Journal of Electroceramics最新文献

In this paper, influence of radius and electronegativities of seven kinds of donors on the composition, microstructure, mechanical, thermal and electrical properties of ZnO varistors were investigated via XRD, SEM, XPS, mechanical, thermal and electrical properties tests. Results showed that when sintered at 1100 °C for 2 h, the obtained varistors exhibited a dense microstructure, where radius of donors played an important role on the grain size and size distribution of varistors; Mechanical properties and coefficient of thermal expansion of varistors were mainly affected by the radius of donors, with specimen 6# possessing the highest values of 123.46 MPa (σ_f), 80.47 GPa (E_f), and 6.58 × 10⁻⁶ °C⁻¹ (λ_c), respectively; Values of E_1mA and α initially increased and then decreased with the increase of donors’ radius, whereas those of J_L and K exhibited opposite trends. E_1mA and α had maximum values of 569.94 V mm^–1 and 26.70, whereas J_L and K possessed the lowest values of 2.31 μA⋅cm⁻² and 1.35, respectively, when Co²⁺ worked as the donor (specimen 6#). The DC aging process of ZnO varistors obeyed the ion migration mechanism, the radius of donors can affect the number of it entering the ZnO lattice, which can limit the migration of zinc gaps via the formation of substitution and filling defects in the ZnO lattice. The electronegativity of donors can reduce the ion migration speed via the stronger electrostatic force, and specimen 6# possessed the lowest DC aging properties (K_T = 1.68).

The YTi_0.5Mn_0.5O₃ (YTMO) perovskite was synthesized by the conventional solid-state method. The structural, electrical, dielectric and optical properties were investigated. The X-ray diffraction analysis and Rietveld refinements indicates that sample under study crystallizes in the orthorhombic structure with the Pmmm space group. The impedance spectroscopy studies show a relaxation phenomenon with non-Debye nature. The Nyquist plot confirms the presence of semicircles which, in turn, indicate the existence of both grain and grain boundary effect in the prepared ceramic. The study of AC conductivity has been discussed in detail and designated on the basis of the NSPT conduction mechanism. Activation energy was determined from DC conductivity as well as modulus spectra. The very equal values of the activation energies suggest that the process of the conduction mechanism and the relaxation behavior are similar. The behavior of dielectric constants was interpreted based on the Maxwell–Wagner’s theory of interfacial polarization. Thermodynamic parameters such as enthalpy, entropy have been calculated. From UV–Vis absorption spectrometry, the reflectance spectrum and the Kubelka-Munk model, reveal a direct and wide optical band gap evaluated at 4.69 eV. Moreover, the obtained Urbach energy (0.240 eV) confirms the presence of localized states in the YTMO structure. The extinction coefficient (k) was used to estimate the evolution of the refractive index n with the wavelength. Additionally, the refractive index (n) obeys to Cauchy relation. Furthermore, the dispersion coefficients were analyzed in the bases of Wemple and Di-Domenico model. The optical constants such as the skin depth and the optical conductivity were calculated and the results are discussed.

This work highlights the electrocaloric (EC) and energy storage (ES) properties of 1-x(0.6Ba(Zr_0.2Ti_0.8)O₃-0.4(Ba_0.7Ca_0.3)TiO₃)-x(BiTa_0.5La_0.5)O₃ (1-xBZCT-xBTL) ceramics with x = 0 to 0.05. The XRD studies revealed that inclusion of BTL content in BZCT does not induce any impurity phase. The peak splitting of BZCT near 2θ = 45(^circ) and 66(^circ) confirms the presence of morphotropic phase boundary corresponding to tetragonal and rhombohedral phases. Further, the solid solution formation of BZCT-BTL has suppressed its morphotropic phase boundary behaviour. The XRD, Raman and temperature dependent dielectric studies suggest the presence of pseudocubic phase in 1-xBZCT-xBTL at higher values of x = 0.025 and 0.05. Moreover, the inclusion of BTL boosts the diffused phase transition behaviour of BZCT ceramics. Further, BTL strengthened its relaxor nature due to a reduction in grain size as evidenced from SEM analysis. It is observed that the 0.99BZCT-0.01BTL ceramics show 95% efficiency and a maximum recoverable energy density of 479 mJ/cm³ at 100 kV/cm. Moreover, the electrocaloric temperature change and responsivity are found to be 1.06 K and 0.01 Kcm/kV near the transition temperature.

In this paper, the Ca²⁺ ion was chosen to substitute the Mg²⁺ ion of Li₂MgSiO₄ ceramics. Li₂Mg_1 − xCa_xSiO₄ (x = 0.0, 0.03, 0.06, 0.09, 0.12) ceramics materials were prepared by solid state reaction at low temperature (925 °C) with 2.5wt% Bi₂O₃ sintering aid. X-ray diffraction (XRD) results showed the ceramics presented the standard Lithium Magnesium Silicate phase formation, and no secondary phases appeared. Scanning electron microscopy (SEM) suggested that Ca²⁺ ions affected the densification of the prepared ceramics. Ca²⁺ ion substitution resulted in increasing relative density, enhancing microwave properties. Ca²⁺ ion substituted Mg²⁺ ion and formed a CaO4 structure, which affected microwave dielectric properties. With the substituted amount increase, the values of dielectric constant ε’ and quality factor Q×f gradually increased, and τ_f values increased from negative to positive values. When x = 0.09 and sintered at 925 °C, Ca²⁺ ion substitution gave ceramics excellent microwave properties: bulk density ρ = 2.479 g/cm³, relative density was 98.68%, dielectric constant ε’=6.59, dielectric loss tanδ_ε = 0.0018, quality factor Q×f = 8976.9 GHz and temperature coefficient τ_f = 1.9 ppm/°C. This ceramic material has excellent microwave dielectric properties and holds a potential for use in integrated antenna and other electronic devices.

The present research work aims to address the rising demand for microwave-absorbing materials (MAMs) due to the relentless growth of detrimental electromagnetic wave pollution. Herein, the absorption behavior of manganese-zirconium co-substituted zinc-cobalt spinel ferrites with chemical composition Zn_0.25Co_0.75(MnZr)_xFe_2−2xO₄ (0.05 ≤ x ≤ 0.25, ∆x = 0.05) were investigated in the Ku (12.4–18 GHz) and K (18-26.5 GHz) frequency bands. Samples of Mn-Zr-Zn-Co ferrites were successfully synthesized via the sol-gel citrate route with sintering at a temperature of 1000 °C for 6 h. Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of two vibrational peaks in the spinel lattice structure. The complex dielectric permittivity and complex magnetic permeability were measured using a vector network analyzer (VNA). The composition MZ 0.15 outperformed all the prepared compositions by exhibiting a minimum reflection loss of -34.55 dB at a matching frequency of 15.09 GHz and a matching thickness of 2.7 mm in Ku-band and a reflection loss as low as -30.40 dB at a matching frequency of 25.48 GHz and a matching thickness of 1.5 mm in K-band. The obtained results indicate that the fabricated specimens have the potential for designing efficient microwave-absorbing materials in the Ku and K frequency bands.