Journal of Electroceramics最新文献

The evolved in-situ phases may tune the structural parameters and magnetic properties of the ferrite-BaTiO₃ based composite. Here, CoFe₂O₄ is prepared, and its particle size is modified by calcination temperature. Further, it investigates the influence of CoFe₂O₄ particle size on the development of in-situ phases in ferrite-BaTiO₃ based composite prepared via an ex-situ gel- combustion and studies its structural parameters as well as magnetic properties at different calcination temperatures. In-situ phases such as plate-like morphologies of barium hexaferrite and hexagonal barium titanate are evolved along with polyhedral barium titanate and cobalt ferrite in these composites, but the development of these in-situ phases is found to be dependent on the particle size of CoFe₂O₄ as well as calcination temperature of the composite powders. Structural parameters, crystallite size, particle size, weight% of phases, and M-H loop as a function of the calcination temperature of these composites have been studied in detail.

The temperature dependent microscopic conduction processes and dielectric relaxations in Eu and Mn co-doped multiferroic bismuth ferrite have been examined using complex frequency-dependent ac conductivity, electric modulus and complex impedance examinations. The modified Debye’s function was used to explore the dispersion behaviour of the dielectric constant. The correlated barrier hopping concept is supported by the frequency variation in ac conductivity at various temperatures, which follows Jonscher’s power law. It was observed that when the co-doping concentration is low, the thermally assisted correlated barrier hopping (CBH) conduction model is better suited for the present samples whereas the overlapping large polaron tunnelling (OLPT) conduction model is better suited for higher co-doping concentrations. By looking at scaling curves for imaginary impedance (Z'') and modulus (M''), thermally induced relaxation processes have been demonstrated. It can be shown from a comparison of the Z'' and M'' spectra that charge carrier motion, particularly the dominance of short-range charge carriers which is effective at low temperatures while long-range charge carriers which is effective at high temperatures, leads to dielectric relaxation. By looking at semi-circular arcs on the Nyquist plot, it can be shown that at high temperature the electrical conduction process for the nanocrystalline sample is influenced by both grain and grain boundaries contributions. According to the study of ac conductivity under different temperatures, all compounds transport electricity with the help of electronic hopping, oxygen vacancy movement, or/and the production of the defects.

The electrical resistance of gas sensors, based on polycrystalline metal-oxide semiconductors, obeys a power-law response with the pressure of different gases (R ~ p^γ). The exponent γ can be derived resorting to the mass action law and its value depends on chemical reactions that take place at the surface of the grains. To explain the gas sensitivity, we revisit two conceptual models, regularly used in the literature: the ionosorption and the vacancy models. We show that they predict different values for the exponent γ. Also, the consequences of considering the bulk oxygen vacancies as deep levels are analyzed. Comparison of γ values obtained from both conceptual models with those found in experiments can indicate what mechanisms are possible to occur.

We demonstrate the influence of lithium on copper-doped ZnO-based thin films for improved NO₂ gas sensing applications fabricated via the sol-gel spin coating technique. Structure studies confirmed hexagonal wurtzite structure and morphological analysis showed evenly dispersed, agglomerated spherical particles with an average grain size ranging from 25.94 to 30.79 nm. Lithium-doped Cu-ZnO with more surface oxygen vacancies and a higher carrier density demonstrated outstanding NO₂ gas sensitivity, excellent repeatability, excellent stability, and high selectivity at 210 °C. A possible gas-sensing mechanism is also discussed and correlated with structural, morphological, spectral, and electrical parameters.

The effect of annealing temperature (T_a= 200, 250, and 300 °C) on the structural properties, ac conductivity, and complex dielectric constants (({epsilon }^{{prime }}) and ({epsilon }^{{prime }{prime }})) of indium-doped tin oxide (ITO) thin films (~ 90 nm thick)/0.5 mm boro-float substrates (BFS) synthesized by radio frequency (RF) sputtering is investigated. The X-ray diffraction (XRD) examination demonstrated that indium was successfully substituted with tin atoms to form ITO films and the crystallite size for the cubic phase, as well as particle size, were impacted by T_a. The real part of complex dielectric constants (({epsilon }^{{prime }})) was significantly reduced for all ITO/BFS from the range of 2.7 × 10⁴–5.1 × 10⁴ to 5.3–19 as the frequency (f) was increased to 0.25 Hz, while it remained constant for further increases in f. The value of ({epsilon }^{{prime }}) for the as-prepared ITO/BFS was increased as T_a increased up to 250 °C, then was decreased at T_a=300 °C. A similar finding was detected for the loss factor with no observation of any relaxation peaks. The Q-factor was increased for all ITO/BFS as f increased to 100 Hz and then was reduced with increasing f up to 20 MHz, while steadily increasing with T_a. The deduced frequency exponent is greater than 0.5 for the ITO/BFS, indicating their electronic conduction nature. The density of the localized states and hopping frequency of the ITO/BFS were increased by annealing at 200 °C, meanwhile was decreased for T_a = 300 °C. The binding energy was decreased from 0.647 eV for the as-prepared ITO/BFS to 0.518 eV by annealing at 200 °C, meanwhile was increased to 0.74 and 0.863 eV for T_a equals 250, and 300 °C, respectively. The Cole-Cole plots revealed a single semicircular arc for all films, and their corresponding equivalent circuit was analyzed. The equivalent bulk resistance was gradually decreased by annealing in the range of 200–300 °C, whereas the equivalent capacitance was increased. The resistance of grains and resistance of grain boundaries of the as-prepared ITO/BFS was gradually decreased by increasing T_a to 250 °C, while it was increased for T_a = 300 °C. These outcomes recommended the RF sputtered ITO/BFS for high-frequency devices, integrated circuits, and supercapacitors.

(0.93 − x)BT − 0.01BZ − 0.06BS − xCT or (Ba_1-xCa_x)(Ti_0.93Zr_0.01Sn_0.06)O₃ (abbreviated as BCZTS) ceramics were produced using the standard solid-state reaction for 0.045 ≤ x ≤ 0.07. For the samples, it was found that orthorhombic (Amm2), rhombohedral (R3m) and tetragonal (P4mm) structures coexisted in two phases as well as three phases with distinct phase fractions. The largest size of crystalline grains was achieved after doping with 0.055 mol% and 0.065 mol% Ca. The optimal properties (P_max = 12.05 μC/cm², P_r = 5.61 μC/cm², E_c = 230 V/mm, d^*₃₃ = 404 pm/V, Q_c = 6.44 µC/cm², T_c = 102 °C) were obtained for x = 0.07 where it has been found that orthorhombic, rhombohedral, and tetragonal phases all occurred at the same time. For compositions in the MPB range, the energy storage characteristics indicate high energy storage efficiency for low value of Ca doping. Given all the developments, it is obvious that Ca, Zr and Sn-doped BCZTS ceramics would be a good choice for lead-free electronics.

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.