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AC Impedance Spectroscopy, Conductivity and Optical Studies of Sr doped Bismuth Ferrite Nanocomposites
摘要： Effect of Sr doping on the structural, optical, dielectric, impedance properties of citrate combustion reaction route prepared Bi1-xSrxFeO3 (BSFO) nanocomposite has been investigated. The study of Fourier Transform Infrared Spectroscopy confirms the formation of perovskite structure of the Sr doped bismuth ferrite samples. SEM analysis shows decrease in grain size with increasing Sr concentration in BSFO nanocomposite. UV–visible absorption spectra in the spectral range 1.0–3.5 eV showed two doubly degenerate d–d transitions and two charge transfer transitions and optical band gap is found to decrease from 2.14 to 2.05 eV with increasing Sr concentration. Studies of frequency and temperature dependences of dielectric permittivity, impedance and electric modulus of the materials in broad frequency (20 Hz- 1 MHz) and temperature (30o C – 500oC) ranges using a complex impedance spectroscopy technique have provided interesting information on the contribution of the microstructure in these parameters. It has been observed that dielectric constant and dielectric losses decreases as the doping of Sr increased from x=0.1 to x=0.3 and attained a maximum value for BSFO (x = 0.1) sample. Impedance analysis indicates the presence of grain (bulk) and grain boundary resistive contributions which are found to increase with the increased Sr content. The ac conductivity of the samples is found to be frequency and temperature dependent and also vary with extent of Sr doping in BFO. Charge transport through short as well as long range conduction contributions has been indicated in different temperature regions of conductivity studies.
关键词： dielectric response,complex impedance spectroscopy,microstructure,Bismuth ferrite
更新于2025-09-23 15:21:01
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Terahertz and Infrared Spectroscopy of Dense and Porous Organosilicate Glass Thin Films
摘要： Wide-range measurements of thin films of SiCxOyHz organosilicate glasses, both dense and porous, deposited on dielectric sapphire substrates and conductive layers of platinum and aluminum, were performed in the THz–IR (5–5000 cm–1) range. This method can be used not only to analyze the evolution of absorption bands in amorphous dielectric films but also to evaluate static conductivity in the framework of the Drude model of conductive layers and to determine the electrodynamic characteristics of organosilicate films with low dielectric permittivity. The original approach proposes a comprehensive analysis of experimental broadband data in order to determine not only the parameters of the individual bands of lattice and molecular vibrations but also the integrated electrodynamic characteristics of the samples obtained.
关键词： simulation of dielectric response spectra,terahertz and infrared spectroscopy,thin films,low-k materials
更新于2025-09-23 15:21:01
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Mn-doping composition dependence of the structures, electrical and magnetic properties, and domain structure/switching of Aurivillius Bi5Ti3FeO15 films
摘要： Mn-doped Bi5Ti3FeO15 (BTFO) ?lms were prepared by a chemical solution deposition route. The e?ect of a series of di?erent Mn-doping concentrations from 0.05 to 0.4 on structures, electrical and magnetic properties, and domain structure/switching was systematically studied. Mn-doping into BTFO can avail the grain growth. Ferroelectric and dielectric properties are improved through Mn-doping, and the optimized Mn-doping content is 0.25 with remnant polarization of 17.2 μC/cm2 and permittivity of 371.2 at 10 kHz. Moreover, similar evolution of the permittivity and loss tangent with frequency to that of parent BTFO ?lms appears in the BTFMO ?lms when Mn-doping content is below 0.25, while obvious dispersion phenomena is demonstrated with further increasing Mn-doping content. A 180° domain structure and local ferroelectric switching are observed in all these Mn-doped BTFO thin ?lms, and the piezo-displacement can reach 416 p.m. in 0.15 Mn-doped BTFO ?lm. Finally, ferromagnetic properties appear in all these Mn-doped BTFO thin ?lms. The coercive ?eld shows weak temperature independence on Mn-doping contents, while the remnant magnetization is raised by Mn-doping.
