Somenath Roy

Critical current in electrophoretically deposited thick films of YBCO superconductor

Abstract Thick films of YB 2 Cu 3 O 7 − δ (YBCO) superconductor have been prepared by the electrophoretic deposition technique using flexible silver strip as the substrate. Effects of several deposition parameters, e.g., time of deposition, particle size of the powder, number of layers deposited, etc., on the various properties of the films have been studied in detail. Microstructural investigation of the films indicates extensive grain growth and recrystallization phenomena particularly in films of large thickness. The microstructural morphology changes significantly as the thickness decreases. The transport J c (at 77 K, B =0) increases from ≈450 A/cm 2 for a film thickness of ∼ 65 μ m to > 4000 A/cm 2 for a reduced thickness of ∼ 3 μ m. Possible reasons for this dimensional dependence are discussed.

Kinetic analysis of low concentration CO detection by Au-loaded cerium oxide sensors

Owing to its high toxicity, even at very low concentration, early detection of carbon monoxide (CO) is imperative. We have fabricated sensors comprising gold nanoparticle-loaded cerium oxide (Au–CeO2). The morphology and elemental composition of the sensing material have been characterized using XRD, FESEM, TEM and XPS. The performance of the Au–CeO2 sensors has been studied for the detection of CO in the concentration range of 10–30 ppm in air. The response and recovery transients of conductance have been modeled using two-site Langmuir adsorption kinetics. In the presence of 30 ppm CO, the calculated response times for two energetically different adsorption sites, CeO2 surface and Au/CeO2 interface are 9 s and 7 s, respectively. Finally, an exponential correlation between the gas concentration and the time constants has been derived.

Non-fluorinated synthesis of anatase TiO2 with dominant {001} facets: influence of faceted structures on formaldehyde sensitivity

Titanium dioxide (TiO2), the most widely investigated metal oxide due to its extraordinary surface, electronic and catalytic properties, is better manifested with exposed {001} facets. This article delineates the room temperature synthesis of TiO2 with 90% exposed {001} facets without using any fluorine containing precursor or hazardous material. Cetyltrimethylammonium bromide (CTAB) is explored as a capping agent to suppress the growth of the thermodynamically stable (101) plane. The {001} faceted nanosheets are decorated with gold nanoparticles of mean diameter 10 nm. The materials are characterized using XRD, TEM, XPS, as well as UV-vis, Raman and photoluminescence spectroscopy. The surface reactivities of different facets of TiO2 are substantiated in the light of formaldehyde (HCHO) oxidation. The synergistic effect between the reactive {001} facet of TiO2 and gold nanoparticles towards the photocatalysis of HCHO is also investigated and corroborated using mass spectroscopy.

Non-covalent functionalization of CNTs with polycarbazole: a chemiresistive humidity sensor with tunable chemo-electric attributes at room temperature

This article describes the non-covalent functionalization of multiwall carbon nanotubes (MWCNTs) with polycarbazole (PCz) via an in situ chemical oxidative polymerization method and subsequent fabrication of resistive humidity sensors. The morphological and optical characterizations have been performed using electron microscopy and UV-visible spectroscopy. The performance of the CNT–PCz sensors has been studied for the resistive detection of humidity ranging from 23% RH to 97% RH. The optimum level of CNT loading is assessed by varying the concentration of the nanotubes in the PCz matrix and the highest response (%) was obtained for 1 wt% MWCNT loaded PCz. The observed fast response (13–25 s) and recovery time (22–65 s) along with a considerable response (%) towards humidity render the nanocomposite as a suitable candidate for humidity sensing applications. Interestingly, the humidity sensing properties can be easily switched by varying the CNT concentration in the nanocomposites. Plausible mechanisms are proposed to describe this tunable chemo-electric humidity sensing behavior of the CNT–PCz composites. Further, effort has been made to explain the role of CNTs and polycarbazole in the detection of humidity.

Development of Low-ppm CO Sensors Using Pristine CeO2 Nanospheres with High Surface Area

Mesoporous CeO2 nanospheres with appreciably high surface area are prepared using reversed micelles by a water-in-oil microemulsion method. The structural morphology and semiconducting properties of the nanoparticles are thoroughly investigated using X-ray diffraction, field effect scanning electron microscopy, transmission electron microscopy, and UV–visible spectroscopic techniques. Even after high-temperature calcination, the morphological retention of the material is apparent by electron microscopy. The deployment of undoped CeO2 nanospheres for the detection of low-ppm CO yields superior performances in terms of sensitivity, response–recovery times, and selectivity compared to those of other sensors of the same genre. These CO sensors exhibit ∼ 52% sensitivity with a response time of only 13 s. The sensor parameters are analyzed as a function of both temperature and gas concentration. In addition to that on the cost-effective and scalable synthesis of CeO2 nanospheres, this article also reports on the fabrication of packaged CO sensors, which can be potentially utilized for industrial and environmental monitoring purposes.

Effect of ageing on Sn6O4(OH)(4) in aqueous medium-simultaneous production of SnO and SnO2 nanoparticles at room temperature

Precipitation is one of the dominant techniques for producing tin oxide which requires calcination of the interim tin oxide hydroxide (Sn6O4(OH)(4)) precipitate at different temperatures to render the requisite oxide states. In this study, we mitigated the necessity for calcination through simple ageing of the the as-synthesized Sn6O4(OH)(4) at room temperature (25 A degrees C) in aqueous medium. Ageing for 12 days resulted in phase transition of the interim precipitate and production of discernible layers of black stannous oxide (SnO) and yellow stannic oxide (SnO2) along with the originally formed white layer of Sn6O4(OH)(4) within the same aqueous medium. The phases of tin oxide was confirmed after extracting individual layer and assessing them through X-ray analysis. Thermogravimetric analysis for the as-obtained stannous oxide established its thermal stability up to around 410 A degrees C. Additionally, Field Emission Scanning Electron Microscopy studies performed on the SnO nanoparticles revealed their dimension to be within 25-30 nm range. The mechanisms for SnO and SnO2 formation through ageing has been delineated.