Grain Boundary Contributions Research Articles

Effect of substitution on the structural, electrical properties, and dielectric relaxor behavior in lead-free BiFeO3-based ceramics.

BiFeO3-based ceramics have recently garnered much interest among researchers owing to their valuable and outstanding characteristics. For this reason, the 0.7(Na0.5Bi0.5)TiO3-0.3(Bi0.7Sm0.3FeO3) ceramic was successfully synthesized by a solid-state route. The central purpose of this research is to investigate the substitution influence of Na, Ti, and Sm on the structural, dielectric, and electric properties of 0.7(Na0.5Bi0.5)TiO3-0.3(Bi0.7Sm0.3FeO3), as well as to explore its potential applications as it exhibits multiple novel functions. Notably, a structural transition from rhombohedral R3c to orthorhombic P4mm occurred within this material. In this respect, a suitable equivalent electrical circuit was invested to assess the contributions of grains and grain boundaries to the complex impedance results. Electrical conductivity was attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the sample. The temperature dependence of the dielectric constants revealed the presence of a phase transition. The local disorder provides a dependence of the real part of the permittivity on the frequency which characterizes a relaxor ferroelectric-type behavior of a lead-free material. The modified Curie-Weiss law, in addition to the Vogel Fulcher and Debye law relationships, was utilized to analyze the diffuse transition phase. Furthermore, the studied compound displayed promising electrical properties and chemical stability and proved to be a good relaxor. In this regard, a correlation between dielectric and electric behavior near the ferro-paraelectric phase transition was established.

Synthesis and investigation; influence of Mn doping on biological, optical, dielectric and electrochemical characteristics of Bi2O4 nanostructures

In this research, bismuth oxide thin films were synthesized with the variation of Mn dopant (1-5 wt %) on a glass slide by sol-gel dip coating method. XRD corroborated the creation of a monoclinic phase for all the samples after annealing at 450 °C for 4 h. The non-uniform cuboid-like granular structures were observed by SEM with a significant number of grain boundaries. Different functional groups were examined by using FTIR spectroscopy. The optical band gap was reduced from 2.01 to 1.81eV by increasing the concentration of Mn dopant. The contribution of grain and grain boundaries to the material electrical response in various frequency ranges was distinguished by impedance analysis. The polaron mechanism was used to investigate conductivity with time variation. The efficiency of supercapacitors was significantly enhanced by using the monoclinic Bi2O4 phase of bismuth oxides, promoting the specific capacitance in the range of 2518.2–6890.2 Fg-1 with high energy and power density. That leads them to the fabrication of supercapacitors in advanced electronic devices. Magnetic analysis showed that saturation magnetization and remanent frequency decreased while coercivity of thin films increased with increasing Mn concentration which was successfully explained by the critical size effect and Néel's collinear two sub-lattice models, making them plausible candidates in spintronics. As from photocatalyst analysis, the number of reactive oxygen species ROS was increased by increasing Mn doping in the Bi2O4 crystal lattice. These species degraded the water pollutants under simple exposure to sunlight (i-e visible range). The production of ROS in the photocatalytic process was also correlated with antibacterial activity. Mn-doped Bi2O4 was found to be more effective towards K. pneumonia than other bacteria. The prepared Mn:Bi2O4 nanostructures with a higher percentage of manganese were effectively used for the treatment of bloodstream infections, meningitis, pneumonia, and urinary tract infections and stopped further bacterial growth.

Reduce the low-frequency dielectric losses of (In0.5Nb0.5)0.05Ti0.95O2 ceramics by increasing grain boundary density and resistance

(In0.5Nb0.5)0.05Ti0.95O2 (INTO) ceramics exhibits unusual colossal permittivity properties. However, the high dielectric loss limits their practical applications. Increasing the contribution of grain boundaries to dielectric properties can reduce their dielectric loss. Therefore, La was added to increase the number of grain boundaries, while annealing was performed to improve the grain boundary resistance. The results show that La addition and annealing in air indeed reduce the grain size of INTO ceramics and low their dielectric loss due to increased grain boundary resistance. Specifically, the permittivity of annealed La-doped INTO ceramic remains at 2 × 104, and its dielectric losses are less than 0.05 from 30 Hz to 6.5 kHz, with a minimum of approximately 0.02. The dielectric loss at 1 kHz is below 0.05 from below −60 °C to about 90 °C. The effects of La-doping and annealing on INTO ceramics, as well as the origin of the colossal permittivity properties, were discussed.