关键词： Domain structure and switching,Dielectric response,Magnetic property,Ferroelectric property,Aurivillius compounds,Element doping
更新于2025-09-19 17:15:36
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Effect of yttrium insertion on the structural, optical, vibrational and dielectric properties of 0.3Bi1?yYyFeO3–0.7Ba0.8Sr0.2TiO3 ceramics
摘要： Perovskite ceramics [Ba0.8Sr0.2]1-x[Bi1-yYy]xTi1-xFexO3 with x = 0.3 and 0.05 \ y \ 0.15 are synthesized by solid-state solution in order to study the effect of yttrium insertion on the physical properties of this material. The XRD patterns showed the formation of single tetragonal phase without any impurities. Using UV–Vis spectroscopy, the absorbance and re?ectance are highlighted. In fact, we note a blueshift on wavelength and the energy band gap is increased with a high doping content. Besides, Raman spectra display a drop in mode intensities, which is followed by the rise of yttrium that can lead to a ?uctuation in the atomic structure. Furthermore, the permittivity and loss dielectric are studied by impedance spectroscopy, revealing that both decrease with rising frequency indicating, as a result, a dielectric dispersion. Finally, the study of permittivity dielectric as a function of temperature exhibits the presence of G-type antiferromagnetic transition.
关键词： Structural analysis,Ba0.8Sr0.2TiO3,Dielectric response,Optical properties,Solid-state reaction,BiFeO3,Raman spectra
更新于2025-09-19 17:15:36
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An approach for the calculation of local dielectric properties in nanosized systems on the basis of coupled dipoles method
摘要： Despite interest in a description of nanoscale systems properties, there is still a lack of methods that can grasp size dependence and variation across the interface of the static dielectric properties. We propose an approach for the calculation of local nanoscopic electric susceptibility and dielectric permittivity tensors in nanosized systems on the basis of the coupled dipoles method. Requiring only the polarizability of individual molecules, this approach allows one to determine the local dielectric properties of arbitrarily shaped nanoparticles as well as (semi)infinite bodies such as bulk material and infinite films, expanding our ability to predict and govern the behavior of nanoscale systems.
关键词： Boundary layers,Coupled dipoles method,Dielectric response,Permittivity anisotropy,Nanoparticles
更新于2025-09-16 10:30:52
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Dielectric response function for colloidal semiconductor quantum dots
摘要： We calculate the optical properties of InP and CdSe colloidal quantum dots (QDs) within the framework of the atomic effective pseudopotential approach and the screened configuration interaction theory. We obtain an excellent agreement with experiment with our microscopic and space-dependent screening function where the dielectric constant varies in real space with a sharp transition (width of ≈0.18 nm) from the QD material high-frequency bulk value inside the QD to the solvent or passivant high-frequency value outside. We obtain a reasonable agreement (with deviations less than 140 meV) for a computationally less demanding solvent-independent screening using the full high-frequency bulk screening, in contrast to the more commonly used reduced QD radius-dependent screening constant. We show theoretically that for QDs passivated with long-chained organic molecules, the influence of the solvent on the optical gap is in the range of 10 meV, while QDs passivated with short ligands can experience shifts in the order of 100 meV. Experiments on CdSe QDs passivated with octadecylphosphonic acid (ODPA, long-chained ligand) in two different solvents (toluene and chloroform) confirm the bandgap dependence. While the optical gap is weakly affected by the environment, the quasiparticle gap and the exciton binding energy show a strong environmental dependence. Finally, we show that the optical bandgap does not depend significantly on the crystal structure (wurtzite or zincblende) or the morphological details (faceted or “spherical” shape).
关键词： optical properties,dielectric response function,screened configuration interaction theory,pseudopotential approach,colloidal quantum dots
更新于2025-09-12 10:27:22
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Structural, Dielectric and Impedance Spectroscopic Studies on Fe Doped BaTiO <sub/>3</sub>
摘要： Compositions with x=0.03, 0.05 and 0.10 are synthesized in the system BaFexTi1–xO3 using conventional solid state reaction method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). XRD patterns reveal the coexistence of tetragonal and hexagonal phases which are strongly affected by the level of Fe doping. The hexagonal phase increases with increasing x, being maximum for x=0.10. SEM images show the presence of agglomerated grains which increase in size with amount of Fe doping. SEM for x=0.10 shows mostly rod-like or rectangular grains indicating predominantly hexagonal phase. Dielectric and impedance measurements have been carried out in the frequency range 20 Hz-1 MHz as a function of temperature (300-650 K). The samples with x=0.03 and 0.05 exhibit diffuse phase transition. Using complex impedance analysis equivalent circuit models have been developed which represent the data well and successfully separate out the contributions of tetragonal phase, hexagonal phase, grain boundaries and electrodes.
