Temperature Dependence Of Conductivity Research Articles

Impedance spectroscopic study of temperature and frequency dependent conduction behaviour of xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 , x = 0.50, 0.55, 0.70, 0.85 ceramic

Here, we report on structural, impedance, modulus and conductivity analyses of xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 (x = 0.50, 0.55, 0.70 and 0.85) polycrystalline ceramic prepared using conventional solid state reaction technique. The X-ray diffraction (XRD) pattern for all the synthesised polycrystalline samples confirmed the formation of pure perovskite phase. A slight variation in the lattice parameters were observed with varying concentration of x in BCZT ceramic. Composition dependence of average crystalline size and lattice strain of the synthesised samples were evaluated by Williamson-Hall plot. The samples near the Morphotropic phase boundary (MPB) were much strained with large crystallite size. The impedance spectroscopic study was done to evaluate the conduction behaviour of the BCZT samples with varying concentration of x in wide temperature and frequency range. All the samples were found to exhibit Negative temperature coefficient of resistance suggestive semiconducting nature of the synthesised samples. A comparative detail conduction behaviour with grain and grain boundary contribution is presented and discussed in detail.

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.

Influence of an Organic Salt-Based Stabilizing Additive on Charge Carrier Dynamics in Triple Cation Perovskite Solar Cells.

Besides further improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSC), their long-term stability must also be ensured. Additives such as organic cations with halide counter anions are considered promising candidates to address this challenge, conferring both higher performance and increased stability to perovskite-based devices. Here, a stabilizing additive (N,N-dimethylmethyleneiminium chloride, [Dmmim]Cl) is identified, and its effect on charge carrier mobility and lifetime under thermal stress in triple cation perovskite (Cs0.05 MA0.05 FA0.90 PbI3 ) thin films is investigated. To explore the fundamental mechanisms limiting charge carrier mobility, temperature-dependent microwave conductivity measurements are performed. Different mobility behaviors across two temperature regions are revealed, following the power law Tm , indicating two different dominant scattering mechanisms. The low-temperature region is assigned to charge carrier scattering with polar optical phonons, while a strong decrease in mobility at high temperatures is due to dynamic disorder. The results obtained rationalize the improved stability of the [Dmmim]Cl-doped films and devices compared to the undoped reference samples, by limiting temperature-activated mobile ions and retarding degradation of the perovskite film.

Investigation on polyvinyl alcohol and sodium alginate blend matrix with ammonium nitrate conducting electrolytes for electrochemical applications

Polyvinyl alcohol (PVA) Sodium alginate (NaAlg) polymer composites were synthesized by solution casting technique and doping with ammonium nitrate (NH4NO3). The functionalization structure of the produced electrolytes was investigated using XRD and AC impedance spectroscopy. XRD confirms amorphous nature. The ionic conductivity of the electrolytes is evaluated using ac impedance measurements at temperatures ranging from 303 to 353 K. PVA: NaAlg: NH4NO3 (60:40:15 wt%) blend polymer electrolyte was observed to have the highest conductivity of 1.05 × 10−6 S cm−1. The Arrhenius plot appears to be obeyed by the temperature dependent ionic conductivity and is of non-debye type. Activation energy for best conducting electrolyte was 0.2364 eV. The dielectric relaxation of the polymer electrolyte has been studied, and the results are described. Relaxation time estimated from loss tangent analysis also affirms that value is low for highest conducting sample. Results of CV and LSV studies gave a plausible approach for electrochemical application.

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.

ELECTRICAL PROPERTIES INVESTIGATION OF Ag8GeS6 SINGLE CRYSTAL

The compounds of the argyrodite structure have high conductivity values in the solid state due to the simultaneous coexistence of a "rigid" anionic framework and disordered cationic sublattice. In this regard, argyrodites are considered to be promising superionic materials for use as a working element of solid-state batteries. This work presents the results of the study of the electrophysical parameters of Ag8GeS6 single crystal grown by directional crystallization from the melt technique. It was found by the XRD method that the grown Ag8GeS6 single crystal crystallizes in a low-temperature orthorhombic modification with unit cell parameters: a = 15.147 Å, b = 7.469 Å, c = 10.584 Å. The frequency (10 Hz - 0.3 MHz) and temperature (20 - 110°C) dependence of the electrical conductivity was studied on a single crystal plate of Ag8GeS6 oriented in the (011) plane by impedance spectroscopy. The frequency dependence of the total electrical conductivity of Ag8GeS6 shows an increase in the total electrical conductivity with increasing frequency, which is typical for mixed ionic-electronic conductors. It was determined that the total conductivity of the Ag8GeS6 single crystal is 3.82 × 10-5 S/cm, and the activation energy is 0.728 eV.
 Keywords: argyrodites; single crystals; electrical conductivity; phase analysis.

