We present a detailed study of electronic structure of diluted magnetic semiconductor quantum dot. A numerical analysis was carried out for InAs/GaAs doped with manganese. First we calculate InMnAs band structure by coupling the band structure of bulk InAs (using 40-band k.p model) with S=5/2 Mn local moments using semi-phenomenological local exchange interaction treated in the mean-field approximation. The κ valence band parameter, g∗ Lande factor and the relevant material parameter useful for the study of the electronic properties of InMnAs/GaAs quantum dot are determined at this stage. Then, using exact numerical diagonalization, the electron and hole energy eigenvalues were calculated based on the Kohn–Luttinger k.p theory and effective mass approximation. We derive the effective hole Hamiltonian by taking into account the cylindrical symmetry of the quantum dot and considering the effect of magnetic field. We find that the hole ground state remains S−3/2 when varying the magnetic field.

We theoretically investigate the electronic and optical properties of charge carriers in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW), to determine their viability for use in intermediate band solar cell (IBSC) devices. This hybrid structure has the advantage of allowing a large flexibility to alter wave function distribution of the electron ground state, which is often considered as an intermediate band (IB) in QD-IBSC. The polarized transitions dipole moment (TDM), the polarized absorption coefficients and the radiative lifetime were studied as a function of QD height. Our theoretical results show an enhancement of inter-band absorption spectrum with a redshift of the peak corresponding to h0→IB transition and a blueshift of the continuum→IB peak, as the height of QD increases. The intra-band light absorption spectrum exhibits a redshift and its magnitude remains almost unchanged, as the height of QD increases. Furthermore this structure provides strong intra-band light absorption comparable to that of type-I QDs and equivalent to h0→IB transition strength. A long carrier lifetime in IB of about 30 ns was found, but remains more than an order of magnitude less than the inter-band radiative time due to the low confinement potentials of the electron along the ρ-axis in this type-II dot-in-well (DWELL) structure.

We report a comparative investigation between the two high temperature superconductor materials YBa2Cu3O7-δ (Y-123) and Y3Ba5Cu8O18±δ (Y-358) by probing the impact of high-energy ball milling (HEBM) technique on the microstructure, transport properties and pinning capacities. Products were elaborated via the solid-state reaction (SSR) by employing two kinds of milling; hand grinding in agate mortar and HEBM in a planetary crusher. The morphology, chemical compositions and crystal structure of all produced products were explored by scanning electron microscope (SEM) along with EDXS and X-ray diffraction (XRD). The superconductivity was confirmed by electrical resistivity measurements. The transport and intra-granular critical currents densities were estimated through the current–voltage and magnetization measurements. The planetary HEBM process generates nano-sized Y-deficient Y-123 and nano-sized Y-deficient Y-358 entities dispersed in the Y-123 and Y-358 matrix, respectively. The Y-358 sample milled by HEBM exhibits the best pinning capacity. This result can be ascribed to the occurrence of more disorder in Y-358 compound compared to Y-123 one.

Samples of YBa2(Cu1-xTix)(3)O-y superconductor with x=0.00, 0.01, 0.03 have been prepared by solide state reaction method. The effect of annealing treatments on normal electrical resistivity has been done using the bipolaron model. The results of this study show the increase of localized charge when the dopant content increases and the reduction of this localization with annealing treatment.

22Aug 2017 INFLUENCE OF Pr2Co7 MAGNETIC NANOMETER PARTICLES ADDITION ON YBa2Cu3Oy SUPERCONDUCTOR MAGNETO-CONDUCTIVITY'S IN FLUCTUATION REGIME. D. Mani Kongnine , M. Baneto , K. Tepe , A. Hamrita and K. Napo. Departement de Physique, Facult? des Sciences, Universit? de Lom?, BP 1515, Lom?, Togo. D?partement de Physique, Facult? des Sciences de Bizerte, Zarzouna 7021, Universit? de Carthage, Bizerte, Tunisie.

