Key Engineering Materials Vols. 280-283

Abstract: The synthesis and electrochemical characteristics of LiNi1-xCoxO2 (0 £ x £ 0.5) used as the promising cathode materials for lithium rechargeable batteries were investigated. The LiNi1-xCoxO2 was prepared by a soft chemistry route in which citric acid was used as the chelating agent to make the sol-gel precursor, then was calcined in oxygen atmosphere at the calcination temperature of 800°C for 12 h. Polycrystalline LiNi1-xCoxO2 possesses a hexagonal lattice of the α-NaFeO2 type characterized by using X-ray diffraction. The discharge capacity of LiNi0.8Co0.2O2 was 169.1 mAh/g with the efficiency of 90.5% in the first cycle and 162.1 mAh/g with only 4% capacity fading in the 10th cycle at 0.2 C rate over a potential range of 3.0-4.2 V.

Abstract: A glass system according to the molar formula (35% mole SiO2- 40% mole B2O3 -(25-x) Li2O), where x=0,1,2 and 3 % mole Fe2O3, was prepared by melting the pure powder chemicals at porcelain crucibles at 1200Co for three hours until the homogenous glass was obtained. The samples were heat treated at 600 and 700 Co for 10 hours. The density, the molar volume, the electrical conductivity and magnetic properties were measured before and after the heat treatment. Replacing the lithium oxide with the iron oxide increases the density, the electrical and magnetic properties. The heat treatment decreases the electrical conductivity and the magnetic susceptibility while increases the density. The crystalline phases due to heat treatment were determined using x-ray diffraction.

Abstract: LiFePO4 powder was obtained by sol-gel processing and was characterized by SEM, XRD, TEM, and surface area measurement of Quantachrome NOVA Automated Gas Sorption system. The cathode performance was evaluated using cylindrical battery. Cycle at C/10, samples sintered at 850°C with specific surface area of 188.5M2/g deliver capacity of 157.5mAh/g and cycle dozens of times without obvious capacity fade.

Abstract: Four kinds of barium-ferrite-containing microcrystalline glass ceramics, such as BaFe12O19/SiO2, BaFe12O19/SiO2-B2O3, BaFe12O19/SiO2-B2O3-K2O and BaFe12O19/SiO2-Al2O3-K2O were prepared by citrate sol-gel process, in which inceptive formation temperatures varied from 850°C to 1100°C. The complex dielectric constant and complex permeability of those glass ceramics were measured at 0.1-5.0GHz, and the frequency dependence of complex dielectric constant and permeability was studied. The microcrystalline glass ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM).

Abstract: The temperature dependence of the magnetization (ac and dc) indicate that Sm1/3Sr2/3FeO3-d undergoes an antiferromagnetic transition at TN = 150 K. In low applied fields, the zero field cooled (ZFC) and field cooled (FC) magnetization below TN exhibit a hysteretic behavior. This behavior is suppressed by high applied field. The ac susceptibility for Sm1/3Sr2/3FeO2.95 shows that there is a clear frequency dependence developing below TN. The relusts of both ac and dc measurements suggest that the antiferromagnetic long-range order coexist with ferromagnetic correlations. Field-dependent resistivity versus temperature measurements reveal the existence of a magnetoresistance (MR) in the temperature below TN. The appearance of some ferromagnetic component within an antiferromagnetically ordered state may be responsible for the MR at low temperature.

Abstract: Strontium hexaferrite powder synthesized conventionally was treated in a hydrogen atmosphere and then recalcined in air. This process had a marked effect on the microstructure and on the magnetic properties of the initial sample. The process was repeated several times and the effects investigated. The results showed that the products of the treatment prior to recalcination are Fe and Sr7Fe10O22 and this resulted in a change in magnetic properties from hard to soft. Consequent calcination, resulted in the reformation of strontium hexaferrite but now with a much finer grain size. This resulted in a significant enhancement of the coercivity. The variation of the coercivity with the number of cycles indicated a maximum value of 413 kA/m which then remained constant with subsequent cycling.

Abstract: Strontium hexaferrite is one of the very important categories of magnetic materials with a wide range applications. One of the very critical parameters in the high temperature method of production of this material is molar ratio of iron oxide to strontium oxide. Although there could be found some reports on the effect of this parameter on the physical properties of the material in the literature but there are very few investigations about the role of this factor on the reactions occurred in the process. In this work the effect of different molar ratios of precursors on the reactions carried out for processing of strontium hexaferrite have been investigated by using thermal analysis techniques such as DTA/TG. Furthermore, the microstructure and the powder and bulk magnetic properties of the products have been studied by SEM, VSM and permeameter.

Abstract: A simple chemical solution deposition method was developed for the preparation of La0.7Ca0.3MnO3 (LCMO) thin films. The LCMO thin films were prepared on Si/SiO2/TiO2/Pt substrates by spin-coating method, followed by heat-treatment at 900°C. The fabrication process of the LCMO thin film was investigated by means of TG-DSC, FTIR, XRD, FE-SEM and EPMA. The electric pulse induced reversible resistance switching is observed in the Ag-LCMO-Pt sandwich structure.

Abstract: The preparation and magnetic properties of Y-type ferroxplana were investigated. Y-type ferroxplana of composition Ba2Zn1.2-xCoxCu0.8Fe12O22 was prepared by citrate sol-gel autocombustion process. X varied from 0 to 1.2. Phase formation was characterized by powder X-ray diffraction (XRD). The microstructure was observed via scanning electron microscopy (SEM). The frequency spectra of initial permeability were measured via an impedance analyzer. Results reveal that a well-defined Y-type phase can be formed after the auto-combusted powders were annealed at 900oC. The synthesized nano-sized powder is very active and can be sintered well at 900oC. The sintered samples have fine-grained microstructure. The samples exhibit excellent magnetic properties in hyper-frequency. As zinc content increases, the initial permeability is enhanced and the cut-off frequency decreases.