Papers by Keyword: Solid State Reaction

Abstract: Present investigation provides experimental studies on cylindrical dielectric resonator antennas (CDRAs) fabricated from SrTi_1-xZr_xO₃ ceramic with different substitution of Zr in place of Ti for (0 ≤ x ≤1). Ceramic powder were prepared using conventional solid state reaction method. X-ray Diffraction exposes physical properties Zr-doped SrTiO₃ which exhibit phase transition from cubic, tetragonal to orthorhombic phase. The electrical properties such as dielectric constant (ε_r) and dielectric loss (tan δ) were studied in variation of temperatures and frequencies. At room temperature the dielectric constant decreased from 240 to 21 with increase of Zr content however the amazing result was obtained for multiband antenna by Zr content. The dielectric loss obtain shows very low loss value roughly below 0.07 for all samples. The variations of return loss, resonance frequency and bandwidth of CDRAs at their respective resonant frequencies are studied experimentally.

Abstract: Conventional solid state reaction method was used to prepare BaTiO₃ and Ba_0.99Er_0.01TiO₃ ceramics. Influence of Er³⁺ ion incorporation on their structural, microstructural and electrical properties was studied. The phase pure samples were obtained when heated at 1400 °C for overnight. The tetragonal perovskite phase of BaTiO₃ and Ba_0.99Er_0.01TiO₃ was confirmed by using X-ray Diffraction (XRD) analysis which is in agreement with results obtained from Rietveld refinement analysis. The lattice parameters and unit cell volume of BaTiO₃ increased when doped with Erbium. Microstructural analysis of BaTiO₃ and Ba_0.99Er_0.01TiO₃ ceramics showed that the grain sizes of BaTiO₃ and Ba_0.99Er_0.01TiO₃ significantly decreased. The dielectric properties of BaTiO₃ and Ba_0.99Er_0.01TiO₃ were investigated as a function of temperature and frequency. It revealed that the Curie temperature (T_C) increased by doping Er content from 110 °C to 120 °C. Ba_0.99Er_0.01TiO₃ exhibited the high value of dielectric constant (ε=5929) at T_C of 120 °C. The capacitance-voltage characteristic revealed that the voltage breakdown for both BaTiO₃ and Ba_0.99Er_0.01TiO₃ exceeded 30 V.

Abstract: In this work, Nono-crystalline aluminum carbide particles were synthesized using both mechanical and thermal treatments. Frist, Al and graphite powders had been milled in a planetary ball mill. Then, milled mixtures have been annealed isothermally after the mechanical activation. The effects of two processes on the synthesized products were separately studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous thermal analysis (STA) methods. Further, the grain size, lattice strain and dislocation density values were calculated according to XRD data. The results showed that mechanical alloying process can create an ultra-fine microstructure. The grain size was mostly reduced after 40 h milling as well as the heat treatment at 550 °c and 2 h. in fact, the high rate of plastic deformation of aluminum particle during milling process lead to rising the internal energy of particles, and finally, nanocrystals of Al₄C₃ formed with the size of 14 nm. However, thermal analysis indicated that the mechanical activation of aluminum and the presence of carbon can play key roles in synthesis of aluminum carbide. Key words: Mechanical alloying, annealing, Al and graphite powders, Solid state reaction, Nono-crystalline aluminum carbide.

Abstract: Nanosized spinel Li4Ti5O12 was successfully synthesized by a solid state reaction method at 800°C according to the Li₄Ti₅O₁₂ cubic spinel phase structure. In this synthesizing process, anatase TiO₂ and Li₂CO₃ were used as reactants. The average grain size of the synthesized powders was around 200 nm. The synthesized Li₄Ti₅O₁₂ powder was characterized X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectrometry (EDS), and Specific Surface Area Analyzer (BET, Brunner-Emmett-Teller) respectively. X-ray diffraction results show that calcination temperature and time have the important effects on the crystal structure of Li₄Ti₅O₁₂ powder. In this study, we used a first principle method, based on the density functional theory to explore electronic and structural properties of Li₄Ti₅O₁₂, as anode material for lithium ion batteries. Differences on these properties between delithiation state Li₄Ti₅O₁₂ and lithiation state Li₇Ti₅O₁₂ are compared. All the predicted structural and electrochemical properties agree closely with the experimental findings in literature. The average intercalation voltage of 1.4V during charging/discharging were obtained. We have shown that the Li₄Ti₅O₁₂ material exhibits insulating behavior with the band gap of 3.16 and 3.90 eV using the GGA and GGA+U+J₀ calculations respectively. Li₇Ti₅O₁₂ becomes metallic as Li atoms inserted in Li₄Ti₅O₁₂ material. Spinel Li₄Ti₅O₁₂ has been regarded as an attractive anode material for the development of high-power lithium-ion batteries because of its unique attributes of high safety and rate capability.

Abstract: It has been generally accepted that doping of dielectric materials could significantly contribute to compositional and microstructural evolution, which consequently lead to alteration in dielectric properties. In this study, the effects of adding magnesium (Mg) at 5,10 and 20at% on the chemical composition, microstructure and dielectric constant of calcium titanate (CaTiO₃) synthesized by solid state reaction was assessed. Chemical composition analysis using an X-ray diffraction technique CaTiO₃ doped with 5 at% Mg has been found to contain a single phase whereas samples doped with 10 and 20 at% Mg both exhibited apparent secondary phase (MgO). Microstructural examination however, revealed that no significant variation in particle size, grain size and density were evident among the samples of different Mg contents. Average dielectric constants obtained from the entire samples ranged from 245.9 to 387.6 (at 1 MHz) and the sample with the highest dielectric constant was that doped with 5 at% Mg. Enhancement of dielectric constant in the samples with the lowest level of Mg doping has been attributed largely to the homogeneity of its chemical composition.

