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The system Zn1-xMnxFe2O4 (x = 0, 2, and 4%) was prepared by sol–gel chemical route at 80 °C. X-Ray powder diffraction and Raman spectrum analysis were used to determine the preliminary phase of obtained samples. W–H and SSP plots were used to determine the crystallite size and micro-strain of samples. The surface charge and morphology of the samples were studied using zeta potential and scanning electron microscope analysis, respectively. The optical bandgap of the samples suggested that they were semiconducting. The dielectric characteristics of samples were examined as a function of temperature (60–600 °C) at various frequencies (1 kHz, 10 kHz, 100 kHz, and 1 MHz). The presence of interfacial and orientational polarization was indicated by dielectric constant and dissipation factor studies, which ranged from (0.7–460) to (0.3–0.8) with Mn and were found thermally stable up to 300 °C. The thermal dependence of DC conductivity demonstrates Arrhenius type transport with one, two, and three regions of conduction in sample ZF-0, ZF-2, and ZF-4 respectively. The sources of charge carriers in samples were V o · · , e ′ and dipole defects V o · · - 2 F e F e 3 + 2 + ′ / 2 M n Z n 2 + 3 + . - 2 F e F e 3 + 2 + ′ . The current work could help to identify the possible applications in semiconductor devices, thermally stable capacitors, and as mixed ionic electronic conductors in solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Powders of a few compositions of the system Sr2Ce1-xNaxO4 (x = 0, 0.02, 0.04, 0.06, and 0.10) have been prepared by the conventional solid-state reaction method. Analysis of the XRD patterns has shown a preference of dopant Na+ for the Sr2+ sites with increasing content of dopant (x). Rietveld refinement of the XRD patterns confirmed that each sample crystallized in orthorhombic structure with space group Pbam. The purity of the synthesized samples was further examined using Raman Fourier Transform Infrared (FTIR) spectroscopy techniques. Raman spectroscopy has further indicated the risk of decomposition of Sr2CeO4 phase with increasing doping concentration. Optical band gap energy computed using UV–visible absorption data (Tauc's plot) falls between 2.91 and 3.10 eV, decreasing with increasing x. The shape of the excitation and emission spectra remains unchanged with increasing Na+ concentration. Two excitation peaks located around 290 nm and 350 nm are seen in photoluminescence (PL) excitation spectra. All Na-doped samples display an intense blue emission at 472 nm similar to undoped Sr2CeO4. SEM images of fractured surfaces of the sintered pellets have shown a significant role of Na doping on the morphology and grain size of the Sr2CeO4. [ABSTRACT FROM AUTHOR]

We have studied a mathematical framework of higher-order multipole fields in the vicinity of optical nanoantennas. We have exemplified at suitably chosen Nanoantennas i.e. a Nano antenna which strongly enhances the quadruple field. The modification of excitation rates in quantum mechanical systems due to this quadrupolar enhancement was studied. The hybrid system consisting of an optical Nano antenna and a quantum mechanical three level system was studied in detail. A properly designed Nano-antenna can excite dipole for bidden transitions in three level systems due to the enhanced higher order multipole fields. The dynamics of the system is strongly altered by the presence of the nanoantenna and cannot be done by the quadrupolar enhancement alone. This can be achieved by enhancing higher order multipole fields near the antenna. A quadrupole transition as the dominant excitation channel in a three level system was considered. It was found that the enhancement of this transition significantly intensify subsequent emission processes with respect to altered emission characteristics. The effects depend on geometrical parameters; the properties of the optical nanoantenna can be tailored and hence allowed for direct implementations in spectroscopies schemes. The obtained results were found in good agreement with previously obtained results. [ABSTRACT FROM AUTHOR]

We have studied the resonant properties of circular optical nanoantennas as well as other shapes of optical antennas without requiring any fitting parameters. This allows for a deeper insight into scaling behavior and do faster further research since a desired simple tool is now available to design such nanoantennas. The theory has been applied to design antennas supporting various resonances at predefined frequencies to respond to the desire to have multi resonant antennas for applications. Raman sensors are extremely broad band resonators. Such circular patch nanoantennas consist in tailoring the dispersion relation and the complex reflection coefficient at will by carefully selecting a particular stack of layers. We have made to characterize the resonance behavior of the potentially simplest optical nanoantennas which is also called nanowire antennas. The nanowire as a plasmonic cavity, a resonance occurs when the phase accumulated on a single round trip amounts to multiple of 2π. This phase is determined by the propagation constant of the plasmonic mode supported by the nanowire and an additional phase on reflection at the wire termination. By fitting many resonance positions with different nanowire lengths, the phase change on reflection is determined. Such results are obtained only for a few simplified geometries. Nanoantennas are made from an arbitrary stack of homogeneous disks. Increasing the radius of a single disk toward infinitely and increasing its thickness yielded the reflection coefficient of surface Plasmon polariton propagating along a single metallic interface at a planar termination. The obtained results were in good agreement with previous results. [ABSTRACT FROM AUTHOR]

