Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

Giant dielectric, low dielectric loss, and non-ohmic properties of nanocrystalline CaCu3Ti4O12

A simple polymer pyrolysis method has been successfully used to prepare CaCu₃Ti₄O₁₂ (CCTO) nanoparticles by calcination the obtained precursor powder at a low temperature of 800 (CCTO-1) and 850 °C (CCTO-2) in air for 4 h. The XRD results show that both of the calcined powders (CCTO-1 and CCTO-2) are pure having perovskite structure with the crystallite sizes, as evaluated by the XRD line boardening technique, of 47.5 and 75 nm, respectively. The particle sizes as estimated from the bright field images of TEM were found to be in the range of 10–35 and 7–52 nm for CCTO-1 and CCTO-2, respectively. The further sintering of CCTO-1 and CCTO-2 at 1,050 °C in air for 6 h, CCTO-1A and CCTO-2A, are also pure with perovskite structure as indicated by the XRD results. The measurements of the dielectric constant ( $ \varepsilon^{\prime } $ ε ′ ) and the low loss tangent (tanδ) at 1 kHz and 20 °C of CCTO-2A were found to be ~11,472 and ~0.0438, respectively. In addition, the CCTO-2A sample shows a small temperature coefficients ( $ \left| {\Updelta \varepsilon^{\prime } } \right| < 15\,\% $ | Δ ε ′ | < 15 % ) in a wide temperature range from ?50 to 110 °C. The non-Ohmic properties non-linear coefficient (α) of CCTO-1A and CCTO-2A were observed and the non-linear coefficient (α) of them determined in the range of 1–10 mA cm^?2 were found to be 12.00 and 7.26, respectively. Moreover, the breakdown field (E _b ) of CCTO-1A and CCTO-2A ceramics obtained at J = 1 mA cm^?2 were calculated and found to be 811 and 1,342 V cm^?1, respectively.     

Optimization of titanium dioxide film prepared by electrophoretic deposition for dye-sensitized solar cell application

Nanocrystalline TiO₂ films were deposited on a conducting glass substrate by the electrophoretic deposition technique. It was found that the thickness of TiO₂ film increased proportionally with an increase in deposition time and deposition voltage. However, as the deposition duration or deposition voltage increased, the film surface was more discontinuous, and microcracks became more evident. The characteristic of the dye-sensitized solar cell using TiO₂ film as a working electrode was analyzed. The results of the energy conversion efficiency and the photocurrent density exhibited a relationship dependent on the TiO₂ thickness. Curve fitting of energy conversion efficiency vs. TiO₂ thickness revealed the optimum solar cell efficiency ~ 2.8% at the film thickness of ~ 14 μm.     

Ultra-stable X9R type CaCu3-xZnxTi4.1O12 ceramics

CaCu_3-xZn_xTi_4.1O₁₂ (x?=?0.00, 0.05 and 0.10) precursor powders were prepared by the polymer pyrolysis (PP) solution method. Ultra-stable X9R type capacitor with very low loss tangent (tanδ) ~0.017 varied within a value of less than 0.05 in a wide temperature range of ?60 to 150?°C and high dielectric constants (ε^′) ~9200 with Δε′ ≤?±?15% in a wide temperature range of ?60 to 210?°C was achieved in CaCu_2.95Zn_0.05Ti_4.1O₁₂ (Zn05-1) ceramic obtained by sintering the precursor powder (x?=?0.05) at 1060?°C for 8?h. A major role for the validity of ε^′ and tanδ in these wider temperature ranges was suggested to originated from the very high grain boundary resistance (R_gb ~413,190?Ω?cm), resulting from the effect of Zn²⁺ doping and TiO₂-rich at grain boundary. With the excellent dielectric properties of (Zn05-1) ceramic, it was suggested to be applied for X8R and X9R capacitors. Interestingly, improvements of nonlinear properties with very high nonlinear coefficient (α ~ 25.94) and breakdown field (E_b~ 3146.25?V.cm^?1) values were achieved in (Zn05-1) ceramic, as well.     

Ferromagnetism and optical properties of La1???x Al x FeO3 nanopowders

La_{1 − x} Al _x FeO₃ (x = 0.0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) nanopowders were prepared by polymerization complex method. All prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and UV-vis spectrophotometry (UV-vis). The magnetic properties were investigated using a vibrating sample magnetometer (VSM). The X-ray results of all samples show the formation of an orthorhombic phase with the second phase of α-Fe₂O₃ in doped samples. The crystallite sizes of nanoparticles decreased with increasing Al content, and they are found to be in the range of 58.45 ± 5.90 to 15.58 ± 4.64 nm. SEM and TEM images show the agglomeration of nanoparticles with average particle size in the range of 60 to 75 nm. The FT-IR spectra confirm the presence of metal oxygen bonds of O-Fe-O and Fe-O in the FeO₆ octahedra. The UV-vis spectra show strong absorption peaks at approximately 285 nm, and the calculated optical band gaps are found to be in the range of 2.05 to 2.09 eV with increasing Al content. The M-H loop of the pure sample is antiferromagnetic, whereas those of the doped samples tend to be ferromagnetic with increasing Al content. The magnetization, remanent magnetization, and coercive field of the Al-doped sample with x = 0.5 are enhanced to 1.665 emu/g, 0.623 emu/g, and 4,087.0 Oe, respectively.     

