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Superconductivity in doped FeTe(1-x)Sx (x=0.00 to 0.25) single crystals
No full textWe report self flux growth and characterization of FeTe1-xSx(x = 0.00 to 0.25) single crystal series. Surface x-ray diffraction (XRD) exhibited crystalline nature with growth in (00l) plane. Microstructural (electron microscopy) images of representative crystals showed the slab-like morphology and near stoichiometric composition. Powder XRD analysis (Rietveld) of single crystals exhibited tetragonal structure with P4/nmm space group and decreasing a and c lattice parameters with increase in x. Electrical resistivity measurements (rho-T) showed superconductivity with T-c(onset) at 9.5 Kand 8.5 K for x = 0.10 and x = 0.25 respectively. The un-doped crystal, i.e., x = 0.00, exhibited known step like anomaly at around 70 K. Upper critical field H-c2(0), as calculated from magneto transport [rho(T)H], for x = 0.25 crystal is around 60Tesla and 45Tesla in H//ab and H//c directions. Thermal activation energy [U-0(H)] calculated for x = 0.10 and 0.25 crystals followed weak power law, indicating single vortex pinning at low fields. Mossbauer spectra for FeTe1-xSx crystals at 300 Kand 5 K are compared with non superconducting FeTe. Both quadrupole splitting (QS) and isomer shift (IS) for S doped crystals were found to decrease. Also at 5 K the hyperfine field for x = 0.10 superconducting crystal is decreased substantially from 10.6Tesla (FeTe) to 7.2Tesla. For x = 0.25 crystal, though small quantity of un-reacted Fe is visible at room temperature, but unlike x = 0.10, the low temperature (5 K) ordered FeTe hyperfine field is nearly zero
A theoretical and experimental formalism of electronic structure of BFO:Cr thin films and modulation of their electrical properties upon visible light illumination
No full textFeO3 (BFO) and BiFe1-xCrxO3 (BFCO) (x = 0, 0.01, 0.02, 0.03) thin films have been fabricated using chemical solution deposition technique. The bandgap of BFO and BFCO thin films is found to be lying in the visible region making these films suitable candidates for potential solar energy harvesting applications. Density functional theory based calculations have also been performed to study the effect of B-site (Cr) doping on the electronic properties of BFO and BFCO. The BiFe1-xCrxO3 (x = 0.02) thin films exhibited well saturated PE hysteresis loops with a maximum remanent and saturation polarization of about 43 mu C/cm(2) and 64 mu C/cm(2), respectively. In contrast to pure BFO, a high value of short circuit current density (J(sc)) of magnitude 766.60 mu A/cm(2) along with the open circuit voltage (V-oc) of 106 mV was obtained for BiFe0.98Cr0.02O3 thin film structure under illumination with a laser of wavelength 470 nm and intensity 20 mW/cm(2). The Au/BiFe0.98Cr0.02O3/ITO/glass heterostructure displays a remarkably enhanced value of I-on/I-off ratio (8.4 x 10(4)). The observed results clearly highlight the potential of Cr doped BFO thin film structure for the development of cost effective light-driven devices. Published by AIP Publishing
Flux Free Single Crystal Growth and Characterization of FeTe1-xSx (x=0.00 and 0.10) Crystals
No full textWe report synthesis of S doped FeTe1-xSx (x= 0.00 and 0.10) single crystals using flux free method via solid state reaction. Single crystal XRD patterns of FeTe1-xSx (x= 0.00 and 0.10) confirm the single crystalline property, as the crystals are grown in (00l) plane only. Powder XRD result of FeTe1-xSx (x= 0.00 and 0.10) crystals show that crystalline in tetragonal structure having P4/nmm space group. Rietveld refinement results show that both a and c lattice parameters decreases with S doping of 10% at Te site in FeTe1-xSx. Detailed scanning electron microscopy (SEM) image of FeTe0.90S0.10 shows that the growth of crystal is in slab-like morphology. Electrical resistivity measurement results confirm the superconductivity in S doped 10% sample at Te site and superconducting transition T-c(onset) occurs at 9.5K and T-c(offset) (rho=0) occurs at 6.5K. rho-T measurement has been performed under various magnetic field up to 12 Tesla down to 2K. Upper critical field H-c2(0), for x= 0.10, which comes around 70Tesla, 60Tesla and 45Tesla of normal resistivity criterion rho(n)=90%, 50% and 10% criterion respectively
High temperature dielectric studies of indium-substituted NiCuZn nanoferrites
