Temperature Dependence Of Electrical Conductivity Research Articles

Signature of strong localization and crossover conduction processes in doped ZnO thin films: synergetic effect of doping fraction and dense electronic excitations

Ga x Zn1−x O thin films with varying Ga fraction within the solubility limit were irradiated with high-energy heavy ions to induce electronic excitations. The films show good transmittance in the visible region and a reduction of about 20% in transmittance was observed for irradiated films at higher ion fluences. The Urbach energy was estimated and showed an augmenting response upon increase in doping fraction and ion irradiation, this divulges an enhancement of localized states in the bandgap or disorder in the films. The evolution of such localized states plays a vital role in charge transport and thus the temperature dependent electrical conductivity of irradiated thin films was studied to elucidate the dominant conduction mechanisms. The detailed analysis unfolds that in the high-temperature regime (180 K < T < 300 K), the charge conduction was dominated by thermally activated band conduction followed by the nearest neighbor hopping (NNH) mechanism. Whereas in the lower temperature regime (25 K < T < 170 K), the conduction mechanism was governed by Mott-VRH (variable range hopping) followed by Efros–Shklovskii (ES)-VRH. A sudden and steep rise in resistivity below 30 K was observed for GZO films with higher doping fraction at higher ion fluence and proclaims the presence of strong localization of carriers.

Effect of cobalt content on the properties of quintuple perovskites Sm2Ba3Fe5-xCoxO15-δ

Quintuple perovskites Sm2Ba3Fe5-xCoxO15-δ (x ​= ​0.5, 1.0 and 1.5) have been prepared by glycerin-nitrate technique in air. The phase purity was confirmed by XRD. Partial substitution of Co for Fe decreases the oxygen content and thus the mean oxidation state of 3d-metals. It also slightly decreases the thermal expansion coefficient of oxides. Positive value of the Seebeck coefficient confirmed p-type conductivity, though the thermopower decreases as the Co content increases. The temperature dependence of electrical conductivity reveals a maximum at 550–750°С.

Multi-layer graphene pirani pressure sensors

The operating principle of Pirani pressure sensors is based on the pressure dependence of a suspended strip’s electrical conductivity, caused by the thermal conductance of the surrounding gas which changes the Joule heating of the strip. To realize such sensors, not only materials with high temperature dependent electrical conductivity are required, but also minimization of the suspended strip dimensions is essential to maximize the responsivity and minimize the power consumption. Due to this, nanomaterials are especially attractive for this application. Here, we demonstrate the use of a multi-layer suspended graphene strip as a Pirani pressure sensor and compare its behavior with existing models. A clear pressure dependence of the strip’s electrical resistance is observed, with a maximum relative change of 2.75% between 1 and 1000 mbar and a power consumption of 8.5 mW. The use of graphene enables miniaturization of the device footprint by 100 times compared to state-of-the-art. Moreover, miniaturization allows for lower power consumption and/or higher responsivity and the sensor’s nanogap enables operation near atmospheric pressure that can be used in applications such as barometers for altitude measurement. Furthermore, we demonstrate that the sensor response depends on the type of gas molecules, which opens up the way to selective gas sensing applications. Finally, the graphene synthesis technology is compatible with wafer-scale fabrication, potentially enabling future chip-level integration with readout electronics.

Global regularity of 2D temperature-dependent MHD-Boussinesq equations with zero thermal diffusivity

This paper is concerned with a model of the two-dimensional zero thermal diffusivity magnetohydrodynamics-Boussinesq equations with the temperature-dependent viscosity and electrical conductivity. The main purpose of this paper is to establish the global regularity to this system with arbitrarily large initial data.

Electrical percolation characteristics and other electrical transport properties of amorphous Se85-xTe15Sbx thin films

The effect of Sb at% on different temperature ranges dc-electrical conductivity are reported for thermally evaporated Se85−xTe15Sbx(x = 2.5, 5 and 7.5 at.%) glassy thin films. The structure and surface morphology of the considered samples were studied by the X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Fourier Transform Infrared (FTIR) and Scanning Electron Microscope (SEM) measurements. The electrical conduction in the Se85−xTe15Sbx chalcogenide glass system was found to be determined by different conduction mechanisms with different activation energy values at various temperature ranges. The relation between various structural parameters and the electrical activation energies was investigated. The analysis of the high-temperature conductivity data identified that the conduction mechanism on the basis of thermionic emission occurs over the grain boundaries according to Seto's model. In the amorphous to crystalline phase transition region, a model has been modified to describe the conduction mechanism. The modification is considering the percolation effects alongside with the effect of thermally activated electrical conductivity of the formed crystalline grains embedded in the sample amorphous matrix. The calculated electrical conductivity was found to be effectively fitted to the temperature-dependent electrical conductivity measurements for thermally evaporated Se85−xTe15Sbx films and showed promising candidates to be examined in different chalcogenide systems .

