Journal of Electroceramics最新文献

In this work, nano ZnO powders, Bi₂O₃, Sb₂O₃, Cr₂O₃, Co₂O₃ and a various content of MnO₂ were blended thoroughly and pre-calcined at 800℃ and then pressed in to pellets which were sintered at 950℃ to form varistor ceramics. Subsequently, the effects of MnO₂ on the microstructure and electrical properties of the ZnO-based varistor were investigated. It was found that the amount of spinel phase (Zn₇Sb₂O₁₂) and Bi₂O₃ phase increased with the MnO₂ increasing, while the content of pyrochlore (Zn₂Bi₃Sb₃O₁₄) phase decreased. As a result, the growth of ZnO grain was reduced with the average grain size from 9.5 μm down to 5.3 μm, leading to the increase of breakdown field of ZnO-based varistor. Particularly, the ZnO-based varistor with 1.2 mol% MnO₂ exhibited the best comprehensive electrical performance with the breakdown field E_b of 901.4 V/mm, the nonlinear coefficient α of 66.7 and the leakage current density J_L of 1.1 µA/cm².

ZnO-B₂O₃-SiO₂/SiO₂ glass-ceramic composites are prepared by solid phase reaction method. The DSC curve of ZnO-B₂O₃-SiO₂ glass is analyzed and the effects of ZnO-B₂O₃-SiO₂ glass on the density, microwave dielectric properties, phase composition and microstructure of ceramic fillings are investigated. The results show that the sintering temperature of the composites can be reduced to 910 °C by adding ZBS glass. When the addition of ZBS is 65% (wt%), the dielectric properties of the sample are best when the composite is sintered in 910 °C for 1 h (εr = 4.6, tanδ = 4.85 × 10^− 4 at 9.2 GHz, τ_f = -13.78 ppm/°C). The prepared ZnO-B₂O₃-SiO₂/SiO₂ composite is promising candidates for LTCC applications.

This research study explores the magnetic and magnetocaloric properties of La_0.67-xEu_xBa_0.33Mn_0.85Fe_0.15O₃ (x = 0 and 0.1) magnetic compounds elaborated using the Sol–Gel method, based on a phenomenological approach proposed by Mahmoud Aly Hamad. The studied compounds exhibit a second-order ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. A correlation between the experimental measurements and the theoretical analysis is established. Indeed, the value of the magnetocaloric effect was determined from the theoretical model based on magnetization as a function of temperature at several magnetic fields. Under an applied magnetic field of 5T, the absolute values of the maximum magnetic entropy change are evaluated at 0.92 and 0.60 J kg⁻¹ K⁻¹ for x = 0 and 0.1 respectively. This reduction may be attributed to a Curie temperature distribution implying also a decrease in the relative cooling power (RCP). The RCP and the specific heat capacity values are also estimated thanks to this model. The results predicted by this model allow us to propose these compounds as promising candidates for magnetic refrigeration.

Piezoelectric ceramics, as an essential electronic material, are widely used in various actuators and ultrasonic transducers. In this study, piezoceramics in the formula Pb_0.94Sr_0.04Ba_0.02(Mg_1/3Nb_2/3)_0.025(Sb_1/2Nb_1/2)_0.025(Ni_1/3Nb_2/3)_x(Zr_0.48Ti_0.52)_0.95−xO₃ + 0.2wt%Li₂CO₃, where x = 0.21 − 0.17(abbreviated as PMN-PSN-xPNN-(0.95-x)PZT) were investigated. By changing the PNN content from 0.21 to 0.17, high piezoelectric coefficient d₃₃ from 860 pC/N to 700 pC/N, high Curie temperature T_c from 137 ℃ to 168 ℃ were obtained. All the ceramics show excellent electrical properties. It is 15 − 20% better than PNN-PZT or doped PNN-PZT piezoelectric ceramics in certain aspects. What’s more, the ceramics also carry extraordinary electromechanical coupling factor k_p (from 67 to 73%). Hence, this is an excellent candidate for actuators and transducers applications.

