Temperature Dependence Of Electrical Conductivity Research Articles

New insights into how temperature affects the electrical conductivity of clay-free porous rocks

Summary Geothermal energy is increasingly important for the global environment and for the sustainable development of our society. Electrical surveys are widely employed for the exploration of geothermal energy, because the electrical geophysical properties provide useful information about the fluids at depth. However, although quantitative interpretation of electrical survey data relies on the knowledge about the effects of temperature on the electrical properties of fluid-bearing rocks, it remains poorly understood about how temperature affects the electrical conductivity of clay-free porous rocks. We bridge this knowledge gap by measuring the electrical conductivity and porosity of five brine saturated clean Berea sandstones with temperature ranging between 25° C and 140° C, and analysing all the factors that impact the rock conductivity. We showed that the effects of surface conductivity on the temperature dependent electrical conductivity can be negligible, whereas the temperature induced variation in the porosity and pore structure quantitatively characterized in terms of cementation exponent can be more significant. We also found that temperature affects the electrical conductivity of brine saturated Berea sandstones by impacting the brine conductivity, and the pore structure and porosity of the samples, with their importance in a descending order. The results have provided new insights into how temperature affects the electrical conductivity of clay-free porous rocks, and will help to improve the quantitative interpretation of electrical survey data for the exploration of geothermal energy.

Enhanced Performance of Fe/WO3 Terahertz Dielectric Lenses

AbstractHerein transparent iron nanosheets deposited by the ionic coating technique onto glass and WO3 dielectric lenses are studied and characterized. The thickness of Fe nanosheets is varied in the range of 70–350 nm. It is observed that the transmittance and reflectance of the Fe nanosheets are highly affected by the layer roughness. Coating of iron nanosheets onto WO3 dielectric lenses increases the light absorption of WO3 by more than 240 times and red‐shifts the energy bandgap. Remarkable enhancements in the dielectric constant and in the optical conductivity are achieved via Fe coatings. In addition, iron coated dielectric lenses show higher terahertz cutoff limits varying in the range of 1.0–30 THz. Iron nanosheets remarkably increase the free charge carrier density and plasmon frequency in the infrared range of light. Moreover, the temperature dependent electrical conductivity shows high temperature stability and an increased electrical conductivity by more than 7 orders of magnitude by coating WO3 with 70 nm thick Fe nanosheets. The stability of the electrical conductivity at low temperatures and the wide range of terahertz cutoff limits in addition to the well‐enhanced light absorbability makes the iron coated tungsten oxide dielectric lenses promising for multifunction optoelectronic applications.

Negative Temperature Coefficient Properties of Natural Clinoptilolite

Negative temperature coefficient (NTC) materials are usually based on ceramic semiconductors, and electrons are involved in their transport mechanism. A new type of NTC material, adequate for alternating current (AC) applications, is represented by zeolites. Indeed, zeolites are single charge carrier ionic conductors with a temperature-dependent electrical conductivity. In particular, electrical transport in zeolites is due to the monovalent charge-balancing cations, like K+, capable of hopping between negatively charged sites in the aluminosilicate framework. Owing to the highly non-linear electrical behavior of the traditional electronic NTC materials, the possibility to have alternative types of materials, showing linearity in their electrical behavior, is very desirable. Among different zeolites, natural clinoptilolite has been selected for investigating NTC behavior since it is characterized by high zeolite content, a convenient Si/Al atomic ratio, good mechanical strength due to its compact microstructure, and low toxicity. Clinoptilolite has shown a rapid and quite reversible impedance change under heating, characterized by a linear dependence on temperature. X-ray diffraction (XRD) has been used to identify the natural zeolite, to establish all types of crystalline phases present in the mineral, and to investigate the thermal stability of these phases up to 150 °C. X-ray photoelectron spectroscopy (XPS) analysis was used for the chemical characterization of this natural clinoptilolite sample, providing important information on the cationic content and framework composition. In addition, since electrical transport takes place in the zeolite free-volume, a Brunauer–Emmett–Teller (BET) analysis of the mineral has also been performed.

