Journal of Electroceramics最新文献

Ultrafine ceramic powders with high tetragonality are the fundamental for the multi-layer ceramic capacitors (MLCCs). In this study, an efficient method of atmospherically hydrothermal assisted solid-state synthesis for ultrafine BaTiO₃ particles is presented. The BaTiO₃ nanopowders with homogeneous distribution, a mean particle size ~ 260 nm and high tetragonality of 1.0095 were obtained by at the optimal parameters of hydrothermal time of 6 h, Ba(OH)₂·8H₂O/BaCO₃ = 0.25/0.75 and calcination temperature of 1000 ^oC. XRD and HRTEM analyses revealed a “core-shell” structure of TiO₂@BaTiO₃ formed in the first-step hydrothermal process, which reduces the diffusion distance between BaCO₃ and TiO₂, resulting in a lower calcination temperature at the second-step solid-state reaction. Compared with pure hydrothermal and solid-state reaction processes, the atmospherically hydrothermal assisted solid-state synthesis in this study shows larger ability for improving the particle size distribution and the tetragonality, reducing defects of BaTiO₃ particles. In particular, the grain size, sintering density, and dielectric constant at the Curie temperature of BaTiO₃ ceramics are 1.93 μm, 98%, and 7066, respectively. In the solid-state reaction stage, the lattice diffusion distance from BaO to TiO₂ tends to decrease due to the formation of BaTiO₃ shells, thus, high tetragonal and relatively small particle size of BaTiO₃ powder was synthesized. This work presents a method for preparing ultrafine BaTiO₃ powders with large tetragonality for MLCCs.

The preliminary structural and frequency-temperature dependence of dielectric and electrical characteristics of Ba/Zr modified Bismuth ferrite(BiFeO₃) i.e.(Bi_1-xBa_x)(Fe_1-xZr_x)O₃; x = 0.05, 0.1, 0.15, 0.20 at room temperature have been reported. The samples are produced in a perovskite rhombohedral structure, according to the X-ray diffraction pattern and analysis of room temperature XRD data. The SEM photographs are useful for the micro-structural view of the synthesized compounds. Dielectric and electrical characteristics across a wide temperature range 25 °C to 300 °C at different frequencies ranging from 1 kHz to 1 MHz have provided many important results including dielectric dispersion, conduction mechanism, relaxation process and ferroelectricity of the prepared samples. The contributions of grains and grain boundaries towards the net resistance and capacitance of the samples are found from the Nyquist plots. The types of conduction mechanism have been studied from ac-conductivity study of the samples. The Ohmic behaviour is verified by the J–E characteristics of the prepared samples, which have a slope closer to 1. The electrical polarization study through hysteresis loops at room temperature confirms the ferroelectric behavior of the studied materials. According to the experimental results obtained here, the synthesized materials could be beneficial as electronic components in the electronic industries.

In this work, it was aimed to synthesize and characterize rare earth metal-free cerium-based electrolytes that might be used in solid oxide fuel cells (SOFCs) by doping calcium, strontium, or magnesium to CeO₂. For this purpose, CeO₂, Ca_xCe_(1-x)O_(2−δ) (0.16 ≤ x ≤ 0.24), Sr_xCe_(1-x)O_(2−δ) (0.02 ≤ x ≤ 0.08) and Mg_xCe_(1-x)O_(2−δ) (0.07 ≤ x ≤ 0.13) were prepared by using citrate-nitrate combustion method. The solubility limits, microstructural and physical properties of the samples were characterized with XRD, SEM, TG-DTA and impedance analysis. It was found that all samples were in fluorite structure similar to the undoped ceria. The solubility limits of Ca²⁺, Sr²⁺ and Mg²⁺ were 21%, 6% and 12% (by mole) respectively based on XRD analysis results. The relative densities of sintered pellets at 1400 °C were more than 90%. Electrochemical impedance spectroscopy analysis, in which the ionic conductivities of the samples were measured, revealed that the Ca_0.2Ce_0.8O_2-δ (CCO20) sample sintered at 1400 °C showed the highest ionic conductivity value of 4.47 x10^-2 S.cm⁻¹ at 800 °C. It was determined that the O^2- ion conductivity decreased with the order of Ca²⁺ ≈ Sr²⁺ >> Mg²⁺. Conductivities increased with increasing dopant ratio, reached a maximum below the ratios of solubility limits, and then decreased. The obtained results showed that Ca or Sr doped electrolytes prepared by the citrate-nitrate method can show ionic conductivities close to the state-of-the-art Sm doped Ceria electrolytes. It has been determined that Mg doping is quite ineffective.