No full textIn this study, indium (In3+)-substituted NiCuZn nanostructured ceramic ferrites with a chemical composition of Ni0.5Cu0.25Zn0.25Fe2-xInxO4 (0.0 <= x <= 0.5) were prepared by chemical synthesis involving sol-gel chemistry. Single phased cubic spinel structure materials were prepared successfully according to X-ray diffraction and transmission electron microscopy analyses. The dielectric properties of the prepared ferrites were measured using an LCR HiTester at temperatures ranging from room temperature to 300 degrees C at different frequencies from 10(2) Hz to 5 x 10(6) Hz. The variations in the dielectric parameters epsilon' and (tan delta) with temperature demonstrated the frequency- and temperature-dependent characteristics due to electron hopping between the ions. The materials had low dielectric loss values in the high frequency range at all temperatures, which makes them suitable for high frequency microwave applications. A qualitative explanation is provided for the dependences of the dielectric constant and dielectric loss tangent on the frequency, temperature, and composition. Mossbauer spectroscopy was employed at room temperature to characterize the magnetic behavior
Light intensity dependent characteristics of micro-textured Si/PEDOT:PSS heterojunction solar cell
No full textHeterojunction solar cells made of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and Si have attracted a lot of attention towards low-cost and efficient devices. Here, heterojunction solar cell using pristine PEDOT:PSS on micro-textured n-Si has been fabricated. Effect of light intensity on photovoltaic characteristics of PEDOT:PSS/Si cells has been investigated via current (J) versus voltage (V) characteristics and quantum efficiency (EQE) measurements. It is found that photocurrent (J(sc)) of such cells deteriorates drastically at higher light intensities resulting in quite low J(sc) ( 15.0 mA/cm(2)) in J-V response under intense white light than that obtained from EQE measurements (> 30.0 mA/cm(2)) under low intensity monochromatic light. The observed effect of light intensity on the cell performances is reversible. Structural stability of PEDOT:PSS layer is also investigated by Raman spectroscopy. No post high intensity light exposure structural transformation in the PEDOT:PSS layer is observed. The observed light sensitive photoresponse of such cells has been attributed to possible light induced instantaneous structural changes in the PEDOT:PSS layer leading to reduced charge carrier dynamics and hence the formation of space charge region at PEDOT:PSS/Si interface at higher intensities. Further, the EQE with varying intensity is done which can help to optimize the illumination condition for such cell. The present study opens up new area of intensive research required in order to optimize polymer layer properties and improving the performance of PEDOT:PSS/Si solar cell leading to efficient, stable and low cost heterojunction solar cell technology
Near room temperature bismuth and lithium co-substituted BaTiO3 relaxor ferroelectrics family
No full textEco-friendly lead-free relaxor ferroelectrics, Ba1-x (Bi0.5Li0.5)(x)TiO3 (BBLT) with x = 0.3, 0.4 and 0.5, have been synthesized by using the conventional solid-state reaction route. The crystal structure and phase purity were verified by x-ray diffraction (XRD) patterns using Rietveld refinement which revealed the presence of tetragonal (95-80%) and orthorhombic phases (5-20%) in the matrix. The temperature dependent dielectric constant and tangent loss dispersion spectra, slim ferroelectric-hysteresis, and nano-scale microstructures suggest the presence of short-range ordering (SRO)/polar nano-regions (PNRs) in the matrix. The dielectric spectra suggest that the dielectric dispersion increases with increase in Bi/Li concentrations which may be due to compositional fluctuations, ordering of cations at nano-scale and presence of metastable states of SRO and long-range ordering (LRO) regions. The nonlinear Vogel-Fulcher relationship is fitted for maximum dielectric constant temperatures (T-m) which provides activation energy and freezing temperature of all compositions. The current density (J) versus electric field (E) (J-E) data obey bulk-limited current conduction mechanisms that may be due to a diffusive displacement of Ti4+ at octahedral center, the creation of random fields due to in-homogeneity at A-site, and trap-assisted hoping of charge carriers under high E-field
Study of crystal structure, dielectric, magnetic and magnetoelecrtic properties of xCoFe(2)O(4)-(1-x)Na0.5Bi0.5TiO3 composites