Thermoelectric properties of sintered Ba2AgSi3 crystals and search for impurities to control conductivity type by first-principles calculation

In this study, the basic properties of Ba2AgSi3 were investigated in detail from both experimental and computational viewpoints. Polycrystalline Ba2AgSi3 formed by an arc-melting apparatus under an argon atmosphere was ground into powders, and then powder samples were sintered using the spark plasma sintering method. Both n-type and p-type samples were obtained. This may be due to a slight deviation from the stoichiometric composition. The energy bandgap of Ba2AgSi3 was measured to be around 0.17 eV from the temperature dependence of electrical conductivity and was in agreement with that by first-principles calculations. Sintered samples exhibited a high Seebeck coefficient of −273 μV K−1 and a high power factor of 0.38 mW m−1 K−2 at 307 K for n-type samples. They were 217 μV K−1 and 0.23 mW m−1 K−2, respectively, at 320 K for p-type samples. The electronic structures of impurity-doped Ba2AgSi3 were also discussed using first-principles calculations to investigate the insertion site of impurity atoms. The calculations suggest that the substitution of B (P) at any Si site shifts the Fermi level and transforms it into p-type (n-type) semiconductors. On the other hand, substitution of Ba or Ag sites with B or P is unlikely to occur in terms of formation energy.

Effect of La, Zr Doping on the Structural and Electrical Conduction Behaviour of BiFeO<sub>3</sub>-BaTiO<sub>3</sub> Ceramics

<p>This study presents a comprehensive investigation of the crystal structure and DC conduction mechanism of [(Ba<sub>0.7-x</sub> La<sub>x</sub>) Bi<sub>0.3</sub>][(Ti<sub>0.5</sub> Zr<sub>0.2</sub>) Fe<sub>0.3</sub>]O<sub>3</sub> with x = 0.00, 0.01, 0.03, 0.05 employing X-ray diffraction (XRD) and electrical conductivity measurements. Various compositions were synthesized through the solid-state ceramic route. XRD was used to investigate phase formation. Analysis of XRD data suggested a structural transition from cubic to tetragonal for x ≥ 0.01. The average crystallite size first increases for x = 0.01 and then decreases for x ≥ 0.03. The temperature-dependent electrical conductivity measurements were investigated over a wide temperature range which revealed distinct conductivity mechanisms governing the material's transport properties. The activation energy (E<sub>a</sub>) has been estimated from temperature-dependent DC conductivity. Overall, this study provides valuable insights into the correlation between crystal structure and electrical properties in [(Ba<sub>0.7-x</sub> La<sub>x</sub>) Bi<sub>0.3</sub>][(Ti<sub>0.5</sub> Zr<sub>0.2</sub>) Fe<sub>0.3</sub>]O<sub>3</sub>, offering significant implications for its potential applications in electronic and optoelectronic devices requiring tailored conductivity characteristics.</p>

Engineered nanocomposites through embedding of smaller “organic inorganic” nanoparticles in thermoplastic Poly(2-Vinylpyridine) polymer matrix

Polymer nanocomposites (PNCs) are significant for modern and future applications owing to their multifunctionality promoted by morphology and tailored interfaces between the constituents. However, ‘forward’ engineered polymer (host) composites with smaller size nanoparticles (guest) providing desired properties remains challenging as they depend upon nanoparticles aggregation, size, shape, and loading (volume or weight) fraction. This study strategically designs and develops PNCs comprising thermoplastic poly (2-vinylpyridine) (P2VP) polymer matrix impregnated with spherical polyhedral oligomeric silsesquioxane (N-POSS) nanoparticles (diameter ∼2–5 nm) and anisotropic planar nitrogenated graphene nanoribbons (GNR, strip width ∼5–10 nm) commensurate with polymer chain radius of gyration, Rg, (or segment length ∼1.5 nm) and comparable energy scales of electrostatic interaction and attractive hydrogen bonding. We investigated static and dynamic structure and thermophysical properties to correlate with interfacial regions and the results are compared with larger graphene oxide (GO, lateral dimension ∼100–200 nm) nanosheets and silica (SiO2, ∼25–50 nm) particles. While electron microscopy revealed nanoparticle distribution, the lattice bonding, conjugation length, and mechanical properties are determined from micro-Raman spectroscopy and atomic force microscopy, respectively. The differential scanning calorimetry provided a measure of glass transition temperature, Tg, with positive shift of ∼10–18 °C with nanoparticles loading indicating strength of structural relaxation/chain rigidity behavior and thermogravimetric analysis displayed increased thermal stability and conductivity (decreased interfacial resistance). We also measured temperature dependent dc electrical conductivity and dielectric relaxation spectroscopy gaining insights into percolation and dynamic interfacial layer. This study signified understanding of interactions and interfacial regions, key element to demystify the microscopic structure-property relationships.

