Dielectric relaxation and conduction mechanism in LaNi3/4M1/4O3 (M = Mo, W) at low temperature

In order to investigate the electrical transport in LaNi_3/4Mo_1/4O₃ and LaNi_3/4W_1/4O₃, the dc conductivity and dielectric properties in these polycrystalline materials are investigated in the temperature range from 163 K to 383 K and frequency range from 50 Hz to 1 MHz. The X-ray diffraction patterns of the samples show monoclinic phase at room temperature. The homogeneity of the samples is determined by energy dispersive analysis of X-ray (EDAX) attached with a scanning electron microscope. The temperature dependence of dc conductivity shows the semiconducting nature of the materials. The complex impedance plane plots show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The frequency-dependent electrical data are also analyzed in the framework of ac conductivity formalism. The ac conductivity spectra follow the universal power law. The activation energies required for bulk conduction is 0.143 and 0.165 eV for LNM and LNW respectively. The scaling behaviour of loss tangent suggests that the relaxation describes the same mechanism at various temperatures.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Study of LiMgVO4 electrical conductivity mechanism

This paper deals with impedance spectroscopy on single-phase polycrystalline LiMgVO₄ in the temperature range of 25–500 °C. Thermogravimetric measurements show a weight loss of 2.7% in the temperature range between 25 °C and 175 °C due to humidity desorption. A conductivity mechanism along the grain boundaries (agb) is identified in the specific temperature range and is attributed to a reversible humidity absorption–desorption mechanism. Equivalent circuits are drawn using the results of the impedance measurements at each temperature. A unique conduction process within the material is assigned to each element of the equivalent circuit and Arrhenius plots are plotted. The calculation of activation energy of each conduction mechanism is based on the Arrhenius plots. The activation energy E_b of the bulk conductivity mechanism was found to be 0.62 eV. The activation energy E_gb of the grain boundaries conductivity mechanism was found to be 1.03 eV up to 275 °C and 0.50 eV in the temperature range of 300–500 °C. The absence of the conductivity mechanism along the grain boundaries above 175 °C can only be due to the complete removal of water from the material's grains.     

Transport mechanism in a ceramic system: LiCo3/5Fe1/5Cu1/5VO4

The electrical impedance and modulus properties of a LiCo_3/5Fe_1/5Cu_1/5VO₄ ceramic system were measured by impedance spectroscopy method in the frequency range 10²-10⁶ Hz and temperature range 22-250 °C. X-ray diffraction study reveals formation of the compound in a cubic crystal system with lattice parameters a = 8.2756 (3) Å. Field emission scanning electron microscopy is used to investigate the grain morphology of the material. Nyquist plots confirm the existence of bulk and grain boundary effects at 22 °C ≤ T ≤ 200 °C, and bulk, grain boundary and polarization effects at T ≥ 225 °C. Electrical modulus study indicates a non-Debye behavior of the material. A detailed study of bulk conductivity shows electric conduction in the material as a thermally activated process.     

Impedance and electric modulus analysis of Sm-modified Pb(Zr0.55Ti0.45)1−x/4O3 ceramics

The polycrystalline ceramic samples of Pb_1−xSm_x(Zr_0.55Ti_0.45)_1−x/4O₃ (x = 0.00, 0.03, 0.06 and 0.09) were prepared by solid-state reaction technique at high temperature. Electric impedance (Z) and modulus (M) properties of the materials have been investigated within a wide range of temperature and frequency using complex impedance spectroscopy (CIS) technique. The complex impedance analysis has suggested the presence of mostly bulk resistive (grain) contributions in the materials. This bulk resistance is found to decrease with the increase in temperature. It indicates that the PSZT compounds exhibit a typical negative temperature coefficient of resistance (NTCR) behavior. The bulk contribution also exhibits an increasing trend with the increase in Sm³⁺ substitution to PZT. The complex modulus plots have confirmed the presence of grain (bulk) as well as grain boundary contributions in the materials. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the materials.     

