Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Department of Physics

Zinc oxide (ZnO) nanostructures have been extensively used as electrochemical sensing material for the development of biosensors and bioimplantable devices. It is important to evaluate their electrochemical performance while developing materials with rapid response time and higher sensitivity. Herein, we present a novel one-step low-temperature hydrothermal technique for simultaneous nitrogen doping and growth of ZnO (N-ZnO) nanostructures. Nitrogen addition is expected to enhance the electron mobility and hence the electrical conductivity of ZnO. The nanostructures were characterized by X-ray diffraction, UV–Vis spectroscopy and field emission scanning electron microscopy. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry using an N-ZnO/Ag/Glass symmetric two-electrode system. The nitrogen addition to ZnO lattice is suggested by XRD peak shift, changing lattice parameters and dislocation density as compared to pristine ZnO. A substantial increase in the electrochemical response and conductivity can be attributed to nitrogen incorporation into ZnO lattice. © 2021, The Author(s), under exclusive licence to The Materials Research Society.

World University root node

School of Advanced Sciences

Vellore Campus

Journal of Materials Research

Single-step hydrothermal synthesis of nitrogen-doped ZnO nanostructures and an insight into its electrochemical properties

Polymer based nanocomposites are gaining attention in various fields of science and technology due to its tunable properties. In this work, we report for the first time, the preparation and study on electrical and mechanical properties of standalone poly(vinyl alcohol) (PVA) based graphite nanoplatelet (GnP) composite films using modified film casting technique. Our modified tape casting method can produce films with uniform thickness, and uniform dispersion of filler deprived of pinholes. This technique is scalable for the mass production of polymer composite films for device application. We have obtained a significant enhancement in the electrical conductivity of 9 orders of magnitude and a maximum value of 0.143 S/m using PVA–GnP composites. To the best of our knowledge, this increase is the highest among the reported values for PVA–GnP composite films. However, a reduction in crystallinity and tensile strength can be seen with the addition of GnP fillers. The maximum tensile strength obtained for PVA–GnP composite films was 15 MPa and is adequate for use in electronic applications and devices. The effect of filler addition in PVA is discussed in detail. © 2020 Wiley Periodicals LLC

Department of Manufacturing Engineering

School of Mechanical Engineering

Journal of Applied Polymer Science

Enhanced electrical conductivity and structural, mechanical characterization of standalone poly(vinyl alcohol)-graphite nanoplatelets composite films

Morphology and properties of ceramics are first attributes of synthesis techniques and sitering temperature. In order to understand the effect of synthesis techniques and sintering temperature 0.55(Ba0·9Ca0.1)TiO3-0.45Ba(Sn0·2Ti0.8)O3(BCT-BST) is synthesized by solid state reaction (SSR), sol-gel method and molten-salt methods. The cubic crystal structure of all the synthesized BCT-BST is confirmed by X-ray powder diffraction analysis. Densification temperature varies between 1250 °C and 1400 °C depending on the synthesis technique. The morphology and particle size of each of BCT-BST is studied using scanning electron microscope. Particle size is found to be in the range of 32 nm–60 nm. Dielectric studies on each of BCT-BST are carried out as a function of temperature and frequency. The morphotropic phase boundary is noticed at 71 °C and a high dielectric constant of 18,000 noticed for sol gel synthesized BCT-BST. A soft ferroelectric hysteresis curve is exhibited by each of BCT-BST. © 2020 Elsevier B.V.

