Tanmoy Maiti

Evaluation of Experimental Resume of BaZrxTi1-xO3 with Perspective to Ferroelectric Relaxor Family: An Overview

In this paper we report the mechanism and nature of relaxor ferroelectric behavior in the environmental friendly lead free Barium Zirconate Titanate (BZT) system. A revised complete (Structure:Property) phase diagram of Ba(ZrxTi1-x)O3, with compositions 0.00≤ × ≤1.00 has been developed based on their electrical properties. Two different kinds of relaxor behaviors have been observed in the BZT system; one is dominated by polar Ti-rich regions and another by non-polar Zr-rich regions. All the BZT relaxor compositions are characterized by dielectric properties with and without bias, pyroelectric and thermal expansion measurements in the wide range of temperatures. The structure of the BZT compositions has been evaluated by XRD, Neutron diffraction study. Further the local structure of the BZT compositions has been probed by micro-Raman spectra. Although the global structure of BZT relaxors is cubic as observed in Neutron diffraction studies, the local symmetry is non-cubic as evident in the micro-Raman spectra of BZT relaxors as well as in their thermal strain measurement, dielectric and pyroelectric behavior.

In situ spinel bonded refractory castable in relation to co-precipitation and sol–gel derived spinel forming agents

Abstract This paper deals with the preparation and characterization of two types of in situ spinel bonded low cement high alumina based castable refractories. Semidried magnesium aluminate mass was prepared from cheaper precursors via coprecipitation and sol–gel routes for application in a refractory castable composition in different concentrations. The pH, average particle size, solid content, DTG analysis and XRD patterns of those two additives were observed. After being fired at elevated temperatures those two kinds of in situ spinel bonded castables were characterized and compared in terms of bulk density, apparent porosity, cold crushing strength, flexural strength, volume shrinkage, spalling resistance, and XRD phase analysis. Scanning electron microscopy of some selected fired samples was done to analyse the mode of interaction of in situ spinel bonds in castable microstructure. The corrosion resistance of the castables was estimated by heating with blast furnace and converter slags.

Environmentally friendly BaxSr2−xTiFeO6 double perovskite with enhanced thermopower for high temperature thermoelectric power generation

In the present work, the prospects of environmental friendly BaxSr2−xTiFeO6 complex double perovskites have been evaluated for applications as high temperature thermoelectric materials with properties converging to the ‘phonon-glass electron-crystal’ model. BaxSr2−xTiFeO6 compositions with 0.0 ≤ x ≤ 0.25 were synthesized by a solid-state reaction method. The oxide samples were then investigated for their crystal structure (single phase) and morphology by XRD and SEM, respectively. Thermo-power or Seebeck coefficient (S) and the electrical conductivity (σ) of these oxide samples were simultaneously measured to calculate the thermoelectric power factor (S2σ). All the BaxSr2−xTiFeO6 compositions showed p-type non-degenerate semiconductor behavior before semiconductor to metal transition occurred as evident from the temperature dependent Seebeck coefficient of these double perovskites. Conduction mechanisms of these oxides were analyzed using variable range hopping and small polaron hopping conduction models. All these double perovskites exhibited more than 100 μV K−1 thermo-power in the wide range of temperature from 300 K to 1223 K. A very high thermo-power (S) value (∼800 μV K−1) was obtained for BaxSr2−xFeTiO6 with x = 0.25 at 1123 K.

Synthesis and characterization of Sr2TiMO6 (M = Fe,Co) double perovskites for high temperature thermoelectric applications

ABSTRACT The prospects of double perovskites based materials as the candidate for high temperature thermoelectric materials were investigated. Among the various complex perovskites, SrTiO3 based oxides had shown great potential for thermoelectric applications. In the current investigation, Sr2TiMO6 (M = Fe, Co) based double perovskites were synthesized using conventional solid-state route. The oxide samples were then investigated for their crystal structure (single phase) and morphology by XRD and SEM, respectively. Thermopower or Seebeck coefficient (S) and electrical conductivity (σ) of these oxide samples were measured simultaneously in the temperature range from 300 K to 1125 K. Large thermopower was obtained for these oxides in the wide range of temperature. Furthermore, thermoelectric power factor (S²σ) of these oxides were calculated to explore their potential for use in the high temperature thermoelectric devices.