Quantifying charge carrier localization in chemically doped semiconducting polymers.

Charge transport in semiconducting polymers ranges from localized (hopping-like) to delocalized (metal-like), yet no quantitative model exists to fully capture this transport spectrum and its dependency on charge carrier density. In this study, using an archetypal polymer-dopant system, we measure the temperature-dependent electrical conductivity, Seebeck coefficient and extent of oxidation. We then use these measurements to develop a semi-localized transport (SLoT) model, which captures both localized and delocalized transport contributions. By applying the SLoT model to published data, we demonstrate its broad utility. We are able to determine system-dependent parameters such as the maximum localization energy of the system, how this localization energy changes with doping, the amount of dopant required to achieve metal-like conductivity and the conductivity a system could have in the absence of localization effects. This proposed SLoT model improves our ability to predict and tailor electronic properties of doped semiconducting polymers.

Enhanced electrical properties of polyaniline carbon nanotube composites: Analysis of temperature dependence of electrical conductivity using variable range hopping and fluctuation induced tunneling models

Hydrochloric acid doped polyaniline – multiwalled carbon nanotube nanocomposites are successfully synthesized by chemical in-situ polymerization and their structural, thermal, morphological and electrical properties are investigated. The synthesized PANI-MWNT composites show quite high room temperature DC electrical conductivity, very good thermal stability and a weak temperature dependence of conductivity comparable to doped polymers showing metallic conductivity. The charge transport mechanism in these nanocomposites is analyzed using variable range hopping and fluctuation induced tunneling models, and validation of these models is also carried out using the statistical methods, regression analysis and the analysis of variance. The temperature variation of electrical conductivity is found to best fit with the three-dimensional variable range hopping model. The one-dimensional nature of MWNT enhanced the charge transport in the composite materials. The present study is significant in polymer/organic materials with high mobility charge carriers for various electrical applications such as EMI shielding. The stable DC electrical conductivity observed in the PANI-MWNT composites even at high temperatures highlights the prospects of application of these composites in the fabrication of devices capable of operating at high temperatures. The multifunctional characteristics of MWNT make these composites a potential candidate for the electrical, thermal, sensing and actuating applications.

Towards Electrothermal Optimization of a HVDC Cable Joint Based on Field Simulation

Extruded high-voltage direct current cable systems transmit electric power over long distances. Numerical field simulation can provide access to the internal electrothermal behavior of cable joints, which interconnect cable sections. However, coupled nonlinear electrothermal field simulations are still a challenge. In this work, a robust numerical solution approach is implemented and validated. This approach allows for efficient parameter studies of resistively graded high-voltage direct current cable joint designs. It is assessed how the dielectric stress distribution between the conductor connection and the grounded cable sheath is influenced by nonlinear field and temperature dependent electric conductivity of the field grading material. Optimal field grading material parameters, which fulfill the field grading and power loss requirements, are suggested based on the simulation studies.

Numerical modelling of CFRP induction heating using temperature-dependent material properties

Induction heating of CFRP is an energy-efficient and fast method that may be used for example during consolidation of thermoset-based CFRP or welding of thermoplastic-based CFRP. This study investigates how induction heating of CFRP is affected by the temperature dependence of the thermal and electrical properties and presents a simple numerical model for computation of the temperature distribution during induction heating with a circular coil. Temperature-dependent electrical and thermal properties are measured on a macroscopic level and used in the numerical model. Thermographic recordings are made during induction heating to validate the results from the numerical model. The result shows the importance of using temperature-dependent thermal properties in the numerical model, while it might not be necessary to use temperature-dependent electrical conductivity because of the small impact on the computed heat generation and temperature.