Dielectric behavior and impedance spectroscopy of Niobium substituted Lanthanum based orthovanadates at high temperatures

We present the detailed study of the temperature dependent dielectric properties, impedance spectroscopy and electrical conductivity of LaV1−xNbxO4 (x=0–1) samples prepared by the solid-state reaction method. The dielectric constant (ϵr′) increases (decreases) with increase in the temperature (frequency); while, the magnitude of ϵr′ remains almost invariant (order of 104 at 100 Hz and 600 °C) with x. The single phase x=0 (monoclinic-monazite, P21/n) and x=1 (monoclinic fergusonite, I2/a) samples show the lower values of loss factor [tanδ= (4–8)] as compared to the x=0–0.8 samples [tanδ= (12–18)] having mixed tetragonal and monoclinic phases, which indicates the strong correlation between the crystal structure and the dielectric properties. The real part of impedance (Z′) decreases with both temperature and frequency, and the observed weak relaxation remains almost unaltered with x. The imaginary part of impedance (Z′′) shows strong relaxation peaks shifting towards higher temperatures with frequency, which is attributed to the effect of grains, grain boundaries, and electrodes in the samples. The activation energy of the relaxation process is estimated to be 0.8–1.0 eV for the x=0–0.6 samples, and ≈1.4 eV for the x=0.8; whereas the x=1 sample shows two values (≈0.5 eV and ≈1.0 eV) in the higher and lower temperature range, respectively. Further, the change in total conductivity with the angular frequency, which found to be in the range of 10−3 to 10−5 S/m, is fitted using the Jonsher power law. The analysis suggests the overlapping large polaron tunneling (OLPT) model for all the samples, whereas the x = 1 sample exhibit a transition near 480 °C and at higher temperatures it shows non-overlapping small polaron tunneling (NSPT) and quantum mechanical tunneling (QMT). This transition is corroborated by the tangent loss curves and may be associated with the change in structure.

Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters

Hot Jupiter atmospheres may be subject to a thermoresistive instability where an increase in the electrical conductivity due to ohmic heating results in runaway of the atmospheric temperature. We introduce a simplified one-dimensional model of the equatorial substellar region of a hot Jupiter that includes the temperature dependence and time dependence of the electrical conductivity, as well as the dynamical back-reaction of the magnetic field on the flow. This model extends our previous one-zone model to include the radial structure of the atmosphere. Spatial gradients of electrical conductivity strongly modify the radial profile of Alfvénic oscillations, leading to steepening and downward transport of magnetic field, enhancing dissipation at depth. We find unstable solutions that lead to self-sustained oscillations for equilibrium temperatures in the range T eq ≈ 1000–1200 K and radial magnetic field strength in the range ≈10–100 G. For a given set of parameters, self-sustained oscillations occur in a narrow range of equilibrium temperatures that allow the magnetic Reynolds number to alternate between large and small values during an oscillation cycle. With our simplified geometry, outside of this temperature window the system reaches a steady state in which the effect of the magnetic field can be approximated as a magnetic drag term. Our results show that thermoresistive instability is a possible source of variability in magnetized hot Jupiters at colder temperatures and emphasize the importance of including the temperature dependence of electrical conductivity in models of atmospheric dynamics.

