K. Azman

Influence of Na, Mg and Yb Substitution for Ca in Bi(Pb)-2223 Superconductor

The effect of Ca substitution by Na, Mg and Yb on the structural and transport properties of Bi1.6Pb0.4Sr2Ca2-xMxCu3Oy (M = Na, Mg and Yb) (x = 0.0 and 0.2) superconducting samples have been investigated. The samples were prepared by the coprecipitation (COP) method. The samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrical resistivity measurement and critical current density. The critical current density (Jc) and transition temperature (Tc zero) of Na, Mg and Yb substituted with x = 0.2 were found to be lower than the pure sample. Tc zero varies between 100 K and 63 K. Mg concentration was found to give the highest Tc zero of 93 K. Tc zero gradually decreased from Mg, Yb to Na corresponding to a small change in the carrier concentration. Jc decreased with Mg, Yb and Na substitution, and it was measured to be 7.4611 A/cm2, 0.0667 A/cm2, 1.4579 A/cm2 and 1.2479 A/cm2 for pure, Na, Mg and Yb substitution, respectively at 60 K. XRD analysis showed that the decrease of the volume fraction for the 2223 phase and increase of the volume fraction for the 2212 phase with substitution of Na, Mg and Yb. The proportion of Bi-2223/Bi-2212 (%) was estimated from 78.13/21.87 for pure to 51.71/48.29 for Na substitution.

Luminescence spectra of TeO 2-PbO-Li 2O doped Nd 2O 3 glass

A tellurite glass of TeO2-PbO-Li2O doped with Nd2O3 has been successfully fabricated by using the conventional melt-quenched technique. The absorption and emission spectroscopy have been identified using UV-VIS-NIR and photoluminescence spectrometer, respectively. From the spectroscopy, ten significant spectra have been observed in the region of 400-900 nm. The absorption wavelength centered at 585 nm attributed to 4I9/2 → 4G5/2 transition is the predominant wavelength to be used as the excitation wavelength. Emission spectra have been determined by using 585 nm excitation wavelength at room temperature. From the emission spectra, seven distinctive upconversion bands contributed from Nd3+ were observed in the region of 400-1500 nm. It was found that the bands were centered at 450 nm (4G11/2 → 4I9/2), 485 nm (4G11/2 → 4I11/2), 605 nm (4G11/2 → 4I15/2), 665 nm (4G7/2 → 4I13/2), 880 nm (4F3/2 → 4I9/2), 1062 nm (4F3/2 → 4I11/2) and 1340 nm (4F3/2 → 4I11/2), respectively. Tthese emission bands showed the possibility of visible and near infrared emission spectra.

Fabrication and characterization of Bi1.6Pb0.4Sr2Ca2Cu3-xFexOy superconductor

This paper reports the properties of Bi-2223 superconductors that had been doped with Fe2O3 at Cu-site of the system. It was prepared in bulk form using high purity oxide powders via solid state reaction technique with intermediate grinding. A series of x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 of Fe were stoichiometrically added to the well balanced of Bi1.6Pb0.4Sr2Ca2Cu3-xFexOy in order to trace the effect of Fe doping. Hence, electrical resistivity, X-ray diffraction and Field Emission Scanning Electron Microscopy have been carried out to assess the effects of Fe doping. These measurements indicate that Fe doping decreased the critical temperature and degrade the formation of high Tc phase compared with the undoped sample. The orthorhombicity parameters were increased due to substitution of Cu 3+ ion by Fe 2+ ion.

DC and Thermal Conductivity of Lithium Zinc Phosphate Glasses

The phosphate glasses, with composition (60-x)P2O5-25ZnO-(15+x)Li2O where 0.0 ≤ x ≤ 5.0 mol% are prepared by conventional melt quenching method. The amorphous nature of the glass is determined by X-Ray Diffraction (XRD). The physical properties are measured in term of their density and molar volume. Glass density is found to increase from 2.700 to 2.785 g cm-3 whereas molar volume is found to decrease from 40.735 to 37.488 cm3 mol-1 with respect to Li2O content. The DC measurements are done by using four point probes and the activation energies are determined. Arrhenius plot shows straight line behavior as observed that confirmed the conductivity increased with Li2O content. The activation energy is found to decreases from 0.75 to 0.08 eV as Li2O content is increased in the temperature range from 310 to 420 K. Measurements of the thermal conductivity using Lee’s disc apparatus have been made. It is observed that the maximum and minimum thermal conductivity are 0.2679 and 0.2168 W m-1 K-1 respectively.