The effect of superconducting Y-deficient YBa2Cu3Oy nano-particles prepared by the planetary ball milling technique and silver inclusion on electrical fluctuation conductivity of polycrystalline YBa2Cu3Oy has been reported. Samples, synthesized by the conventional solid-state reaction technique, have been investigated using X-ray diffraction, scanning electron microscope and electrical resistivity. Scanning electron microscope analyses show that nano-particles of Y-deficient YBa2Cu3Oy are embedded in the superconducting matrix. The density of these nano-particles strongly depends on milling parameters. The fluctuation conductivity has been analyzed as a function of reduced temperature using the Aslamazov–Larkin model. Three different fluctuation regions namely critical, mean-field and short-wave are observed. The zero-temperature coherence length, the effective layer thickness of the two-dimensional system, critical magnetic fields and critical current density are estimated. Superconducting parameters are affected by Y-deficient YBa2Cu3Oy nano-particles. It has been found that attainment of an optimum concentration and well-dispersed of nano-sized inclusions by ball milling process improves the physical properties. On the other hand, the sample with Y-deficient YBa2Cu3Oy nano-particles and Ag exhibits better superconducting properties in comparison with free added one.

We compare the electrical magneto-conductivity fluctuation between YBa2Cu3Oy (Y-123) and YBa2Cu3Oy embedded by an Y-deficient Y-123 nano-phase, generated by planetary ball-milling. Both samples were synthesized by solid state reaction with two stages of sintering at 950 degrees C and separated by energetic milling (milled sample) and hand grinding (unmilled sample). SEM analysis of the milled samples shows the appearance of spherical shaped nano-entities of Y-deficient Y-123 embedded in the Y-123 matrix. The magneto-conductivity data are analysed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity. The results show the occurrence of two-stage transitions: intragranular and intergranular, as well as a pairing transition splitting in the milled sample related to the presence of the Y-deficient nanoparticles. In the normal state, we identify a contribution of the Gaussian regimes for both samples. In the presence of a high magnetic field, the critical exponent near T-co of the milled material is higher than the one of the unmilled, indicating that the nanoparticles strengthen the effects of the order-parameter phase of individual grains of the Y-123 strongly disordered. This result fits well into a description based on a dirty limit of the general vortex-glass theory. In the paracoherent state, a crossover occurs and a small temperature range appears where the fluctuation conductivity may be governed by others mechanisms related to vortices dynamics. This temperature range is smaller in the milled sample. (C) 2015 Elsevier B.V. All rights reserved.

The magnet-resistivity measurements of the Y-based Y3Ba5Cu8O18−x superconductor under different magnetic fields ranging from 0 to 200 mT have been carried out to understand the dissipation mechanisms in the resistive transition. Samples were synthesized in air by solid-state reaction method. Three models are employed to investigate the broadening of the resistive transition. The Ambegaokar–Halperin phase slip (AH), thermally activated flux creep (TAFC) models for granular superconductors, and Kosterlitz–Thouless (KT) model describing the vortex–antivortex unbinding for 2D. Phase analysis by X-ray diffraction (XRD) and morphology examination by scanning electron microscopy (SEM) were carried out. The AH and TAFC models cannot explain the whole of the broadening of resistive transition; a small temperature range is not described by these two models. Furthermore, our experimental data shows a good agreement with the KT model over the entire transition range justifying the picture of vortex–antivortex unbinding.

We report electrical conductivity fluctuation analyses on YBa2Cu3O7−d (noted Y-123) and Y3Ba5Cu8O18±x (noted Y-358) polycrystalline samples added with nano-sized ferrite cobalt (CoFe2O4) particles. Phases and microstructure have been systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations show that the grain size is reduced with increasing the content of CoFe2O4 in the yttrium-based superconductor (YBCO) matrix The temperature dependence of electrical resistivity ρ(T) has been measured and the effect of addition of magnetic CoFe2O4 in the paraconductivity region has been reported. The thermodynamic fluctuation is obtained by analyzing the excess of conductivity on the basis of the Aslamazov–Larkin theory. The coherence length, the effective layer thickness, critical magnetic fields, and critical current density are estimated. Superconducting parameters are affected by the nanoparticle addition, and results are discussed in relevance to the structural and microstructure differences between Y-123 and Y-358.

