S. V. Bhat

Bio: S. V. Bhat is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: Electron paramagnetic resonance & Antiferromagnetism. The author has an hindex of 27, co-authored 151 publications receiving 2747 citations. Previous affiliations of S. V. Bhat include Texas Christian University & Bangalore University.

ZnO/Ag nanohybrid: synthesis, characterization, synergistic antibacterial activity and its mechanism

Abstract: A highly homogeneous ZnO/Ag nanohybrid has been synthesized by a novel route, employing chitosan as mediator by purely electrostatic interaction. By employing various techniques such as powder XRD, UV-visible, IR spectroscopy and electron (SEM, TEM) microscopy, the formation of the nanohybrid has been established. The synergistic antibacterial effect of ZnO/Ag nanohybrid on Gram-positive and Gram-negative bacteria is found to be more effective, compared to the individual components (ZnO and Ag). Cytotoxicity experiments are carried out and the results are correlated to the solubility of the nanohybrid. A possible mechanism has been proposed for the antibacterial activity of ZnO/Ag nanohybrid, based on TEM studies on bacteria, carried out by employing the microtome technique and by EPR measurements on the hybrid.

ESR of Mn2 and Mn5 molecules in rare‐gas matricesa)

Abstract: Mn2 and Mn5 have been isolated in argon, krypton, and xenon matrices and their X‐band ESR spectra observed at 4 and up to 70 K, depending upon the matrix. As predicted by Nesbet, the lowest state of Mn2 is 1Σ, and the two atoms are exchange coupled (antiferromagnetically). The temperature behavior of the ESR bands in the higher spin states (S=1,2,3) was approximately in accord with a Lande interval rule, and a value of J=−9±3 cm−1 was obtained from the S=2 intensity variations. Each fine structure line appears with a superimposed 11‐line hyperfine pattern with splitting one‐half that of isolated 55Mn atoms (30 G). The anisotropic exchange interactions fit the Judd–Owen relationship with De=−0.043(2) and Dc=−0.001(4) cm−1. Assuming De arises solely from magnetic dipole interaction, the interatomic distance in Mn2 is calculated to be 3.4 A. Mn5 appears in more concentrated matrices as a highly oriented axial molecule with its axis perpendicular to the flat sapphire substrate surface. The observed fine struc...

Suppression of charge order, disappearance of antiferromagnetism, and emergence of ferromagnetism in Nd 0.5 Ca 0.5 MnO 3 nanoparticles

Abstract: Nd0.5Ca0.5MnO3 nanoparticles (average diameter similar to 20 and 40 nm) are synthesized by the polymeric precursor sol-gel method and characterized by various physico-chemical techniques. Quite strikingly, in the 20 nm particles, the charge-ordered (CO) and the antiferromagnetic phases observed in the bulk below 250 K and 160 K, respectively, are completely absent. Instead, a ferromagnetic (FM) transition is observed at 95 K followed by an insulator-to-metal transition at 75 K. The 40 nm particles show a residual CO phase but a transition to the FM state also occurs, at a slightly higher temperature of 110 K.

A Study of Mn2+ Doping in CdS Nanocrystals

Abstract: We report here the synthesis of water soluble Mn2+-doped CdS nanocrystals in which it has been possible for the first time to obtain a distinct Mn2+ d-related emission well-separated from the defect state emissions. By varying the reaction temperature systematically, we establish 55 °C as the optimum temperature to maximize the Mn2+ d emission, the existence of this optimum synthesis temperature being shown as the result of two opposing influences of the temperature. Most interestingly, present results establish that Mn2+ favors preferential doping of larger-sized particles even within the narrow size distribution achieved in the present synthesis, rendering the relatively smaller-sized nanocrystals depleted of Mn2+ for any given synthesis. One important aspect of the present approach is that the synthesized nanocrystals readily dissolve in water without any deleterious effect on the Mn2+ d-related emission intensity.

Effect of sintering temperature on electrical transport properties of La0.67Ca0.33MnO3

Abstract: A systematic investigation of lanthanum-based manganite, La0.67Ca0.33MnO3, has been undertaken with a view to understand the influence of varying crystallite size, in the nanoscale, on various physical properties. The materials were prepared by the sol–gel route by sintering at four different temperatures starting from 800 to 1100 °C, with an interval of 100 °C. After the usual characterization of these materials structurally by XRD, their metal-insulator transition (TP) as well as magnetic transition (TC) temperatures were determined. Surprisingly these materials are found to exhibit two different types of behaviors, viz, while TC is found to decrease from 253 to 219 K, TP is increasing from 145 to 195 K with increasing sintering temperature. A systematic study of electrical conductivity of all four materials was undertaken not only as a function of temperature (80–300 K), but also as a function of magnetic field up to 7 T mainly to understand the detailed conduction mechanism in these materials. On analyzing the data by using several theoretical models, it has been concluded that the metallic (ferromagnetic) part of the resistivity (ρ) (below TP) fits well with the equation ρ ( T ) = ρ 0 + ρ 2.5 T 2.5 , indicating the importance of grain/domain boundary effects (ρ0) and electron–magnon scattering processes (∼T2.5). On the other hand, in the high temperature (T>TP) paramagnetic insulating regime, the adiabatic small polaron and VRH models fit well in different temperature regions, thereby indicating that polaron hopping might be responsible for the conduction mechanism.

Perspective on the Development of Lead-free Piezoceramics

Abstract: A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Poly(ethylene oxide)-based electrolytes for lithium-ion batteries

Abstract: Poly(ethylene oxide) (PEO) based materials are widely considered as promising candidates of polymer hosts in solid-state electrolytes for high energy density secondary lithium batteries. They have several specific advantages such as high safety, easy fabrication, low cost, high energy density, good electrochemical stability, and excellent compatibility with lithium salts. However, the typical linear PEO does not meet the production requirement because of its insufficient ionic conductivity due to the high crystallinity of the ethylene oxide (EO) chains, which can restrain the ionic transition due to the stiff structure especially at low temperature. Scientists have explored different approaches to reduce the crystallinity and hence to improve the ionic conductivity of PEO-based electrolytes, including blending, modifying and making PEO derivatives. This review is focused on surveying the recent developments and issues concerning PEO-based electrolytes for lithium-ion batteries.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

The flux-line lattice in superconductors

Abstract: Magnetic flux can penetrate a type-II superconductor in the form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons) each carrying a quantum of magnetic flux phi 0=h/2e. These tiny vortices of supercurrent tend to arrange themselves in a triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-Tc superconductors (HTSCs) also by thermal fluctuations. Many properties of the FLL are well described by the phenomenological Ginzburg-Landau theory or by the electromagnetic London theory, which treats the vortex core as a singularity. In Nb alloys and HTSCs the FLL is very soft mainly because of the large magnetic penetration depth lambda . The shear modulus of the FLL is c66~1/ lambda 2, and the tilt modulus c44(k)~(1+k2 lambda 2)-1 is dispersive and becomes very small for short distortion wavelengths 2 pi /k<< lambda . This softness is enhanced further by the pronounced anisotropy and layered structure of HTSCs, which strongly increases the penetration depth for currents along the c axis of these (nearly uniaxial) crystals and may even cause a decoupling of two-dimensional vortex lattices in the Cu-O layers. Thermal fluctuations and softening may `melt` the FLL and cause thermally activated depinning of the flux lines or ofthe two-dimensional `pancake vortices` in the layers. Various phase transitions are predicted for the FLL in layered HTSCs. Although large pinning forces and high critical currents have been achieved, the small depinning energy so far prevents the application of HTSCs as conductors at high temperatures except in cases when the applied current and the surrounding magnetic field are small.