The fatigue behavior of Bi_0.5Na_0.4K_0.1TiO₃-based ceramics depends on the polarity. While the non-ergodic relaxor ceramics have large residual polarization but poor fatigue behavior, the ergodic relaxor ceramics have excellent fatigue resistance but tiny residual polarization. Therefore, obtaining ferroelectric ceramics with high residual polarization and excellent fatigue resistance is challenging due to the trade-off between non-ergodic relaxor and ergodic relaxor. Here, we modulate the free energy barrier by doping relaxant Nb to achieve the coexistence of non-ergodic and ergodic relaxor phases. At 0.6% Nb doping, the residual polarization is large at 2P_r = 49.3 µC/cm², increased to 54.23 µC/cm² after 10² cycles and decreased to 53.04 µC/cm² after 10⁵ cycles, indicating good fatigue resistance behavior. The large residual polarization is due to the metastable ferroelectric state, while the excellent fatigue resistance may be attributed to the field-induced ferroelectric-relaxor phase transition.

(Bi_0.5La_0.5)FeO₃ Orthoferrite ceramics were prepared by a conventional solid-state reaction method on a bulk scale and on a nano range by sol–gel auto combustion and Hydrothermal methods, respectively. The phase purity and crystallinity of the prepared ceramics have been examined by X–ray diffraction study. Broadening of the maximum intensity peak (hkl) and smaller crystallite size has been noticed in both chemical methods i.e., sol–gel and hydrothermal. Rietveld refinement confirmed the presence of orthorhombic symmetry with a space group (Pnma) for the ceramics synthesized through all three processes. The crystallite size, particle morphology, and grain microstructure formation mechanism were correlated for prepared ceramics with FESEM and XRD results. The influence of synthesis conditions on structure, microstructure, and magnetic studies has been studied. The M-H hysteresis loop study reflects that tuning of particles or crystallite size might induce a productive enhancement in magnetization response for chemically synthesized ceramics.

The double perovskite Sr₂YbNbO₆ (Strontium ytterbium niobium oxide, SYN) has been synthesized by solid-state ceramic processing technique. SYN crystallizes in monoclinic structure with P2₁/n space group. SYN is polycrystalline in nature with grain size ~ 2.38 μm. The Raman spectrum analysis of SYN reveals the presence of 24 Raman active modes. The bands associated with the bending and stretching vibrations of the YbO₆ and NbO₆ octahedra has been analysed using its FTIR spectrum. The optical band gap of SYN has been obtained to be 3.08 eV. The dielectric properties of the sample have been investigated in between 50 Hz to 1 MHz frequency and 303‒513 K temperature. The dielectric relaxation of SYN is polydispersive in nature and has been analysed using the Cole-Cole model. The activation energy of SYN is 0.52 eV which points towards the conduction associated with the hopping of p-type polaron.

In this report, we present the fabrication through the solid-state method and subsequent characterization (structural, electrical, optical, and thermal properties) of a lead-free Na/W modified complex BiMnO₃ ceramic of a chemical composition (Bi_1/2Na_1/2)(Mn_1/2W_1/2)O₃. The structural analysis, including the determination of structure and lattice parameters, was performed using X-ray diffraction data, revealing a monoclinic crystal structure of the material. Additional insights into its vibrational properties were obtained through Raman spectroscopy and Fourier Transform Infrared spectrum. The electronic behaviour of the prepared sample was investigated using photoluminescence (PL). Scanning electron microscope analysis revealed a uniform distribution of grains. The energy-dispersive X-ray study confirmed compositional uniformity. Furthermore, a comprehensive analysis of dielectric properties, impedance, modulus, and conductivity was carried out over a range of frequencies (1 kHz – 1 MHz) and temperatures (25 °C – 500 °C) to understand the Maxwell–Wagner type of dielectric dispersion, relaxation, and transport mechanisms. The Nyquist plots and the temperature-dependent conductivity data exhibited a negative temperature coefficient of resistance behavior. The modulus data indicated a scaling nature, indicative of non-Debye type relaxation. Additionally, the study of polarization with an electric field suggested the possibility of a ferroelectric behavior of the material.