Structural, dielectric and electrical properties of (Ba0.95Zn0.05)(Ti0.95Sn0.05Se0.05)O3 ferroelectric ceramic

In this report, the proposed compound (Ba0.95Zn0.05)(Ti0.95Sn0.05Se0.05)O3 is synthesized by mixed oxide route for the extensive study of the dielectric and electrical properties. The crystallization, symmetry, structure (tetragonal), space group (P4mm), and lattice parameters were confirmed by an X-ray diffraction study. The dielectric and electrical properties in a wide range of temperatures and frequencies of this particular composition deduce various interesting properties on high dielectric permittivity, low tangent loss, relaxation mechanism, non-Debye type conduction, and negative temperature coefficient of resistance. From the frequency and temperature dependence, dielectric loss shows a very low loss factor (<0.06) at low temperatures (<250 °C). Nyquist plots discuss the contribution of grain and grain boundary by fitting it with the help of the software ZSimpWin. The PE loop measurement showed that the corresponding hysteresis had main parameters for (Ba0.95Zn0.05)(Ti0.95Sn0.05Se0.05)O3 compound, remnant polarization (Pr = 0.28 µC/cm2) and coercive field (Ec = 1.35 kV/cm). All the above characteristics conclude that it may be applicable in electronic device industries.

Synthesis and investigation on the optical and complex impedance analysis in LiCrO2 prepared using solid-state reaction

Lithium-ion batteries (LIB) have been employed extensively as energy delivery and storage technologies in electronic devices, electric cars, and utility grids. In this paper, the LiCrO2 compound was successfully synthesized using the solid-state method. The X-ray powder diffraction (XRPD) data confirmed the formation of a single-phase with a rhombohedral structure (R3̅m space group). The surface morphology of the compound was studied by scanning electron microscopy (SEM), to find that the average size is around 3.5 µm. UV-Vis-NIR diffuse reflectance and impedance spectroscopy thoroughly investigated the optical and electrical properties. The optical band gap is approximately 2.2 ± 0.1 eV for direct transition, determined using the absorption spectrum. The latter proves a semiconductor characteristic of the studied sample. The Nyquist plots (-Z" vs. Z′) display the contribution of grains and grain boundaries in the electrical conductivity, confirming the existence of a non-Debye type relaxation. The studied compound displays enhanced capacitance behavior, semiconducting properties that follow the Arrhenius relation, and an increase in conductivity as a function of frequency for different voltage values in the range of 0.5–3 V. The best electrical response in terms of capacitance and conductivity was found for the voltage value of 3 V. This study will expand knowledge by shedding light on the electrical conductivity for this value. The hopping of charge carriers over the potential barrier and the tunneling of polarons created because of lattice deformation at high bias voltages combine to produce the electrical conduction in this ceramic.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Superplastic deformation inside the knife-sharp shear bands in mid-crustal granites

We examined the microstructures of three ductile shear bands of granitic composition that deformed under mid-to-upper greenschist facies. These shear bands, from the Bundelkhand Craton, India, are 0.8–4.4 mm thick with 20–30 μm median grain sizes and share sharp contacts with the host granite. Comminution of the rheologically stronger feldspars increased permeability, promoted fluid influx, and allowed strain localisation in the incipient shear bands. The major components, quartz and feldspars, deformed via phase-specific crystal plastic deformation mechanisms. Quartz in the monomineralic bands deformed predominantly via dislocation creep, while the feldspars deformed via diffusion creep. Finer quartz grains, which occur at plagioclase triple junctions, resulted from myrmekitisation – also evident from the anti-clustered distribution of quartz-plagioclase phase boundaries and CPO inheritance. The weak CPOs and high mean misorientation angles of the fine plagioclase and K-feldspar grains and yet a high shear strain (γ = 16–37) suggest a significant contribution of grain boundary sliding (GBS) in strain localisation inside the ductile shear bands. Since intracrystalline slip alone cannot explain the high ductile strain in the shear bands, we suggest that GBS controlled the deformation and maturation of the shear bands and promoted superplasticity to accommodate further shearing.

