NiO thin films grown on Si(100) substrate by electron beam evaporation and sintered at 500 °C and 700 °C were irradiated with 120 MeV 197Au9+ ions. The FCC structure of the sintered films was retained up to the highest fluence (3 × l013... more
NiO thin films grown on Si(100) substrate by electron beam evaporation and sintered at 500 °C and 700 °C were irradiated with 120 MeV 197Au9+ ions. The FCC structure of the sintered films was retained up to the highest fluence (3 × l013 ions.cm-2) of irradiation. As against the expected amorphization due to ion irradiation when electronic energy loss exceeds
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ABSTRACT Ac conductivity of the cobalt ferrite at high temperature was systematically studied by the jumping model and Jonscher single power law. The material was synthesized by a conventional ceramic route had confirmed its single phase... more
ABSTRACT Ac conductivity of the cobalt ferrite at high temperature was systematically studied by the jumping model and Jonscher single power law. The material was synthesized by a conventional ceramic route had confirmed its single phase from XRD pattern and well grain growth of micrometer range was found in SEM image. The conduction in cobalt ferrite is explained by the multiple oxidation states of the cobalt and iron ions. Depending on the variation of the frequency exponent ‘n’ with temperature, conduction mechanism is explained.
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ABSTRACT We have prepared Bismuth substituted nano-cobalt ferrite (CoFe 2Àx Bi x O 4 , x = 0, 0.05, 0.1, 0.15) by auto combustion technique. The single phase XRD pattern confirmed the successful substitution of the larger cation. Surface... more
ABSTRACT We have prepared Bismuth substituted nano-cobalt ferrite (CoFe 2Àx Bi x O 4 , x = 0, 0.05, 0.1, 0.15) by auto combustion technique. The single phase XRD pattern confirmed the successful substitution of the larger cation. Surface morphology from FESEM image indicated the control particle growth (50–160 nm) as a result of bismuth substitution. The increased particle size has effectively modified the electrical properties of the system in three major ways: (a) increase in resistivity, (b) evolution of grain relaxation and (c) reduction in dielectric loss and surface conduction. Additionally, magnetic behavior is also affected due to control particle growth. Magnetic hysteresis study at room temperature confirmed the rise in saturation magnetization (M S = 74.5–86.5 emu/g) and reduction in coercivity (H C = 1633–1524 Oe).
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Y1−xCaxBa2Cu3O7−δ (x=0.1)+Y2O3 (10 wt%) composite thick film has been prepared by the diffusion reaction technique. Samples are irradiated with 200 MeV Ag ions. X-ray diffraction and scanning electron microscopy reveal microstructural... more
Y1−xCaxBa2Cu3O7−δ (x=0.1)+Y2O3 (10 wt%) composite thick film has been prepared by the diffusion reaction technique. Samples are irradiated with 200 MeV Ag ions. X-ray diffraction and scanning electron microscopy reveal microstructural changes in the irradiated samples. The enhancement of the critical current density (Jc) from 1.4×10 to 6.7×10 A/cm with irradiation in YCaBCO samples is observed, indicating that flux pinning increases due to the creation of columnar defects induced by irradiation. On addition of Y2O3 to YCaBCO, Jc increases to 8.3×10 A/cm. The insulating inclusions of Y2O3 cause Jc to increase by the process of flux pinning in the unirradiated YCABCO/Y2O3 composite. However, Jc starts decreasing for YCABCO/Y2O3 composite with the increase in ion fluence. The main mechanism of the decrease in the critical current density is the reduction in the effective pinning potential, which is caused by an increase in the defect concentration.