A comparative study of the fluctuation magneto-conductivity in [Formula: see text] (noted [Formula: see text]) and [Formula: see text] (noted [Formula: see text]) polycrystalline samples was carried out. Samples were synthesized in oxygen atmosphere using a standard solid state reaction technique. Phases and microstructure have been systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magneto-conductivity was measured in a magnetic field ranging from 0 T to 7 T applied perpendicular to the current path direction. The magneto-conductivity data were analyzed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity [Formula: see text], where [Formula: see text] is the fluctuation conductivity. Analyses of the magneto-conductivity data reveal that [Formula: see text] possesses a better quality of intrinsic Josephson junction compared to [Formula: see text] one while in the former one the depression in superconducting temperature is more pronounced. The applied magnetic field narrowed substantially the three dimensions (3D) Gaussian regime and for [Formula: see text] sample this regime is vanished for high magnetic field ([Formula: see text][Formula: see text]1 T). Results are discussed in relation with the difference in the structure and microstructure [Formula: see text] and [Formula: see text]. The upper critical and the irreversibility magnetic fields were estimated and were found to be higher in the [Formula: see text] sample.

We have studied the flux-pinning mechanisms of YBa 2Cu 3 O y (Y-123) and YBa 2Cu 3 O y embedded by Y-deficient Y-123 nanoparticles induced by planetary ball-milling technique. Samples were synthesized in air using a standard solid-state reaction technique by considering a thermal cycle with two stages of sintering at 950 °C separated by intermediate crushing; a traditional crushing (in a mortar) and another energetic (in a planetary crusher). Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM), and the global critical current density dependence on temperature (J ct(T)) at several applied magnetic fields were carried out. The temperature dependence of J ct(T) was analyzed within the collective pinning model. For both samples and at self-magnetic field, the temperature dependence of the critical current density is in agreement with the δ T c pinning mechanism which is due to the spatial fluctuation of the Ginsburg-Landau coefficient associated with the transition temperature T c. Under an applied magnetic field of 100 mT there is evidence of δ ε and δ l pinning mechanisms in the unmilled sample; however, the δ ε pinning is strongly dominant in the milled one These results agree with TEM observations showing the appearance of defects and contrast deformation due to the nanophases generated by ball milling and embedded inside the superconducting matrix.

The effects of nano-sized CoFe2O4 particles (10nm) addition on the structural and the normal state resistivity of YBa2Cu3O7 (noted Y-123) and Y3Ba5Cu8O18 (noted Y-358) polycrystalline were systematically studied. Samples were synthesized in oxygen atmosphere using a standard solid state reaction technique by adding CoFe2O4 up to 2wt%. Phases, microstructure and superconductivity have been systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical measurements ρ(T). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations reveal that the grain size is reduced with increasing the content of CoFe2O4. The measurements for the resistivity dependence of temperature show that the depression in superconducting temperature is more pronounced for CoFe2O4 addition in Y-358 compound than in Y-123 one. These results may be attributed to the existence of much more disorder due to a greater number of Cu sites to be substituted by Fe and Co in Y-358 compared to Y-123.

The effects of nanosized silicon oxide nanoparticles and nanowires additions on the microstructure and the normal state transport properties of polycrystalline YBa2Cu3Oy (YBCO, or Y-123) were systematically studied. Samples were synthesized in air using a standard solid state reaction technique by adding nanosized entities up to 3 wt.%. Phases, microstructure, superconductivity, have been systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrical measurements. When nanosized SiO2 entities are added to the YBCO the orthorhombic structure is maintained. SEM results reveal that the grain size is reduced with increasing the content of SiO2. TEM investigation shows the presence of inhomogeneities embedded in the superconducting matrix along with the presence of columnar defects in the case of SiO2 nanoparticles added samples. Nanowires tend to agglomerate by entangling with each other in the intergrain regions. To analyze the normal state properties of the samples, the percolation theory based on localized states is applied. A change from Coulomb gap to variable-range hopping mechanisms is observed as a result of increasing the nano-entities concentration. The SiO2 nanowires addition modifies the electrical behavior of samples from metallic to insulating with a much lower concentration comparatively to SiO2 nanoparticles addition. The localization length d and the range hopping R of samples are estimated. (C) 2013 Elsevier B.V. All rights reserved.