Dielectric Relaxation Behavior and Electrical Conduction Mechanism of PVA/ZnO Nanocomposites for Flexible Electronic Device Application

Transport properties of polyvinyl alcohol/ZnO nanocomposites (PVA/ZnO) of varying ZnO nanofiller are studied focussing on their potential application in electronic device application. The structural, morphological, and elemental composition studies of the prepared samples are done by X‐ray diffraction (XRD), scanning electron microscope (SEM), and energy‐dispersive X‐ray analysis (EDX). XRD confirms the formation of nanocomposites. SEM image shows the dispersion of ZnO nanoparticles on the surface of PVA matrix. EDX verifies that no external impurities are present in the nanocomposite samples. Frequency‐ and temperature‐dependent dielectric measurement of the samples reveals maximum dielectric constant at PVA/15 wt% ZnO nanocomposite. Dielectric loss results show a lossless behavior at higher frequencies (&lt;0.2), indicating their suitability for high‐frequency applications. The AC conductivity studies reveal that electrical conduction mechanism in the nanocomposites is governed by the correlated barrier hopping mechanism. Activation energy of the samples reveals the presence of two thermally activated transport mechanism above and below 353 K. The imaginary part of electric modulus with frequency shows a single relaxation peak indicating the transition from long‐range to short‐range mobility with increasing frequency and temperature above 353 K. The contribution of grain and grain boundary in the electrical conduction process is confirmed from the Nyquist plot.

Dielectric relaxations without colossal permittivity in Mg and Nb co-doped BaTiO3 ceramics

Magnesium (Mg) and Niobium (Nb) co-doped BaTiO3 ceramics are prepared using a solid-state reaction method under an air atmosphere, and their crystal structures, microstructures, valence states and dielectric properties are studied. The ceramics adopt a cubic perovskite structure, and the lattice parameter increases with doping content owing to the larger ionic radii of dopants. The complex permittivity and electric modulus as a function of frequency and temperature are analyzed. Dielectric relaxations without colossal permittivity are observed. The relaxation processes are thermally activated and their variations with temperature are analyzed. The activation energy values for the relaxation processes are determined by the Arrhenius relationship and increase with doping content. By analyzing the electric modulus, the activation values for high-frequency relaxation are found to be associated with the electrical properties of grain, and the contribution of grain boundary could be neglected based on internal barrier layer capacitor (IBLC) model. The electron hopping between the different Ti valences, which is confirmed by X-ray photoelectron spectroscopy, is supposed to play an important role in high-frequency relaxation. The permittivity plateaus are related to the inhomogeneous structures of grain and grain boundary, and the low-frequency permittivity plateau is attributed to the space-charge polarization at grain boundaries. By comparing with Cu/Nb co-doped BaTiO3, the absence of colossal permittivity is ascribed to high resistivity of the samples. Charge density and migration as well as the insulating grain boundaries are critical for the formation of space charge and a high permittivity.

Discontinuous yielding behavior, strengthening effect and deformation mechanism of double wall copper-brazed steel tube under various continuous sectional cooling

