Journal of Electroceramics最新文献

Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃-x wt% CuO (BCZT-xCu) lead-free piezoelectric ceramics were designed and synthesized using a traditional solid-state reaction method to improve both the relaxor behavior and the electrical properties of BCZT lead-free piezoelectric ceramics. The Cu²⁺ diffuses into the BCZT lattice and forms ABO₃ perovskite solid solution. Additionally, X-ray diffraction patterns and Raman spectra reveal that the introduction of CuO causes phase transition from the O-T phase coexistence to the O phase in BCZT-xCu. SEM displays that BCZT-xCu has a well microstructure at CuO doping amount between 0.5 wt% and 1 wt%. With the increasing CuO content, the orthorhombic-tetragonal (T_O-T) phase transition shifted towards higher temperature, while Curie temperature (T_c) shifted towards lower temperature. Moreover, the dielectric diffusivity γ increases from 1.63 to 1.92 as x increases. Results indicate that optimal electrical properties, namely d₃₃ = 315 pC/N, k_p = 34%, ε_r = 3213, tanδ = 2.71%, P_r = 7.45 µC/cm² and E_c = 2.75 kV/cm are achieved in the 1 wt% CuO added ceramic sintered at 1250°C for 2 h.

Piezoceramic composition (1-z) (0.67Bi_1.05FeO₃–0.33BaTiO₃)–zBi(Mg_0.5Zr_0.5)O₃ (z = 0.00−0.10) were framed in this work. Regular firing technique succeeding by quenching method was applied. Effect of Bi(Mg_0.5Zr_0.5)O₃, abbreviated as BMZ, modification on structural and electrical properties were systematically analyzed. A large-field piezoelectric coefficient (S_max/E_max = d₃₃*) of 560 pm/V at 4 kV/mm and relatively small hysteresis (~ 28%) were obtained. The possible enhancement in strain, d₃₃ and P_r values near the optimal compositions z = 0.060, 0.080 can be ascribed to the augmented anharmonicity of lattice vibrations that may facilitate the flexiblity (at unit cell level) of these narrow compositions and triggers the enrichment of piezoelectric properties. A large piezoactuation constant with relatively low hysteresis loss and high working temperature (T_m around 415 ^οC) without unwanted depolarization temperature T_d made the investigated piezomaterial promising for the ceramic actuators’ applications. Unlike BNT-based systems, where mixed ergodic relaxor (ER) and nonergodic relaxor (NR) states are supposed to generate high strains, in the present BF-based ceramics, based on obtained results, BMZ-modified BF-BT materials are hypothesized to spontaneously switch from a high-temperature ER state to a ferroelectric state without transitioning to an intermediary NR state.

The flake alumina filler is added to improve the bending strength in BaZrO₃ (BZ)/BaO-MgO-ZnO-SiO₂-B₂O₃ (BBSMZ) glass for the application of low temperature co-fired ceramics. The effects of flake alumina filler for BaZrO₃/BaO-MgO-ZnO-SiO₂-B₂O₃ on phase, microstructure, dielectric and mechanical property are studied. With the increase of flake Al₂O₃ content, flake Al₂O₃ phase appears, BaZrO₃, BaZr(BO₃)_2, BaZn₂Si₂O₇ phase decreases, dielectric constant decreases and dielectric loss increases. By adding flake Al₂O₃, the mechanical strength of the material increases. Under the same sintering conditions, the bending strength (205 MPa) of the laminated sample increased by nearly 60% compared with the same content flake alumina block sample (124 MPa), and increased by 162% compared with the sample without flake alumina (78 MPa). BZ-BBSMZ-5 wt% flake Al₂O₃ ceramic sintered satisfactorily at 940 °C with tanδ = 4.82*10^–4 (10 GHz), ε_r = 11.66. The bending strength of the sample is 205 Mpa.

