Journal of Electroceramics最新文献

Bayesian calibration is a powerful tool for measurement techniques that involve the estimation of physical parameters via calibrating (or “fitting”) a model to an experimental dataset. In contrast to optimization techniques, which produce a ’point estimate’ of the parameters devoid of uncertainty quantification, Bayesian calibration returns a distribution on the parameter space, revealing the extent to which each parameter can be considered well-estimated as well as any confounding uncertainty in multi-parameter calibration. This article covers the basic theory along with the practicalities of implementation for Bayesian calibration, linking these principles to a new open source software package for Bayesian calibration of electrical conductivity relaxation and isotope-exchange / secondary ion mass spectrometry measurements.

The effect of Sr²⁺ doping on electrical conductivity and dielectric constant was studied in Y_2 − xSr_xNiMnO₆ (YSNMO). Rietveld refinement of XRD data showed the coexistence of monoclinic (P21/n) and rhombohedral (R(bar 3)) as major and minor phases, respectively. Impedance analysis of YSNMO was performed to investigate the presence of various electro-active regions, electrical conduction mechanisms and the origin of the colossal dielectric constant in wide temperature (83-303 K) and frequency (40 Hz-6 MHz) ranges. An equivalent circuit model (R_gC_g)(R_gbQ_gb)(R_eQ_e) has been proposed to correlate the electrical properties. The R_g and R_gb obtained using ZView fitting revealed the semiconducting nature of the sample. The transition in the conduction mechanism from variable range hopping to small polaronic hopping was observed at about 213 K. DC bias measurements, which followed the Mott-Schottky law, confirmed the existence of non-Ohmic electrode contact. The dielectric spectra of ceramic were described using the modified Cole-Cole equation. The frequency dependent ac conductivity was investigated with the Jonscher’s power law.

This study investigated the effects of CaTiO₃, BaTiO₃, and BaZrO₃ doping on the phase transition and strain properties of lead-free 0.76Bi_1/2Na_1/2TiO₃-0.24SrTiO₃ (BNT-24ST) piezoceramics. The nonergodicity of the BNT-24ST ceramic was stabilized as a function of CaTiO₃ doping, corresponding to the existence of the ferroelectric-to-relaxor phase transition temperature (T_F-R) peak in the dielectric permittivity curves of the samples. However, the BaTiO₃- or BaZrO₃- doped NBT-24ST samples promote the transition from a nonergodic to an ergodic relaxor phase. The 0.01 mol BaTiO₃ or 0.01 mol BaZrO₃ doping decreases the T_F-R peak of the NBT-24ST sample to below room temperature. Interestingly, it is noted that the nonergodic-to-ergodic relaxor phase transition of the BaTiO₃-doped BNT-24ST ceramics was faster than that of the BaZrO₃-doped BNT-24ST ceramics. The 0.01 mol BaTiO₃-doped BNT-24ST sample presents a maximum dielectric constant of ~ 8000. The maximum piezoelectric actuator coefficient (uni-S_max/E_max) of ~ 525 pm/V was observed for the 0.01 mol BaTiO₃-doped BNT-24ST ceramic. The effect of the tolerance factor on the phase transition and electrical properties of the BNT-24ST-ABO₃ ceramics is suggested.

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering.

In this study, Zinc oxide nanoparticles are synthesized by the sol-gel method. The as-synthesized nanoparticles are characterized by X-Ray Diffraction, Scanning Electronic Microscope, Transmission Electronic Microscope, Atomic Force Microscope, Fourier-Transform InfraRed and Ultraviolet-Visible spectroscopies. In a structure-properties relationship, an important part of our work is devoted to a theoretical study by the Density Functional Theory method. The structural analysis shows that the particles have a polycrystalline hexagonal structure (P6₃mc). The morphological characterization revealed the formation of agglomerates of Nanoparticles in the range of 20-60 nm. The optical study shows the of absorption spectrum and optical bandgap 3.31 eV. The studies of electronic structure, and the linear and nonlinear optical parameters, explain where the response of Zinc Oxide nanoparticles comes from. All obtained results confirm the multifunctionality of Zinc Oxide in its nanoscale form, whether for optoelectronics and photonic applications.

Novel ultra-low loss NaLn(WO₄)₂ (Ln = La (NLW), Nd (NNW), Sm (NSW)) (NLnW) microwave dielectric ceramics were prepared by a reaction sintering method. The sintering process of the samples was investigated by TG-DSC. XRD refinement and Raman spectra results ascertained that the NLnW ceramics have scheelite structure with space group of I4₁/a. The microwave dielectric properties of NLnW ceramics and the relationship between the structure and performances were studied. The relationship between lattice vibration and Qf were analyzed by Raman spectroscopy. Especially, the NSW ceramics sintered at 1100 ℃ for 4 h show outstanding microwave dielectric properties of ε_r = 10.07, Qf = 73,734 GHz (at 12.21 GHz), τ_f = -42.6 ppm/°C, which providing a promising application in fifth generation communications.