Synthesis and electrical properties of PANI/CeO2 nanocomposites: A study on the fluctuation-induced tunneling conduction

This study presents the preparation of PANI/CeO2 nanocomposites via in situ chemical oxidative polymerization in an acidic environment at subzero temperatures to optimize nanocomposite properties. Two compositions of PANI/CeO2, with 2% and 5% CeO2 nanoparticles, were synthesized and characterized structurally using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The temperature-dependent electrical conductivity was measured employing the four-probe technique and analyzed theoretically using the fluctuation-induced tunneling (FIT) model. The analysis of variance (ANOVA) confirmed the validity of the FIT model in elucidating charge transport mechanisms within the PANI/CeO2 composites.

Thermoelectric properties of Fe2VAl in the temperature range 300–800 K: A combined experimental and theoretical study

Here, the experimentally observed thermoelectric (TE) properties of Fe2VAl are understood through electronic structure calculations in the temperature range of 300–800 K. The Seebeck coefficient (S) is observed as ∼−138μV/K at 300 K. Then, the |S| decreases with increase in temperature, with a value of ∼−18μV/K at 800 K. The temperature dependence of electrical conductivity, σ (thermal conductivity, κ) exhibits the increasing (decreasing) trend with values of ∼1.2× 105Ω−1 m−1 (∼23.7 W/m K) and ∼2.2× 105Ω−1 m−1 (∼15.3 W/m K) at 300 K and 800 K, respectively. In order to understand these transport properties, the DFT based semi-classical Boltzmann theory is used. The contributions of multi-band electron and hole pockets are found to be mainly responsible for the temperature dependent trend of these properties. The present study suggests that DFT based calculations provide reasonably good explanations of experimental TE properties of Fe2VAl in the high-temperature range of 300–800 K.

Wavy Two-Dimensional Conjugated Metal-Organic Framework with Metallic Charge Transport.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as a new class of crystalline layered conducting materials that hold significant promise for applications in electronics and spintronics. However, current 2D c-MOFs are mainly made from organic planar ligands, whereas layered 2D c-MOFs constructed by curved or twisted ligands featuring novel orbital structures and electronic states remain less developed. Herein, we report a Cu-catecholate wavy 2D c-MOF (Cu3(HFcHBC)2) based on a fluorinated core-twisted contorted hexahydroxy-hexa-cata-hexabenzocoronene (HFcHBC) ligand. We show that the resulting film is composed of rod-like single crystals with lengths up to ∼4 μm. The crystal structure is resolved by high-resolution transmission electron microscopy (HRTEM) and continuous rotation electron diffraction (cRED), indicating a wavy honeycomb lattice with AA-eclipsed stacking. Cu3(HFcHBC)2 is predicted to be metallic based on theoretical calculation, while the crystalline film sample with numerous grain boundaries apparently exhibits semiconducting behavior at the macroscopic scale, characterized by obvious thermally activated conductivity. Temperature-dependent electrical conductivity measurements on the isolated single-crystal devices indeed demonstrate the metallic nature of Cu3(HFcHBC)2, with a very weak thermally activated transport behavior and a room-temperature conductivity of 5.2 S cm-1. Furthermore, the 2D c-MOFs can be utilized as potential electrode materials for energy storage, which display decent capacity (163.3 F g-1) and excellent cyclability in an aqueous 5 M LiCl electrolyte. Our work demonstrates that wavy 2D c-MOF using contorted ligands are capable of intrinsic metallic transport, marking the emergence of new conductive MOFs for electronic and energy applications.

Peristaltic transport of radiative and dissipative MHD third order nanofluid through the vertical asymmetric channel with heat and mass convection

: The fundamental purpose of the present study is to provide a novel framework for investigating the peristaltic flow through a vertical asymmetric channel filled with a magnetic third order nanofluid model saturated in a porous medium under the influence of varying electrical conductivity. The essential characteristics of Brownian and thermophoresis phenomena are additionally included in the modelling of the heat equation, in besides joule heating, viscous dissipation, heat generation/absorption, and nonlinear thermal radiation. Furthermore, the effects of double diffusion convection are examined, with a small Reynolds number along with extended wavelength examples that reflect biological scientific assumptions are used. The software Mathematica's built-in command ND Solve is implemented to solve the derived nonlinear ordinary differential equations system numerically. One of the most significant phenomena concerning peristaltic motion, known as the trapping phenomenon, has also been spotlighted using contour plots and circulating bolus. The key discoveries showed that the size of the trapping bolus tends to decrease while the density of trapping bolus increases with an enhancement in the temperature- and concentration-dependent electrical conductivity coefficient. Further, for all areas under consideration, the rate of heat and mass transmission is enhanced due to an augmentation in the coefficient of temperature-dependent electrical conductivity.

