Journal of Electroceramics最新文献

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.

In order to improve the energy storage performance of Bi-based lead-free ceramics in dielectric capacitors, K_0.5Bi_0.5TiO₃ is doped into Bi_0.5Na_0.5TiO₃-Bi_0.2Sr_0.7TiO₃ (NBT-SBT) ceramics. We find that NBT-SBT-xK_0.5Bi_0.5TiO₃ (NBT-SBT-xBKT, x=0, 0.02, 0.03, 0.05 and 0.08) ceramic sheets maintain the perfect pure perovskite structures and show the character of relaxor ferroelectrics, indicating that the doped K⁺ ions smoothly infiltrate into the host lattice of binary system NBT-SBT ceramics and then disturb the long-range order of ferroelectric material and cause the lattice deformation in NBT-SBT. As such, the NBT-SBT-0.03BKT ceramic sample obtains dielectric constant (ε_r) of 1736, dielectric loss (tanδ) of 0.05, and energy storage efficiency (η) of 70.7%, respectively. More strikingly, NBT-SBT-xBKT ceramics exhibit excellent temperature stability, which helps to store energy at high temperatures. This paper can provide an effective method for manufacturing ceramic based capacitors with high energy storage property.

In this research work, the microwave dielectric and shielding properties of (0.96M_xMg_1-xTiO₃ – 0.04SrTiO₃) (M = 0, x = 0.0; M = Zn, x = 0.05; M = Zn, x = 0.075; M = Co, x = 0.05; and M = Co, x = 0.075) solid solutions were studied in a Ku and K frequency band using a vector network analyzer. The samples were prepared via the auto-ignition combustion method and sintered at a temperature of 1200°C for 4 hours. An investigation of the shielding properties revealed that these materials' shielding effectiveness (SE) varied as a function of composition and frequency. The shielding analysis exhibited that compositions (M = Zn, x = 0.05) and (M = Co, x = 0.05) showed maximum shielding effectiveness by providing SE > 10 dB for a bandwidth of 2.72 GHz and 4.48 GHz, respectively. The highest SE was observed for composition (M = Co, x = 0.05) at a frequency of 17.21 GHz with SE~31.05 dB corresponding to a restriction of 99.81 % of incident power. These compositions are proposed as effective shielding materials for electromagnetic radiations in Ku-band and K-band.

The reaction sintering, without calcination and following re-grinding, has been paid increasing attention. Non - stoichiometric Li₂Mg₃Sn_1 − xO₆ (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were successfully gained through reaction sintering process in the study, and its phase composition, morphology and dielectric characteristics were studied. This XRD patterns of Li₂Mg₃Sn_1 − xO₆ samples prepared after sintering at 1,305 ℃ for 6 h indicates that green bodies are mainly composed of Li₂Mg₃SnO₆ phase, accompanied by the second phase of Mg₂SnO₄. A host of pores, elliptic - like grains and wrinkle - like grains were visibly observed from the SEM images of Li₂Mg₃Sn_1 − xO₆ ceramics, which is because of the severe volatilization of Li elements at high temperature. The apparent density, relative permittivity, quality factor and temperature coefficient of resonant frequency of samples will be devastate owing to porous morphology and Mg₂SnO₄ phase to a large extent. Finally, when x = 0.08, Li₂Mg₃Sn_0.92O₆ ceramics have optimal dielectric performances: ε_r = 9.133, Q×f = 55,429 GHz, τ_f = -36.1 ppm/℃.

We describe the development and characterization of a stretchy and resilient micro-strip antenna made from a nanocomposite of polydimethylsiloxane (PDMS) and bentonite clay loaded with silver, copper, and graphene nanoparticles. The physical, mechanical, and thermal characteristics of the nanocomposite were extensively evaluated in relation to the different nanomaterial loading into the PDMS. This has included UV-Vis spectroscopy, X-ray diffraction, and other techniques in addition to tensile and flexural tests, rheological analysis, thermogravimetric analysis, scanning and transmission electron microscopy, dynamic viscosity study, and ion coupled plasma. The conductivity of the fabricated micro-strip antennas was assessed using electrochemical impedance spectroscopy, and the antenna pattern was suitable for usage in RF equipment for cutting-edge applications like military, sensing, and space.

Oxygen non-stoichiometry profoundly impacts the electrical, magnetic, and catalytic properties of metal oxide. Limited by the low mass and volume of thin oxide films, conventional quantification methods, such as thermogravimetry, are not directly applicable. While chemical capacitance has been successfully applied to monitor oxygen non-stoichiometry in thin oxide films, detailed a-priori understanding of the defect chemistry is often very helpful in its interpretation. In this study, changes in non-stoichiometry in Pr doped CeO₂ (PCO) thin films are measured by coulometric titration. I-V titration measurements are performed on electrochemical cells, over the temperature range from 550 to 700 ℃, oxygen partial pressure range from 10^-4 to 0.21 atm, and bias range of -50 mV to 50 mV, to extract changes in stoichiometry. The results agree well with values obtained by chemical capacitance, demonstrating the utility in applying coulometric titration to investigate oxygen non-stoichiometry in oxide thin films.