Materials Chemistry and Physics

Effects of synthesis and sintering temperature in BCT-BST ceramics

The ability to design and tune the local crystal structure of chalcogenide materials with the R3¯ m space group in superlattices allows the performance and properties of interfacial phase-change memory materials to be engineered. Designing superlattice materials with high in-plane biaxial strain provides a further path to decrease the switching energy of memory devices. Here, we report how the hexagonal crystal lattice constants and the concomitant phonon modes of Sb2Te3-Bi2Te3, Sb2Te3-Bi2Se3, and Bi2Te3-Bi2Se3 materials can be controlled with a c-axis-oriented texture. Highly oriented iPCM superlattices composed of these pnictogen chalcogenides (Bi2Te3 and Bi2Se3) and GeTe are also demonstrated with a series of variants. This study demonstrates that pnictogen chalcogenide materials can be designed using high-throughput composition spreading. The materials that stem from this study are expected to be useful in high-speed, high endurance, and energy-efficient electronic memory devices. ©

ACS Applied Electronic Materials

Design of c-Axis-Oriented Pnictogen Chalcogenides

Metamaterial (MM) perfect absorbers are realised over various spectra from visible to microwave. Recently, different approaches have been explored to integrate tunability into MM absorbers. Particularly, tuning has been illustrated through electrical-, thermal-, and photo-induced changes to the permittivity of the active medium within MM absorbers. However, the intricate design, expensive nanofabrication process, and the volatile nature of the active medium limit the widespread applications of MM absorbers. Metal-dielectric stack layered hyperbolic metamaterials (HMMs) have recently attracted much attention due to their extraordinary optical properties and rather simple design. Herein, we experimentally realised a reconfigurable HMM perfect absorber based on alternating gold (Au) and Ge2Sb2Te5(GST225) layers for the near-infrared (N-IR) region. It shows that a red-shift of 500 nm of the absorptance peak can be obtained by changing the GST225 state from amorphous to crystalline. The nearly perfect absorptance is omnidirectional and polarisation-independent. Additionally, the absorptance peak can be reversibly switched in just five nanoseconds by re-amorphising the GST225, enabling a dynamically reconfigurable HMM absorber. Experimental data are validated numerically using the finite-difference time-domain method. The absorber fabricated using our strategy has advantages of being reconfigurable, uncomplicated, and lithography-free over conventional MM absorbers, which may open up a new path for applications in energy harvesting, photodetectors, biochemical sensing, and thermal camouflage techniques. © The Royal Society of Chemistry 2021.

Nanoscale Advances

A reconfigurable hyperbolic metamaterial perfect absorber

Owing to their enhanced electrical conductivity, flexibility, cost-effective and simple sampling methods, polymer-carbon nanocomposite material composed of conducting polymers have been referred as an elegant system for supercapacitor applications. Indeed, integration of engineering polymer, which has an insulating property, such as Polyvinyl butyral (PVB), into the conducting matrix is a challenging task. Herein, we introduce a ternary polymer nanocomposite composed of PVB, PANI, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT: PSS) and green-synthesized GQD based functionally stable and optically active system for an efficient supercapacitor application. The polymer-carbon nanocomposite has been prepared as a film by the solution-casting method. The “as prepared” polymeric film was characterized using XRD, TEM, Raman, IR, UV-Vis spectroscopic, laser-optical profilometric imaging and electrochemical techniques. From the collective results, it has been revealed that there is a chemical interaction between the GQD and polymeric systems, presumably due to strong intermolecular hydrogen bonding. Supercapacitor application of the polymer nanocomposite was demonstrated by simply modifying the composite mixture on a conducting substrate-disposable screen-printed carbon electrode. Cyclic voltammetry, electrochemical impedance and galvanostatic charge/discharge experiments were performed with the modified electrode. 1 wt. % GQD loaded ternary polymer-nanocomposite is found to be an optimal system for supercapacitor application. This material showed a capacitance value of 4998 Fg−1cm−2 © 2021

Department of Chemistry

Journal of Energy Storage

A ternary polymer nanocomposite film composed of green-synthesized graphene quantum dots, polyaniline, polyvinyl butyral and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate for supercapacitor application