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A series of systematic substitution of isovalent Sr ion into the Ca site of La0.67Ca0.33-xSrxMnO3 system has been studied for different x values ranging from x=0.00,0.033,0.066,…,0.33. It is observed that at x=0.066, the system begins to... more
A series of systematic substitution of isovalent Sr ion into the Ca site of La0.67Ca0.33-xSrxMnO3 system has been studied for different x values ranging from x=0.00,0.033,0.066,…,0.33. It is observed that at x=0.066, the system begins to exhibit multiphasic behavior with the onset of X-ray shoulder peak at 2θ value of 32.96∘. In this paper, we report low field SQUID magnetization behavior and electrotransport properties of the above system with x=0.00, 0.033 and 0.066. It is noted that larger cationic size (Sr2+) does not allow the system to attain low bandwidth, which is the important parameter to control the electric and magnetic properties including Curie temperature (Tc) and metal insulator transition temperature (TIM). The role of Sr2+ ion substitution as larger radius with respect to Ca2+ ion in the La0.67Ca0.33-xSrxMnO3 system can specifically be assigned to enhance the electron bandwidth (W), which promotes higher Tc and TIM. In addition to this, an interesting spin glass cluster and transition phenomena are observed at low temperature region (≈50K) for x=0.066.
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ABSTRACT The effect of 200 MeV Ag ions on YBa2Cu3O7−δ /5 wt.% Y2O3 composite thick films is studied. The structural deformity is analysed with X-ray diffraction showing reduced peak intensity. The decrease of transition temperature as a... more
ABSTRACT The effect of 200 MeV Ag ions on YBa2Cu3O7−δ /5 wt.% Y2O3 composite thick films is studied. The structural deformity is analysed with X-ray diffraction showing reduced peak intensity. The decrease of transition temperature as a function of ion fluence has been observed from temperature-dependent resistivity and magnetization measurement. Fluctuation conductivity studied within the framework of Aslamazov–Larkin and Lawrence–Doniach theories fits well for 3D and 2D regimes with the appearance of critical region beyond 3D regime. Pseudogap temperature estimated above 100 K shifts to lower temperature zone as a function of ion doses. We report an enhancement of critical current density and flux pinning due to dual impact of swift heavy ion and Y2O3 inclusions at isothermal temperatures 40 K and 60 K.
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ABSTRACT A series of samples of YBa2Cu3-xAgxO7-y with 0≤x≤0.12 composition was studied to probe into the Ag substitution effect on oxygen stoichiometry, lattice parameters, and superconducting properties. With the samples prepared at a... more
ABSTRACT A series of samples of YBa2Cu3-xAgxO7-y with 0≤x≤0.12 composition was studied to probe into the Ag substitution effect on oxygen stoichiometry, lattice parameters, and superconducting properties. With the samples prepared at a relatively lower sintering temperature, Ag could be doped in the grains rather than precipitate at grain boundaries. Thus, unlike in the case of YBCO + Ag composites or in doped systems annealed at high temperatures where Ag occupies mostly the grain boundary, the present system showed a drastic change inT c, oxygen stoichiometry, and lattice parameters with Ag concentration, indicating the substitution of Ag at the Cu(l) sites in the grains. The stable 2-fold oxygen coordination of Ag substituting Cu(l)’s explains the observed variation of oxygen deficiency with Ag. A crystallochemical analysis has been made to reveal the crucial role of Ag-substitution-induced coordination incompatibility and charge state instability on carrier concentration andT c.
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Our in-situ temperature dependent resistance studies in a set of YBa2Cu3O7-y (YBCO) thin films irradiated with 200 MeV Ag ions at 79 K show that in addition to amorphized latent tracks, a large concentration of point defects are created... more
Our in-situ temperature dependent resistance studies in a set of YBa2Cu3O7-y (YBCO) thin films irradiated with 200 MeV Ag ions at 79 K show that in addition to amorphized latent tracks, a large concentration of point defects are created by the secondary electrons emitted radially from the ion path. Detailed calculation of the energetics indicates that in the YBCO matrix,
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The variations of superconducting and mechanical properties of La0.67Sr0.33MnO3 (LSMO) [x = 0.0, 0.1, and 0.2] doped YBa2Cu3O7−δ (YBCO) composite thick films were examined. All the composite films were synthesized by diffusion reaction... more
The variations of superconducting and mechanical properties of La0.67Sr0.33MnO3 (LSMO) [x = 0.0, 0.1, and 0.2] doped YBa2Cu3O7−δ (YBCO) composite thick films were examined. All the composite films were synthesized by diffusion reaction technique. The structural and morphological analysis were investigated through X-ray powder diffraction along with Rietveld refinement and Field emission scanning electron microscopy (FESEM) respectively. The transport measurement suggested that the inclusion of ferromagnetic LSMO decreases the superconducting transition temperature ($$ T_{C}^{on} $$TCon) and enhances the residual resistivity (ρ0). The broadening of resistive transition occurs below the onset transition temperature and shows the dissipative flux pinning. Various superconducting parameters were obtained from the excess conductivity analysis of the composite films and were in good agreement with the experimental findings. The mechanical strength of all the composite films was explained through different models like Hays–Kendall model, Elastic/Plastic deformation model and Proportional specimen resistance model.
