Jiten Ghosh

Dielectric relaxation and ac conductivity behaviour of polyvinyl alcohol–HgSe quantum dot hybrid films

Here we report a comparative study on the dielectric relaxation and ac conductivity behaviour of pure polyvinyl alcohol (PVA) and PVA?mercury selenide (HgSe) quantum dot hybrid films in the temperature range 298?K???T???420?K and in the frequency range 100?Hz???f???1?MHz. The prepared nanocomposite exhibits a larger dielectric constant as compared to the pure PVA. The real and imaginary parts of the dielectric constants were found to fit appreciably with the modified Cole?Cole equation, from which temperature-dependent values of the relaxation times, free charge carrier conductivity and space charge carrier conductivity were calculated. The relaxation time decreases with the quantum dots inclusion in the PVA matrix and with an increase in temperature, whereas free charge carrier conductivity and space charge carrier conductivity increases with an increase in temperature. An increase in ac conductivity for the nanocomposites has also been observed, while the charge transport mechanism was found to follow the correlated barrier hopping model in both cases. An easy-path model with a suitable electrical equivalent circuit has been employed to analyse the temperature-dependent impedance spectra. The imaginary part of the complex electric modulus spectra exhibit an asymmetric nature and a non-Debye type of behaviour, which has been elucidated considering a generalized susceptibility function. The electric modulus spectra of the nanocomposite demonstrate a smaller amplitude and broader width, as compared to the pure PVA sample.

Room temperature multiferroicity in orthorhombic LuFeO3

From the measurement of dielectric, ferroelectric, and magnetic properties, we observe simultaneous ferroelectric and magnetic transitions around ∼600 K in orthorhombic LuFeO3. We also observe suppression of the remanent polarization by ∼95% under a magnetic field of ∼15 kOe at room temperature. The extent of suppression of the polarization under magnetic field increases monotonically with the field. These results show that even the orthorhombic LuFeO3 is a room temperature multiferroic of type-II variety exhibiting quite a strong coupling between magnetization and polarization.

Semiconducting selenium nanoparticles: Structural, electrical characterization, and formation of a back-to-back Schottky diode device

Well crystalline selenium nanoparticles having an optical band gap of 2.95 eV have been synthesized using oxalic acid. Microstructural parameters such as crystallite size, lattice strain, cell parameters, and unit cell volume are estimated from X-ray diffraction line profile analysis by Rietveld refinement technique. dc and ac transport properties of the nanoparticles in the temperature range 300 K ≤ T ≤ 390 K and frequency range 20 Hz ≤ f ≤ 2 MHz have also been studied. The values of dc activation energies in the low and high temperature regions are found to be 0.083 eV and 0.382 eV, respectively. The charge transport mechanism of the sample follows correlated barrier hopping (CBH) model and the calculated value of barrier height and relaxation time is 0.786 eV and 2.023 × 10−11 s, respectively, while grain boundary contribution being greater than the grain contribution. Considering metal electrode-semiconductor contact as a back-to-back Schottky diode device, analysis of the current-voltage and capacita...

Structural characterization and observation of variable range hopping conduction mechanism at high temperature in CdSe quantum dot solids

We have used Rietveld refinement technique to extract the microstructural parameters of thioglycolic acid capped CdSe quantum dots. The quantum dot formation and its efficient capping are further confirmed by HR-TEM, UV-visible and FT-IR spectroscopy. Comparative study of the variation of dc conductivity with temperature (298 K ≤ T ≤ 460 K) is given considering Arrhenius formalism, small polaron hopping and Schnakenberg model. We observe that only Schnakenberg model provides good fit to the non-linear region of the variation of dc conductivity with temperature. Experimental variation of ac conductivity and dielectric parameters with temperature (298 K ≤ T ≤ 460 K) and frequency (80 Hz ≤ f ≤ 2 MHz) are discussed in the light of hopping theory and quantum confinement effect. We have elucidated the observed non-linearity in the I-V curves (measured within ±50 V), at dark and at ambient light, in view of tunneling mechanism. Tunnel exponents and non-linearity weight factors have also been evaluated in this re...

Structural phase transitions during high-energy ball milling of BaTiO3

Microstructural characterization of ball milled perovskite BaTiO3 powders has been done by the modeling of X-ray diffraction profiles. The study reveals that on size reduction, BaTiO3 powders undergo a continuous, displacive, and diffusionless dynamic phase transitions involving tetragonal (T), monoclinic (M), and orthorhombic (O) symmetry via the second-order type [T → (T + M) → (M + O) → O] when stimulated by a high-power pulse of pressure in a planetary mill. The order parameter, a phenomenological quantity to describe the general behavior of a system going through phase transitions has been estimated using spontaneous strain calculated from lattice parameters or physical distortions derived from atomic coordinates or both. At room temperature, BaTiO3 nanoparticle achieved an orthorhombic phase when a critical size (<15 nm) has been reached at later stage of milling (≥70 h). Ramans study reveals similar structural phase transitions sequence on size reduction and TEM study reveals the corresponding particle diameter.