Mechanisms of Heat Transfer in Thermoelectric Materials

The analysis of methods for calculating the components of thermal conductivity of solid materials is carried out. The problems of using these methods are identified and their assessment is given from the point of view of obtaining reliable results. Experimental data on the temperature dependences of thermoelectric parameters of the main thermoelectric materials (TEMs) used for the manufacturing of Peltier and Seebeck thermoelements are presented. Using the obtained data, we calculated the main components of the thermal conductivity of TEMs (phonon, electronic, and bipolar) in the temperature range from 250 to 1200 K for solid solutions based on Bi, Sb, Pb, and Ge chalcogenides, as well as SiGe obtained by various methods of directional crystallization. The relationship between the mechanisms of heat transfer in TEMs and the temperature dependences of electrical conductivity and thermoelectric power has been established. It is shown that the use of nanostructured TEMs is promising for increasing the thermoelectric figure of merit.

Correlation of Electrical Properties and Acoustic Loss in Single Crystalline Lithium Niobate-Tantalate Solid Solutions at Elevated Temperatures

Electrical conductivity and acoustic loss Q−1 of single crystalline Li(Nb,Ta)O3 solid solutions (LNT) are studied as a function of temperature by means of impedance spectroscopy and resonant piezoelectric spectroscopy, respectively. For this purpose, bulk acoustic wave resonators with two different Nb/Ta ratios are investigated. The obtained results are compared to those previously reported for congruent LiNbO3. The temperature dependent electrical conductivity of LNT and LiNbO3 show similar behavior in air at high temperatures from 400 to 700 °C. Therefore, it is concluded that the dominant transport mechanism in LNT is the same as in LN, which is the Li transport via Li vacancies. Further, it is shown that losses in LNT strongly increase above about 500 °C, which is interpreted to originate from conductivity-related relaxation mechanism. Finally, it is shown that LNT bulk acoustic resonators exhibit significantly lower loss, comparing to that of LiNbO3.

Optical and Thermoelectric properties of Gd doped Wurtzite GaN

In this paper,We investigate physical properties of Gd doped stable wurtzite (w-GaN) using Wien2K code, by employing DFT+U. We consider pure GaN and we dope Gd concentration 6.25% into the host GaN lattice. We elaborate and present a detailed electronic, optical and thermoelectric properties of Gd0.06Ga0.94N. The absorption coefficient has been enhancing in the ultraviolet (UV) region. That system is mostly suitable for UV optoelectronics. Our results, on the optical properties suggest this material for potential uses in UV optoelectronics, LEDs, and photovoltaics. The thermoelectric properties as a temperature were studied by solving the BoltzTrap transport equations in conjunction with Density Functional Theory (DFT). In this work, we present the theoretical results of electric conductivity, Seebeck coefficient, power factor and figure-of-merit. Our predictions for temperature dependence of electrical conductivity and power factor revealed a promising use of Gd0.06Ga0.94N for high temperature thermoelectric applications. It was found that the thermoelectric figure-of-merit for at T=250 K is about 0.37 while it can reach 1.29 at 800 K on n-type and about 2.51 at 800 K on p-type.

Role of grain alignment and oxide impurity in thermoelectric properties of textured n-type Bi–Te–Se alloy

A nanostructured n-type Bi2Te2.7Se0.3 (BTS) alloy with a unique microstructure was prepared using a facile melting-rotation-quenching process followed by ball-milling and uniaxial hot-press sintering at 623 K. Anisotropy in the resulting microstructure showed anisotropic electrical and thermal transport properties in two directions normal to the pressing axis. The texture of the nanostructured BTS alloy was analyzed by x-ray diffraction and scanning electron microscopy. Based on the geometric phase analysis of a high resolution transmission electron microscopy images, abundant dislocations, high grain boundary density, and oxide impurity were identified, which act as phonon scattering centers. Higher anisotropy in thermal conductivity combined with oxide impurity resulted in an ultra-low phonon thermal conductivity of ∼0.305 W mK−1 at 423 K in the nanostructured n-type BTS in the direction parallel to the pressing axis. Laser power- and temperature-dependent Raman spectra analyses provided a deeper insight into the anisotropy in thermal transport properties. Optimum power factor and low thermal conductivity, due to the combination of grain alignment and oxide impurity, resulted in a dimensionless figure of merit (zT ) value of ∼0.75 at 423 K. In comparison, the high and opposite temperature dependences of electrical conductivity and thermal conductivity led to a better average zT value of ∼0.68 and a thermoelectric energy conversion efficiency percentage of ∼4.4% in the operating temperature range (300–423 K) in the direction parallel to the pressing axis.