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Abstract This study reports on the construction of nano nickel ferrite NAND logic gate utilizing the concept of fluorescence quenching mechanism due to its possible applications for the TiO2 sensor. Sol-gel auto combustion route and... more
Abstract This study reports on the construction of nano nickel ferrite NAND logic gate utilizing the concept of fluorescence quenching mechanism due to its possible applications for the TiO2 sensor. Sol-gel auto combustion route and two-step synthesis procedures were adopted for synthesis and characterization of NiO, NiTiO3, NiFe2O4, and novel magnetic core-shell NiFe2O4@TiO2. The high crystalline phase formation, surface morphology and identical particle size formation (23–32 nm) were confirmed from XRD, SEM and W H plot respectively. The TEM micrographs of core-shell NiFe2O4@TiO2 revels the inhomogeneous cages of TiO2 and unsymmetrical boundary around the magnetic NiFe2O4 core. The optical band gap (determined from UV-DRS spectra using Kubelka-Munk equation) decreases significantly from NiO (3.94 eV) to NiFe2O4@TiO2(1.84 eV) indicates enhanced semiconducting nature. The FTIR-ATR spectra spotlighted on the relaxation of the intrinsic metallic [Ni(octa/tetra)-O] stretching vibrations from NiO to NiFe2O4@TiO2 core-shell. The quenching intensity of photoluminescence (PL) spectra in core@shell nanostructured materials inspires us to design an analogical nano ferrite NAND logic gate. The threshold value of logic gate response was established on 0.5 for the desired output signal. Finally, the potential applications of the ferrite NAND logic gate have utilized for TiO2 sensing. The saturation magnetization was lessened in magnetic core-shell NiFe2O4@TiO2 (7.13 emu/gm.) due to TiO2 shell.
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Influence of Fe substitutions by rare-earth (La3+) ions on structural, electric, dielectric and magnetic properties of cobalt ferrite employing glycine nitrate method is investigated. The FTIR spectra and Mossbauer spectroscopy... more
Influence of Fe substitutions by rare-earth (La3+) ions on structural, electric, dielectric and magnetic properties of cobalt ferrite employing glycine nitrate method is investigated. The FTIR spectra and Mossbauer spectroscopy measurements illustrate spinel phase formation of CoFe2−xLaxO4 nanoferrites supporting structural analysis from X-ray diffraction patterns. Magnetic analysis revealed that with increasing La concentration to 0.1, the coercivity and squareness values increased from 1958 to 3312 Oe, and 0.52–0.57, respectively. To obtain accuracy in the saturation magnetization values, a theoretical approach was used considering the ferromagnetic (FM) and antiferromagnetic/paramagnetic (AFM/PM) components. Dielectric measurements studied in the range of 100 Hz–1 MHz frequency from room temperature to 300 °C indicated enhanced dielectric constant with low loss on increasing La3+ concentration. The ferrite nanoparticles with improved magnetic and dielectric properties make these materials suitable for magneto-recording and high-frequency devices.