ELECTRICAL CONDUCTIVITY OF SINGLE CRYSTALLINE Ag7PS6

The search and study of new materials suitable for use in the newest solid-state batteries is an important direction of modern solid-state ionics. Among the potential materials, it is worth mentioning compounds of the argyrodite family. The characteristic feature of these phases is the presence of a disordered cationic sublattice, which provides significant cationic conductivity in the solid state. This work presents the results of studies of the electrical conductivity of a single crystalline sample of ltm-Ag7PS6. The single crystal of Ag7PS6 was grown by the method of directional crystallization from the melt. The crystal was identified by means of XRD method. It was found that the grown Ag7PS6 sample crystallizes in a low-temperature modification in a primitive cubic cell. The frequency (1×101–3×105 Hz) and temperature (25-100°C) dependence of the total electrical conductivity was measured on an oriented and specially prepared ltm-Ag7PS6 single crystalline plate (using gold contacts). The total conductivity of Ag7PS6 single crystals is 6.51×10–7 S/cm (t = 25°C). According to the results of temperature studies of the dependence of the total conductivity, the thermal activation nature of the conductivity was established.
 Keywords: argyrodites; single crystals; phase analysis; electrical conductivity.

Effects of Temperature-Dependent Conductivity and Magnetic Field on the Radiated Carreau Nanofluid Flow and Entropy Generation

This investigation is related to this study of entropy generation during Carreau nanofluid flow under variable thermal conductivity conditions. The heat and mass transfer phenomena are observed in the presence of thermal radiation and activation energy. The flow is induced by a porous stretching surface. Appropriate variables are used in order to simplify the problem into dimensionless form. The numerical simulations are performed by using the shooting technique. The physical aspects of the problem in view of different flow parameters are reported. It is observed that consideration of variable fluid thermal conductivity enhances heat transfer. An enhancement in heat and mass transfer phenomena is observed with increasing the Weissenberg number. Moreover, entropy generation increases with Weissenberg and Brinkman numbers. Current results present applications in thermal processes, heat exchangers, energy systems, combustion and engine design, chemical processes, refrigeration systems, etc.

Synthesis and Characterization of Tb–Er Co–Doped Bi2O3 Solid Electrolyte Systems

In this study, solid state reactions were used to create Er–Tb co–doped Bi2O3 solid electrolyte systems. Four Point Tip Technique (FPPT), Thermo–gravimetric and Differential Thermal Analysis (TG & DTA), and X–Ray Diffraction (XRD) were used to characterize the generated samples' structural and thermal properties, and electrical conductivity. The samples 05Er05TbSB, 05Er10TbSB, and 15Er05TbSB stabilized with cubic δ–phase at room temperature, according to XRD data. Due to the smaller dopants ions compared to the host Bi3+ cation, the lattice constants estimated for these samples were lower than those of the pure cubic phase. The samples were thought to be thermally stable in the studied temperature range since the thermal curves did not show endothermic or exothermic peak development indicating a potential phase change. According to the Arrhenius equation, the temperature–dependent conductivity graphs displayed a linear change. The conductivity measurements clearly indicated that an increase in doping rate results in a sudden drop in electrical conductivity. The calculated activation energies increased with the doping ratio and varied from 0.64 eV to 1.12 eV. At 700 °C, it was determined to be 0.128 S.cm–1 for the sample 05Er05TbSB, which had the greatest conductivity and lowest activation energy among all samples. The conductivity was discovered to decrease and activation energy to increase when the doping ratio was gradually raised.

Effect of interfacial layers on the temperature-dependent dielectric and impedance behavior of flexible PVDF-BST nanocomposite thick films

High energy storage performance of polymer-ceramic nanocomposites at elevated temperatures (room temperature to 100 °C) becomes unstable because of thermally unstable dielectric behavior (permittivity and loss tangent). Therefore, the present work describes the experimental and analytical investigation of the temperature-dependent dielectric behavior, AC conductivity, and impedance of flexible poly(vinylidene difluoride) (PVDF)-Ba0.8Sr0.2TiO3 (BST) nanocomposite thick films. An increase in the dielectric constant and a decrease in the loss tangent is found with an increase in the loading of BST nanoparticles in the nanocomposite thick films. The highest dielectric constant, approximately 25, and the lowest loss tangent, approximately 0.03, are observed for 10 wt% BST–loaded PVDF-BST nanocomposite at 1 kHz; the dielectric constant and the loss tangent increase to approximately 93 and approximately 1.64, respectively, at 150 °C. The dielectric constant and the loss tangent of all the PVDF-BST nanocomposites are thermally stable up to 70 °C, and then increase with further increase of the temperature. A phenomenological model is proposed to explain the experimentally observed behavior, which might be attributed to the thermally induced translational motion in the polymeric chains of PVDF, the motion of ions, and the migration of space charge in the interfacial layer of the PVDF matrix and BST nanoparticles.

