Key Engineering Materials Vol. 388

Abstract: Carbon doped LiFePO4 precursor particles were successfully prepared by spray pyrolysis. The saccharides such as monosaccharide and disaccharide or organic acid were used as carbon source. SEM observation showed that as-prepared particles had spherical morphology with narrow size distribution. XRD analysis revealed that olivine phase was obtained by heating at 700°C under the atmosphere of argon/hydrogen (5%). Electrochemical measurement revealed that the discharge capacity of LiFePO4 was improved by the addition of carbon. The addition of citric acid was most effective for the stabilization of cycle life.

Abstract: Internal combustion type spray pyrolysis apparatus was used to prepare cathode materials for lithium ion batteries. Spherical LiNi0.5Mn1.5O4 precursor powders with an average size of about 2 m were successfully produced by this technique. After calcination at 800°C, LiNi0.5Mn1.5O4 precursor powders crystallized to a spinel structure. The spherical morphology changed to an irregular morphology at temperatures higher than 900°C. The discharge capacity of the LiNi0.5Mn1.5O4 cathode was 130 mAh/g at 1C. After 300 cycles at 1C, 90% of the initial discharge capacity was maintained, and after 100 cycles at 6C, 70% of the discharge capacity at 1C was maintained.

Abstract: LiNi1/3Co1/3Mn1/3O2 precursor powders were successfully prepared by internal combustion type spray pyrolysis. The production capacity of precursor powders was about 1 kg/h when the solution concentration was 0.5 mol/dm3. Particle size, morphology and crystal phase of LiNi1/3Co1/3Mn1/3O2 powders were characterized by XRD and SEM. XRD showed that a layered rock salt structure with a R3m space group was formed by calcination at 750 °C for 10 h. SEM showed that hollow powders with a particle size of 6 μm and irregular morphology were obtained. The discharge capacity of LiNi1/3Co1/3Mn1/3O2 was 130 mAh/g, which showed good cycle performance.

Abstract: The ternary oxide compositions xZrO2-(0.5–x/2)Al2O3-yP2O5(x=0.8, 0.9, 0.95, 1.0; y=1.0, 1.2, 1.4) and 0.9ZrO2-0.05In2O3-1.4P2O5, xSiO2-(0.5–x/2)Al2O3-1.4P2O5(x=0.9, 1.0) were synthesized by sol-gel methods, and their conductivities were investigated by ac-impedance spectroscopy. The conductivity increased with increasing P2O5 content and with decreasing heat-treatment temperature. The maximum conductivities reached over 10-2 Scm-1 at 150°C for 0.9ZrO2-0.05Al2O3-1.4P2O5 and at 225°C for 0.9SiO2-0.05Al2O3-1.4P2O5.

Abstract: The layer structured titanate KxTi2-xFexO4 (x = 0.80) with the lepidocrocite (-FeOOH) type structure has been prepared in a solid state reaction using K2CO3, anatase type TiO2 and -Fe2O3 at 1373 K. Ion exchange reactions of K+ in the interlayer space were studied in aqueouse solutions. The host layers of the titanate were maintained on the ion exchange reactions and the resulting products were found to contain interlayer water. The interlayer water in the hydrogen ion exchange product was removed by heating at 383 K in a vacuum. The resulting titanate H0.79K0.01Ti1.20Fe0.80O4 was evaluated for its use as the cathode in a rechargeable lithium battery. The cathode exhibited discharge and charge capacities of 107 and 69 mAh/g for the first cycle in the voltage range of 1.5 - 4.2 V.

Abstract: TiO2 was crystallized to form particles in aqueous solutions containing ammonium hexafluorotitanate and boric acid. XRD diffraction patterns indicated they were in a single phase of anatase TiO2. TiO2 particles prepared at 90 °C exhibited N2 adsorption-desorption isotherms of type IV. BET specific surface area of the particles was estimated to 13 m2/g. On the other hand, TiO2 particles prepared at 50 °C exhibited N2 adsorption-desorption isotherms of type I. BET specific surface area of the particles was estimated to 168 m2/g. Crystal growth of TiO2 was strongly affected by synthesis temperature. Nano-sized pores or surface structure of TiO2 particles prepared at 50 °C would increase N2 adsorption volume to realize high BET specific surface area. Additionally, aqueous solution process described here had an advantage that TiO2 crystallized at ambient temperature. Anatase TiO2 was prepared without annealing at high temperature which caused aggregation of particles and disappearance of surface nanostructures. The particles with large surface area can be thus utilized for catalyst, cosmetic, photocatalyst, dye-sensitized solar cell or sensors.

Abstract: We report synthesis of well-grown blue phosphor powder, CaMgSi2O6:Eu2+, from new vapor phase method (Flash creation method) derived nanopowder precursor. Single phase phosphor sample was obtained by post-annealing at 1100 oC. Luminescence properties were compared with that of the sample synthesized by a conventional solid state reaction. The post-annealed sample showed intense blue emission under UV excitation.

Abstract: Barium titanate (BaTiO3) nanocube particles below 20 nm were prepared by solvothermal method. To prepare nanocubes, a selection of organic solvent and inorganic materials of Ba and Ti sourses was most important. At the temperatures above 200 °C, a nucleation and particle growth of BaTiO3 nanoparticles led to a formation of the BaTiO3 nanocubes with a size of 10-15 nm.

Abstract: The purpose of this study is to prepare high-quality TiO2 thin films suitable for dye-sensitized solar cells using electrophoresis method. A high-quality TiO2 thin film without crack could be deposited using highly dispersed colloidal solution of TiO2 fine particles. Highly dispersed colloidal solution was prepared using mechanical milling (MM). The two electrodes of electrophoresis were set parallel to liquid level. Optimum preparing condition to disperse TiO2 fine particles using MM could be found. Under this condition, homogeneous TiO2 thin film was deposited on ITO glass. The open-electromotive force and short-circuit current of dye-sensitized solar cell showed excellent reproducibility.

Abstract: Two-dimensional (2D) Ti1-xCoxO2 nanosheet, a recently discovered ferromagnic nanomaterial, has been investigated by magnetic and magneto-optical measurements. The multilayer films of Ti0.8Co0.2O2 nanosheets exhibit room-temperature ferromagnetism with magnetic moment of 1.4 μ B/Co. We also observe robust magnetic circular dichroism near the absorption edge at 4 eV, indicating a strong spin polarization in this 2D system. The first-principles study of Ti1-xCoxO2 nanosheet characterizes the ferromagnetic state with a spin-orbit-induced anisotropy.