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Abstract Rose flower shaped cobalt ferrite has been synthesized by a facile and template-free hydrothermal method. The advantages of CoFe2O4 for fabricating efficient photovoltaic devices are investigated in this work. As-synthesized... more
Abstract Rose flower shaped cobalt ferrite has been synthesized by a facile and template-free hydrothermal method. The advantages of CoFe2O4 for fabricating efficient photovoltaic devices are investigated in this work. As-synthesized material was investigated by X-ray diffraction, field-emission scanning electron microscope which revealed the formation of rose shaped single phase CoFe2O4. Dielectric study in the frequency range from 100 Hz to 1 mHz revealed an increase in dielectric constant along with a decrease in dielectric loss under illumination (λ ≥ 390 nm). Achievement of such high dielectric constant as well as low dielectric loss simultaneously in a particular material is very rare. It was found that CoFe2O4 exhibited obvious photocurrent responses under illumination. The electrical properties were further analysed by current-voltage (I-V) measurements under dark and illuminated condition and with increasing temperature. As a result a temperature dependence of the current-voltage characteristics was obtained. These results indicate that the CoFe2O4 possess significant photovoltaic properties and the electrical properties vary under illumination.
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Abstract We report the structural modifications and variation of superconducting parameters of high temperature superconductor (HTSc) YBa2Cu3O7-δ (YBCO) by addition of different wt% of CNTs (0.0, 0.2, 0.4, 0.6, 0.8 & 1.0 wt%)... more
Abstract We report the structural modifications and variation of superconducting parameters of high temperature superconductor (HTSc) YBa2Cu3O7-δ (YBCO) by addition of different wt% of CNTs (0.0, 0.2, 0.4, 0.6, 0.8 & 1.0 wt%) synthesized by standard solid state reaction route. The orthorhombic structure of all the samples with Pmmm space group was confirmed from the X-ray Diffraction (XRD) analysis through Rietveld refinements. No significant variation is observed in the lattice parameters of the orthorhombic structure of YBCO superconducting matrix with increasing wt% of CNTs. The Field emission scanning electron microscope (FESEM) analysis shows better connectivity between the grains of CNTs doped samples. From the temperature dependent resistivity measurement, it is observed that there is no chemical reaction between superconducting YBCO and CNTs, rather addition of CNTs enhances the room temperature resistivity and more importantly reduces the critical temperature ( T C on ) for lower doped sample and then increases for higher doped sample but not for the pristine one. The paraconductivity studies reveal the 2D-3D transition in parent YBCO and the composites, with a signature of percolative behavior in the composites. Inclusion of CNTs to the YBCO enhances the value of critical current density and gives maximum value of JC which is 12 times more than that of pure YBCO sample for 0.8 wt% of YBCO.
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Cobalt ferrites nanoparticles doped with gadolinium CoFe2−xGdxO4, referred to as CFGO (x = 0.0, 0.1, 0.3, 0.5 and 0.7) was achieved by glycine nitrate process. The phase confirmation and crystallite size were obtained from X-ray... more
Cobalt ferrites nanoparticles doped with gadolinium CoFe2−xGdxO4, referred to as CFGO (x = 0.0, 0.1, 0.3, 0.5 and 0.7) was achieved by glycine nitrate process. The phase confirmation and crystallite size were obtained from X-ray diffraction spectra and their variation with dopants content was determined. The Williamson–Hall plot was used to investigate the individual contributions of crystallite sizes and lattice strain on the peak broadening of the CFGO nanoparticles. Further confirmation of the spinel structure was done by Fourier transform infrared spectra. Dielectric properties such as dielectric constant (ε′) and dielectric loss (ε″) have been investigated in the frequency range 100 Hz–1 MHz. The dielectric constant (ε′) dispersion for CFGO nanoferrites is fitted in accordance with the modified Debye’s function. The complex impedances and complex modulus analysis confirm a grain interior mechanism contributing to the dielectric properties. The electrical behaviour of the CFGO nanoferrites exhibited small polaron conduction mechanism. From the temperature dependence curve of dielectric relaxation, activation energies for CFGO samples have been calculated. The low loss dielectric makes these samples promising materials to be used at high frequencies.