Investigation of the structural and electrical conductivity properties in pure and cation exchanged rectorite

Clay minerals, as biofriendly and low-cost materials, are highly essential for the modern industrial applications including the production of clean energy, its storage and conversion. Here, the capabilities of pure and cation exchanged rectorite, a regularly interstratified phyllosilicate from Beatrix Mine (South Africa) were explored and discussed. A comprehensive characterization was performed by means of high resolution solid-state NMR, electrochemical impedance spectroscopy and powder X-ray diffraction. 23Na MAS and 3QMAS NMR spectroscopy was used to characterize accessibility of interlayer space in rectorite for exchangeable cations. Three Na sites attributed to easily exchangeable Na+ on the surface or in large pores, Na+ in dehydrated micaceous interlayers and Na+ in hydrated smectite interlayers were identified. Differences in hydration states in smectitic interlayers depending on the type of intercalation were detected using 1H MAS NMR. A higher amount of hydrating water molecules in pure and Mg-exchanged rectorites was attributed to the higher hydration energy of Ca2+ and Mg2+. The temperature dependences of electrical conductivity in this work were best described using the empirical Vogel-Tammann-Fulcher equation with the temperature-dependent effective activation energy parameter. Significantly stronger change of activation energy in Mg2+ exchanged rectorite in the temperature range of 10 °C to 50 °C as compared to pure rectorite and its Na+, Li+ and NH4+ modifications was related to an extensive H-bond network in the interlayers, which facilitated an effective proton transfer responsible for electric conductivity. The obtained resutls suggested a greater potential for the use of Mg-exchanged rectorite as ionic conductor at enhanced temperatures.

Temperature and frequency dependent electrical conductivity of Al-Mo co-doped WO3 nanoparticles

Temperature and frequency dependent electrical conductivity of Al-Mo co-doped WO3 nanoparticles

Impedance Spectroscopy and Study of Electrical Properties of Pb(Zr<sub>0.52</sub>Ti<sub>0.48</sub>)<sub>1-x</sub>Fe<sub>x</sub>O<sub>3-x</sub> (0≤x≤0.20) Ceramics

Iron substituted Lead zirconate titanate nanoparticles Pb (Zr0.52Ti0.48) 1-x FexO3-x (PZTFx) (for (x=0.00, 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20) was prepared using the sol-gel route in the morphotropic phase boundary (MPB) region. The X-ray diffraction data revealed the formation of both rhombohedral and tetragonal structures. The microstructural properties of the compounds were examined through the scanning electron microscopy (SEM) technique. The impedance spectroscopy and conductivity spectroscopy were carried out over a wide range of temperatures (RT–400°C) and frequencies (100 Hz–2 MHz) to investigate the grain and grain boundary effect on the electrical properties of PZTFx. The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters. Cole– Cole plots indicate Debye-type dielectric relaxation and the grain boundaries resistance is dominant at room temperature. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of PZTFx ceramics. The dielectric properties of (PZTFx) ceramics as a function of temperature are studied and displayed a resonance phenomenon for all samples. Temperature-dependent conductivity behavior indicated an Arrhenius type of thermally activated process in the low-temperature region. Activation energy has been calculated from the temperature-dependent DC electrical conductivity measurements for all the samples.