The dielectric constant of material ultimately decides the level of miniaturization in electronic devices based on capacitive components and the development of wireless communications technologies operating at microwave frequencies. Similar to well-known PZT type high k (dielectric constant) Ferroelectrics, Ti⁴⁺ ion doping is tried here in a novel Trirutile CoNb₂O₆ lattice as smaller Ti⁴⁺ can vibrate from its mean position in Trirutile octahedral resulting in the net polarization in the octahedral that can result in high k dielectricity and overall can turn Trirutile into a new family of ferroelectrics. Single phase Ti substituted Trirutile CoNb₂O₆ ceramic were synthesized for the first time by solid-state ceramic synthesis route and Phase purity and substitution of Ti⁴⁺ ions in CoNb₂O₆ Trirutile lattice was confirmed using Powder x-ray diffraction (XRD), Scanning Electron Microscope(SEM), and Energy Dispersive X-ray analysis (EDX), X-ray Photoelectron Spectroscopy (XPS). Both dielectric constant and dielectric loss were decreasing with increasing frequencies. Ti⁴⁺ substitution in the Trirutile CoNb₂O₆ lattice enhances the dielectric constant of the material. The dielectric constant (ɛ_r′) for CoNb₂O₆ was found to be 500, CoNb_1.95Ti_0.05O₆ is 700 and CoNb_1.9Ti_0.1O₆ is 14,000 respectively at 100 Hz frequency at 200 ^oC and then decreases, it clearly shows the relaxor type behavior. Samples also exhibit ferroelectric behavior with remnant polarization Pr and Vc at 50 Hz frequency equal to 0.05 µC/cm² and 8e + 03 V/cm for CoNb_1.95Ti_0.05O₆ and 0.05 µC/cm² and 10e + 03 V/cm for CoNb_1.9Ti_0.1O₆.

Nb-modified lead-free ceramics (K_0.48Bi_0.52)(Mg_0.02Ti_0.98−xNb_x)O₃, (KBT-BMTNbx with x = 0.00 − 0.05) were synthesized by a conventional solid-state reaction route followed by furnace cooling. The effects of Nb-doping on the structural properties and electrical properties of KBT-BMTNbx ceramics have been investigated. The X-ray diffraction pattern indicates a mixed tetragonal and cubic phase for the pure KBT-BMTNbx ceramics. Therefore, a large piezoelectric actuator coefficient d₃₃^* ≈ 700 pm/V, piezoelectric sensor coefficient (d₃₃ ≈ 133 pC/N) along with remnant polarization (P_r ≈ 17.5 µC/cm²), maximum electromechanical strain ≈ 0.35% and maximum temperature (T_m ≈ 336 ºC) were obtained for KBT-BMTNbx. However, with Nb-doping, a compositionally driven phase transformation occurred from mixed rhombohedral and tetragonal phases to cubic phase. Because of the excess Nb-doping in the KBT-BMT ceramics, the grain size suddenly decreased, as a result, the long-range ferroelectric phase was converted into a short-range relaxor phase. Hence, a low dielectric loss tanδ ≈ 0.02 was achieved at x = 0.02 composition. This superior dielectric performance is correlated to the crystal structure morphotropic phase boundary, optimum grain size (≈ 2 μm), maximum lattice distortion, and soft-ferroelectric effect induced by the donor doping. The main aim of recent research is to investigate P_r, d₃₃, d₃₃^*, S_max, and reduced tanδ for practical applications in the real world.

The substitution of Dy³⁺ ions in the M-type hexaferrite structure has been successfully synthesized by sol-gel combustion method according to the formula SrDy_xFe_12-xO₁₉ (x = 0.0, 0.08, 0.16, 0.24, 0.32, and 0.40). The XRD analysis confirmed the formation of single-phase M-type hexagonal structures up to x = 0.24 compositions. The average crystallite size for the SrDy_xFe_12-xO₁₉ samples ranges from 90.64 to 290.04 nm, whereas the value of the lattice parameters 'a' and 'c' vary from 5.8590 - 5.8879 Å and 22.9675 - 23.0761 Å, respectively. Scanning electron microscopy (SEM) was used for morphological analysis. Due to ceasing effect of polarization, the dielectric constant decreases in the higher frequencies. The SrDy_xFe_12-xO₁₉ hexaferrites exhibit non-Debye type dielectric relaxation behavior confirmed by complex impedance spectroscopy (CIS) investigation. The SrDy_xFe_12-xO₁₉ samples can be utilized as a promising material for various device applications due to a decrease in dielectric loss and an increase in dielectric constant with increasing Dy³⁺ ions concentration.

Barium titanate ceramics with A- site and B-site substitutions are intriguing alternative to lead-based Pb (Zr, Ti) O₃ (PZT) because of its comparable properties to soft-PZTs. In this paper, (Ba_xCa_1-xSn_0.09 Ti_0.91) O₃ (x = 0.0525, 0.0575, 0.060) ceramics are prepared using a solid-state reaction technique followed by microwave sintering at 1350 °C for 30 minutes. Structural and electrical properties are investigated. X -ray diffraction shows that the compositions exhibit a tetragonal crystal structure having P4mm symmetry. Temperature dependent dielectric constant measurements in the temperature range of 25 °C to 120 °C shows high dielectric constant of 26250 at 40kHz for BCST ceramics with x=0.0525 and the Curie temperature T_c increases with Ca concentration. The results of dielectric measurements as a function of frequency are also reported. The dielectric loss (tan δ) values in the temperature range 25 °C to 120 °C are observed to be less than 0.03, for all BCST ceramics. The AC conductivity, impedance spectroscopy studies and the conduction mechanism on the basis of Arrhenius plot are discussed in the above-mentioned temperature range.