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Polycrystalline (1-x)YBa2Cu3O7-y + xBaTiO3–CoFe2O4(x = 0.0, 0.2, 0.4, 0.6 wt.%) superconductors were prepared by solid state route. XRD analysis reveals no significant change in "b" parameter and increase in "a" and... more
Polycrystalline (1-x)YBa2Cu3O7-y + xBaTiO3–CoFe2O4(x = 0.0, 0.2, 0.4, 0.6 wt.%) superconductors were prepared by solid state route. XRD analysis reveals no significant change in "b" parameter and increase in "a" and "c" parameters. SEM micrographs show no change in grain size of the samples. With the increase of BaTiO3–CoFe2O4 (BTO–CFO) addition it has been analyzed that the superconducting transition temperatures (Tc) determined from standard four-probe method was decreased and dropped sharply with higher wt.% addition. Excess conductivity fluctuation analysis using Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above Tc. The decrease in 2D–3D crossover temperature TLD (Lawerence–Doniach temperature) in the mean field region has been observed as a consequent dominance of 3D region to increase in wt.% in the composite. The increasing value of ρwl and ρ0 and the decreasing trend in the value of zero-resistance criti...
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Research Interests: Materials Engineering, Condensed Matter Physics, Scanning Electron Microscopy, Composite Materials, Magnetic field, and 12 moreGrain Boundaries, Superconductors, XRD, Texture, Fluctuations, Grain Boundary, Electrical Conductivity, Magnetoresistance, Crystal Defects, Electric Conductivity, Electrical And Electronic Engineering, and Critical Temperature
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Ferroelectric and high temperature superconducting materials are two promising materials for future electronic devices. The superconducting properties and the related microstructures of YBa2Cu3O7−δ with BaTiO3 addition, prepared by... more
Ferroelectric and high temperature superconducting materials are two promising materials for future electronic devices. The superconducting properties and the related microstructures of YBa2Cu3O7−δ with BaTiO3 addition, prepared by partial melt processing, were investigated with temperature‐resistivity, X‐ray diffraction and SEM‐EDX analysis. For lower concentration of BaTiO3 it shows a fractal behaviour approaching the exponent of three‐dimensional percolation model. The transport properties studied by four‐probe arrangement show a different behaviour depending on the wt.% of ferroelectric to superconductor.
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ABSTRACT Various defects arising from lattice mismatch and coordination incompatibility at the cation sites are known to lend the cuprates a metastable state at temperatures and pressures where they exhibit superconductivity. The present... more
ABSTRACT Various defects arising from lattice mismatch and coordination incompatibility at the cation sites are known to lend the cuprates a metastable state at temperatures and pressures where they exhibit superconductivity. The present paper considers the metastability induced by coordination incompatibility at Cu(1) sites in oxygen-deficient 123 type systems and looks for their possible effects on charge and spin degrees of freedom. Depending upon the concentration of oxygen vacancies, the resulting unstable charge state at the Cu(1) sites is shown to either temporally fluctuate or spatially equilibrate, providing a mechanism for the 90 K and the 60 K plateaus, with a peak in the former observed in the YBa2Cu3O7-y , samples prepared under thermodynamic equilibrium conditions.
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ABSTRACT (1−x)YBa2Cu3O7 + xBaTiO3 composites were synthesized following the standard solid state reaction route. Analysis of the resulting morphological structure confirmed that BaTiO3 resides at the grain boundary of the granular matrix... more
ABSTRACT (1−x)YBa2Cu3O7 + xBaTiO3 composites were synthesized following the standard solid state reaction route. Analysis of the resulting morphological structure confirmed that BaTiO3 resides at the grain boundary of the granular matrix of YBCO. Fluctuation conductivity obtained for zero magnetic field confirms that superconducting region is affected by the BaTiO3 incorporation. The values of the crossover temperature from 2D to 3D behavior are found to shift towards higher temperatures with increasing BaTiO3 concentration. The excess magnetoconductivity measured at 8 T revealed a dimensionality crossover in accordance with the Aslamazov–Larkin theory. The overall analysis of the obtained experimental results suggests manifestation of Gaussian, critical and short wavelength type fluctuations in the behavior of the observed paraconductivity.
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Page 1. Fluctuation conductivity and inhomogeneity in granular YBa2Cu3O7−y/Ag composite thick films This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2006 Supercond. Sci. Technol. 19 635 ...