Donor and acceptor-like self-doping by mechanically induced dislocations in bulk TiO2

Dislocations have been recently introduced as a novel tool to tailor the conductivity of functional ceramics. However, tuning strategies suffer from poor insight into the structural complexity of dislocations and their networks. Here, we demonstrate that dislocations can be used to both enhance and reduce the overall conductivity in the same ceramic material. Accurate control of the arrangement of dislocations within the dislocation network enables tailoring TiO2 bulk samples to behave like being chemically modified either with an acceptor or donor dopant. Our approach combines ultra-high voltage electron microscopy, oxygen partial pressure, and temperature dependent electrical conductivity measurements combined with time-of-flight secondary ion mass spectrometry. This allows us to focus on mechanically tailored interaction of next neighbor dislocations and to differentiate between percolating conductive pathways and separated charge carrier zones. This seemingly simple approach purposefully tailors the conductivity of TiO2, opening new avenues to engineer functional ceramics beyond common chemical doping strategies.

Low temperature carrier transport mechanism and photo-conductivity of WSe2

This work reports the electrical-transport and temperature-dependent photoconductivity in tungsten diselenide (WSe2) thin films. Temperature-dependent electrical conductivity has been demonstrated using different models. At lower temperatures (< 190 K), carriers become localized to small regions in the film due to Mott’s hopping mechanism. The middle-temperature region (190–273 K) follows Seto’s parameters and obtained low barrier height (0.0873 eV) may be responsible for the improved carrier mobility. At higher temperature (> 273 K) region, thermally activated conduction is dominated with two activation energies of ~138 meV and 98 meV. The peaks obtained in photoluminescent analysis attributes to the presence of mid-bandgap states or defect states which play an important role in the photoconductivity of WSe2. The transient photoconductivity measurements show consistent temperature-dependent behaviour. The effect of light intensity and wavelength variation on the photoconductivity of WSe2 thin films is also discussed. The photo-current is 1.19 * 10−5 A at 125 K, while at 350 K was observed to be 3.12 * 10−4 A. The light-on/off current cycles show that the current can recover to its initial state after various cycles, which points to the WSe2 thin-film device's stable and reversible properties that can be used in optoelectronic applications.

High Temperature Insulation Materials for DC Cable Insulation — Part I: Space Charge and Conduction

Fundamental studies of potential candidates for DC electric power transmission in high temperature environment, including ETFE, FEP, PTFE, PI and PEEK, are carried out and presented in form of the series papers containing space charge and conduction as part I, partial discharge as part II, and the degradation and surface breakdown as part III. In this part, the space charge at 20kV/mm was measured at 25 °C and with a thermal gradient at 50 °C. The electrical conductivity was measured at electric fields ranging from 10kV/mm to 30kV/mm in temperatures ranging from 25 °C to 200 °C. The experimental results showed that considering the effect of thermal condition and electric field, FEP has the lowest total amount of space charge accumulation and electric field distortion among these materials at the measured conditions. PI and PEEK have the lowest amount of trap-controlled mobility at 25 °C due to deeper average trap level because of the aromatic rings in the structure. PTFE and PI have the lowest amount of thermal activation energy and temperature-dependent electrical conductivity due to the more uniform morphological phase comparing to ETFE, FEP, and PEEK. The outcomes of this paper serve as a benchmark for the fundamental researches over high temperature materials for DC applications and lay a basis for Part II and Part III.

Effects of spin-orbit coupling and magnetic field on electronic properties of Germanene structure

In this paper, we present a Kane-Mele model in the presence of magnetic field and next nearest neighbors hopping amplitudes for investigations the electronic and optical properties of monolayer Germanene. Specially, we address the dynamical conductivity of the structure as a function of photon frequency and in the presence of magnetic field and spin-orbit coupling at finite temperature. Using linear response theory and Green’s function approach, the frequency dependence of optical conductivity has been obtained in the context of Kane-Mele model Hamiltonian. Our results show a finite Drude response at low frequency at non zero value for magnetic field in the presence of spin-orbit coupling. However Drude weight gets remarkable amount in the presence of electron doping. The thermal conductivity and specific heat increase with increasing the temperature at low amounts of temperature due to the increasing of thermal energy of charge carriers and excitation of them to the conduction bands. The results for Seebeck coefficient show the sign of thermopower is negative in the presence of spin-orbit coupling. Also we have studied the temperature dependence of electrical conductivity of Germanene monolayer due to both spin orbit coupling and magnetic field factors in details.

