Preparation process,microstructure and dielectric properties of Na0.5La0.5Cu3Ti4O12 ceramics by a sol–gel method

Effect of concentration, water content (molar ratio of the water and titanium) and pH value of the sol, and sintering temperatures and holding time on microstructure and dielectric properties of Na_0.5La_0.5Cu₃Ti₄O₁₂ (NLCTO) ceramics by a sol–gel method were investigated in detail, respectively. It is found that the optimum concentration, the molar ratio of the water and titanium, and pH value of the sol were 1.00 mol/L, 11.0, and 0.3, respectively. The NLCTO ceramics sintered at 1,080 °C for 10 h exhibited more homogeneous microstructure, higher dielectric constant (about 1.1–1.8 × 10⁴) and lower dielectric loss (about 0.051–0.064 at 1–10 kHz). The higher dielectric constant of the NLCTO ceramics might be due to the internal barrier layer capacitor effect. The NLCTO ceramics prepared by the sol–gel method showed two kinds of dielectric relaxation at higher temperature by electric modulus analysis, and two relaxation activation energy values were obtained.     

Microstructure and dielectric properties of BaZr x Ti1−x O3 ceramics

The crystalline structure and dielectric properties of BaZr _x Ti_1−x O₃ ceramics with x = 0.05, 0.10, 0.15, and 0.20 were investigated. As zirconium increased, the a-axis lattice constant gradually increased, however, the c-axis lattice constant and c/a ratio gradually decreased. When x = 0.20, the crystal structures of the BZT ceramics are very close to cubic, different from the tetragonal structure when x < 0.20. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the increased Zr content. The decreases of coercive electric field and remanent polarization were the result of increase of Zr/Ti ratio in BaZr _x Ti_1−x O₃.     

Preparation,microstructure, and improved dielectric and nonlinear electrical properties of Na1/2La1/2Cu3Ti4O12 ceramics by sol–gel method

Na_1/2La_1/2Cu₃Ti₄O₁₂ (NLCTO) ceramics were prepared by the sol–gel method (SG) and solid-state method (SS), and the effect of sintered temperature on microstructure and dielectric and nonlinear electrical properties has investigated. The experimental results indicated that NLCTO-SG ceramics sintered at 1090 °C for 10 h showed larger grain size, higher density and more homogeneous microstructure, especially higher dielectric constant up to ca 1.3–1.8 × 10⁴, lower dielectric loss of about 0.057 and better temperature stability than NLCTO-SS counterparts. However, the good low-voltage varistor behavior and the third kind of dielectric relaxation behavior could not be observed from the NLCTO-SS ceramics. The higher dielectric constant of the NLCTO-SG ceramics may be due to the stronger internal barrier layer capacitor (IBLC) effect. Two values of grain activation energy were obtained above room temperature for the first time. The transition temperature of two values was basically coincident with that of sudden changes of the dielectric properties.     

Synthesis and dielectric and nonlinear properties of BaTi1 − x Zr x O3 ceramics

We have studied the formation of BaTi_{1 ? x} Zr _x O₃ solid solutions with the perovskite structure. The phase composition, microstructure, and electrical properties of the BaTi_{1 ? x} Zr _x O₃ materials have been investigated. The results demonstrate that their dielectric permittivity (?) and loss tangent (tan δ) decrease with increasing zirconium content. At the same time, their nonlinearity coefficient (n ^R ) remains large (n _R = 30–50%) in relatively low fields (E = 30–50 kV/cm). The present data suggest that the materials studied here are potentially attractive for use in creating nonlinear devices of modern microelectronics.     

Synthesis, characterization and electrical properties of nanostructured LaAlO3 by sol–gel auto combustion method

Semiconductive nanostructured LaAlO₃ was synthesized by sol–gel auto combustion method using inorganic reagents as La (NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and glycine as a fuel. Structural characterization of prepared sample was characterized by X-ray diffraction technique (XRD), and Fourier transforms infrared spectroscopy (FTIR). The morphology of the particle was found by scanning electron microscopy while elemental composition by energy dispersive X-ray spectroscopy and transmission electron microscopy (TEM) was used to study the nanostructure of the material. XRD pattern reveals the formation of single phase orthorhombic structure without any other phase formation. The system LaAlO₃ show porous morphology. Particle size obtained from TEM analysis was found to be ~40 nm. The FTIR spectra showed the characteristic of two strong absorption bands at 656 and 442 cm^?1 corresponding to metal–oxygen bond vibrations for the perovskite structure compound. Superhydrophilic nature of LaAlO₃ was investigated at room temperature by sessile drop technique. The electrical properties of the compound showed that LaAlO₃ exhibits conducting behavior.     

Synthesis and characterization of NiO nanoparticles by sol–gel method

Nickel oxide nanoparticles have been synthesized in the presence of agarose polysaccharide by sol–gel method. The structure, morphology, optical and magnetic properties of the product was examined by X-ray diffraction, transmission electron microscopy, UV–visible spectrophotometer and superconducting quantum interference device magnetometer. The result of thermogravimetric analysis of the precursor product showed that the proper calcination temperature was 400 °C. X-ray diffraction result revealed that the obtained product was nickel oxide with face-centered cubic structure. TEM image demonstrated that the nickel oxide nanoparticles have spherical shape with size around 3 nm. Analysis of FTIR spectra confirmed the composition of product. The optical absorption band gap of the NiO nanoparticles was estimated to be 3.51 eV. Magnetic measurement showed that the nickel oxide nanoparticles exhibit superparamagnetic behavior at 300 K. Moreover, the nanoparticles show ferromagnetic interactions at 4.2 K owing to the existence of uncompensated moments on the surface of the nanoparticles.     

Oleic acid assisted synthesis of CaCu3Ti4O12 powders and ceramics by sol–gel process

The CaCu₃Ti₄O₁₂ (CCTO) powders were prepared via a sol–gel method using oleic acid (OA) as surfactant. The obtained samples were characterized by thermogravimetric/differential scanning calorimeter Fourier transform-infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscope, the relative density and the dielectric properties of the ceramics were also investigated. The XRD patterns confirm the formation of CCTO crystal phase and no new peaks appeared whether the dispersant was added or not. The dispersibility of the CCTO powders is improved by adding OA as surfactant. The CCTO prepared without surfactant contains particles of various sizes ranging from 200 to 250 nm whereas the CCTO prepared with OA shows uniform particle size about 120–150 nm. The CCTO ceramics prepared with OA has higher dielectric constant (199484) and lower dielectric loss (0.0977) at 25 °C (10 kHz).     

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti_{1 ? x} (Ln_1/2Nb_1/2) _x ]O₃. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.     

Structure and ferroelectric properties of barium titanate films synthesized by sol–gel method

The barium strontium titanate (Ba_0.7Sr_0.3TiO₃, BST) thin films were synthesized by a sol–gel technique on a silicon nanoporous pillar array (Si-NPA) substrate. SEM observation reveals that the as-prepared BST thin film has uniformly covered the inherited pillar-like surface of the Si-NPA substrate. X-ray diffraction analysis indicates that the perovskite phase was able to be generated in the BST film when the annealing temperature was higher than 600 °C. The remnant polarization (Pr) and coercive field (Ec) values were also found to increase with the annealing temperature, with the maxima of 4.57 μC cm⁻² for Pr and 7.61 kV mm⁻¹ for Ec at 800 °C, respectively. The measurement of leakage current density against voltage applied suggested that the BST films are excellent insulators along with fair resistance to breakdown, and the mechanism of leakage current was discussed.