The global demand for Bi_0.5Na_0.5TiO₃ (BNT) based perovskite materials with wide-ranging applications in the sensors, detectors, capacitors, random access memories, and environmental fields is on the increase. The Sr²⁺ doped BNT system has been extensively investigated in the past decade due to its excellent structural, electrical and microstructural applications. This review encompasses the fundamental state-of-the-art development of BNT-based ceramics, focusing on the underlying SrTiO₃ (ST) composition and enhanced crystal structure mechanisms. The diffuse phase transition related to the ferroelectric nature of the sample is specifically demonstrated. BNT-ST in various forms like single crystals, thin films, multi-layers, and polycrystals for enhanced piezoelectric and ferroelectric activities were discussed in detail. Finally, these systems' key challenges and future directions are also included. Indeed, this review will propagate more exhaustive research on non-toxic and cost-effective pathways to produce BNT-based components with dynamic properties, which can be applied in several industrial applications with outstanding performance.

In this work, we prepared La_1 − xSr_xGa_1−yMg_yO₃ (LSGM) by the fast combustion method and assessed the electrical properties with respect to the composition and sintering temperature (1200, 1300, and 1400 °C by 6 h) as an electrolyte material for the reversible solid oxide cells (ReSOCs). For the preparation of samples, two different fuels, such as tartaric acid (TA) and citric acid (CA), with corresponding nitrate salts as precursors, were adopted for the fast combustion method (at 500 °C for 10 min). From the X-ray diffractograms, two main phases corresponding to LSGM orthorhombic (space group Imma) and LSGM-cubic (space group Pm-3 m) were identified. From the literature, both structures are reported as high oxygen ion conductive species, but normally they are not reported to appear together. Additionally, in some cases, an isolating (secondary) phase of LaSrGaO₄ in a low concentration < 1.98% was observed. The scanning electron microscopy (SEM) studies on samples sintered at 1200 and 1300 °C revealed the smaller grain size and irregular morphology. The SEM micrographs depicted a well-defined superficial morphology with less porosity for the samples sintered at 1400 °C. For comparative analysis, the conductivity (S.cm^− 1) was measured at varying temperatures (300–800 °C) for the samples sintered at 1300 and 1400 °C. Because of the large number of insulating phases produced by the incomplete sintering process, the samples sintered at 1300 °C had lower conductivities. A higher conductivity of 0.125 S.cm^− 1 was observed for La_0.80Sr_0.20Ga_0.80Mg_0.20O₃ (LSGM), which was obtained using the citric acid (sintered at 1400 °C), which is in the range of earlier reported similar studies. The observed variation in the conductivity with respect to different phases of LSGM, the influence of the secondary phase, and the wt% of the constituents of LSGM are discussed.

The effect of grain size on crystal structure and the ferroelectric, dielectric, and piezoelectric properties of 0.38Bi(Ni_2/3Ta_1/3)O₃-0.62PbTiO₃ ceramics was studied herein. By controlling the sintering time, 0.38Bi(Ni_2/3Ta_1/3)O₃-0.62PbTiO₃ ceramics with different grain sizes were prepared by the conventional solid-state reaction. It was found that the crystal structure of the ceramics changed slightly with the increase of grain size, from a pure tetragonal perovskite structure to a combination of tetragonal and rhombohedral phases. Both the Curie temperature T_C and the depolarization temperature T_d of the ceramics decreased with increasing grain size. However, the degree of dielectric relaxation first increased and then decreased, with the relaxation factor γ ranging from 1.35 to 1.87. The remnant polarization P_r and coercive field E_C also first increased and then decreased, whereas the strain increased with the increase of grain size. The high field strain coefficient d^*₃₃ and piezoelectric coefficient d₃₃ both increased with the increase of grain size. However, in this ceramic system, the electromechanical coupling coefficient k_p and mechanical quality factor Q_m changed independently of the variation in grain size.