Study of the electrical conduction behaviour of the Ba1−xLaxTi1−xNixO3 (x 0.10) system

The electrical conduction behaviour of the Ba_1−xLa_xTi_1−xNi_xO₃ (x 0.10) system has been studied by complex plane impedance analysis and measurements of a.c. conductivity in the temperature range 400–575 K. The values of the bulk resistance for these samples are obtained from a circular arc passing through the origin in their impedance plots. A.c. conductivity obeys the relation σ_a.c.αω⁸ in the temperature range of measurements. These results indicate that conduction occurs in this system because of hopping of charge carriers between localized nickel sites.     

Electrical conductivity of Na3AlF6-AlF3-Al2O3-CaF2-LiF（NaCl） system electrolyte

A PGSTAT 30 and a BOOSTER 20A were used to measure cell impedance.Electrical conductivity was gained by the Continuously Varying Cell Constant Technique.Electrical conductivity of KCl was measured for comparison.The results prove that the method is reliable and accurate.The electrical conductivity of Na3AlF6-AlF3-Al2O3-CaF2-LiF(NaCl)system was studied by this method.Activation energy of conductance was obtained based on the experiment results.The experiments show that electrical conductivity is increased greatly with NaCl and LiF added.Increasing 1%LiF(mass fraction)results in corresponding increase of 0.0276 S/cm for superheat condition of 15℃.For NaCl,it is 0.024 S/cm.Electrical conductivity is increased by 0.003 S/cm with 1℃temperature increase.The electrical conductivity is lower than that predicted by the WANG Model and higher than that predicted by the Choudhary Model.     

Correlation between the chemical composition and the conduction mechanism of barium strontium titanate thin films

Sol-gel barium strontium titanate thin films with different barium-to-strontium (Ba:Sr) values have been fabricated as MFM configurations. The Perovskite phase for the films is confirmed via XRD. In order to correlate the effect of the chemical composition of the films with the conduction mechanism, different AC electrical parameters have been addressed. The results show that the impedance and dielectric constant decrease as Ba content in the film increases, whereas the conductivity shows the opposite variation; this is attributed to the grain size and dipole dynamics. Complex impedance (Z*) and electric modulus (M*) planes show three overlapping regions as the response for the bulk, the grain boundaries and the film/electrode interface mechanisms. These mechanisms have been represented by an equivalent circuit. The imaginary component of electric modulus (M″) versus frequency plots, which reveal relaxation peaks that are not observed in the dielectric loss (?″) plots, and it is found that these peaks are of a non-Debye-type. Furthermore, the frequency dependent conductivity plot shows three regions of conduction processes.     

Precipitation behavior in Al-Zn-Mg-Cu alloy after direct quenching

The precipitation behavior in an Al-6.8Zn-1.9Mg-1.0Cu-0.12Zr alloy after direct quenching from solution heat treatment temperature of 470 °C to 205–355 °C was investigated by means of hardness tests, electrical conductivity tests, and transmission electron microscopy. At temperatures below 265 °C, the hardness increased gradually to a peak value and then decreased rapidly with time. At 265 °C, the hardness was almost unchanged within the initial 2000 s and then decreased gradually. At higher temperatures, the hardness decreased slowly with time. The electrical conductivity started to increase after a certain period of time and then tended to maintain a constant value at all temperatures. Microstructure examination indicated heterogeneous precipitation of the η phase at grain boundaries and inside grains during holding at 205 °C and 325 °C. Based on the electrical conductivity data, the precipitation kinetics could be described quite well by the Johnson-Mehl-Avrami-Komolgorov relationship with a n value varying between 0.78 and 1.33. The activation energy was estimated to be about 44.9 kJ/mol, which is close to that expected for a dislocation diffusion mechanism. Time-temperature-transformation diagrams were constructed and the nose temperature ranged from 295 °C to 325 °C.     