Enhanced thermoelectric figure-of-merit in environmentally benign BaxSr2-xTiCoO6 double perovskites

Environmental friendly, non-toxic double perovskite BaxSr2-xTiCoO6 compositions with 0 ≤ x ≤ 0.2 were synthesized using solid-state reaction route for high temperature thermoelectric (TE) applications. XRD and SEM studies confirmed the presence of single-phase solid solution with highly dense microstructure for all the oxide compositions. Temperature dependent electrical conductivity measurement showed semiconductor to metal (M-S) transition in these double perovskites. Incorporation of barium in Sr2TiCoO6 pushed M-S transition to higher temperature making it a potential candidate for high temperature TE applications. Conductivity behaviors of these oxides were explained by small polaron model. Furthermore, these oxides exhibit a glass like behavior resulting in low thermal conductivity. Low temperature dielectric measurement revealed relaxor ferroelectric behavior in these oxides below room temperature. Transition of these relaxors into a glassy state beyond Burns temperature (TD) was found responsible f...

Far field superfocusing along with enhanced near field emission from hybrid spiral plasmonic lens inscribed with nano corrals slit diffractor

Here, we have numerically calculated electric field intensity and phase of the emission from various hybrid spiral plasmonic lenses (HSPL) in near field as well as in far-field. We have proposed a novel HSPL inscribed with nano corrals slit (NCS) and compared its focusing ability with other HSPLs inscribed with circular slit and circular grating. With the use of nano corrals slit, we have been able to improve light intensity in the far-field without compromising near-field intensity. Our NCS-HSPL outperforms other HSPLs and standalone SPL in near-field as well as far-field. We have also found that proposed circular slit diffractor is far more superior than previously reported circular grating diffractor. We have been able to extend the focal length of hybrid plasmonic lens upto 3 um and observed a two-fold increment in the far field intensity compared to existing spiral plasmonic lens even though size of focal spot remains same. Optical complex fields produced by NCS based HSPL can be used for various applications such as super resolution microscopy, nanolithography, bioimaging and sensing, angular momentum detectors, etc. Moreover, enhanced near-field intensity in conjunction with far-field superfocusing with reasonable focal length may lead to the development of novel multifunctional lab-on-chip devices.

Simulation and Analytical Study of Optical Complex Field in Nano-corral Slits Plasmonic Lens

Although spiral plasmonic lens has been proposed as circular polarization analyzer, there is no such plasmonic nanostructure available for linear polarization. In the current work, we have designed nano-corral slits (NCS) plasmonic lens, which focuses the x- and y-polarized light into spatially distinguished plasmonic fields. We have calculated analytically and numerically the electric field intensity and phase of the emission from nano-corral slits plasmonic lens with different pitch lengths under various polarizations of the illumination. It has been shown that one can control the wave front of the output beam of these plasmonic lenses by manipulating the illumination of both circular and linear polarization. Our theoretical study in correlation with FDTD simulation has shown that NCS plasmonic lens with pitch length equal to λspp produces scalar vortex beam having optical complex fields with helical wave front and optical singularity at the center under circular polarization of light. When NCS lens (pitch = λspp) is illuminated with linearly polarized light, it exhibits binary distribution of phase with same electric field intensity around the center. However, with pitch length of 0.5λspp, NCS shows linear dichroism under linearly polarized illumination unlike spiral plasmonic lens (SPL) eliminating the use of circularly polarized light. Optical complex fields produced by these NCS plasmonic lenses may find applications for faster quantum computing, data storage, and telecommunications.

Role of GO and r-GO in resistance switching behavior of bilayer TiO2 based RRAM

Graphene-based resistance random access memory devices (RRAMs) have shown promise as a suitable replacement for flash memories, owing to their fast switching speed, low programming voltage, better scalability and great reliability. Furthermore, recent research works have shown bi-layer RRAM devices exhibiting better performance along the same parameters, where titania is one of the most commonly used materials. In the present work, we have studied the resistance switching behavior in a bi-layer RRAM device structure of TiO2 with graphene oxide (GO) and reduced graphene oxide (rGO). Switching mechanism in these devices has been investigated by detailed experimental characterization in conjunction with a finite element modeling (FEM) simulation. A dual conical conductive filament has been used in the present work, based on the modeling of the electroforming process carried out by FEM. It has been demonstrated that for the GO/TiO2 based hybrid RRAM device structure, GO acts as an active filament formation layer, whereas in the rGO/TiO2 bi-layer structure, rGO acts as a mere electrode.

