-earth oxide content in sealants on the electrical conductivities of the sealants were investigated. The results showed that the electrical conductivity of a glass composite sealant containing ZrO2 filler increased ten times after 48 hours of heat treatment. The electrical conductivity of a ZrO2 filler-containing glass after heat treatment was similar to that of an Al2O3 filler-containing glass. This was attributed to the densification of sealing glass by heat treatment.

Effects of transition metal additives on redox stability and high-temperature electrical conductivity of (Fe,Mg)3O4 spinels

Abstract Magnetite-based spinels are considered as promising oxide materials to meet the requirements for ceramic consumable anodes in molten oxide pyroelectrolysis process, a breakthrough low-CO2 steel technology aimed to overcome the environmental impact of classical extractive metallurgy. The present work focuses on the assessment of phase relationships, redox stability and electrical conductivity of Fe2.6Me0.2Mg0.2O4 (M = Ni, Cr, Al, Mn, Ti) spinel-type materials at 300–1773 K and p(O2) from 10−5 to 0.21 atm. The oxidation state of substituting transition metal cation, affecting the fraction of Fe2+ in spinel lattice, was found to be a key factor, which determines the electronic transport and tolerance against oxidative decomposition, while the impact of preferred coordination of additives on these properties was less pronounced. At T > 650 K thermal expansion of Fe2.6Me0.2Mg0.2O4 ceramics exhibited complex behaviour, and, in highly oxidizing conditions, resulted in significant volume changes, unfavourable for high-temperature electrochemical applications.

Thermoelectric transport properties of p-type silver-doped PbS with in situ Ag2S nanoprecipitates

In this study, a series of p-type Ag-doped PbS compounds were prepared by a vacuum melting combined with subsequent spark plasma sintering process. Ag partially occupies Pb sites acting as an electron acceptor to increase the hole concentration, and also in situ forms Ag2S nanoprecipitates at the grain boundaries which are detectable in thermal analysis and microstructural observations. The two existences of Ag both exert significant influences on the electrical transport properties. With increasing temperature, dissolution of Ag2S nanoprecipitates into the PbS matrix as interstitial Ag gradually decreases the hole concentration. Very low mobility of Ag-doped samples is unexpected at low temperatures, which indicates a strong carrier scattering. From temperature dependent mobility, it can be concluded that neutral impurity scattering (μ ∼ Ta, a = 0) dominates at low temperature (T < 200 K), and energy barrier scattering (a > 1.5) governs until lattice vibrations take over at T > 450 K (a ∼ −2.5). The complex scattering mechanisms at T < 450 K in Ag-doped samples should be originated from the multiple existences of Ag (Ag+, interstitial Ag, Ag2S nanoprecipitates). In particular, Ag doping increases the high temperature electrical conductivity, giving rise to an enhanced power factor of ∼0.8 × 10−3 W m−1 K−2 at 870 K for the 1.5 at% Ag-doped sample. Benefiting from the improved power factor and low lattice thermal conductivity originating from strong lattice anharmonicity, a doubled ZT value of ∼0.6 can be achieved for Pb0.985Ag0.015S in comparison to that of pristine PbS.

A simple demonstration of the high-temperature electrical conductivity of glass

We usually think of glass as a good electrical insulator; this, however, is not always the case. There are several ways to show that glass becomes conducting at high temperatures,1,2 but the following approach, devised by Brown University demonstration manager Gerald Zani, may be one of the simplest to perform.

An inversion layer at the surface of n-type iron pyrite

Numerical modeling of Hall effect data is used to demonstrate the existence of a conductive inversion layer at the surface of high-quality n-type single crystals of iron pyrite (cubic FeS2) grown by a flux technique. The presence of the inversion layer is corroborated by Hall measurements as a function of crystal thickness and photoemission spectroscopy. This hole-rich surface layer may explain both the low photovoltage of pyrite solar cells and the widely-observed high p-type conductivity of polycrystalline pyrite thin films that have together perplexed researchers for the past thirty years. We find that the thickness and conductivity of the inversion layer can be modified by mechanical and chemical treatments of the pyrite surface, suggesting that it may be possible to eliminate this hole-rich layer by passivating surface states and subsurface defects. Furthermore, modeling of the high-temperature electrical conductivity shows that the electronic band gap is 0.80 ± 0.05 eV at room temperature (compared to 0.94 eV according to optical transmission data), confirming that photovoltages of ∼500 mV should be attainable from pyrite under solar illumination.

