Mohd Mustafa Awang Kechik

Role of Nd2O3 nanoparticles addition on microstructural and superconducting properties of YBa2Cu3O7-δ ceramics

Abstract The effects of Nd2O3 nanoparticles addition on microstructure, transport and AC susceptibility properties of YBa2Cu3O7-δ (Y123) superconductors were systematically investigated using X-ray diffraction (XRD), scanning electron micrograph (SEM), four point probe measurement and AC spectrometer. It was found that the added samples were predominant by Y-123 phase beside small amount of Y-211 and unreacted Nd2O3 secondary phases. All added samples preserved the orthorhombic structure similar to the pure sample and no orthorhombic-to-tetragonal transition occurred. The samples became more porous and their grain size significantly decreased with addition of Nd2O3. The addition of nano-Nd2O3 disturbed the grain growth of Y123, thus resulting in the degradation of superconducting properties of the samples. The superconducting transition temperature (Tc onset) of samples decreased from 92 K for x=0.0 to 78 K for x=1.0 wt.%, which could be attributable to oxygen vacancy disorder. From AC susceptibility result, the inter- and intra-granular loss peaks became wider and broader with increase of Nd2O3 addition due to the weakening of grains coupling. On the other hand, the inter-granular critical current density, Jcm, was found to increase with Nd2O3 addition and had the highest value at x=0.6, confirming that Nd2O3 nanoparticles acted as pinning centers in Y123 matrix.

Influence of uncertainty in dielectric properties on the design performance of a tunable composite right/left handed leaky wave antenna

Uncertainties of the order of 8 % in the accuracy of lithography used to define co-planar waveguides on ferroelectric thin films lead to a similar uncertainty in the value of relative permittivity of the film extracted from measurements. When such films are used as the tunable elements in a tunable composite right/left handed leaky wave antenna, such variations of the capacitance of the varactors can lead to a reduction in radiation and total efficiency around of the order of 1 dB in 5 dB due to the appearance of a bandgap in the frequency response.

Structural, electrical and magnetic properties of polycrystalline La0.67(Ca1−x Sr x )0.33MnO3 manganites

Polycrystalline La0.67(Ca1−xSrx)0.33MnO3 with different substitution level of strontium element, were synthesized via solid state reaction. Structure of samples was characterized by X-ray diffraction (XRD). XRD patterns reveal that La0.67Ca0.33MnO3 exhibits orthorhombic structure with space group Pnma. Phase transitions from orthorhombic to rhombohedral take place as Ca ions were gradually substituted by Sr ions. The XRD data were further analyzed by Rietveld refinement technique. The data show that Mn–O–Mn bond angle increases as x increases. Microstructures obtained from SEM show that substitution of Sr ions has demoted the grain growth and densification process during sintering. The substitution of Sr ions has greatly influenced the hopping integral of electron via double exchange interaction, thus affecting the electrical properties and magnetic properties as well. The resistivity decreases and the metal–insulator transition temperature (Tp) shifts to higher temperature as x increases. The magnetoresistance (MR) effect gradually decreases and MR peak shifts to higher temperature as x increases. The magnetization measured at room temperature is found to be increasing as x increases.

Effects of Calcination Temperature on Microstructure and Superconducting Properties of Y123 Ceramic Prepared Using Thermal Treatment Method

Thermal treatment method was employed to produce YBa2Cu3Ox superconductor ceramic. The effects of calcination temperature at 850 °C, set A, and 910 °C, set B, for 24 h followed by sintering at 930, 950 and 980 °C, were investigate using X-ray diffraction (XRD), scanning electron microscope (SEM) and four point probe measurement. The orthorhombic structure appears after calcination at 850 and 910 °C beside small amount of impurity phase such as Y2BaCuO5 (Y211). The samples exhibited metallic behaviour and the critical temperature, TC(R=0), increases with increasing sintering temperature. The TC(R=0) of samples calcined at 910 °C is higher than that of sample calcined at 850 °C. The highest TC(R=0), 87 K, was found for sample sintered at 980 °C of set B. An increase in grain size and homogeneity was observed as the sintering temperature increases. The set B sample sintered at 980 °C showed compact grains, which could result in the highest Tc (R=0).

Effect of heat treatment condition on the phase formation of YBa2Cu3O7-δ superconductor

Polycrystalline samples with the nominal composition YBa2Cu3O7-δ (Y-123) were prepared using the co-precipitation method. The effect of the calcination process (single and multiple calcinations) on the samples was investigated by using the four-point temperature-resistance measurement, x-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM). This study is divided into two parts. For the first part, the obtained oxalate powder underwent two calcination processes at 900 °C for 12 h and 900 °C for 24 h, respectively. Then, the powders were pressed into pellets and sintered at 920 °C for 15 h with oxygen flow during the entire heat treatment. In the second part, only one calcination process was undertaken at 900 °C for 24 h before the sintering process in oxygen flow at 920 °C for 15 h. From the XRD patterns, all of the peaks were indexed to the Y-123 phase showing that this superconducting phase was already formed after the first calcination. The volume fraction of Y-123 of the samples with single calcination process was higher compared to multiple calcination processes. From the temperature-resistance measurement, all the samples showed metallic behavior in the normal state and a superconducting transition to zero resistance. The superconducting transition temperature, Tc, for the samples prepared in a single calcination process is higher than that of the multiple calcination processes.

Phase Formation and Electrical Transport Properties of Nano-Sized SnO 2 Added (Tl 0.85 Cr 0.15 )Sr 2 CaCu 2 O 7-δ Superconductors

In this work, the effect of nano-sized SnO2 addition on the phase formation and electrical transport properties of (Tl0.85Cr0.15)Sr2CaCu2O7-δ (Tl-1212) superconductor was investigated. Thallium-based high temperature superconductor (HTS) with nominal starting composition (Tl0.85Cr0.15) Sr2CaCu2O7-δ was prepared using high purity oxide powders via solid state reaction method. Nano-sized SnO2 with 0.01 – 0.05 wt.% were added into Tl-1212 superconductors. The characteristic of the samples were determined by powder X-ray diffraction method (XRD), scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), electrical resistance measurements and transport critical current density measurements. Nano-sized SnO2 added (Tl0.85Cr0.15)Sr2CaCu2O7-δ showed Tc-zero between 93 and 95 K. All of the samples indicated a dominant phase of Tl-1212 with a minor phase of Tl-1201. The highest Jc (at 77 K) was shown by sample with 0.03 wt.% at 3260 mA/cm2. SnO2 has significantly enhanced the transport critical current density of Tl-1212 superconductor by acting as flux pinning centers. However, further addition of nano-sized SnO2 in Tl-1212 superconductor caused degradation in Jc. The SEM micrographs with energy dispersive X-Ray analysis (EDX) showed that SnO2 were well distributed in all the samples.