B K Godwal
Articles written in Bulletin of Materials Science
Volume 23 Issue 2 April 2000 pp 151-154 Instrumentation
Details of a two-dimensional X-ray area detector developed using a charge coupled device, a image intensifier and a fibre optic taper are given. The detector system is especially optimized for angle dispersive X-ray diffraction set up using rotating anode generator as X-ray source. The performance of this detector was tested by successfully carrying out powder X-ray diffraction measurements on various materials such as intermetallics AuIn2, AuGa2, high Z material Pd and low Z scatterer adamantane (C10H16) at ambient conditions. Its utility for quick detection of phase transitions at high pressures with diamond anvil cell is demonstrated by reproducing the known pressure induced structural transitions in RbI, KI and a new structural phase transition in AuGa2 above 10 GPa. Various softwares have also been developed to analyze data from this detector.
Volume 26 Issue 1 January 2003 pp 137-141
Volume 26 Issue 1 January 2003 pp 175-181
We discuss the high pressure behaviour of zinc as an interesting example of controversy, and of extensive interplay between theory and experiment. We present its room temperature electronic structure calculations to study the temperature effect on the occurrence of its controversial axial ratio (𝑐/𝑎) anomaly under pressure, and the related electronic topological transition (ETT). We have employed a dense 63 × 63 × 29 k-point sampling of the Brillouin zone and find that the small (𝑐/𝑎) anomaly near 10 GPa pressure persists at room temperature. A weak signature of the anomaly can be seen in the pressure–volume curve, which gets enhanced in the universal equation of state, along with that of 𝐾-point ETTs. We attribute the change of slope in the universal equation of state near 10 GPa pressure, mainly to hybridization effects. The temperature effect in fact enhances the possibility of 𝐿-point ETT. We find that the 𝐿-point ETT is very sensitive to exchange correlation terms, and hence we suggest that further refinements in the theoretical techniques are needed to resolve the controversies on the ETT in Zn.
Volume 26 Issue 1 January 2003 pp 183-187
We have carried out electronic structure total energy calculations on rhenium in the hexagonal close packed (
Volume 27 Issue 1 February 2004 pp 79-84 Simulation Studies
X-ray holography is a new method of structure determination based on measurement of interference of a known reference wave with an unknown object wave (containing information on atomic sites scattering the reference wave) so that phase information is preserved. Unlike X-ray diffraction, it does not demand for translational periodicity in the material. It is based on the idea similar to that of optical holography and has been tested on crystals, quasicrystals, thin films and doped semiconductors for their structure determination. In order to analyse potentials and limitations of this technique, we have carried out theoretical simulation studies on simple structures. In this paper we describe the basic algorithm of hologram generation and reconstruction of atomic positions from generated data. We illustrate this technique using Fe (
Volume 43, 2020
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