High-Temperature Electromechanical Properties Single Crystalline Lithium Niobate-Lithium Tantalate Solid Solutions at Different Oxygen Partial Pressures

LiNbO3 (LN) is one of the most investigated electro-acoustic and electro-optical materials. Its high piezoelectric coefficients are a favorable condition for its use beyond optical applications, which includes, for example, high-temperature actuators. Compared for example to crystals of the langasite family, LN shows significantly higher piezoelectric coefficients but limited thermal stability. The latter is caused by evaporation of Li2O and related changes of e.g. electrical conductivity. As a consequence, long-term applications of LN are limited to temperatures of a few hundred degrees Celsius. A related material that offers improved thermal stability is LiNbO3 (LT). However, the Curie temperature is only about 600 °C. Furthermore, the piezoelectric coefficients are lower than for LN. The miscibility of LN and LT over the entire compositional range should allow, however, to tailor the crystal properties and, for example, to take advantage of the high piezoelectric coefficients of LT and the better thermal stability of LT. Therefore, the subject of this study are lithium niobate-lithium tantalate (LiNb1-xTaxO3, LNT) solid solutions with respect to their electroacoustic properties at temperatures between 400 and 900 °C. The objectives include the determination, understanding and correlation of defect structures, electronic and atomic transport and acoustic losses in LNT over a wide temperature range.The electromechanical properties of LNT crystals are determined as function of temperature and oxygen partial pressure (pO2) and compared with those of the congruent edge compounds LN and LT. Characterization methods include impedance spectroscopy, application of 6Li as tracer in combination with secondary ion mass spectrometry, resonant piezoelectric spectroscopy, noncontacting resonant ringdown spectroscopy and laser vibrometry. The latter reflects displacements of the sample surface even in the order of nanometers which enables the identification of the resonant modes.LNT crystals with different Nb-Ta compositions prepared by Czochralski growth and a µ-pulling down process are used to determine the overall electrical conductivity by electrical impedance spectroscopy. Further, Z- and Y-cut plates are applied as bulk acoustic wave resonators to measure the acoustic loss. When determined in air, the temperature-dependent electrical conductivity of LNT below about 600 °C is virtually independent of composition. In particular, for each sample a single activation energy is found from 400 to 600 °C which is the same for all samples within the error margins. Furthermore, the diffusive ion transport studied directly using 6Li tracers results in good agreement with the electrical conductivity when the diffusion coefficients are converted correspondingly using the Nernst-Einstein relation. Consequently lithium-ion migration can explain the overall electrical conductivity. Above about 600 °C the behavior depends on composition. At high Nb contents, a continuous increase of the slope of the electrical conductivity in an Arrhenius representation with temperature is observed, which is attributed to thermal instability.The pO2 dependent electrical conductivity shows constant values at high pO2. At sufficiently low pO2, a slope of -1/4 in a double logarithmic representation is found (see attached figure). This slope indicates electronic conduction which is caused by compensation of NbLi antisite defects. The behavior is already reported for LN by Smyth et al. (Ferroelectrics 50 (1983) 93). As the slope is independent of the composition x, it can be concluded that the same defect formation occurs in LNT. Important with respect to thermal stability is that, at a given temperature, the increase in conductivity for Ta-rich compositions starts at lower pO2 than for Nb-rich compositions.The acoustic loss is determined in a wide temperature range by the methods mentioned above. It shows some impact of the metal electrodes at low temperatures. In air and at temperatures above about 400 °C the acoustic loss is governed by the piezoelectric/carrier relaxation. It is caused by the motion of charge carriers in an oscillating piezoelectric field and, therefore, related to electrical conductivity. The finding is confirmed by modelling with independent materials data including electrical conductivity. Low pO2 result in additional loss contributions.In summary, the study leads to an understanding of the acoustic losses of LNT at high temperatures, which provides opportunities to reduce them. Furthermore, it becomes clear that Ta-rich compositions exhibit improved thermal stability. Figure 1

Mechanosynthesis, Structure and Photoluminescent Properties of the Pr3+ Doped LiNbO3, LiNbO3:Mg, LiTaO3 Nanopowders