A study of structural, optical and electrical properties have been investigated in this paper. The powder and ceramic of Ruddlesden popper oxide Ba2SnO4 are prepared by the solid state ceramic route. Single phase of Ba2SnO4 has been obtained by calcination at 1000°C for 8 h. Rietveld refinement of powder x-ray diffraction data indicated the tetragonal crystal structure of calcined powder with lattice constants a = b = 4.1458 Å, c = 13.2899 Å. Further, the phase identification of powder is studied by Fourier transform infrared and Raman spectroscopy. Analysis of the obtained powder by transmission electron microscope reflected the spherical shape of the particle in the range (74 ± 8) nm. AC conductivity of ceramic follows the universal power law, σ = σ dc 1 + f f H n . Temperature dependence behaviour of dc conductivity ( σ dc ) and hopping frequency ( f H ) indicated that the origin of dc conduction and ac conduction mechanisms are similar. Conductivity spectra at different temperatures scaled by Ghosh scaling σ ′ f σ dc = F f f H perfectly follows the time temperature superposition principle. X-ray photoelectron spectroscopy analysis of ceramic indicated the presence of Ba in Ba2+, Sn in Sn4+ and Sn2+ and oxygen vacancies in the sample. Thermal expansion coefficient of the prepared ceramic is found to be 3.44 × 10−6/°K. [ABSTRACT FROM AUTHOR]

The reaction mechanism for the formation of Sr2SnO4 by solid-state reaction between SrCO3 and SnO2 has been investigated using thermal analysis (TG and DSC) combined with X-ray diffraction (XRD) techniques. It is observed that the formation of single-phase Sr2SnO4 takes place by reaction between SrO and SrSnO3 at temperatures ≥ 900 °C. Based on these studies, a few compositions of the system Sr2−xLaxSnO4 (x = 0.01, 0.02, 0.04, 0.06 and 0.10) have been synthesized by calcination at 1000 °C for 8 h. Rietveld refinement of the XRD data confirmed that all the synthesized samples have tetragonal structure, space group (I4/mmm) and symmetry group D4h17. The crystallite size and induced lattice strain has been calculated using size strain plot (SSP), varies from 30 to 50 nm and from (3.00 to 6.27) × 10−3, respectively. Raman and Fourier transformed infrared (FTIR) spectroscopy techniques have been utilized to ponder local changes in the structure of Sr2SnO4 with La incorporation. The optical properties of the samples have been studied using UV-Vis spectroscopy. The systematic shift in the position of the absorption edge (toward the higher wavelength) indicates the incorporation of La in the lattice of Sr2SnO4. The direct and indirect band gap of the samples calculated through Tauc's plot. The variation in the value of direct band gap is attributed to changes in the charge compensation mechanism or/reduction in particle size. [ABSTRACT FROM AUTHOR]