Unlike traditional cooling, continuous sectional cooling (CSC) consists of various cooling modes, which is of decisive significance to the microstructure and performance of double wall copper-brazed steel tube (DWBT). In this work, three CSC (CSC-A/B/C) processes are chosen to reveal strengthening and deformation mechanisms of DWBT. The results show that there are significant differences in discontinuous yield behavior, natural aging phenomenon, and tensile properties of the DWBT among three CSC processes due to diverse grain size and precipitates, but a similar texture is obtained due to Kurdjumov-Sachs relationship. For discontinuous yielding, the propagation velocity of Lüders band is a key factor to determine the yield point elongation (YPE), which reduces with decreasing grain sizes due to the interaction between dislocation and grain boundary. Thus, the CSC-C (1120 °C→4s940 °C…360 °C→16s110 °C) with small grains has a longer YPE. Meanwhile, the precipitation strengthening dominates the highest strength and lowest elongation of the CSC-A (1120 °C…100 °C) due to abundant MC carbides. Compared with CSC-B (1120 °C…170 °C), the yield strength of CSC-C is higher while ultimate tensile strength is lower, which is attributed to different contributions of precipitation and grain boundary strengthening to both. The MC carbide causes the natural aging of DWBT. Moreover, the geometrically necessary dislocations (GNDs) and low angle grain boundaries (LAGBs) raise linearly with strain. The GNDs prefer to be distributed in small grains, and uniform grain can weaken the difference of GNDs distribution in different grain sizes. The LAGBs including dense dislocation walls or microbands are formed by the grain subdivision mechanism.

Structural modifications, low temperature magnetic behavior and optoelectronic trends in A-site substituted spinel ferrites

MnxZn1-xFe2O4nanoparticles having cubic spinel phase were synthesized through chemical sol–gel method. The results showed a linear increase in crystallite size, lattice constant, packing factor, and number of unit cells per sample with x, following Vegard's law. High specific surface area (20.34–34.35 m2/g) has been observed which shows suitability for energy storage applications. Magnetic propertieswere improved, likely due to the blocking state of tiny nanoparticles. Switching in direct (4.26–5.12 eV) and indirect (3.03–4.63 eV) bandgaps and Urbach energy was observed at x = 0.5. Refractive index showedtunable trend against incident wavelength making the system a potential candidate for hetero-lasers and non-linear optics. Nyquist plot revealed a non-Debye relaxation phenomenon and the contribution of grain boundaries and grains. Variations in dispersion energy (2.61–30.49 eV), excitation energy (8.44–10.25 eV), optical spectrum moments (M−1: 0.3047 to 2.9757, M−3: 0.0041 to 0.0283 eV−2), and high frequency dielectric constants (1.30–3.98)have been observed.

Study of the effect of the substitution of Fe by Ti on the microstructure and the physical properties of the perovskite system La0.67Ca0.2Ba0.13Fe1-xTixO3 with x = 0 and 0.03 at low temperatures.

La0.67Ca0.2Ba0.13Fe1-xTixO3 samples (x = 0 and 0.03) were synthesized by the auto-combustion method. Analysis of XRD diffractograms revealed that these compounds crystallize in the cubic system with the space group Pm3̄m. The dielectric properties have been studied in the 102-106 frequency range and the 120-280 K temperature range. Analysis of AC conductivity shows that the conduction mechanisms are of polaronic origin and that they are co-dominated by the NSPT and OLPT models. The monotonic increase in conductivity with increasing temperature results from the reduction of defect centers and the increase in charge carrier mobility. Such variation is consistent with impedance variation at different frequencies and temperatures indicating semiconductor behavior. Nyquist diagrams are characterized by the appearance of semi-circular arcs. These spectra are modeled in terms of equivalent electrical circuits confirming the contribution of grains (Rg//CPEg) and grain boundaries (Rgb//CPEgb). The dielectric analysis showed an evolution of the dielectric constant in accordance with Koop's theory and the phenomenological model of Maxwell-Wagner. The low conductivity and the high values of the real permittivity at low frequency make our compounds potential candidates for energy storage and applications for electronic devices and microwaves.

Contribution of grain boundary to strength and electrical conductivity of annealed copper wires

The effect of grain boundaries on the strength and electrical conductivity of annealed copper wires was studied. After annealing at 100 °C for 30 min, the copper wires retained a fiber-like structure. The increase in electrical conductivity is believed to stem from the decrease of crystallographic defects introduced by drawing. Recrystallization occurred when the annealing temperature reached 150 °C. The formation of small recrystallized grains led to the introduction of additional grain boundaries perpendicular to the drawing direction, resulting in a slight decrease in electrical conductivity. When the annealing temperature rose up to 200 °C, complete recrystallization took place in the copper wires. The grain boundaries parallel to the drawing direction play an important role in boundary strengthening, while the grain boundaries perpendicular to the drawing direction play an important role in both boundary strengthening and electron scattering. The electrical resistivity of grain boundaries in fully recrystallized copper wires at room temperature was determined experimentally, and an empirical relation is proposed to quickly determine the electric conductivity of copper wires at room temperature based on the boundary spacing along the drawing direction.