Lasing Efficiency of Nd 3+ -Doped Lead Tellurite Glass

Neodymium doped tellurite glass have been proven to be one of the most efficient candidates for photonic application. Nd3+ ions are well known excellent as lasing ions at 1.06μm. However, the efficiency of the lasing activity of the Nd3+ doped tellurite glass need for more discussion especially on the contribution of the atom-atom and atom-ligand bonding based on the Judd-Ofelt theory. Therefore, initiative has been taken in this work to determine the laser efficiency by mean of their oscillator strength and Judd-Ofelt parameters. In order to identify the optical behaviour, good quality of Nd doped tellurite glass should firstly be ready. From the results, it is found that the experimental and calculated oscillator strength results of the glass are found varies from 1.157 x 10-6 to 0.804 x 10-6 and from 2.527 x 10-6 to 2.243 x 10-6 respectively with respect to Nd2O3 composition. The small rms deviation ~10% indicates good fit between experimental and calculated oscillator strength. Meanwhile, the Judd-Ofelt intensity parameters with t = 2, 4 and 6 are found to vary with respect to mol% of Nd content. The 4F3/2→4I11/2 transition for 1.06μm emission which is useful for lasers and optical amplification is totally contributed from electric dipole whereas the magnetic dipole shows no effect. Some other results will be discussed in details.

Study on Optical Absorption and Structural Bonding of Lithium Zinc Phosphate Glasses

Glasses with chemical composition of (60-x)P2O5-25ZnO-(15+x)Li2O with 0.0 ≤ x ≤ 5.0 mol % are prepared by melt quenching technique. The physical properties, by mean of density and molar volume are determined. The amorphous nature, absorption and structural behaviour are characterized using X-ray Diffraction (XRD), Ultraviolet-visible-near infrared (UV-Vis-NIR) and Fourier transform infrared (FTIR) respectively. In this work, the glass densities are found increases in the range of 2.70 - 2.78 gcm-3 and molar volume decreases from 37.48 - 40.75 gcm-3 with respect to Li2O concentration. Meanwhile, the optical band gap energy for direct and indirect transition are found decreases from 3.074 eV to 2.525 eV and 2.699 eV to 1.670 eV respectively. The Urbach energy is varies as Li2O content increases. The refractive index of these glasses is ranging from 2.48 to 2.90. FTIR spectra exhibited seven bands which centered at 512 cm−1, 767 cm−1, 918 cm−1, 1087 cm−1, 1281 cm−1, 1627 cm−1 and 3441 cm−1 wavenumber that assigned as vibration of Zn-O, symmetric stretching vibration of P-O-P rings, asymmetric stretching vibration of P-O-P groups, asymmetric stretching of PO2-group, asymmetric stretching vibration P=O, bending vibration of water molecule and fundamental stretching of hydroxyl group.

The Influence of Ce-Doping on Structural and Superconducting Properties in Low-Density Bi1.6Pb0.4Sr2Ca2-xCexCu3Oy Superconductor

The influences of cerium doped on low density Bi-2223 superconductor have been studied and this study examines the significant changes in the structural and superconducting properties. The nominal compositions of low density Bi1.6Pb0.4Sr2Ca2-xCexCu3Oy (where x =0.000, 0.025, 0.05, 0.1 and 0.2) ceramic superconductor were prepared by solid state method. The effects of different Ce doping levels on the superconductor structure and superconducting properties has been investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), electrical resistance and transport critical current density (JC) measurements. The results show that TC zero and JC of the samples reduced gradually with the increase in the Ce addition. It has been observed that, the JC of low density Bi-2223 for Ce-free was measured to be 12.120 A/cm2 and 0.448 A/cm2 in x=0.025 at 60 K under zero magnetic field. As for XRD analysis showed the doping of Ce reduced the volume fraction of the 2223 phase and increased the volume fraction of the 2212 phase. FESEM results showed the surface morphology not homogenous and weak links between superconducting grains of the samples due to increase of the Ce doping.