In the current work, nanocrystalline powders with different compositions, namely Li0.98Pr0.02NbO3, Li0.93Pr0.02Mg0.05NbO3 and Li0.98Pr0.02TaO3 were synthesized for the first time using the method of high-energy ball milling of the starting materials (Li2CO3, Nb2O5, Ta2O5, MgO, Pr6O11), followed by high-temperature annealing. XRD data analysis confirmed the absence of parasitic phases in the obtained nanocrystalline compounds. The estimated particle sizes ranged from 20 to 80 nm. From the obtained nanopowders, ceramic samples were prepared using specially developed equipment, which allowed for pressing at elevated temperatures with a simultaneous application of a constant electric field. The obtained photoluminescence spectra exhibit characteristic features of Pr3+ ions in the crystal structure of LiNbO3 and LiTaO3 and are most efficiently excited by UV light. Samples pressed with an electric field application show higher intensity of photoluminescence. Investigations of the temperature dependence of electrical conductivity of the Li0.98Pr0.02NbO3 sample, pressed with the application of an electric field, indicate that the conductivity mechanism is similar to that of LiNbO3 single crystals and, at high temperatures, is attributed to the lithium conduction mechanism.

Effect of Sr-doping on electronic and thermal properties of Pr2-xSrxFeCrO6 (0≤x≤1) oxide materials synthesized by using sol-gel technique

ABSTRACT The thermoelectric properties of a new type of Pr2-xSrxFeCrO6 double perovskite were investigated at higher temperature after its sol-gel synthesis. The XRD results validate the single-phase orthorhombic structure, and the crystallite sizes meet the morphological measurements. XPS examination, which formed the defect sites in these oxides, confirmed the varied oxidation states of constituents. The temperature-dependent electrical conductivity (σ) was poor in the original Pr2FeCrO6 composition, but after substituting Sr on the Pr-site, a significant rise in σ with two semiconductors and one metal transition was observed. A positive Seebeck coefficient confirmed the presence of a p-type charge carrier in the entire composition, and the charge transport mechanism was driven by the SPH model. Thermal conductivity increases in all doped samples, while it decreases in pristine compounds over the broad analyzed temperature range. Thermal expansion coefficient increased after doping in oxygen-deficient compound. The PrSrFeCrO6 compound had the maximum ZT (0.105), which was 3.9 times higher than that of the pristine compound.

A Formulation for a Nonlinear Axisymmetric Magneto-Heat Coupling Problem with an Unknown Nonlocal Boundary Condition

Abstract This paper investigates a nonlinear axisymmetric magneto-heat coupling problem described by the quasi-static Maxwell’s equations and a heat equation. The coupling between them is provided through the temperature-dependent electric conductivity. The behavior of the material is defined by an anhysteretic 𝑯-𝑩 curve. The magnetic flux across a meridian section of the medium gives rise to the magnetic field equation with the unknown nonlocal boundary condition. We present a variational formulation for this coupling problem and prove its solvability in terms of the Rothe method. The nonlinearity is handled by the theory of monotone operators. We also suggest a discrete decoupled scheme to solve this problem by employing the finite element method and show some numerical results in the final section.

Study on the Frequency and Temperature Dependence of Electrical Conductivity of Zinc Oxide Valve Plate

Under the action of overvoltage and harmonic voltage, the on-board zinc oxide arrester of electric motor units (EMUs) will affect its action characteristics due to heating. In this paper, the nonlinear current-volt characteristics of the arrester valve plate are measured experimentally to study the dependence of the electrical conductivity of the zinc oxide valve piece on temperature and frequency under AC voltage. The current-volt characteristic curve of the arrester valve piece shifts to the right in turn as the temperature rises. The corresponding resistive leakage current of 3500V valve plate increases by 250% as the temperature increases from 20 °C to 120 °C. The voltage value of the corresponding valve piece at the resistance current of 1mA gradually decreases with the increase of temperature, and the maximum drop of the voltage of a single valve piece is close to 25%. The high-frequency conductivity of the valve plate is increased by 31% compared with that under power frequency. The dependence characteristics are divided into three parts: linear region, transition region and nonlinear region. The conductivity dependence characteristics of zinc oxide valve sheet on frequency and temperature are studied by bivariate fitting. The fitting model is established based on Arrhenius formula, Schottky barrier model and Richardson equation. The correlation coefficient of fitting results is above 0.99.