Very low loss tangent and giant dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics prepared by the sol–gel process

The pure phase of CaCu₃Ti₄O₁₂ (CCTO) powder can be successfully synthesized by the sol–gel process. CCTO ceramic samples were synthesized at different sintering temperatures of 1015 and 1050?°C and sintering times of 8 and 10 h. X-ray diffraction results indicated a pure phase for all ceramic samples. Rietveld refinements were adopted for the calculation of lattice constants. Scanning electron microscopy micrographs revealed the effect of sintering conditions on the microstructural evolution of ceramic samples. X-ray absorption near edge spectroscopy was performed to determine the oxidation state of Cu and Ti ions in ceramic samples. The dielectric and non-linear current voltage properties of CCTO ceramic samples were systematically investigated. Interestingly, very low loss tangent (tanδ?<?0.017 at 30?°C and 1 kHz) and giant dielectric constant (ε′?～?10,942) with temperature coefficients less than ±15% in a wide temperature range of ?60 to 125?°C were obtained in the CCTO ceramic sample sintered at 1015?°C for 10 h (CCTO1-10). This suggests a potential use for CCTO1-10 sample in capacitor applications. All CCTO ceramic samples display non-linear characteristic with non-linear coefficient (α) and breakdown field (E _b ) values in the range of 5.69–11.02 and 1415–4294, respectively.     

Synthesis and structure analysis of La0.5SR0.5TiO3 nanoparticles prepared by thermal decomposition method

La0.5Sr0.5TiO3 (LSTO) nanoparticles were synthesized by thermal decomposition method using Cl3La, CI2Sr x 6H2O and C16H28O6Ti as starting materials. The obtained precursor in a powder form was calcined at 700, 900, 1100 and 1300 degrees C for 3, 6 and 9 h in air. The structures of all samples were analyzed by XRD and some of them were taken for SEM, TEM and VSM measurements. The results from SEM showed the parallelpipe like shape of the particles with sizes distributed between 80 and 180 nm and the sizes of these particles were increased with the increasing of calcination temperature and time. The XRD's results showed the perovskite structure with the lattice type of orthorhombic at the calcination temperature of 900, 1100 and 1300 degrees C for 3, 6 and 9 h. The TiO and others unknown phase were found at low calcination temperature and they were disappeared as the calcination temperature and time were increased. The results of TEM support the orthorhombic structure of LSTO nanoparticles with crystallite size less than 200 nm as revealed by SEM and XRD. The magnetic property of all samples was measured by VSM and revealed that those prepared at 700, 900, and 1100 degrees C exhibit diamagnetic behavior, whereas one at 1300 shows ferromagnetism at room temperature. In this work, it is found that the nano-LSTO of high crystalline phase and purity can be prepared by thermal decomposition method at calcination temperature of 900 to 1300 degrees C in air for 6-9 h.     

Hydrogen adsorption of Li functionalized Covalent Organic Framework-366: An ab initio study

This work deals with the investigations of hydrogen adsorption energies of the Li functionalized Covalent Organic Framework-366 (COF-366) by using the density functional theory method. Based on total energy calculations, it was found that Li atom is preferentially trapped at the center site of the tetra(p-amino-phenyl) porphyrin and the onN site of a terephthaldehyde chain. Moreover, hydrogen adsorption energies per H₂ for 1–3 H₂ loadings range from 0.03 to 0.22 eV. According to ab initio molecular dynamics simulations, our results found that hydrogen capacities of Li functionalized COF-366 at ambient pressure are 2.06, 1.58, and 1.05 wt% for 77, 150 and 298 K, respectively.     

La0.5Sr0.5TiO3 nanopowders prepared by the hydrothermal method

La_0.5Sr_0.5TiO₃ nanopowders were prepared by the hydrothermal method. The influence of processing parameters, including KOH concentration, reaction temperature and reaction time on the obtained products were studied. The structure and morphology of the obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that pure phase La_0.5Sr_0.5TiO₃ nanopowders can be successfully synthesized with 2 M KOH concentration at a low temperature of 220 °C for 24 h. In addition, the product has a plate-like shape with particle sizes in the range of 25–100 nm as estimated by TEM.