关键词： Impedance spectroscopy,Fe doped BaTiO3,Dielectric response,Diffuse phase transition
更新于2025-09-09 09:28:46
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Particle size effect on the dielectric properties of ZnO nanoparticles
摘要： Zinc oxide (ZnO) nanoparticles with di?erent particle sizes were synthesized by thermal annealing T A of zinc hydroxide at various temperatures. X-ray di?raction measurements show that all nanoparticles possess a typical wurtzite structure and no other impurity phases are observed. The average particle size (d ) increases from 22 to 98 nm as T A increases from 100 to 850?C. The dielectric properties of nanocrystalline ZnO with various particle sizes were studied in the frequency range of 20 Hz to 1 MHz between 80 K and 320 K. Dielectric measurement indicates that the particle size of samples has great in?uence on the dielectric behavior of ZnO nanoparticles. The M ” curves show strong grain peaks in all ZnO nanoparticles, whereas only 22 nm and 98 nm particles show weak grain boundary peaks. In addition, the ac conductivity (σac) follows Jonscher,s power law for all ZnO nanoparticles, but two types of conduction mechanisms were observed. It is concluded that the σac behavior of 22-nm particles is well accounted by the correlated-barrier-hopping model (CBH), whereas the d >22-nm particles behavior is probably due to Quantum Tunneling Mechanism (QMT). The di?erent σac behavior can be attributed to the various defects in grain boundary and formation of inhomogeneous dielectric structures.
关键词： A. Oxide materials,C. Grain boundaries,B. Precipitation,D. X-ray di?raction,C. Dielectric response,A. Semiconductors
更新于2025-09-09 09:28:46
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Dielectric, electrical and impedance study of single perovskite Pb(Ni1/3Mn1/3W1/3)O3
摘要： A multiferroic material Pb(Ni1/3Mn1/3W1/3)O3 with ferroelectric and ferromagnetic properties at room temperature is designed for multifunctional applications. A orthorhombic perovskite crystal structure has been assigned for the present perovskite according to the X-ray diffraction patterns. At 1 kHz, dielectric constant (er) increases from 1655 at 298 K to its ?rst maximum 3514 at 457 K referred as magnetic transition. The high values of er in the low frequency range show better dispersion, and with the increase in frequency, a gradual decrease in the er values was observed. The contribution of grain and/or electrode/interface effects in the resistive/capacitive properties was ascertained by the Nyquist plots. An equivalent circuit has been suggested consisting of resistive and capacitive components (R, C, Q) estimates the bulk (grain) and grain boundary resistance and capacitance. The activation energy was found to be greater than 0.2 eV, supporting the conduction mechanism due to hopping of charge carriers.
关键词： Solid-state reaction,Multiferroic material,Dielectric response,Electrochemical impedance spectroscopy,Ceramics
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Budapest (2018.7.1-2018.7.5)] 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Characterization of LDPE-Metal Oxide Nanocomposites Using Thermo-Analytical and Spectroscopic Techniques
摘要： Polyethylene metal oxide nanocomposites find their application as high voltage insulation for direct current cables, to mitigate the space charge and other issues. Nano particles like SiO2, MgO, ZnO etc are used as filler materials in polyethylene matrix to achieve good electrical and mechanical properties like: space charge reduction, enhanced surface & volume resistivity and higher dielectric stress withstand capabilities. Surface modification of metal particles is usually done by treating the nanoparticles with silane to have good distribution and dispersion of metal particles. However, characterization of nanocomposite based on spectroscopic and thermo-analytical techniques is very essential to understand its long term performance and its reliability when used as insulation in HVDC extruded power cables. Different metal oxide nanoparticles such as MgO and SiO2 have been investigated as fillers in low density polyethylene. The distribution and dispersion of the nanoparticles in the LDPE is determined by SEM (Scanning Electron Microscopy). Kinetic studies were carried out by measuring enthalpy, melting temperature, percentage decomposition using simultaneous thermal analyser. Fourier Infrared spectrometer, X-ray diffractometer and dielectric spectrometer are used for characterization and dielectric response. The results are presented and discussed.
关键词： LDPE,Dielectric response,Polyethylene-metal oxide nanocomposite,HVDC cable insulation
更新于2025-09-09 09:28:46