含钒石煤的悬浮焙烧过程：特性表征、热力学、动力学（英文）

系统地研究含钒石煤在悬浮焙烧过程中的热力学、动力学、物相转化和微观结构演变。热力学计算表明,在焙烧过程中,石煤中的碳在氧气充足的情况下燃烧并生成CO₂,石煤的主要质量损失区间为600～840℃,热分解反应速率在700℃左右达到峰值。通过Flynn-Wall-Ozawa(FWO)和Kissinger-Akahira-Sunose(KAS)方法验证,石煤的热分解反应由Ginstling-Brounshtein方程描述,表观活化能和指数前因子分别为136.09 k J/mol和12.40 s^-1。石煤中的伊利石在650℃时失去羟基,产生脱水伊利石,绢云母结构被逐渐破坏。随着温度的升高,石煤表面变得粗糙且不规则,焙烧温度为850℃时烧结严重。     

Double-walled carbon nanotube/polymer nanocomposites: Electrical properties under dc and ac fields

The electrical properties of the poly(methyl methacrylate:carbon nanotubes nanocomposites) have been investigated by direct current conductivity and complex impedance spectroscopy methods. The direct current conductivity results of the poly(methyl methacrylate):carbon nanotube as a nanocomposites show that the electrical conductivity property of the poly(methyl methacrylate) changes from insulating state to semiconducting state with incorporation of double wall carbon nanotube DWCNTs into insulating polymer matrix. The alternating current conductivity mechanism of the nanocomposites is controlled by the correlated barrier hopping mechanism. The correlated barrier hopping CBH model for intimate valence alternation pairs IVAP's describes the conduction mechanism of PMMA doped with (1%) DWCNTs, while correlated barrier hopping CBH model for non-intimate valence alternation pairs describes the conduction mechanism of PMMA doped with (5% and 8%) DWCNTs. The real part of the complex impedance decreases with the increase of the applied frequency which revealed that the PMMA:DWCNT nanocomposites behaves like semiconducting materials. The complex impedance Nyquist plots for PMMA doped with different concentration DWCNTs over are characterized by the appearance of a single semicircular arc whose radii of curvature decreases with increasing the temperature. Cole and Cole plots show the presence of temperature dependent electrical relaxation phenomena in the PMMA:DWCNT nanocomposites. The obtained electronic parameters confirm that PMMA:DWCNTs exhibit organic semiconductor behavior.     

Bias Voltage-Dependent Impedance Spectroscopy Analysis of Hydrothermally Synthesized ZnS Nanoparticles

In this report, bias voltage-dependent dielectric and electron transport properties of ZnS nanoparticles were discussed. ZnS nanoparticles were synthesized by introducing a modified hydrothermal process. The powder XRD pattern indicates the phase purity, and field emission scanning electron microscope image demonstrates the morphology of the synthesized sample. The optical band gap energy (E_g?=?4.2 eV) from UV measurement explores semiconductor behavior of the synthesized material. The electrical properties were performed at room temperature using complex impedance spectroscopy (CIS) technique as a function of frequency (40 Hz-10 MHz) under different forward dc bias voltages (0-1 V). The CIS analysis demonstrates the contribution of bulk resistance in conduction mechanism and its dependency on forward dc bias voltages. The imaginary part of the impedance versus frequency curve exhibits the existence of relaxation peak which shifts with increasing dc forward bias voltages. The dc bias voltage-dependent ac and dc conductivity of the synthesized ZnS was studied on thin film structure. A possible hopping mechanism for electrical transport processes in the system was investigated. Finally, it is worth to mention that this analysis of bias voltage-dependent dielectric and transport properties of as-synthesized ZnS showed excellent properties for emerging energy applications.     

Dielectric relaxation, conductivity behaviour and magnetic properties of Mg substituted Ni-Li ferrites

The dielectric properties of Mg substituted Ni-Li spinel ferrites synthesized by sol-gel auto combustion process have been studied using impedance measurements in the frequency range from 10 Hz to 10 MHz and in the temperature range from 310 K to 473 K. The effect of frequency, temperature and composition on dielectric constant (?′), dielectric loss (tan δ) and conductivity (σ) has been discussed in terms of hopping of charge carriers between Fe²⁺ and Fe³⁺ ions. The electrical modulus formulism has been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in the present ferrites. Similar values of activation energies for dc conduction (E_dc) and for conductivity relaxation (E_M″) reveal that the mechanisms of electrical conduction and dielectric polarization are same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of dynamical process for charge carriers. The saturation magnetization and coercivity have been calculated from the hysteresis loop measurements and show striking dependence on the composition.     