Microstructural features and mechanical behavior of duplex stainless steel/low carbon steel friction stir dissimilar weld

This paper aims to understand the effect of friction stir butt welding on the microstructure and mechanical performance, measured in terms of hardness characteristics, transverse tensile test, and shear punch, of dissimilar weld of duplex stainless steel (DSS) and low carbon steel (LCS). The dynamic recrystallization, material intermixing, and atomic interdiffusion between DSS and LCS governed the microstructure of the stirred zone. The stirred zone was free from harmful intermetallic phases like the sigma phase. It was identified that three distinct metallurgical regions feature the stirred zone, including (i) dual-phase zone (DPZ) with an unbalanced fine duplex microstructure of austenite and ferrite, (ii) ferrite phase zone (FPZ) with fine-grained ferrite strengthened by an enhanced Ni and Cr content, (iii) martensite zone (MRZ), which was formed due to the formation of thermally unstable austenite at high temperatures due to Cr, Ni, and C interdiffusion between DPZ and FPZ. Furthermore, when LCS was positioned on the advancing side, a higher fraction of martensite was formed in the stirred zone due to the more efficient material mixing. The shear punch test indicated that the shear strength of the stirred zone in the dissimilar welds was ∼130% and ∼16% higher than that in the LCS and DSS base metals, respectively. The contributions of solid solution hardening and grain boundary hardening to the hardness/strength of the stirred zone were elucidated.

Studies of structural, dielectric and impedance characteristics of Gd modified Bi4Ti3O12 Aurivillius ceramic

The synthesis and characterization (structure, dielectric, electrical properties) of ceramic technology prepared gadolinium modified bismuth titanate of a composition Bi4-x GdxTi3O12 (x = 0, 0.1) have been reported in this paper. The development of a single-phase orthorhombic structure with a space group Aba2 has been confirmed by analysing room temperature X-rays diffraction (XRD) patterns. The plate-like microstructures of the samples are revealed by scanning electron microscope, which confirmed the layered perovskite structure of Bi4-x GdxTi3O12 (x = 0,0.1). The crystallite size (D) and strain (ε), calculated from the W–H (Williamson-Hall) plots, are found to be 64 nm, 0.001, respectively for BIT (bismuth titanate, Bi4Ti3O12) and 53 nm, 0.009, respectively for Gd modified BIT. Some obtained electrical parameters (dielectric constant, conductivity, electrical impedance, and modulus) of BIT and Gd modified BIT have provided useful data on the conduction mechanism, structure-properties relationship, etc. The Nyquist plots confirm the contribution of grain boundary and the bulk effect to the properties (physical) of the materials.

Small polaron hopping transport mechanism, dielectric relaxation and electrical conduction in NiAl2O4 electro-ceramic spinel oxide

In this study, the frequency and temperature dependent dielectric relaxation and electrical conduction mechanisms in NiAl2O4 spinel oxide ceramic have been explored in a frequency range of over a measured temperature from 163–283 K. The polycrystalline NiAl2O4 was synthesized via solid state reaction route and sintered at 1000 °C. The room temperature x-ray powder diffraction pattern confirmed the formation of NiAl2O4 spinel phase with Fd3m space group. The surface morphology of the sample was investigated by scanning electron microscopy and chemical properties by Fourier transform infrared spectroscopic analysis. Complex impedance studies revealed the presence of relaxation time distribution and charge carriers were found to be thermally activated. The Nyquist plots exhibited depressed semicircles and their fitting by an equivalent circuit model with configuration (RGCG)(RGBCGB) resolved the contributions of grains and grain-boundaries to the electrical transport properties of the material. Electrical conductivity analysis followed the Jonscher’s power law behavior and the frequency exponent suggested small polaron hopping as the governing transport mechanism in NiAl2O4 spinel oxide. Non-Debye type nature of dielectric relaxation was confirmed by the complex modulus analysis whereas dielectric constant and tangent loss analysis verified that the hopping mechanism was thermally activated.