Physical, structural, conductive and magneto-optical properties of rare earths (Yb, Gd) doped Ni–Zn spinel nanoferrites for data and energy storage devices

In this study, an attempt has been made using different concentrations of rare-earth (RE) elements Yb, Gd in Ni–Zn spinel ferrite to examine the magneto-optical and electrical conductivity analysis of the prepared samples. RE doped Ni–Zn ferrite with composition Ni0.5Zn0.5YbxGdxFe2-xO4 (where, x = 0.00, 0.20, 0.40, 0. 60, 0.80 and 1.00) were prepared by one step sol-gel self-ignition approach. XRD and FESEM were used to examine the formation of a single-phase and variations in the grain size with the increasing contents of RE elements in Ni–Zn ferrite NPs. FTIR confirmed the vibrational studies of the RE doped spinel ferrite. The saturation magnetization, remanence, and coercivity elucidated the magnetic nature of the prepared samples. The decreasing trend was observed in the magnetization which may be due to the doping of RE elements at the B sites. UV–Vis spectroscopy verified the semiconducting nature of the synthesized samples which was because of the emergence of optical band gap in the semiconductor region (2.04 eV–2.28 eV). The temperature-dependent electrical conductivity (σDC) was also studied to investigate the conduction mechanism over the 323 K–563 K temperature range. Yb and Gd doped NiZn ferrite is a good candidate for the nanoantennas, quantum information, sensing, isolators, modulators, data storage applications and energy storage devices because of their excellent magneto-optical and electrical properties.

Nanofiller-assisted Na+-conducting polymer nanocomposite for ultracapacitor: structural, dielectric and electrochemical properties

We report the preparation of ZrO2 nanofiller-incorporated polymer nanocomposite electrolyte based on the PEO-NaPF6 matrix via standard solution cast method. The structure and morphology of polymeric films have been examined with X-ray diffraction and field emission scanning electron microscopy. Different interactions between the polymer, salt and nanofiller have been examined by Fourier transform infrared technique. The temperature-dependent (40–100 °C) electrical conductivity has been examined from complex impedance spectroscopy (CIS). The highest ionic conductivity is exhibited by 5 wt% nanofiller-based electrolyte and recorded ~ 2 × 10–4 S cm−1 at 100 °C. The voltage stability window of polymeric film checked from linear sweep voltammetry is about ~ 4 V, and ion transference number close to unity confirms the major contribution from ion conduction. The dielectric properties have been explored in terms of complex permittivity, loss tangent and complex conductivity. The dielectric plots have been further fitted with an associated equation to evaluate principal dielectric parameters. The optimized polymer electrolyte possesses the lowest relaxation time and the highest dielectric constant that suggests the highest ionic conductivity, which is in good correlation with impedance results. The dc conductivity is also highest for the optimum system, and relaxation time decreases with an increase in temperature. The thermal stability of polymer electrolytes is about 200 °C, as examined by thermogravimetric analysis (TGA). The ion transport parameters n, μ, D have been evaluated via FTIR, impedance spectroscopy and Bandara and Mellander (B–M) approach. Finally, the optimized polymer nanocomposite film has been used as an electrolyte-cum-separator for the fabrication of a solid-state symmetric supercapacitor. The electrochemical parameters specific capacitance, energy density, power density have been examined from cyclic voltammetry and galvanostatic charge–discharge technique. It may be concluded that nanofiller incorporation is an effective strategy to enhance the properties of electrolyte and has the potential to adopt as an electrolyte-cum-separator for ultracapacitor.

INFLUENCE OF THE OBTAINING CONDITIONS ON THE ELECTROCONDUCTIVITY OF Ga2O3 THIN FILMS

The structure and electrical conductivity of β-Ga 2 O 3 thin films obtained by the method of RF ion-plasma sputtering, depending on the composition of the thermal treatment atmosphere, were studied. It was found that β-Ga 2 O 3 thin films annealed in an argon atmosphere and an oxygen atmosphere have a significant value of resistivity up to 10 11 Ohm×cm, and after annealing in a reducing hydrogen atmosphere there is a significant decrease in the value of resistivity of the films up to 10 8 Ohm×cm. Studies of the temperature dependence of electrical conductivity in the temperature range from 300 to 450 K allowed determine the value of activation energy of thermal quenching of electrical conductivity due to donor centers that occur in the obtained films and the analysis of the received results is carried. Key words : gallium oxide, thin films, electrical conductivity.