The studies carried out in this paper are directed towards preparation of nanocomposite films of PVA (polyvinyl alcohol)-GO (graphene oxide) with variable wt% of GO by simple solution mixing technique and exploration of spectroscopic, surface morphological, structural, optical, electrical, and mechanical properties. In this article, the detailed molecular structure of PVA-GO polymer nanocomposites (PNCs) was optimized by using the Gaussian code (B.01 version). Experimentally, the structural information was gathered by using the X-ray diffractometer and determined the crystalline size (varying from 12. 82 nm to 24.62 nm for 1–5 wt% of GO in PVA/GO PNCs) and micro-strain (varying between 7.21 × 10−3 and 42.12 × 10−3) produced in the samples through Williamson-hall plot. The existence of the functional groups with their role in the nanocomposites was also examined with the help of FTIR technique. In order to identify the Raman bands (availability of D and G bands at ~1340 and 1595 cm−1, respectively, while the 2D band at ~2910 cm−1) and corresponding structural changes were studied by Raman spectrometer (with the usage of 532 nm laser). The study of surface morphology was performed by utilizing the AFM and FESEM (with EDAX) techniques and effect of GO on the surface roughness of the nanocomposite film was studied. The r.m.s. roughness of the films were set up to be 90.375 nm, 96.449 nm, 98.120 nm, 99.006 nm and 99.891 nm for GO of 1–5 wt%, respectively. The optical properties were determined using UV–Vis-NIR spectrophotometer and tuning of optical bandgap (varied from 3.56 eV to 2.45 eV with 1–4 GO wt%) was investigated. The resulting variation due to GO concentration was also confirmed with structural information. The electrical characteristics (capacitance, dissipation factor and electrical conductivity) were also investigated. The DMA analysis of the nanocomposites was performed to measure the mechanical property (Young's Modulus varying from 2 GPa to 16 GPa for 1–5 GO wt%) and found that the nanofillers (GO) plays an important role to enhance the various abovementioned properties. [Display omitted] • Reparation of PVA-GO nanocomposites and understanding role of GO in the composite via their characterizations • Determining the crystallized phase of GO dominating over the PVA giving modification in crystallite size and presence of micro-strain. • Confirmation of functional groups and their role in the nanocomposite and study of Raman bands and corresponding structural changes in the composites • Study of tunability of the optical bandgap on incorporation of GO. This tuning in band gap has also been supported by XRD and computational results. • Study of capacitance, dissipation factor, electrical conductivity and observation of significant enhancement of mechanical properties of the prepared nanocomposites [ABSTRACT FROM AUTHOR]

Abstract: Anomalous Rabi oscillations in single and bilayer graphene, in the absence of time-reversal symmetry, are described. The main findings of this work are that intra-layer sublattice space asymmetry has a remarkable effect on anomalous Rabi frequency in single and bilayer graphene, namely it is offset by the asymmetry parameter. However, the conventional Rabi frequency is nearly independent of the asymmetry parameter. Inter-layer asymmetry in bilayer graphene has an even more significant effect on anomalous Rabi frequency. When inter-layer asymmetry is taken into account, the anomalous Rabi frequency versus the external field goes through a minimum. The induced current in the frequency domain in these systems shows a finite threshold behavior even for vanishingly small applied fields. These offset oscillations are attributable to the asymmetry parameter in these systems, and are observable only for weak applied fields. For stronger applied fields these phenomena tend towards those without asymmetry. [Copyright &y& Elsevier]

KBiFe 2 O 5 (KBFO) is an interesting multiferroic compound with the coexistence of ferroelectric and ferromagnetic phases with a narrow band gap. In this work, KBiFe 2 O 5 (KBFO) is synthesized using a sol-gel technique, followed by calcination at 973 K. Rietveld refinement analysis of XRD data confirms the presence of monoclinic crystal structure with space group P 2/ c. The SEM micrograph of KBFO reflects the irregular shape of grains with slight agglomeration. The optical band gap measured by UV visible spectroscopy of KBFO is found to be 1.56 eV. The multiferroic behavior of KBFO has been confirmed by the electrical (dielectric) and magnetic (M-H loop) measurements. A weak ferromagnetic nature is observed due to canting of the magnetic moment of G-type anti-ferromagnetic ordering. The dielectric studies reveal the Maxwell-Wagner type dispersion and an anomaly near magnetic phase transition temperature. KBFO shows negative magneto-dielectric (MD) coupling as both ε and tan δ decreases with the increasing magnetic field. Impedance spectroscopy is performed to analyze the intrinsic and extrinsic effects in MD coupling. The Nyquist plot shows positive magneto-resistance and negative magneto-capacitance which represent strong MD coupling in KBFO. It also reveals that the bulk property (intrinsic effect) dominates over the extrinsic effect in the sample. These results affirm that KBFO is a new candidate for room-temperature multiferroicity with a suitable bandgap and strong MD coupling for photovoltaic applications. • Crystal field splitting energy in KBFO is applied to describe the lower bandgap. • Photocatalysis effect is described using e--e- interaction influenced magnetic ordering. • The KBFO shows only a negative magneto-dielectric coupling effect. • The magneto impedance (MI) effect is considered as an interface driven effect. • KBFO shows positive magneto-resistance and negative magneto-capacitance effect. [ABSTRACT FROM AUTHOR]