No full textMultiferroic composites of spinel ferrite and ferroelectric xCoFe(2)O(4) - (1-x)Na0.5Bi0.5TiO3 (with x = 0.10,0.30,0.50) were efficiently prepared by standard solid state reaction mechanism. X-ray diffractometer was used to analyze crystal structure of the prepared composites. The observed XRD patterns of the composites comprise peaks of both the phases i.e. ferrite and ferroelectric, with no sign of secondary peaks. Rietveld refinement of XRD data further confirms the coexistence of these two phases with cubic (Fd3m) and rhombohedral (R3c) symmetry corresponding to ferrite and ferroelectric phase respectively. The 3-dimensional overview of crystal structure of pure CoFe2O4 and Na0.5Bi0.5TiO3 and of composite 0.50CoFe(2)O(4) - 0.50Na(0.5)Bi(0.5)TiO(3) is generated by using refined parameters. The dielectric constant (epsilon') and dielectric loss (tan delta) values were recorded as a function of frequency ranging from 100 Hz to 7 MHz and at different temperatures. Both epsilon' and tan delta follow dispersion pattern at lower frequencies while show frequency independent behavior at higher frequencies. The magnetic evaluation carried by analyzing M-H hysteresis loop reveals the ferrimagnetic characteristics of these composites. The highest value of magnetic moment is 1.12 mu(B) observed for composite 0.50CoFe(2)O(4) - 0.50Na(0.5)Bi(0.5)TiO(3). Magnetoelectric (ME) voltage coefficient (alpha) was also demonstrated to observe the interaction between ferrite and ferroelectric phases. The highest value of alpha (72.72 mu V/Oe cm) is obtained for low ferrite composition 0.10CoFe(2)O(4) - 0.90Na(0.5)Bi(0.5)TiO(3), which suggests the dependence of magnetoelectric response on the resistivity of the composites
WO3-doped LiF as gate dielectric for p-channel vertical organic field effect transistor application
No full textWe report low voltage operable p-channel vertical organic field effect transistors (VOFETs) using 5,5'""-Dihexyl-2,2':5',2 '':5 '',2'":5'",2"":5'"',2'""-sexithiophene (DH6T) as organic semiconductor and tungsten trioxide (WO3) doped lithium fluoride (LiF) nano-composite of various concentrations as high-k dielectric. Among the various doping concentrations of WO3, the 5 wt% WO3-doped LiF shows the best performance. The gate leakage was effectively reduced from 10(-4) A/cm(2) order to 10(-6) A/cm(2) by the addition of 5 wt% WO3-doped LiF as compare to 0 wt% WO3-doped LiF, resulted in higher drain current for this device. The best values of threshold voltage, mobility, on/off ratio, trans-conductance and sub-threshold slope for the devices made were estimated to be 0.85 V, 0.034 cm(2)/Vs, 10(5), 60 mu S and 0.32 V/decade respectively
Thermal properties of La0.7Ca0.2Sr0.1MnO3:PdO composites
No full textA systematic study on the thermal conductivity, Seebeck coefficient and specific heat of La(0.7)Ca(0.2)Sr(0.1)MnO3:PdO composites is presented. Solid state reaction procedure was employed to synthesis the samples. It is seen from thermal conductivity (kappa(T)) studies that the samples exhibit a slope change nature close to their corresponding magnetic phase transition temperature, T-c. The overall magnitude of kappa is observed to decrease with increasing Pd concentration. The analysis of Seebeck coefficient data, S(T) versus temperature, T was done using Mott's polaron hopping model reveals that the electron-magnon scattering is governing the low temperature region. The temperature dependent specific heat C-p(T) is analyzed to determine the entropy change (Delta S) during the magnetic phase transition
Synergistic effect of polypyrrole/BST/RGO/Fe3O4 composite for enhanced microwave absorption and EMI shielding in X-Band
No full textPresent study focus on the designing of high performance microwave absorbing material against electromagnetic pollution. Herein we synthesize conducting polymer based composite encapsulated with Barium strontium titanate (BST), reduced graphene oxide (RGO), and Fe3O4 nanoparticles via chemical oxidative polymerization of pyrrole. The synthesized composite materials were thoroughly characterized using SEM, FTIR, XRD, TGA, and VSM techniques. The presence of filler materials in conducting polymer matrix leads to absorption dominated shielding effectiveness value of 48 dB in the frequency range of 8.2-12.4 GHz (X-band). Moreover, presence of dielectric and magnetic fillers increases the thermal and chemical stability of the composite material. The obtained shielding effectiveness value is above the recommended limit (30-40 dB) required for the commercial applications, therefore these composite material could be used as effective shield against EM pollution