Interface state analysis of Schottky-gated p-AlGaN/u-GaN/AlGaN p-FET with negligible hysteresis at high temperatures

In this Letter, we demonstrate the Schottky gated p-AlGaN/u-GaN/AlGaN p-channel field-effect transistors (p-FETs) with an extremely low interface state density of 2.5 × 1011 cm−2 eV−1. Benefiting from the high-quality Schottky interface with suppressed interface states, the excellent stability with negligible hysteresis is proved, even after ten sequential dual I–V sweeps at 150 °C. Meanwhile, the trap density, confirmed by the temperature-dependent conductance method, is still below 1012 cm−2 eV−1 at high temperature. Furthermore, the fabricated p-AlGaN/u-GaN/AlGaN p-FET with a gate to drain distance of 1.8 μm shows a breakdown voltage of −128 V and an effective on-resistance of 7.2 kΩ mm, which allows the further scale down in terms of the source–drain spacing to improve the conduction current for low voltage application. The ultra-stable I–V characteristics of the fabricated Schottky-gated p-AlGaN/u-GaN/AlGaN p-FETs show great potential for next-generation integrated circuit application at high temperatures.

INVESTIGATION OF PHASE EQUILIBRIA AND PHYSICO-CHEMICAL PROPERTIES OF OBTAINED PHASES IN THE Sb2S3-Cr2Se3 SYSTEM

Using complex of physicochemical methods of analysis (DTA, XRD, MSA, as well as measurements of density and microhardness), the phase equilibria in the Sb2S3-Cr2Se3 system was studied and a phase diagram was constructed. It is established that the system is quasi-binary and has eutectic type T-x diagram. In the process of chemical interaction, a compound with composition Cr2Sb2S3Se3 is formed in the system. The Cr2Sb2S3Se3 compound melts incongruently at 6500C., A limited area of the solid solution based on the initial components of the system is formed. The coordinates of the eutectic formed between the α-solid solution and the Cr2Sb2S3Se3 compound is 17 mol % Cr2Se3 at 4500C. At room temperature, solid solutions based on Sb2S3 reach up to 5 mol % Cr2Se3, and based on Cr2Se3 up to – 3 mol % Sb2S3. According to the results of X-ray diffraction analysis, Cr2Sb2S3Se3 crystallizes in a tetragonal system with lattice parameters: a=16.37; c=11.69 Å, ρpuc.=5.40 q/sm3, ρX-ray=5.42 q/sm3. The temperature dependence of the electrical conductivity and thermo-EMF of the (Sb2S3)1-x(Cr2Se3)x (x=0.01; 0.02; 0.03;) solid solution has been studied

Intrinsic Ferromagnetic Semiconductors with High Saturation Magnetization from Hybrid Perovskites.

Ferromagnetic semiconductors (FMS) enable simultaneous control of both charge and spin transport of charge carriers, which have emerged as a class of highly desirable but rare material for applications in spin field-effect transistors and quantum computing. Organic-inorganic hybrid perovskite with high compositional adjustability and structural versatility can offer unique benefits in the design of FMS but has not been fully explored. Here we demonstrate a series of molecular FMSs based on two-dimensional organic-inorganic hybrid perovskite structure, namely (2ampy)CuCl4 , (3ampy)CuCl4 and (4ampy)CuCl4 , which exhibits high saturation magnetization, dramatic temperature-dependent conductivity change and tunable ferromagnetic resonance. Magnetic measurements revealed high saturation magnetization up to 18.56 emu/g for (4ampy)CuCl4 , which is one of the highest value among reported hybrid FMSs to date. Conductivity studies of the three FMSs demonstrate that the smaller adjacent octahedron distance in the two-dimensional layer results in higher conductivity. Systematic ferromagnetic resonance investigation shows that the gyromagnetic ratio and Landau factor values are strongly dependent on the types of organic cations used. This work demonstrates that two-dimensional hybrid perovskite materials can simultaneously possess both tunable long-range ferromagnetic ordering and semiconductivity, providing a straightforward strategy for designing and synthesizing high-performance intrinsic FMSs. This article is protected by copyright. All rights reserved.