The preparation of CuCo₂O₄ material with a suitable phase structure and grain size can improve its lithium storage performance. In this paper, CuCo₂O₄ hexagonal nanocrystal were successfully obtained by molten salt modified urea combustion method. Compared with the traditional high temperature solid state methods such as combustion method, rheological phase method and precipitation method, this method maintains the advantage of simple operation, and the particle size of the sample is smaller. The effect of heat treatment temperature on the lithium storage performance of CuCo₂O₄ was also studied systematically in this paper. The result shows that 800 ℃ is the best heat treatment temperature for CuCo₂O₄, and the sample synthesized by the molten salt urea combustion method exhibited the best electrochemical properties with a specific capacity of 705 mA h g^-1 after 100 cycles under a constant current of 200 mA g^-1 in the voltage range of 0.01-3 V. Therefore, a new strategy of high temperature solid state preparation has been developed in this paper, and the CuCo₂O₄ synthesized by this method is a promising anode material for lithium ion battery application.

The present study aimed to verify the experimentally obtained results by exploring the several properties of the material (i.e. magnetic, structural, and direct current (DC)-electrical properties). Trivalent rare-earth element samarium (Sm³⁺)doped barium spinel ferrites BaSm_xFe_2−xO₄ for compositions with the following x values: 0, 0.025, 0.05, 0.075, and 0.1 were subjected to the sol-gel procedure for processing. All of the samples, according to X-ray diffraction (XRD) investigation, developed a structure with a single phase that is cubic. The structural parameters, including lattice constants, crystalline size (nm), densities (bulk and X-ray), and unit-cell volume, were observed. The semiconductor natureof the prepared materials was demonstrated by the use of two-probe tests to estimate DC resistivity (ρ_dc), Curie temperature (T_c). Ferromagnetic materials’ properties resemble remenance (M_r), coercivity (H_c), saturation magnetization (M_s), and changes that resulted from the insertion of Sm³⁺ was injected in the M-H condition (magnetization-applied field) loops are assigned to each individual nanoparticle. It’s been discovered that the evolution of the anisotropic constant is kind of analogous to those of the coercivity. The current synthesized barium ferrites have been confirmed to really be useful as in manufacturing of high-density magnetic storage applications.

The 0.9Mg₂SiO₄-0.1CaTiO₃ (MSCT) ceramics with 60ZnO-20B₂O₃-20SiO₂ glass (ZBS) and LiF compound additives were prepared by solid-state reaction method. The effects of different ZBS contents on the phase, densification temperature, surface morphology and dielectric properties of MSCT ceramics were studied. The results show that ZBS can inhibit the reaction between LiF and CaTiO₃, which improve the surface morphology and reduce the sintering temperature of MSCT ceramics. The sample of MSCT with 2wt%ZBS-1.5wt%LiF sintered at 900 °C for 90 min shows excellent microwave dielectric properties: ε_r = 9.26, Q × f = 68,580 GHz (at 15.5 GHz) and τ_f = -1.49 ppm/ °C. There is no obvious element diffusion at the co-firing interface between dielectrics and Ag electrodes, indicating it is a promising candidate for LTCC applications.