Iron ore tailing: a waste material used in ceramic tile compositions as alternative source of raw materials

In the present study, three batch compositions were prepared utilizing iron ore tailing in the range of 45-60 wt%, clay 25-35 wt% and feldspar 15-20 wt%. The compacts were heated in the temperature range of 1100o-1150oC. All the samples heated at 1150oC possess very high cold crushing strength (>150 MPa) and high flexural strength (>60 MPa) with less than 0.1% water absorption. Such high mechanical strength is beneficial for floor tiles to prevent impact damage. The phase evolution during heating of the mixture of iron ore tailing, clay and feldspar have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) studies with energy dispersive X-ray analysis (EDX) of selected samples.

Multiphase transformation and hybrid nanostructure under non-equilibrium and equilibrium condition during high-energy ball milling of BaTiO3 powders

BaTiO3 is a well-known technologically important electroceramic material. In the present study high-energy ball-milling processing for producing distortion in the parent thermodynamically stable tetragonal BaTiO3 has been followed. This has produced nano-sized particles as well as a reactive surface. The intention of the present work is to study (i) structural changes on mechanical activation of perovskite BaTiO3 phase and (ii) possible formation of lattice defect as a result of lattice strain generated during milling that can serve peculiar channels of enhanced diffusion of gas molecules at ambient condition. Catalytic activity of nano-sized BaTiO3 has been explained on a result of high structural distortion brought into solid by milling.

ROS mediated high anti-bacterial efficacy of strain tolerant layered phase pure nano-calcium hydroxide

The present work provides the first ever report on extraordinarily high antibacterial efficacy of phase pure micro-layered calcium hydroxide nanoparticles (LCHNPs) even under dark condition. The LCHNPs synthesized especially in aqueous medium by a simple, inexpensive method show adequate mechanical properties along with the presence of a unique strain tolerant behaviour. The LCHNPs are characterized by FTIR, Raman spectroscopy, XRD, Rietveld analysis, FE-SEM, TEM, TG-DTA, surface area, particle size distribution, zeta potential analysis and nanoindentation techniques. The LCHNPs have 98.1% phase pure hexagonal Ca(OH)2 as the major phase having micro-layered architecture made up of about ~100-200nm thick individual nano-layers. The nanomechanical properties e.g., nanohardness (H) and Youngs modulus (E) of the LCHNPs are found to have a unique load independent behavior. The dielectric responses (e.g., dielectric constant and dielectric loss) and antibacterial properties are evaluated for such LCHNPs. Further, the LCHNPs show much better antibacterial potency against both gram-positive e.g., Staphylococcus aureus (S. aureus) and gram-negative e.g., Pseudomonas putida (P. putida) bacteria even in dark especially, with the lowest ever reported MIC value (e.g., 1 μg ml-1) against the P. putida bacterial strain and exhibit ROS mediated antibacterial proficiency. Finally, such LCHNPs has almost ~8-16% inhibition efficacy towards the development of biofilm of these microorganisms quantified by colorimetric detection process. So, such LCHNPs may find potential applications in the areas of healthcare industry and environmental engineering.

Nano- and micro-tribological behaviours of plasma nitrided Ti6Al4V alloys

Plasma nitriding of the Ti-6Al-4V alloy (TA) sample was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as TAPN. The TA and TAPN samples were characterized by XRD, Optical microscopy, FESEM, TEM, EDX, AFM, nanoindentation, micro scratch, nanotribology, sliding wear resistance evaluation and in vitro cytotoxicity evaluation techniques. The experimental results confirmed that the nanohardness, Youngs modulus, micro scratch wear resistance, nanowear resistance, sliding wear resistance of the TAPN samples were much better than those of the TA samples. Further, when the data are normalized with respect to those of the TA alloy, the TAPN sample showed cell viability about 11% higher than that of the TA alloy used in the present work. This happened due to the formation of a surface hardened embedded nitrided metallic alloy layer zone (ENMALZ) having a finer microstructure characterized by presence of hard ceramic Ti2N, TiN etc. phases in the TAPN samples, which could find enhanced application as a bioimplant material.

Nanotribological response of a plasma nitrided bio-steel.

AISI 316L is a well known biocompatible, austenitic stainless steel (SS). It is thus a bio-steel. Considering its importance as a bio-prosthesis material here we report the plasma nitriding of AISI 316L (SS) followed by its microstructural and nanotribological characterization. Plasma nitriding of the SS samples was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as SSPN. The experimental results confirmed the formations of an embedded nitrided metal layer zone (ENMLZ) and an interface zone (IZ) between the ENMLZ and the unnitrided bulk metallic layer zone (BMLZ) in the SSPN sample. These ENMLZ and IZ in the SSPN sample were richer in iron nitride (FeN) chromium nitride (CrN) along with the austenite phase. The results from nanoindentation, microscratch, nanoscratch and sliding wear studies confirmed that the static contact deformation resistance, the microwear, nanowear and sliding wear resistance of the SSPN samples were much better than those of the SS samples. These results were explained in terms of structure-property correlations.