The effect of ball milling on the superconducting properties of polycrystalline YBa2Cu3Oy compounds has ben studied. The samples were synthesized by a solid state reaction by considering a thermal cycle with two stages of sintering at 950°C separated by intermediate crushing; a traditional crushing (in a mortar) and another energetic (in a planetary crusher). The correlations between milling parameters, microstructure and superconducting properties have been investigated. The samples were characterized by X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy. The critical current density of the samples was examined using current–voltage, ac-susceptibility and magnetization measurements. The temperature dependence of the resistivity under magnetic field has been studied to evaluate the upper critical and the irreversibility magnetic fields of these samples. It is demonstrated that ball milling is an effective approach for obtaining fine particles with size about 15nm gathered into coral-like agglomerates and embedded in the matrix. Such decorated finer structure contributes to the enhancement of the inter-grains and intra-grains critical current density of the material under an applied magnetic field.

The effect of Ag inclusion on the structure microstructure and the critical current density of the YBa2Cu3O7−δ sample prepared using the planetary ball milling process has been investigated. YBa2Cu3O7−δ ceramics have been synthesized in air by a solid state reaction method from an oxide precursor powder, which was prepared from the starting powders of Y2O3, Ba2CO3, and CuO via a one-step annealing process in air at 950 ∘C. After planetary ball milling for 4 h of the oxide precursor powders, it was mixed with an AgNO3 solution, and then was dried and uniaxially pressed, and subsequently annealed at 950 ∘C in air. Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDXS) were carried out. To understand the effects of the ball milling on the pinning behavior, magnetic field and temperature dependences on a critical current density have been studied. Analyses show that Ag-milled YBCO samples exhibit higher values of critical current density in applied magnetic field compared to Ag-unmilled one. The better pinning properties of the Ag-milled samples are believed to be due to the microstructure of more fine and uniform distribution of silver and Y-deficient nanosized generated by ball milling.

The effect of nano-sized CoFe2O4 particles (10 nm in diameter) addition on the structure and the normal state transport properties of polycrystalline Bi-based superconductors were systematically studied. The additional amount, x wt.%, of CoFe2O4 in this case varied from 0.0 to 1 wt.% of the total mass of the sample. Phase analysis by X-ray diffraction (XRD) and Electrical resistance as a function of temperature, ρ(T) were carried out. Nano-sized particles addition modifies the electrical behavior of the normal state with increasing the CoFe2O4 concentration. The bipolaron model can explain properly the normal state resistivity of the samples.

Magnetoresistivity (ρ(T,H)) measurements of polycrystalline YBa2Cu3Oy (Y-123) and YBa2Cu3Oy embedded with nanoparticles of Y-deficient Y-123, generated by the planetary ball milling, have been compared and analyzed by the Ambegaokar and Halperin phase slip model (AH) and thermally activated flux creep (TAFC). Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS), were carried out. SEM analyses show that nanoparticles of Y-deficient Y-123, generated by ball milling, are embedded in the superconducting matrix. The broadening of the resistive transition under magnetic field is found to possess two distinct regions, which suggests that dissipation phenomenon in milled and unmilled samples is caused by two mechanisms: the order parameter fluctuations and the vortex-dynamics separated by a crossover temperature T⁎. The critical current Jc(0) at zero temperature in the grain boundaries decreases as a power law, Hn, which is an indication of the sensitivity of a single junction between the superconducting grains to the applied magnetic field. Jc(0) of the milled material is higher than the one of the unmilled and the activation energies of vortex flux motion U(H)behavior in the applied magnetic field is enhanced by the presence of the nanoparticles embedded in the matrix.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation M. K. Ben Salem, E. Hannachi, Y. Slimani, A. Hamrita, L. Bessais, F. Ben Azzouz, M. Ben Salem; Effect of nanowires SiO2 on superconducting properties of YBa2Cu3O7−d bulks. AIP Conf. Proc. 16 December 2013; 1569 (1): 73–76. https://doi.org/10.1063/1.4849231 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search