Improving aging and creep resistance in a dilute Al–Sc alloy by microalloying with Si, Zr and Er

Nanosized precipitates in an Al–0.06Scat.% alloy containing various microalloying additions were studied, with the goal of developing cost-effective aluminum alloys for high-temperature applications, using micro-hardness, electrical conductivity and atom-probe tomography measurements. Substituting 0.005at.% Er for the more expensive Sc maintains high ambient-temperature strength, and dramatically improves the high-temperature creep resistance, as anticipated from the increase in lattice parameter mismatch between the α-Al(fcc) matrix and the coherent L12-ordered Al3(Sc,Zr,Er) precipitates. A concentration of the slow-diffuser Zr as low as 0.02at.% is sufficient to provide coarsening resistance at 400°C (an homologous temperature of 0.72) for up to 66days by forming a Zr-enriched outer shell encapsulating the precipitates. Finally, adding 0.05at.% Si enhances ambient-temperature strength by increasing the number density of precipitates, while decreasing the homogenization and peak-aging heat-treatment times, which is caused by the Si atoms accelerating the Er and Sc diffusion kinetics. Si-containing alloys are also cost effective, owing to the existence of Si in commercial purity Al. But addition of Si reduces the precipitate coarsening resistance: the magnitude of this effect is, however, determined by the Si concentration.

Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides

Novel complex oxides Sr2Ga1+x In1−x O5, x = 0.0–0.2 with brownmillerite-type structure were prepared in air at T = 1,273 K, 24 h. Study of the crystal structure of Sr2Ga1.1In0.9O5 refined using X-ray powder diffraction data (S.G. Icmm, a = 5.9694(1) A, b = 15.2091(3) A, c = 5.7122(1) A, χ 2 = 2.48, R F 2 = 0.0504, R p = 0.0458) revealed ordering of Ga3+ and In3+ cations over tetrahedral and octahedral positions, respectively. A partial replacement of Sr2+ by La3+ according to formula Sr1−y La y Ga0.5In0.5O2.5+y/2, leads to the formation of a cubic perovskite (a = 4.0291(5) A) for y = 0.3. No ordering of oxygen vacancies or cations was observed in Sr0.7La0.3Ga0.5In0.5O2.65 as revealed by electron diffraction study. The trace diffusion coefficient (D T) of oxygen for cubic perovskite Sr0.7La0.3Ga0.5In0.5O2.65 is in the range 2.0 × 10−9–6.3 × 10−8 cm2/s with activation energy 1.4(1) eV as determined by isotopic exchange depth profile technique using secondary ion mass spectrometry at 973–1,223 K. These values are close to those reported for Ca-doped ZrO2. High-temperature electrical conductivity of Sr0.7La0.3Ga0.5In0.5O2.65 studied by AC impedance was found to be nearly independent on oxygen partial pressure. Calculated values of activation energy at T < 1,073 K for hole and oxide-ion conductivities are 0.96 and 1.10 eV, respectively.