Microstructures and electrical responses of pure and chromium-doped CaCu3Ti4O12 ceramics

Pure and chromium-doped CCTO (CaCu₃Ti₄O₁₂) ceramics were prepared by a conventional solid-state reaction method, and the effects of chromium doping on the microstructures and electrical properties of these ceramics were investigated. Efficient crystalline phase formation accompanied by dopant-induced lattice constant expansion was confirmed through X-ray diffraction studies. Scanning electron microscopy (SEM) results show that doping effectively enhanced grain growth or densification, which should increase the complex permittivity. The dielectric constant reached a value as high as 20,000 (at 1 kHz) at a chromium-doping concentration of 3%. The electrical relaxation and dc conductivity of the pure and chromium-doped CCTO ceramics were measured in the 300-500 K temperature range, and the electrical data were analyzed in the framework of the dielectric as well as the electric modulus formalisms. The obtained activation energy associated with the electrical relaxation, determined from the electric modulus spectra, was 0.50-0.60 eV, which was very close to the value of the activation energy for dc conductivity (0.50 ± 0.05 eV). These results suggest that the movement of oxygen vacancies at the grain boundaries is responsible for both the conduction and relaxation processes. The short-range hopping of oxygen vacancies as “polarons” is similar to the reorientation of the dipole and leads to dielectric relaxation. The proposed explanation of the electric properties of pure and chromium-doped CCTO ceramics is supported by the data from the impedance spectrum.     

Electrochemical assessment of spray-applied thermoplastic coating barrier properties

Flame-sprayed thermoplastic powder coatings act as barrier-type coatings for corrosion protection. Characteristic electrical properties for this type of coating are high resistance and capacitance, and low permeability to water and ions. Electrochemical impedance spectroscopy was used to evaluate the corrosion protection performance and electrical resistance of this type of coating during immersion in 3% NaCl solution. The variations with time of impedance and capacitance of two types of this coating, blue and black, were measured at three immersion temperatures (22, 50, and 80 °C). The impedance of both coatings remained consistently high when the solution temperature was maintained around ambient (22 °C). At the higher temperature of 50 °C, both coatings performed well initially, then showed signs of damage by a drop in the impedance. Both samples maintained at 80 °C failed after 12 and 25 days for the blue and the black coatings, respectively, with blistering occurring on both panels.     

Plastic flow of the mechanically alloyed Fe-0.6%O at temperatures of 550–700°C

Creep of steel Fe-0.6%O produced by the method of powder metallurgy has been studied in a temperature range of 550–700°C at flow stresses from 100 to 400 MPa. It has been shown that the creep of the material is characterized by high values of the apparent activation energy for deformation, which considerably exceeds the value of the activation energy for self-diffusion in α iron, and by high values of the stress exponent in the power law of creep. An analysis of the deformation behavior of the alloy showed that there are observed high threshold stresses as a result of retardation of moving dislocations by small incoherent particles of oxides. Taking into account the threshold stresses and the temperature dependence of the shear modulus, it has been established that the deformation behavior of the powder material is described by a power law of creep. The true values of the stress exponent were found to be approximately 8, and the values of the true activation energy for deformation, to be close to the activation energy for bulk (at T = 700°C) and pipe (at T = 550–650°C) self-diffusion.     

Solution-cast polypyrrole film: the electrical and thermal properties

Polypyrrole (PPy) solution has been prepared by dissolving PPy powder in m-cresol after doping with sodium dodecylbenzenesulfonate, and free-standing film of PPy has been cast from the solution. The PPy prepared in this way has very shiny smooth surfaces and contains approximately 13% of the solvent. The activation energy of electrical conduction was found to be 0.14 eV. It has been concluded that the solvent, i.e. m-cresol, plays an important role in electrical conduction as well as the enhancement of electrical conductivity during annealing at around 120 °C. The decrease in electrical conductivity as the PPy film is heated above 140 °C is due to the loss of solvent.     

