Kar Ban Tan

Stoichiometry and doping mechanism of the cubic pyrochlore phase in the system Bi2O3–ZnO–Nb2O5

The subsolidus phase diagram of the system Bi2O3–ZnO–Nb2O5 in the region of the cubic pyrochlore phase has been determined at 950 °C. This phase forms a solid solution area that does not include the so-called ideal composition P, Bi3Zn2Nb3O14. It may be described in terms of two compositional variables: ZnO deficiency compared to P together with variable Bi : Nb ratio. Density measurements, preliminary crystallographic studies and the phase diagram indicate the solid solutions to have general formula, Bi3+yZn2−xNb3−yO14−x−y: −0.11(1) ≤ y ≤ 0.14(1) and −0.03(1) ≤ x ≤ 0.31(1).

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 surface morphology of nickel doped Ba1−xSrxTiO3 ceramics prepared by sol–gel technique

Abstract Varied compositions in the barium strontium titanate ternary system were prepared through the slow injection sol–gel technique. Nickel dopant was introduced through a general formula of Ba1 −xSrxTi1 −yNiyO3 (x = 0·4 and 0·5; y = 0·1 and 0·4 mol-%). Thermogravimetric analysis revealed that barium strontium titanate gels were completely dried and stabilised at 1000°C. All barium strontium titanate samples were confirmed as phase pure perovskite by qualitative X-ray diffraction analysis in which Nickel-doped subsolidus solution was formed successfully after calcinations at 1000°C. On the other hand, there was a sign of agglomeration discernible in the prepared BST samples and the grain sizes were found to be in the range of 39·66–71·87 nm.

Synthesis and Characterization of Electrical Properties of Bismuth Titanate

Bismuth titanate solid solutions, Bi12+xTiO10+δ (0 ≤ x ≤ 0.6), were synthesized by conventional solid state method at sintering temperature of 700°C for 48 h. Structural studies were performed by powder X-ray diffraction (XRD) analysis and revealed that single-phase materials were obtained with a general formula of Bi12+xTiO10+δ (0 ≤ x ≤ 0.6). The electrical properties of all the single-phase samples were studied using the impedance spectroscopy technique. Further characterization of the materials was carried out using differential thermal analysis (DTA) and indicated that no phase transition was observed. The TGA analysis was observed and found that all the materials were thermally stable.

Surface morphology of Ni-Fe thin films grown on copper substrates using pulse electrodeposition in ultrasonic field

Nickel-Iron (Ni-Fe) thin films were pulse-electrodeposited on copper (Cu) substrates under galvanostatic mode in the presence/absence of an ultrasonic field. The as-prepared thin films were characterized by X-Ray Diffractometer (XRD) and Scanning Electron Microscopy (SEM). The XRD results confirmed the deposition of NiFe on Cu substrates and the crystallite size calculated from Scherrerpsilas formula is 22.28 nm and 20.17 nm respectively for the films fabricated in the absence and presence of ultrasonic field. The grain sizes, from SEM micrographs, were found to be 225.52 nm and 79.64 nm respectively for the films fabricated in the absence and presence of ultrasonic field and the grains were in the shape of spherical balls.

Surface morphology and particle size analysis of Ba0 .5 Sr 0.5 TiO 3 nano-powder grown using sol-gel method

Barium Strontium Titanate powder in the form of nano cubic particles has been prepared using slow rate gellification by sol-gel method. X-Ray Diffractometer results show that single phase formation occurred at 800 degC and the crystallite size for this sample was found to be 36.06 nm. Scanning Electron Microscopy analysis shows that the particles in the sample calcinated at 800 degC do not agglomerate and the average particle size was found to be 42.30 nm. The nano particle size analyzer results show a narrow particle distribution with good uniformity.