Polycrystalline samples of Bi₄V_2(1-x)Cu_2xO_11-3× were prepared by solid state reaction method. Thrust of the work is to stabilize high temperature conducting γ-phase at room temperature. XRD and DSC analysis indicates orthorhombic ‘α’ phase for x ≤ 0.08 to tetragonal γ-phase transition for x = 0.1, at room temperature. Variations of real and imaginary impedance as well as complex electrical modulus with frequency are reported. Experimental impedance spectroscopic data was theoretically fitted and equivalent circuits are proposed. Nyquist plots revealed contribution from grain as well as interface. Variations of impedance, dielectric permittivity and AC conductivity as a function of frequency at selected temperatures are reported. The AC conductivity was fitted with Jonscher’s power law and the power law exponent (η) was found to be < 1, indicating that the conduction process follows CBH mechanism. The dielectric behaviour was found to follow UDR model. Cu²⁺ ions was observed to introduce defects and oxygen vacancies, space charge accumulation, reduction in dielectric permittivity and increase in the conductivity as high as up to 0.45 S·cm⁻¹ for the expected γ-phase.

The (Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)(Ti_1-xSc_x)O₃ (BNKLST-xSc) high entropy ceramics (HECs) have been successfully synthesized via a citrate acid method. The effects of Sc-doping on the lattice structure, microstructural morphology, dielectric and energy-storage properties of HECs are comprehensively investigated. The results indicate that although Sc³⁺ doped at B-site does not alternate the perovskite structure of BNKLST with a single phase, it results in lattice expansion and weakened bonding in TiO₆ octahedron. The dielectric constant of BNKLST-xSc is reduced while the dielectric relaxation is enhanced with increasing Sc content x, due to the enhanced structural inhomogeneity in nano-regions. In addition, the lattice structure of BNKLST-0.2Sc exhibits ultra-high thermal stability at 30–300 °C, which achieves the maximum energy storage density of 1.094 J/cm³ with an outstanding efficiency better than 80%, accompanying by the mechanical and dielectric losses as low as ~ 10^–3. It is suggested that BNKLST-0.2Sc could be promising dielectric materials in capacitors and energy-storage devices with an excellent combination of ultrahigh power density, high energy density, thermal stability as well as low mechanical and dielectric losses.

Structural, morphological, FTIR, optical and photoluminescence (PL) measurements of Zn_1-xRE_xO nanoparticles with RE = Y, La and x (0.00 ≤ x ≤ 0.20) are reported. The wurtzite structure is confirmed for all samples and the lattice parameters, Zn–O bond length, porosity, crystallite size, lattice strain and residual stress are increased by increasing x to 0.20, but they are higher for La samples than Y. The grain sizes are 180, 330, and 460 nm for the pure, Y and La samples. The addition of RE to ZnO generally shifts FTIR absorption peaks, Debye temperature, and elastic modulus to higher values, but the shift is higher for La samples than Y. Although excitonic energy is constant for all samples, the energy gap E_g was increased by increasing x to 0.20, but it is higher for La samples than Y. Furthermore, the dielectric lattice constant, density of charge carriers, and electrical conductivity are increased by increasing x to 0.10, followed by a decrease to 0.20. The opposite behavior is true for dielectric loss and optical conductivity. The PL intensity shows four continuous visible peaks of near UV, blue, green, and red. Interestingly, the intensity of blue emission is greater than that of near UV, such that [(I_blue/I_UV)] > 1]. Furthermore, for x > 0.10 samples, there is another lowest intensity IR emission peak centred at 824 nm (1.507 eV). These results are well explained and strongly recommend the RE doped samples for the applications of optoelectronic and high-power operating devices. To our knowledge, the present investigation probably has never been reported elsewhere.

The new technologies such as the fifth generation of telecommunications (5G) and the internet of things (IoT) present a set of demanding technical requirements at device level that can be reached through devices based on piezoelectric materials using nonlinear effects to increase their performance. However, in the literature can not be found a physics formulation for the unified nonlinear effects of these materials that allow an easy implementation in FEM simulators. Thus, in this work we use the stress-charge formulation to obtain the transformation laws, the unique components of the higher order tensors and the equations of state, which unify the nonlinear phenomena of the piezoelectric effect reported experimentally and, which can be used to increase the performance of the devices and extend the range of applications based on these materials. In addition, the methodology for their implementation on the main FEM simulators is presented.