Controlled synthesis pure-phase Bi0.98Tb0.02Fe1−xCoxO3 (BTFCO, x = 0.01, 0.03, 0.05 and 0.07) nanoparticles with rhombohedral structure using a facile sol–gel method opens the doors to robust their magnetic and photocatalytic properties significantly. The microstructure analysis revealed improvement in the surface morphology with a decrease of average particle size from 64 to 38 nm. No mixed valance state of iron detected for any sample, which is confirmed by Mössbauer spectra. The saturation magnetization and remnant magnetization were increased dramatically from 0.802 and 0.118 emu/g for BFO to 2.261 and 0.737 emu/g, respectively by Tb, Co co-doping. The enhancement of the magnetic property is attributed to the breakdown of spin cycloidal structure, spin canting, and uncompensated spin on the surface of nanoparticles. Furthermore, the as-synthesized samples are highly effective for rhodamin B (RhB) degradation under visible light irradiation, and the possible photocatalytic mechanism discussed in detail. Bi0.98Tb0.02Fe0.93Co0.07O3 nanoparticles exhibit the best photocatalytic activity owing to their larger specific surface area, lower band gap, and reduced average particle size. Besides, 1.2% efficiency retention for the degradation of RhB dye using BTFCO7 after the 20th cycle suggests a potential candidate to address the current scenario in the environmental remediation technology. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.

Journal of Materials Science: Materials in Electronics

Surface engineered Tb and Co co-doped BiFeO3 nanoparticles for enhanced photocatalytic and magnetic properties

Nickel ferrite (NiFe2O4) thin films are grown epitaxially on two different isostructural substrates, (100)-oriented MgGa2O4 and ZnGa2O4, using pulsed laser deposition. These spinel substrates have a lattice mismatch of 0.62% and 0.04%, respectively, with NiFe2O4 crystal. While the films grown on MgGa2O4 substrates exhibit significant strain resulting in a tetragonal distortion of the crystal structure, the films on ZnGa2O4 substrate are essentially strain-free and retain their cubic structure because of the near-perfect lattice match. Magnetometry data suggest that film strain is the principal factor determining the anisotropy of these NiFe2O4 films. This is also confirmed by the effective magnetization values obtained from ferromagnetic resonance (FMR) measurements. While there is only a modest decrease in effective Gilbert damping constant with strain reduction, an enhancement in the spin voltage is observed in the spin Seebeck effect (SSE) measurements for NiFe2O4 films grown on ZnGa2O4 substrate with thickness ≤200 nm. © 2021 Author(s).

Applied Physics Letters

Structural and magnetic properties of NiFe2O4 thin films grown on isostructural lattice-matched substrates

Strontium hexaferrite has achieved immense attention in industries, manufacturing crucial components for devices, technological applications, and machine making due to its high coercivity value. The efficient technique of sol–gel auto-combustion was espoused for the synthesis, and the morphological studies affirmed the hexagonal shape of the particles. The magnetic analysis revealed the sample being a potential substance for perpendicular recording media applications. The dielectric studies disclosed relaxations and polarization effects existing in the material. The linkage of structural, magnetic, and dielectric properties and their inter-influences are the remarkable consequences of the research work. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.

Scrutiny and correlations of structural, magnetic, and dielectric properties of M-type strontium hexaferrite (SrFe12O19) for permanent magnet applications

Resistive switching in lateral devices using vanadium oxide sheets is reported. The devices undergo an electric field induced insulator-to-metal transition (E-IMT). A sudden jump in the current level up to two orders in magnitude at a defined bias voltage and linearly increasing with a further increase in the bias voltage is observed. Further, the devices also show up multi-step sequential breakdown. The relative change in the resistance from high resistance state (HRS) to low resistance states (LRS) during the resistive switching is up to 700. The breakdown voltage and the switching characteristics of the devices strongly depend on the relative humidity. By varying relative humidity controllably from 11% to 95%, the robustness of the switching device is studied. Clear hysteresis in the switching cycles is shown (current–voltage characteristics) at various humidity levels at room temperature. The threshold voltage reduces exponentially with humidity. This dependence of switching voltage with humidity is attributed to the dissociation of water molecules on the VO2 surface. The water molecule donates charge carriers to the VO2 by dissociating on the surface resulting in two hydroxyl ions on the surface in combination with oxygen defect available on the VO2 surface. © 2020 Elsevier B.V.