Abstract: We report a novel soft chemical synthesis method, water assisted solid state reaction (WASSR) method. This method is very simple and can synthesize many ceramic materials just by storing or mixing raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, well-crystalline SrMoO₄ was obtained using the WASSR method.

Abstract: Structure evolution and morphology of La_0.7Sr_0.3Co_0.8Fe_0.2O_3-δ (LSCF 7328) were investigated during two different preparation methods namely mechanochemical and combination of mechanochemical-solid state. The result shows that no characteristic peak of perovskite oxide was found on the diffractogram of the product of sole mechanochemical method at 600 rpm and up to 12 h of high energy milling process. On the other hand, the manual grinding method that was followed by solid state calcination produces irregular particle size. Due to the result, the combination of both methods was proposed to obtain the fine structure formation and particle size distribution. Rietveld refinement was used to investigate the lattice distortion. It was found that unit cell remains unchanged at increasing milling time. Moreover, the combination method produces regular particle size at milling time of 0.5 h. At longer milling time, the more regular particle size is formed which comes from highly energy transfer of milling.

Abstract: In this research, The effects of NiO nanoparticles on the physical and mechanical properties of Bi_0.5(Na_0.81,K_0.19)_0.5TiO₃ (BNKT) were investigated. The ceramics were synthesized by solid state reaction technique. The powder of BNKT was calcined at 850 °C for 4 h. The ceramics of BNKT/x NiO vol.% ( i.e. x= 0.0, 1.0, 2.0 and 3.0) were sintered at 1000-1150 °C for 2 h for optimize condition. Densification, phase formation, microstructure and micro hardness of samples were characterized via Archimedes method, X-ray diffraction techniques (XRD), scanning electron microscope (SEM) and Vickers micro hardness tester. The X-ray diffraction analysis of the ceramics suggests that all samples exhibited a perovskite structure. Densification of samples tended to increase with increasing amount of NiO content with minimun at 1.0 vol.% NiO additive. The NiO additive influenced densification as well as the mechanical properties of the samples. The results of this research suggest that NiO nanoparticles have influence on physical and mechanical properties of BNKT ceramics.

Abstract: The novel white light emitting phosphors Sr₃Lu_(1-x)Dy_x(PO₄)₃ (x = 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized via a conventional high-temperature solid-state reaction method at 1250°C. The excitation spectrum indicated that these phosphors had a strong absorption in near UV region in the range from 260 to 460 nm. And under 350 nm excitation, the blue emission at 483nm (⁴F_9/2→⁶H_15/2) and yellow emission at 576 nm (⁴F_9/2→⁶H_13/2) were observed in the phosphors, respectively. We studied the effect of different doping concentrations of Dy³⁺ activator on the luminescence properties and found that the optimum doping concentration is 6 mol%. According to the Dexter’s theory, this quenching behavior is ascribed to be electric d-d interaction. Furthermore, the chromaticity coordinate (x = 0.28, y = 0.32) of Sr₃Lu (PO₄)₃:0.06Dy³⁺ phosphor was very close to the “ideal white” (x = 0.33, y = 0.33) in the chromaticity diagram. Our results indicate that the Sr₃Lu (PO₄)₃:Dy³⁺ phosphor can serve as a promising candidate for single-component white light emitting phosphor under near UV excitation.

Abstract: Sc_0.88-xLu_0.05VO₄:Eu³⁺_0.07,Bi³⁺_x(0≤x≤0.05) red phosphors were synthesized by solid state reaction at 1200°C for 3h. The structure, morphology and luminescence spectra of samples are investigated by X-ray diffraction (XRD), Scanning electron microscope (SEM) and fluorescence spectrophotometer, respectively. The samples doped with Eu³⁺, Lu³⁺ and Bi³⁺ maintain the body-centered tetragonal structure of ScVO₄ and the morphology remains essentially unchanged with slight agglomeration. The excitation spectrum of Sc_0.88-xLu_0.05VO₄:Eu³⁺_0.07,Bi³⁺_x emerged redshift and the excitation intensity increase within the near UV excitation (360-400nm). The optimum doping concentration of Bi³⁺ is 0.02(x value), and the maximum emission intensity of Sc_0.86Lu_0.05VO₄:Eu³⁺_0.07,Bi³⁺_0.02 is higher than 88 % in comparison with Sc_0.88Lu_0.05VO₄:Eu³⁺_0.07 under 365 nm excitation. Decay curve of ⁵D₀ state for as-prepared samples fits the single order exponential behavior, the lifetime of ⁵D₀ increase first and then decrease with the increase of Bi³⁺ doping concentration. The internal quantum efficiency is up to 74.08% under 365nm excitation; When the temperature raises to 200°C, the emission intensity maintains 79% of that in the room temperature. Sc_0.86Lu_0.05VO₄:Eu³⁺_0.07,Bi³⁺_0.02 phosphor show high internal quantum efficiency and thermal stability, which is suitable for the UV-pumped white LED as red phosphor.