Redox stability and high-temperature electrical conductivity of magnesium- and aluminium-substituted magnetite

Abstract Spinel-type magnetite-based oxides, possessing relatively high electrical conductivity, are considered as promising consumable anode materials for high temperature pyroelectrolysis, a breakthrough low-CO 2 steel technology to overcome the environmental impact of classical extractive metallurgy. The present work was focused on the analysis of phase stability, thermal expansion and high-temperature electrical conductivity in (Fe,Mg,Al) 3 O 4 system under oxidizing and mildly reducing conditions. Metastable, nearly single-phase at room temperature (Fe,Mg,Al) 3 O 4 ceramics was obtained by sintering at 1753–1773 K for 10 h in argon atmosphere. Thermal expansion and redox induced dimensional changes were studied on heating, using TG, XRD and dilatometry. The results revealed that magnesium improves the tolerance against oxidative decomposition and minimizes unfavorable dimensional changes in ceramic samples upon thermal cycling. Co-substitution of iron with aluminium and magnesium was proved to be a promising strategy for improvement of refractoriness and phase stability of Fe 3 O 4 -based spinels at elevated temperatures, without significant reduction in the electrical conductivity.

Electrical Properties of La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.3&lt;/sub&gt;CuO&lt;sub&gt;3-δ&lt;/sub&gt;Cathode Based on SDC-YSZ Composite Electrolyte

The cathode material La0.7Sr0.3CuO3-δ was synthesized by a sol-gel method. X-ray diffraction revealed it to be form a single phase of perovskite. The SDC（Sm0.15Ce0.85O1.925）was synthesized by glycine-nitrate processes. The 90%SDC and 10%YSZ powders are mixed to prepare as SDC-YSZ composite electrolyte. The high temperature electrical conductivity of La0.7Sr0.3CuO3-δ was measured by using the four-point dc technique, and cathodic overpotential with SDC-YSZ composite electrolyte support was measured by using a current-interruption technique. Using La0.7Sr0.3CuO3-δ as cathode and 65%NiO/SDC as anode based on SDC-YSZ composite electrolyte one can obtain high current density and power density at intermediate temperatures.

Reliable and repeatable bonding technology for high temperature automotive power modules for electrified vehicles

This paper presents the feasibility of highly reliable and repeatable copper–tin transient liquid phase (Cu–Sn TLP) bonding as applied to die attachment in high temperature operational power modules. Electrified vehicles are attracting particular interest as eco-friendly vehicles, but their power modules are challenged because of increasing power densities which lead to high temperatures. Such high temperature operation addresses the importance of advanced bonding technology that is highly reliable (for high temperature operation) and repeatable (for fabrication of advanced structures). Cu–Sn TLP bonding is employed herein because of its high remelting temperature and desirable thermal and electrical conductivities. The bonding starts with a stack of Cu–Sn–Cu metal layers that eventually transforms to Cu–Sn alloys. As the alloys have melting temperatures (Cu3Sn: > 600 °C, Cu6Sn5: > 400 °C) significantly higher than the process temperature, the process can be repeated without damaging previously bonded layers. A Cu–Sn TLP bonding process was developed using thin Sn metal sheets inserted between copper layers on silicon die and direct bonded copper substrates, emulating the process used to construct automotive power modules. Bond quality is characterized using (1) proof-of-concept fabrication, (2) material identification using scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis, and (3) optical analysis using optical microscopy and scanning acoustic microscope. The feasibility of multiple-sided Cu–Sn TLP bonding is demonstrated by the absence of bondline damage in multiple test samples fabricated with double- or four-sided bonding using the TLP bonding process.

SOFC 연결재용 Al이 도핑된 (La0.8Ca0.2)(Cr0.9Co0.1)O3(LCCC)계 세라믹스의 합성 및 치밀화 특성

In the (LCCC), which has been using as interconnector materials in SOFC, Al ions were substituted for Co because ionic radius of Al is similar to that of Co. Because of the almost identical ionic radius of Al and Co, the substitution was not thought to be affect the tolerance factor of LCCC, and the densification behavior, high temperature electrical conductivity and thermal expansion coefficient were examined as a function of Al concentration. In the cases of the x

Optimisation of Metallic Interconnects for Hydrogen Production by High Temperature Water Vapour Electrolysis

For economical and environmental reasons, hydrogen is considered as a major energetic vector for the future. Hydrogen production via high temperature water vapour electrolysis (HTE) is a promising technology. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800°C enables the use of metallic materials as interconnects. Chromia forming alloys are among the best candidates. The interconnect material chosen in the present study is a ferritic stainless steel with 18% chromium content. High temperature corrosion resistance and electrical conductivity of the alloy was tested in both cathode (H2/H2O) and anode (O2/H2O) atmospheres. Corrosion products were then characterized by SEM-EDX and XRD. Moreover chromium evaporation measurements were carried out under anode atmosphere.

