B. K. Roul

Structure of high-Tc superconducting Bi-Sr-Ca-Cu-O films prepared by spray pyrolysis

Abstract High- T c superconducting films of Bi-Sr-Ca-Cu-O have been synthesized by spray pyrolysis of nitrate precursors onto yttria stabilized zirconia (YSZ), followed by rapid annealing at 840°C in air/oxygen. The films are preferentially oriented with c -axis parallel to the plane of the substrate surface. The diffraction patterns of the films correspond to a mixed phase orthorhombic structure, with different c -values of 24.49 A, 30.78 A and 37.25 A. These films exhibit superconductivity at 91 K and zero resistance at 77 K.

Extended arc thermal plasma assisted sintering of Al-Zr oxide composites

An inexpensive and simple sintering technique using an extended arc thermal plasma assisted heating (EATPAH) source has been designed and fabricated for rapid sintering of Al x -Zr100-x (X = 0, 10, 20,…, 100) oxide composites. High heat and mass transfer kinetics of thermal plasma assisted heating allows quick densification within a few minutes when compared with conventional heating source that takes tens of hours for identical densification. Sintering parameters such as sintering time, plasma power and plasmagen gas flowrate, and initial green density of composites are critically optimized. The green powder compacts sintered at a higher heating rate produced a sample with higher density and fine grain microstructure, whereas abnormal grain growth and lower density result at lower heating rate. This reveals that rapid sintering by EATPAH is effective for promoting the physical densification of the sintered end product. Hardness of the sintered products is studied to understand the density and shrinkage behaviour during plasma sintering. It is observed that highly dense sintered product with greater hardness and homogeneous phase distribution can be prepared within a few minutes by low cost EATPAH technique.

Synthesis of La0.67Ca0.33MnO3 Nanosized Powder Materials by Versatile Chemical Technique

A simple low cost novel synthesis method was developed to prepare nanosized La0.67Ca0.3MnO3 (LCMO) without any requirement of a calcinations step at high temperature. Powders synthesized by a new chemical technique were fine and nano‐sized with high purity perovskite structure. The size and topography of the oxides are dependent on the calcinating temperature of the precursors. The resulting particle size is in the range of 20 to 100 nm as determined by transmission electron microscopy. The magnetization of LCMO nanophase is strikingly dependent on the particle size. The sample prepared from 600°C calcined sample sintered at 1200°C for 4 hour shows metal‐to‐insulator transitions at around 265 K. Bulk LCMO prepared from these powders shows excellent structural, magnetic and magneto‐transport properties.