Achieving High Strength and Good Ductility in a Nb-Containing CoCrNi-Based High-Entropy Alloy by Grain Boundary and Precipitates Strengthening

Face-centered cubic (FCC) high-entropy alloys (HEAs) have attracted considerable attention due to their excellent mechanical properties; however, an insufficient yield strength (YS) limits their widespread engineering applications. To improve the strength of FCC HEAs, the present work aims to develop fine-grained Nb-containing CoCrNi-based HEAs with precipitates. In the present work, a single-phase FCC CoCrNi1.5Nb0.2 HEA was processed by cold rolling followed by annealing at a higher temperature and aging at a lower temperature, yielding fine- and ultra-fine-grained FCC matrices and two types of precipitates: ultra-fine granular C15 Laves phase CoCrNb-based precipitates and ultra-fine lath-shaped D019-structured ε-Ni3Nb-based precipitates. The resultant alloy exhibits a combination of high strength (approximately 1409 MPa of yield strength) and good ductility (10.1% of uniform elongation). The contributions of grain boundary and precipitation strengthening to YS were analyzed and calculated. The mechanisms underlying good ductility were discussed.

The contribution of grain boundary sliding to the deformation in an ultrafine-grained Mg–Al–Zn alloy

The contribution of grain boundary sliding to the deformation in an ultrafine-grained Mg–Al–Zn alloy

Structural study and temperature dependent relaxation and conduction mechanism of orthorhombic tungsten bronze Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic

In this study, the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic was prepared using the solid-state technique. The X-ray diffraction technique was used in this study to investigate the Ba/La order in the solid solution Ba4La28/3(Zr0.05Ti0.95)18O54. We have developed a structural model, to represent the order within the structure. The formula of model [Ba4−a□a]A2[La8+2b3□2−2b3]A1,A1′(Zr0.05Ti0.95)18O54 is described as perovskite layers with a thickness of 3 octahedral parallel to the xOz plane. Scanning electron microscopy (SEM) showed that Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic exhibits a typical columnar grain with a heterogeneous distribution over the entire surface. Complex impedance spectroscopy was used to analyze the dielectric and electrical properties of Ba4La28/3(Zr0.05Ti0.95)18O54 materials over a frequency range of 10 Hz to 1 MHz and a temperature range of 350°C to 400°C. An appropriate equivalent electrical circuit was also used to investigate the contributions of grains and grain boundaries. The AC-conductivity data was analyzed using Jonscher's universal power law. The thermal behavior of the exponent parameter "s" indicates that the dominant conduction mechanism in our compound is the non-overlapping small polaron tunneling (NSPT) model. The activation energies calculated from the conduction and relaxation mechanisms are nearly identical for the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic.

Low-temperature dielectric relaxation mechanism and correlated barrier hopping transport in neodymium perovskite chromite

Herein, neodymium chromite (NdCrO3) has been synthesized by the sol–gel auto-combustion method. The Rietveld analysis of the X-ray diffraction pattern has shown that NdCrO3 crystalizes in the perovskite structure with orthorhombic unit cell and Pbnm space group symmetry. The electrical transport properties have been investigated by complex impedance spectroscopy over the experimental frequency and temperature ranging from 40 to 1 × 106 Hz and 158–283 K, respectively. The equivalent circuit modeling of Nyquist plots revealed the contribution of grains and grain boundaries to the charge conduction and the relaxation mechanism of NdCrO3, respectively. The AC conductivity analysis divulged the correlated barrier hopping transport mechanism in the NdCrO3. The imaginary electrical modulus spectra fitted by the Kohlrausch, Williams, and Watts function presented the non-Debye type nature of the relaxation mechanism in the material. The dielectric permittivity has exhibited the Maxwell–Wagner type polarization of the material, and the loss factor has exhibited an increasing trend with temperature.