Practical approach to thermal conductivity calculations of small SiO2 samples

We compute the thermal conductivity of amorphous SiO2 combining density functional theory calculations and lifetime models. The supercell we use to represent amorphous SiO2 is small, 78 atoms. We show that this rudimentary model is nevertheless sufficient to reproduce the temperature dependence of the thermal conductivity from 0.1 K to 1000 K if we use a lifetime model at low frequencies accounting for Rayleigh scattering, the absorption of phonons by two levels systems and structural relaxations. The necessary conditions needed to observe the plateau in the thermal conductivity around 10 K are also discussed according to this model.

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.

Conjugate heat transfer from a discrete-source heated plate by offset jet impingement

Convection/conduction simulations have been performed to determine flow and heat transfer phenomena in steady-state, for a plate carrying few embedded discrete heaters, exposed to by a turbulent offset cooling jet. This configuration is relevant, for example, in thermal design of vehicle body segments in aerodynamics conditions: when realized in certain alloys, their configuration will be determined based their discrete structural state prompted by supplied electrical heating. In order to approach an appropriate thermal design of the plate and obtain their precise state, the space of geometric and operating variables needs to be explored by a thorough parametric study based on the governing momentum and energy equations.In this paper, the interaction between the impinging boundary layer and the conductive effects produced by such discrete heaters is explored, giving rise to a conjugate heat transfer situation. With a flexible notation for discretized heating and temperature-dependent conduction, dimensionless heat transfer is discussed spanning the entire range of design parameters. Results report considerable variation in heat transfer: as an example, air jet over polypropylene plates brings about peak Nusselt numbers between 2000 and 4000 for an inclined configuration at Re≈1×106 based on nozzle width, with related strong temperature gradients that must be addressed during design, depending on discrete heaters' configuration and properties; whereas for alumina plates the peak Nusselt numbers fall down between 600 and 750, featuring much smoother temperature variations and consequent more stable structural states.

AC conductivity and dielectric properties of InxTe20−xSe80 chalcogenides

Chalcogenide samples with chemical formula InxTe20−xSe80 (x = 5, 10 and 15 at %) were prepared using melt quenching method. AC conductivity σ, dielectric constant κ and loss tangent tanδ were measured using two probe method in frequency range from 100 Hz to 5 MHz and temperature range from 26 to 100 °C. All samples exhibited usual dispersion and temperature variation of chalcogenides. Conduction activation energy E was determined from temperature dependence of conductivity using Arrhenius relation. Conductivity, activation energy, dielectric constant and loss tangent decreased with increasing In-content.

Temperature dependences of permittivity and conductivity of sodium-lithium niobate ceramics

As a result of comparative studies of the electric and dielectric properties of sodium-lithium niobate ceramics with a percentage of Li equal to 10 and 40 mass %, it was found that both materials have a hopping conduction mechanism. At frequencies from 500 Hz to 100 kHz, thermal ionic polarization predominates. In the low-frequency region, migratory polarization predominates. The revealed difference in the temperature behavior of the complex conductivity of the studied samples made it possible to explain the presence of ferroelectric properties in the sample with 10% Li and their absence in the sample with 40% Li.

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

Evaluation of bioconvection for sinusoidally moving Jeffrey nanoparticles in view of temperature dependent thermal conductivity and Cattaneo-Christov heat diffusion model

With impressive thermal outcomes, the nanofluids present multidisciplinary applications in the cooling processes, thermal systems, extrusion processes, heat storage devices and many more. The aim of current research is to inspect thermal impact of Jeffrey fluid with tiny particles under the assumptions of variable thermal conductivity. The problem is supported with applications of chemical reaction, activation energy and magnetic force. For heat and mass transfer phenomenon, Cattaneo-Christov diffusion theories have been implemented. The formulated model is solved by using the homotopy analysis method (HAM) with excellent accuracy. The graphical analysis is performed with specified range of parameters like 0.2⩽H⩽0.8, 0.1⩽ϖ⩽1.7, 0.0⩽N⩽1.5, 0.0⩽Π⩽3.1, 0.3⩽γ⩽0.6, 0.6⩽Ψ⩽3.2, 0.5⩽Ω⩽2.0, 0.0⩽Σ⩽1.5, 0.2⩽Nt⩽1.7, 1.0⩽Pr⩽1.9, 0.5⩽Sc⩽1.4,0.3⩽β⩽1.5, 0.1⩽ε⩽1.0, 0.2⩽Nb⩽1.7. The assessment of flow parameters is graphically evaluated. It is observed that both velocity profiles periodically enhance for Deborah number while temperature, microorganisms and concentration distributions decelerate. The greater estimates of variable thermal conductivity and heat generation improve the temperature distribution while conflicting scenario ensures for thermic relaxation constant.