Role of structural distortion on thermoelectric aspects of heavily Sr2+ doped GdMnO3

Manganites had been proposed as one of the potential n-type oxide materials to develop thermoelectric power generators. In the present investigation, we studied the structural and thermoelectric properties of Gd1-xSrxMnO3 (GSMO) (0.5 ≤ x  ≤ 0.8) polycrystalline ceramics synthesized by a conventional solid-state route. Rietveld refinement of XRD patterns revealed the distorted orthorhombic Pbnm crystal structure in all the compositions. The decrease in J-T distortions, present on the Gd-rich side of GSMO (x  ≤  0.6), due to favored formation of Mn4+ was calculated. Thermoelectric properties such as Seebeck coefficient (S) and electrical conductivity (σ) of these ceramics were measured in the temperature range from room temperature to 900 °C. The negative values of the Seebeck coefficient throughout the temperature range confirm the n-type semiconducting nature in all the compositions. The conduction mechanism (below metal-semiconductor transition) of these materials was analyzed using the small polaron hopping conduction model.Manganites had been proposed as one of the potential n-type oxide materials to develop thermoelectric power generators. In the present investigation, we studied the structural and thermoelectric properties of Gd1-xSrxMnO3 (GSMO) (0.5 ≤ x  ≤ 0.8) polycrystalline ceramics synthesized by a conventional solid-state route. Rietveld refinement of XRD patterns revealed the distorted orthorhombic Pbnm crystal structure in all the compositions. The decrease in J-T distortions, present on the Gd-rich side of GSMO (x  ≤  0.6), due to favored formation of Mn4+ was calculated. Thermoelectric properties such as Seebeck coefficient (S) and electrical conductivity (σ) of these ceramics were measured in the temperature range from room temperature to 900 °C. The negative values of the Seebeck coefficient throughout the temperature range confirm the n-type semiconducting nature in all the compositions. The conduction mechanism (below metal-semiconductor transition) of these materials was analyzed using the small polaro...

Enhancement of thermoelectric power factor of Sr2CoMoO6 double perovskite by annealing in reducing atmosphere

In general, n-type thermoelectric materials are rather difficult to design. This study particularly pivoted on designing potential environmentally benign oxides based n-type thermoelectric material. We synthesized Sr2CoMoO6 (SCMO) polycrystalline ceramics via the solid-state synthesis route. XRD, SEM, and thermoelectric measurements were carried out for phase constitution, microstructure analysis, and to determine its potential for thermoelectric applications. As-sintered SCMO sample showed an insulator like behavior till 640 °C after which it exhibited an n-type non-degenerate semiconductor behavior followed by a p-n type conduction switching. To stabilize a high temperature n-type behavior, annealing of SCMO in reducing atmosphere (H2) at 1000 °C was carried out. After annealing, the SCMO demonstrated an n-type semiconductor behavior throughout the temperature range of measurement. The electrical conductivity (σ) and the power factor (S2σ) were found to be increased manifold in the annealed SCMO double perovskite.In general, n-type thermoelectric materials are rather difficult to design. This study particularly pivoted on designing potential environmentally benign oxides based n-type thermoelectric material. We synthesized Sr2CoMoO6 (SCMO) polycrystalline ceramics via the solid-state synthesis route. XRD, SEM, and thermoelectric measurements were carried out for phase constitution, microstructure analysis, and to determine its potential for thermoelectric applications. As-sintered SCMO sample showed an insulator like behavior till 640 °C after which it exhibited an n-type non-degenerate semiconductor behavior followed by a p-n type conduction switching. To stabilize a high temperature n-type behavior, annealing of SCMO in reducing atmosphere (H2) at 1000 °C was carried out. After annealing, the SCMO demonstrated an n-type semiconductor behavior throughout the temperature range of measurement. The electrical conductivity (σ) and the power factor (S2σ) were found to be increased manifold in the annealed SCMO double ...