Thermal, micro-structural, and electrical properties of a La1−x Sr x Mn0.85Fe0.05Co0.05Ni0.05O3+δ (x = 0–0.4 mole) cathode system

The oxygen stoichiometry, thermal expansion, morphology, and electrical conductivity of a co-doped perovskitetype cathode system, La_1?x Sr _x Mn_0.85Fe_0.05Co_0.05Ni_0.05O_3+ä (x = 0–0.4 mole), are studied for intermediate-temperature solid oxide fuel cell applications. Sr²⁺-doping led to a decrease in the unit cell volume, oxygen stoichiometry, particle size, and activation energy, and an increase in the coefficient of thermal expansion and electrical conductivity. The sample with x = 0.3 mole exhibited four to five fold weight loss with respect to La_0.75Sr_0.25MnO_3+δ at an intermediate temperature range and suggested the availability of a large number of oxygen vacancies due to a co-doping effect. This sample also showed sufficiently high electrical conductivity (～76 S cm^?1) at 650 °C, a low activation energy (～0.15 eV), and a coefficient of thermal expansion (～12.1 × 10^?6 °C^?1) comparable to those of the adjacent components and submicron sized particles. The experimental results are explained using defect models.     

Magnetic,Dielectric and Complex Impedance Properties of xBa_(0.95)Sr_(0.05)TiO_3–(1-x)BiFe_(0.9)Gd_(0.1)O_3Multiferroic Ceramics

xBa_(0.95)Sr_(0.05)TiO_3–(1-x)BiFe_(0.9)Gd_(0.1)O_3[x BST–(1-x)BFGO](x = 0.00, 0.10, 0.20 and 0.25) multiferroic ceramics were prepared by the standard solid-state reaction technique. Structural characterization was performed by X-ray diffraction. All the samples showed rhombohedral distorted perovskite structure. Surface morphology of the ceramics was studied by the field emission scanning electron microscope(FESEM). From the FESEM observation, the grain size was observed to be decreased with increasing BST content. Enhanced magnetic properties were observed in BFGO with the increase in BST content because of large lattice distortion. The complex initial permeability increased with the increasing of BST content. The study of dielectric properties showed that the dielectric constant increased, whereas dielectric loss decreased with increasing of BST content due to the reduction of oxygen vacancies. An analysis of the electric impedance and modulus with frequency was performed at different temperatures. Non-Debye-type relaxation processes occur in the compound which was confirmed from the nature of the Cole–Cole plot. The DC conductivity was found to increase with the rise in temperature which indicates the semiconducting behavior of the compound with characteristics of the negative temperature coefficient of resistance. The activation energy, responsible for the relaxation determined from the modulus spectra(0.246 eV), was found to be almost same as the value obtained from the impedance study(0.240 eV), indicating that charge carriers overcome the same energy barrier during relaxation. The frequency response of imaginary parts of electric impedance and modulus suggested that the relaxation in xB ST–(1-x)BFGO ceramics follows the same mechanism at various temperatures.     

An Integrated Assessment of Process-Microstructure-Property Relationships for Thermal-Sprayed NiCr Coatings

Process-microstructure-property relationships have been systematically investigated and quantified for a large process window of thermal-sprayed Ni-20 wt.%Cr coatings. Detailed monitoring of particle state, coating formation, and multifunctional characterization has been performed providing a framework to not only examine the product coating, but also concurrently their evolution dynamics. Several distinct microstructures resulted from this expanded process window and shed light into the effects of in-flight particle state, nature of the interfaces, impact-induced peening, strain hardening, oxide content, on coating properties notably hardness, residual stress, elastic modulus, electrical and thermal conductivity. Nine processing conditions from five different thermal spray torches provided a wide range of particle velocities from 150 to 800 m/s and temperatures from 1800 to 2400 °C. Correlation between particle states and evolving stress obtained via in situ monitoring of coating deposition indicated increment of compressive stress at high particle kinetic energies, as well as enhanced strain hardening via peening. Hardness, therefore, showed strong dependency on the residual stress evolution. Elastic modulus was found to be strongly dependent on densification and intersplat bonding, whereas electrical and thermal conductivities were found to be more sensitive to defects in the intersplat interfaces (oxides, interlamellar porosity). In comparison to bulk properties, elastic modulus, and thermal conductivity of the sprayed coatings were generally lower, while electrical conductivity can approach the bulk value. Coating hardness exceeds the bulk property in most cases owing to the strain hardening during impact. Hardness was the most sensitive property to the process condition.