Traditional Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ based relaxor ferroelectrics have attracted much attention. However, the relatively low T_m restricts their application in the high temperature range. In the present study, a novel (0.8-x)Bi(Mg_1/2Ti_1/2)O₃-xPbTiO₃-0.2PbZrO₃ ((0.8-x)BMT-xPT-PZ) relaxor ferroelectric based on the high temperature BMT-PT piezoelectrics was designed. All samples exhibit pure perovskite structures and the phase structures show a gradual transition from relaxor rhombohedral (R) to normal tetragonal (T) phases via the morphotropic phase boundary (MPB) in the composition range x = 0.36–0.39. The dielectric relaxation behavior can be observed in all samples although a spontaneous normal-relaxor ferroelectric transformation is observed in the T phase region. The x = 0.38 sample exhibits the optimal overall electrical properties with the d₃₃ value of 325 pC/N, the k_p value of 0.38, the T_m value of 290 ^oC. The results indicate that the present studied ternary system has a good potential as high temperature relaxor ferroelectrics.

In this article, the actuating performance for functionally graded piezoelectric materials (FGPM) using the (d_{33}) mode actuation is investigated. The material properties vary continuously across the thickness direction, according to a fraction volume power law distribution, so that top and bottom surfaces consist of pure PZTG and the mid surface is composed of pure aluminium. The percolation phenomenon is taken into account. The optimization of the interdigitated electrode (IDE) design for FGPM is performed using finite element analysis. Several design parameters (electrodes number, width and spacing) are considered to improve the produced displacement for a cantilever plate, and the use of multilayered IDE is intended. Results are discussed for several distributions of the components in the FGPM thickness. A comparison with the (d_{31}) mode actuation is presented.

Poly (vinylidene fluoride- hexafluoroproylene) PVDF-HFP has been employed as a host polymer because of its strong chemical resistance, mechanical and dielectric properties and low cost. However, further changes employing other polymers, nanomaterials, additives and fillers to improve the properties of the host polymers are of significant interest. TiO₂ has gained a lot of attention because of its high k dielectric and photo catalytic capabilities. Graphene oxide (GO) has received a lot of attention because of its larger mechanical strength, dielectric behavior and other qualities. Using the doctor blade coating process, varied amounts of TiO₂ and GO were successfully integrated into PVDF-HFP to form composite films. The XRD result reveals that TiO₂/GO has been successfully incorporated into the PVDF-HFP polymer matrix, while FTIR, SEM experiments have demonstrated the effectiveness of TiO₂/GO fillers on PVDF-HFP film. AC impedance spectroscopy reveals the dielectric behavior and resistivity of polymer nanocomposite film. The film has been tested for its loading bearing capacity during electroadhesion with different applied voltages. The maximum load bearing capacity based on electroadhesion has been estimated.

Graphical abstract

The structural, vibrational and microwave dielectric properties of xBa(Zn_1/3Ta_2/3)O₃ - (1-x)La(Zn_1/2Ti_1/2)O₃ [x = 1, 0.7, 0.5, 0.3 and 0] are investigated. The materials are synthesized by the solid-state reaction technique. The crystal structure of the materials is obtained from the Rietveld refinement of the X-ray diffraction (XRD) profile. All other materials except Ba(Zn_1/3Ta_2/3)O₃ (x = 1) are crystallized in monoclinic P2₁/n symmetry. The crystal structure of Ba(Zn_1/3Ta_2/3)O₃ is trigonal with P-3m1 space group. The vibrational properties of the materials obtained from Raman spectroscopy are correlated with the structural parameters. The microwave dielectric constant ε_r is maximum for x = 0.5 whereas the quality factor Q.f is maximum for x = 1. The effects of vibrational and structural parameters on the microwave dielectric properties are discussed in detail. The dielectric relaxation and the Ac conductivity of the materials are also studied using the alternating current impedance spectroscopy in the frequency range from 50 Hz to 5 MHz.