Journal of Electroceramics最新文献

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.

The ferroelectric Ir/PZT/Pt and Au/PZT/Pt capacitor structures are studied by the electron beam induced current (EBIC) technique and the steady-state current–voltage dependencies. EBIC data reveal the change in the local field at the PZT/metal interfaces caused by migration of oxygen vacancies ({V}_{o}^{**}) under an action of applied electric field. Ir/PZT and Pt/PZT interfaces block ({V}_{o}^{**}) movement causing their accumulation near the cathode interface. An electrons injection from the metal cathode to the PZT leads to formation of induced p–n junction. The steady-state leakage current in this case is well described by modified equation for the p-n diode, which considers an action of the counter electric field caused by electrons injection. In the case of transparent for oxygen vacancies Au/PZT cathode oxygen vacancies leave the PZT bulk and current–voltage dependence demonstrates a region of negative differential conductivity at high electric fields. The proposed p–n junction formalism can be used for engineering of PZT-based devices.

The attractive bismuth-based cubic pyrochlores possess large dielectric constant, high dielectric tunability, and extremely low dielectric loss. The Bi_1.5Mg_1-xCo_xNb_1.5O₇ (Co-BMN, x = 0.0–0.5) cubic pyrochlore ceramics were prepared by solid-state reaction. All the Co-BMN ceramics maintained the cubic pyrochlore phase with a preferential (111) orientation. The forbidden (442) diffraction plane was found in Co-BMN pyrochlores. The crystallization of the Co-BMN ceramics was promoted by Co²⁺ doping modification. The Co-BMN at x = 0.3 achieved the maximum of cell volume, force constant of A-O stretching, and binding energy of Co²⁺. The dielectric constant of Co-BMN significantly increased due to the larger polarizability of Co²⁺. The increasing dielectric constant of Co-BMN pyrochlores (x ≤ 0.3) with increasing Co²⁺ doping was attributed to the displacive disorder of A-site and O’ ions. Co-BMN with moderate Co²⁺ doping (x ≤ 0.4) presented a low dielectric loss (< 0.0007). The temperature coefficient of dielectric constant of Co-BMN pyrochlores (x ≤ 0.4) increased from -382 ppm/^oC to -84 ppm/^oC after Co²⁺ doping. However, high concentration of Co²⁺ resulted in deterioration of dielectric properties of Co-BMN.

The Skutterudite compounds have been extensively studied worldwide over the past several years for their potential advanced thermoelectric applications in the intermediate temperature range. However, most methods for synthesis of CoSb₃ materials require a long-duration heating process and complex equipments. In this study, a simple solid-state reaction method was used to prepare copper-tellurium co-doped CoSb₃ ( Cu_xCo₄Sb_11.7Te_0.3, x = 0-0.4) bulk thermoelectric materials. The obtained samples show enhanced thermoelectric properties compared to Cu-undoped sample. Especially in the case of Cu-doped CoSb₃, the compound Cu_0.4Co₄Sb_11.7Te_0.3 exhibits a maximal Seebeck coefficient of 234.2 µVK^− 1 at 617 K, the sample Cu_0.1Co₄Sb_11.7Te_0.3 reaches a power factor of 2012.35 mWm^− 1 K^− 2 at 715.7 K. Moreover, phonon scattering appears to be enhanced due to the significant reduction in grain size of the samples prepared by the solid-state reaction method, resulting in a minimum thermal conductivity of 1.67 Wm^− 1 K^− 1. A dimensionless figure of merit (ZT) of 0.68 was obtained for Cu_0.3Co₄Sb_11.7Te_0.3 at 716 K. Thus, the solid-state reaction method is a feasible strategy for the preparation of Skutterudite thermoelectric materials.

NaNbO₃-based antiferroelectric (AFE) ceramics have the prominent advantages of stable performance and low cost. However, its energy storage property is often remarkably limited by the hysteresis of the antiferroelectric to ferroelectric phase transformation. In this work, 0.88Na(Nb_1−xTa_x)O₃–0.12Bi_0.2Sr_0.7TiO₃ (x = 0–0.075) antiferroelectric ceramics were synthesized using a conventional mixed oxide route. Ta⁵⁺ were completely dissolved into the lattice of 0.88NaNbO₃–0.12Bi_0.2Sr_0.7TiO₃ to form a pure perovskite structure. With increased Ta content, the AFE orthogonal P phase was replaced by AFE orthogonal R phase progressively. Meanwhile, the dielectric constant curve showed relaxor-like properties. As a result, slender P–E curves with reduced hysteresis loss and decreased residual polarization were achieved. Interestingly, a large recoverable energy storage density (W_rec ~ 2.16 J cm⁻³) and high energy storage efficiency (η ~ 80.7%) were obtained simultaneously under a low driving electric field of 15 kV mm⁻¹ at doping ratio (x) of 0.075. In addition, the 0.88Na(Nb_0.925Ta_0.075)O₃–0.12Bi_0.2Sr_0.7TiO₃ sample exhibited excellent temperature stability, indicating an ideal candidate in future pulsed power capacitor.

