• N GOPALAKRISHNAN

Articles written in Bulletin of Materials Science

• Synthesis of ZrO$_2$ nanostructure for gas sensing application

ZrO$_2$ nanopowder has been synthesized by the conventional precipitation method for gas-sensing application. The synthesized powder was dropcast and subsequently annealed at 100$^{\circ}$C. The drop-casted film has been subjected to X-ray diffraction analysis, scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy, photoluminescence study and $I –V$ measurement in order to observe its structural, morphological, optical and electrical properties. The gas sensing measurement has been performed for the thus prepared ZrO$_2$ film by an exposure to different reducing gases(ammonia, ethanol, formaldehyde, acetone and xylene) at different temperatures for various gas concentrations. It has been observed that the film shows a better response towards ammonia (about 18%) compared to all other gases due to faster diffusion. Also, a quick response and recovery time have been found as 70 and 70 s, respectively, for ammonia.

• Effect of heat treatment on the optical properties of layered muscovite single crystal sheets

Naturally, thin sheets of layered, dioctahedral muscovite single crystals are transparent to visible light. Upon heat treatments performed up to 900$^{\circ}$C, the single crystal sheets of thickness $\sim$200 $\mu$m exhibited changes in its optical transparent character. The muscovite sheets exhibited either translucent or nontransparent, dark-brown, gold or copper like luster, varying optical band gap (from $\sim$3.7 to 2.7 eV) and photoluminescence (PL) properties, which depend on the temperature of the heat treatment. A comprehensive investigation has been made using X-ray diffraction, thermal analyses, energy dispersive X-ray and Raman spectroscopies to understand how/why the optical properties of the muscovite sheets changed up on heat treatments. Besides, no phase changes were found in the layered, lamellar crystal structure, evidences for the known dehydroxylation of muscovite were clearly seen from the thermal analyses data. Further, the Raman spectrum of the muscovite sheet heat treated at 900$^{\circ}$C showed no evidence for the presence of hydroxyl group (OH$^−$), which confirmed the completion of the dehydroxylation. The dihydroxylation-induced changes in the structural-elements (for example, Al-(O,OH)$_6$ partly or fully changing to Al-O$_5$/O$_6$ and its effects on the lattice constants, and also the defect levels introduced by the heat treatments are responsible for the changes in the optical transparency, colour of appearance, band gap and PL of the muscovite natural single crystal sheets.

• # Bulletin of Materials Science

Volume 43, 2020
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020