Effect of Eu Substitution in Low Density Bi (Pb)-2223 High Temperature Superconductors

High temperature superconductor ceramic of low density Bi1.6Pb0.4Sr2(Ca2-xEux)Cu3Oy both doped and non-doped, have been produced by the method of conventional solid state reaction synthesis. The effects of rare earth doping on the low density superconducting compound have been studied by considering Eu substitution at Ca site to stoichiometric of Bi (Pb)-2223 with x ranging from 0.000 to 0.2000. The experimental works in this study consist of direct-current (DC) electrical resistance-temperature and critical current density measurements for both electrical and superconducting properties, and powder X-ray diffraction (XRD) for phase analyses and lattice parameters while Field Emission Scanning Electron Microscopy (FESEM) for surface morphology. All the Eu-doped samples consist of both low-Tc Bi (Pb)-2212 and High-Tc Bi (Pb)-2223 phases. The substitution of Eu at the Ca site induced the decrease of volume fraction for the Bi (Pb)-2223 phase and the increase of the volume fraction for Bi (Pb)-2212 phase. Eu doping does not enhance the Tc zero but gradually decrease its value and become semiconducting at higher dopant concentration with x=0.200. From FESEM investigation, the grain size started to degrade from x=0.000 to x=0.0100 and form smaller plate-like grain which belong to Bi (Pb)-2212 phase and the grain particles are seem to be coagulated to form clusters for x=0.200.

Influence of Rare-Earth (Doped) on Low-Density Bi1.6Pb0.4Sr2Ca1.9RE0.1Cu3Oδ (RE=Nd, Er) Superconductors via Co-Precipitation Method

Effect of Ca doped by rare-earth elements, Nd and Er (x=0.10) on the structural and transport properties of low density Bi1.6Pb0.4Sr2Ca1,9RE0.1Cu3Oδ (RE=Nd,Er) samples have been investigated. The samples have been prepared via co-precipitation (COP) method from precipitate of saturated solutions of metal acetates, iso-propanol solution and oxalic acid. The metal oxalates powder was subjected to thermal treatment of 24 hours calcination at 845oC and mixed with 0.10 g sucrose C12H22O11 which is used as supplementary filler. The pelletized powder was heated for 2 hours at 400 oC and sintered for at 850oC for 48 hours. All samples show a single step transition in the R-T curves. The critical current density (Jc) and transition temperature (Tczero) for both Nd and Er doped with x = 0.10 were found to be lower than standard samples. Tczero obtained varies between 98 K and 66 K. XRD data showed the decrease of volume fraction for the Bi-2223 phase and increase of the volume fraction Bi-2212 phase with the doping of Nd and Er.

The Preparation and Physical Characteristic of Sm3+ Doped Borotellurite Glass

Borotellurite glasses were generally applied in rare earth optical materials due to their excellent physical properties. Samarium doped borotellurite glasses have been identified as one of the potential candidate for optical applications. Therefore, the aim of this study is to identify the physical properties of Sm3+ doped borotellurite glasses by mean of their density, molar volume, microhardness and X-ray diffraction. In this study, the Sm3+ doped borotellurite glasses of the system (70-x)TeO2-20B2O3-10ZnO-xSm2O3 as the samarium trioxide varies from (x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) have been prepared by melt-quenching method. The amorphous nature of the prepared glass samples have been confirmed through XRD spectral analysis. The values of density are found to vary from 4.541g/cm3 to 4.837g/cm3 as well as the values of molar volume as it varies from 29.118cm3/mol to 28.314cm3/mol with the increase of Sm3+ content. The physical properties corresponding to compositional changes have been analysed and the result are reported and presented.