The importance of using divalent ion doped BiFeO₃ ceramics in-place of pure BiFeO₃ informing solid solutions with other ferroelectric materials is emphasized. The phase stability for the (1-y)Bi_0.90Ca_0.10FeO₃-(y)PbTiO₃ system in the complete composition range show occurrence of interesting structure modulations. The changes in the crystal unit cell also seem to have significant effects on the microscopic structure. The SEM studies indicate the formation of more than one type of grains in the system. Such coexistence of one type of grains is found to show relaxor type characteristics both in dielectric and magnetic properties. Suitable models are used to explain the origin of the observed bi-relaxor type characteristics. The low temperature ac-magnetic studies suggest stabilization of a predominant spin-glass type characteristics in samples with 0.30 < y < 0.50.

In this study, Al₂TiO₅ –based multifunctional ceramics were prepared using the spark plasma sintering method within a temperature range of 1573–1773 K. The influence of the sintering temperature on the microstructure, phase composition, and electrochemical and optical properties of the Al₂O₃-TiO₂-Al₂TiO₅ ceramics was evaluated. The results showed that ceramic composites sintered at T = 1773 K possessed the lowest porosity and optical reflectance (5%) in the visible, UV and infrared wavelength ranges. They were characterized by an average crystallite size of approximately 35 nm and the bandgap of 2.2 eV. Considerable changes in the electronic band structure and density of states inside the bandgap lead to enhanced charge carrier separation and reduced charge transfer resistance (R_CT = -1.7).

Magnetic nanoparticles (NPs) are of interest for use in magnetic hyperthermia. To achieve high efficient NPs as a heating agent, it is important to know the effect of processing parameters on the synthesis, microstructure and magnetic properties of NPs and their relationship with the systems’ specific loss power (SLP). In the present study, zinc cobalt ferrite NPs were precipitated using the co-precipitation method, and calcined at 550, 650 and 750 °C for 1 and 2 h. Then to evaluate their hyperthermia properties, ferrofluids of neat and PEGylated NPs (NPs@PEG) were studied. The analysis of X-ray diffraction (XRD), field emission electron microscopy (FESEM), vibrating sample magnetometer (VSM), Fourier transform infrared spectroscopy (FTIR), zeta potential and transmission electron microscopy (TEM) were used to characterize the NPs. It was found that the processing parameters had a significant effect on the microstructure, magnetic and hyperthermia properties of the synthesized NPs. With increasing the time and temperature of calcination, particle size and magnetic properties like anisotropic constant, magnetic moment and saturation magnetization increased too. Hyperthermia results showed that the synthesized NPs at 550 °C for 2 h produced more heat than the other samples. It was also found that the concentration of NPs had a great influence on the heat generated by the prepared ferrofluids. Ferrofluids containing 5 mg/ml of NPs synthesized at 550 °C for 2 h had the highest heating efficiency such that the SLP value of NPs and NPs@PEG was 139.3 and 83.6 W/g, respectively.

The present work describes the effect of Neodymium (Nd) in the NBT-BT (0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃ (NBT-BT (94/06)) + xNd (x = 0, 0.4, 0.6, 0.8, 1.0 wt%)) crystal grown by flux method. As the concentration of the Nd increases beyond 0.4 wt%, homogeneity of the solution is lost and the multinucleation was observed. Color of the crystal changed from yellow to muddy green and size of the crystals were reduced due to the incorporation of Nd in NBT-BT. Nd completely diffused into the NBT-BT lattice, hence no secondary phase formation was observed in XRD. But the peaks were shifted towards the higher angle side due to the shrinkage of NBT-BT lattice. Optical properties of the crystals are studied using UV–visible and photoluminescence spectra. Except 0.4 wt% of Nd, for all other concentration emission at 1064 nm was observed in the PL spectra. Effect of Nd in dielectric constant and the relaxor properties are discussed in detail.