Lim Kean Pah

Modeling of Electrical Transport in YBCO Single Layer Thin Films using Flux Motion Model

The electrical transport properties of YBCO single layers thin film have been investigated using different physical techniques. For the purpose, the physical properties are probed numerically with help of simulation modelling. The physical transport properties were also estimated with temperature and magnetic fields limits using thermally-activated flux flow model with some modifications. The result of present simulation modelling indicated that the magnitude of activation energy depends on temperature and magnetic field. The simulations revealed thickness dependent physical transport properties including electrical and magnetic properties of deposited YBCO single layers thin films. Furthermore, it shows the temperature dependence of the pinning energy. In the nutshell, the result can be used to improve the Superconducting Properties (Tc) of the YBCO single layers thin films.

The Effect of Sintering Temperature on Crystal Structure and Microstructure of Pr0.67Ba0.33MnO3 Ceramic

Polycrystalline perovskite manganites of Pr0.67Ba0.33MnO3 bulk ceramic samples were prepared via conventional solid-state reaction. The influence of structure and microstructure towards sintering temperature of the samples were studied. At lower sintering temperature (900°C, 1100°C and 1100°C) other phases such as PrO2 and BaMnO3 were detected using XRD and further confirmed with EDX analysis. Furthermore, phase purification and crystal structure transformation was observed in sample sintered at 1200°C and 1300°C respectively. SEM analysis indicated that higher sintering temperature promotes grain growth and densification. Overall, in this paper, phase purification and crystal structure transformation had been observed. Orthorhombic structure is more favorable to form at higher sintering temperature for Pr0.67Ba0.33MnO3.

Modeling of electrical properties in the fabrication of layered superconducting thin films

The Pulse laser deposition (PLD) is a sole tool that is used to develop fine quality superconducting (YBCO) epitaxial films. The description and devices application aspect of the PLD on high temperature superconducting epitaxial films have an important role in the field of superconductivity. In the present study, thin films fabrication by PLD, buffer layers and electrical properties have been probed numerically with computer simulations. The electrical transport properties are discussed in term of thermally-activated flux motion model. The present study concludes that the plume dynamics is important in fabricating high quality epitaxial films thus improving the superconducting electrical transport properties.

Effect of Sintering Temperature on the Microstructure, Electrical and Magnetotransport Properties of La0.67Sr0.33MnO3 Compound

In this work, we report the effect of sintering temperature (900°C, 1000°C, 1100°C and 1200°C) on the electrical and magnetotransport properties of polycrystalline La0.67Sr0.33MnO3 (LSMO). Single phase of LSMO hexagonal structure (R-3c) accompanied with minor phases was successfully synthesized by co-precipitation method. With increasing sintering temperature, grain growth was promoted and grain connectivity was improved. It was found that an enhancement of resistivity on smaller grain size was due to larger grain surface over volume (grain boundaries effect). The shifting of the metal-insulator transition (TMI) to higher temperature was also responsible for observed changes in physical properties. TMI of 900°C, 1000°C and 1100°C were 232 K, 278 K and 298 K respectively however 1200°C was out of measurement range (higher than 300 K). In summary, CP900 with smaller grain size distribution (~200 nm) displayed the highest resistivity and MR% of -19.2% (at 80 K, 10 kG).

Purification of Carbon Nanotubes Synthesized by Catalytic Decomposition of Methane using Bimetallic Fe-Co Catalysts Supported on MgO

This work reports the synthesis of carbon nanotubes by catalytic decomposition of methane using bimetallic Fe-Co catalysts supported on MgO. Transmission electron microscopy (TEM) results show the as-prepared carbon nanotubes are multi-walled carbon nanotubes (MWCNTs) with diameter in the range of 15nm to 45nm. Purification of as-prepared MWCNTs was carried out by acid and heat treatment method. EDX results show the Fe, Co and MgO catalysts were successfully removed by refluxing the as-prepared MWCNTs in 3M H2SO4.

X-Ray Powder Diffraction Study on the MgB2 Superconductor Reacted with Nano-SiC: The Effects of Sintering Temperature

SiC added MgB2 polycrystalline samples were synthesized at low (650°C) and high (850°C) temperatures in order to study the sintering effect on the phase formation and superconducting properties. The MgB2 bulks with additions of 0wt%, 1wt%, 3wt% and 5wt% SiC were studied with powder X-ray diffraction technique. We observed that MgB2 remained as the primary phase for both sintering temperatures in all samples with the presence of MgO and Mg2Si as the main impurities. Some diffraction peaks associated with unreacted SiC is also noticeable. The relative intensity of the Mg2Si peaks was found to decrease in samples sintered at higher temperature. Temperature dependent magnetic moment measurements showed that the superconducting transition temperature, Tc decreases as the SiC addition level increases while lower sintering temperature degrades Tc to a greater extent. The changes in the physical properties is discussed based on the results of phase formation, full width half maximum (FWHM), lattice parameter and crystallite size.