Evaluation of a new Cr-free alloy as interconnect material for hydrogen production by high temperature water vapour electrolysis: Study in cathode atmosphere

For economic and ecological reasons, hydrogen is considered as a major energetic vector for the future. Hydrogen production via high temperature water vapour electrolysis (HTE) is a promising technology. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800 °C enables the use of metallic materials as interconnects. High temperature corrosion behaviour and electrical conductivity of a new Cr-free Fe–Ni–Co alloy were tested in cathode atmosphere (H2/H2O) at 800 °C. The alloy exhibits a poor oxidation resistance but an excellent ASR parameter, as a result of the formation of a highly-conductive Cr-free surface spinel layer. Moreover, the role of water vapour and hydrogen was discussed and a diffusion mechanism in cathode atmosphere could be suggested.

氮化铝薄膜的硅热扩散掺杂研究

This paper deals with the characteristics of aluminium nitride (AlN) films doped by silicon (Si) thermal diffusion. The films are analyzed by energy dispersive X-ray spectroscopy (EDS) and high-temperature dependent electrical conductivity. The results of EDS show that the Si element is successfully doped into the AlN films using SiNx as the diffusion source at the temperature of 1250C. The high-temperature current-voltage (I-V) measurements show that the electrical properties of the AlN films can be prominently improved by Si thermal diffusion, and at the measured temperature of 460C their electrical conductivities increase from 1.910-3 S&middotm-1 to 2.110-2 S&middotm-1 after the Si thermal diffusion. The high-temperature dependence of thermal conductivity suggests that the activation energies of VN3+ and Si are about 1.03 eV and 0.45 eV, respectively.

Polyaniline films doped with ladder-type sulfonated polyphenylsilsesquioxane and unusual dependence of their electrical conductivity on temperature

We report on conducting polyaniline (PANI) films doped with a thermally stable polymer dopant, linear ladder-type sulfonated polyphenylsilsesquioxane (S-PPSQ). The PANI/S-PPSQ films exhibited high-temperature stable electrical conductivity. With a heat treatment at 120 °C, the electrical conductivity of conventional PANI films doped with the molecular dopant camphorsulfuric acid (CSA) rapidly decreased to half of its initial value, while that of PANI/S-PPSQ films were relatively unaffected. Moreover, PANI/S-PPSQ films with high electrical conductivity exhibited unusual negative temperature coefficient of resistance (TCR) values above room temperature, in contrast to conventional PANI/CSA films that exhibited positive TCR values. By using a solution blend of PANI/S-PPSQ and PANI/CSA with negative and positive TCR values, respectively, we successfully demonstrated control of TCR behavior. Therefore, PANI/S-PPSQ materials are very promising for organic electronic applications.

Oxygen-vacancy-related high-temperature dielectric relaxation and electrical conduction in 0.95K 0.5Na 0.5NbO 3–0.05BaZrO 3 ceramic

The crystal structure and dielectric properties of 0.95K 0.5Na 0.5NbO 3–0.05BaZrO 3 (KNN–BZ) ceramic have been investigated by X-ray diffraction and dielectric measurement. A rhombohedral distortion was caused and the dielectric permittivity near Curie temperature was significantly enhanced by introducing BZ into KNN. The dielectric and conductivity properties of the sample were studied by using AC impedance spectroscopy and universal dielectric relaxation law in detail. The typical high-temperature dielectric relaxation process was confirmed to be related to the oxygen vacancies inside the ceramic. The effect of lattice distortion on the activation energy for oxygen vacancy migration in KNN–BZ was discussed by comparing with KNN and KNN–BaTiO 3.