R. Awad

Replacement study of Thallium by Zn and Ni in Tl-1223 superconductor phase

Abstract Preparation, characterization and investigation of (Tl 1−x M x )Ba 2 Ca 2 Cu 3 O 9−δ , where MZn and Ni with 0 ≤ x ≤ 0.6, are performed. Our results show that the transition temperature “T c ” increases up to x=0.2 for Zn substitution samples whereas it decreases with increasing Ni content.

Synthesis, Characterization, and Magnetic Properties of Pure and EDTA-Capped NiO Nanosized Particles

The effect of ethylenediaminetetraacetic acid (EDTA) as a capping agent on the structure, morphology, optical, and magnetic properties of nickel oxide (NiO) nanosized particles, synthesized by coprecipitation method, was investigated. Nickel chloride hexahydrate and sodium hydroxide (NaOH) were used as precursors. The resultant nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). XRD patterns showed that NiO have a face-centered cubic (FCC) structure. The crystallite size, estimated by Scherrer formula, has been found in the range of 28ź33źnm. It is noticed that EDTA-capped NiO nanoparticles have a smaller size than pure nanoparticles. Thus, the addition of 0.1źM capping agent EDTA can form a nucleation point for nanoparticles growth. The optical and magnetic properties were investigated by Fourier transform infrared spectroscopy (FTIR) and UV-vis absorption spectroscopy (UV) as well as electron paramagnetic resonance (EPR) and magnetization measurements. FTIR spectra indicated the presence of absorption bands in the range of 402ź425źcmź1, which is a common feature of NiO. EPR for NiO nanosized particles was measured at room temperature. An EPR line with g factor ź1.9ź2 is detected for NiO nanoparticles, corresponding to Ni2+ ions. The magnetic hysteresis of NiO nanoparticles showed that EDTA capping recovers the surface magnetization of the nanoparticles.

Superconducting properties of Tl1−xYbxBa2Ca2Cu3O9−δ

A series of high temperature superconductor samples of type Tl1−xYbxBa2Ca2Cu3O9−δ with x ranging from 0 to 0.5 have been synthesized at 860 °C for 4 h. The x-ray powder diffraction and the electrical resistivity measurements for the prepared samples have been reported. X-ray data indicate that the solubility limit xs between Tl3+ and Yb3+ ions in Tl1−xYbxBa2Ca2Cu3O9−δ phase is about 0.3. The transition temperature Tc, determined from the electrical resistivity data, shows a depression in its value with increasing Yb-content. The critical concentration xc, at which the superconductivity disappeared, is estimated to be 0.58. The effect of external magnetic field on the electrical resistivity behaviour has been studied. The activation energy, calculated from these data, shows a decrease in its value as the applied magnetic field and Yb-content increase.

Ab initio calculations of the electronic structure of the low-lying states for the ultracold LiYb molecule

Ab initio techniques have been applied to investigate the electronic structure of the LiYb molecule. The potential energy curves have been computed in the Born-Oppenheimer approximation for the ground and 29 low-lying doublet and quartet excited electronic states. Complete active space self-consistent field, multi-reference configuration interaction, and Rayleigh Schrödinger perturbation theory to second order calculations have been utilized to investigate these states. The spectroscopic constants, ωe, Re, Be, …, and the static dipole moment, μ, have been investigated by using the two different techniques of calculation with five different types of basis. The eigenvalues, Ev, the rotational constant, Bv, the centrifugal distortion constant, Dv, and the abscissas of the turning points, Rmin and Rmax, have been calculated by using the canonical functions approach. The comparison between the values of the present work, calculated by different techniques, and those available in the literature for several electronic states shows a very good agreement. Twenty-one new electronic states have been studied here for the first time.

Synthesis and electrical resistivity studies of Tl1−xPrxBa2Ca2Cu3O9−δ superconductors

Several high-temperature superconductor samples of the general composition Tl1−xPrxBa2Ca2Cu3O9−δ, with 0 ≤ x ≤ 0.3, have been synthesized by a single solid-state reaction. Within a narrow range of composition, x 0.2, the samples are almost single phase possessing a tetragonal unit cell similar to the Tl-1223 phase. The electrical resistivity exhibits a metallic behaviour for 0 ≤ x ≤ 0.2 above the transition temperature whereas it exhibits a semiconductor-like behaviour for x > 0.2. The normal electrical resistivity ρn is enhanced as the Pr content increases and the resistivity data, in the semiconductor regime, are well fitted according to the variable range hopping model. The transition temperature, determined from electrical resistivity measurements, decreases monotonically with x and the superconductivity disappears at around xc = 0.29. The depression in the transition temperature as Pr content increases is due to two different mechanisms involving hole filling or Cooper pairs breaking.

Thermal expansion measurements using x-ray powder diffraction of Tl-1223 substituted by molybdenum

Lattice parameters and the volume thermal expansion coefficient, from room temperature down to 80 K, have been calculated for TlBa2Ca2Cu3−xMoxO9−δ with x = 0.0, 0.05, 0.1 and 0.2 using x-ray powder diffraction. The superconducting transition temperature for the prepared samples, determined from electrical resistivity measurements, is suppressed from 122 to 98 K as the Mo content increases from 0.0 to 0.2. This suppression is discussed in terms of the uniaxial pressure induced by the changing of the Jahn–Teller effect and the hole-filling mechanism. The lattice parameters a and c contract with decreasing temperature and the rate of contraction of the lattice parameter a (a80/a300 = 0.9997) is lower than that of c (c80/c300 = 0.9967). The volume thermal expansion coefficient increases from 4.6 × 10−5 to 6.04 × 10−5 K−1 as x increases from 0.0 to 0.2. The Debye temperature, calculated from volume thermal expansion coefficient measurements, is reported as a function of Mo content and superconducting transition temperature and it agrees with that determined from specific heat measurements.

Electrical and mechanical properties of (Bi,Pb)-2223 substituted by holmium

The effect of the partial substitution of Ca2+ by Ho3+ ions on the electrical and mechanical properties of the superconducting phase (Bi,Pb)-2223 was studied. Superconducting samples of the type (Bi1.8Pb0.4)Sr2Ca2.1−xHoxCu3.1O10+δ were prepared by solid-state reaction technique under ambient pressure, and characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The superconducting transition temperature Tc and pseudogap temperature T* were estimated from electrical resistivity measurements, while the critical current density Jc was determined from I–V curves. The electrical resistivity data were discussed according to bipolaron model in the absence of thermally excited individual polarons. The sample with x = 0.025 showed the highest phase volume fraction, Tc, and Jc. Room temperature Vickers microhardness measurements were carried out at different applied loads (0.25–5 N) in order to investigate the performance of the mechanical properties of (Bi1.8Pb0.4)Sr2Ca2.1−xHoxCu3.1O10+δ phase. It was found that all the samples exhibit normal indentation size effect (ISE). The Vickers microhardness number HV increased as x increased from 0 to 0.025. The experimental results were discussed in view of Meyer’s law, Hays–Kendall (HK) approach, elastic/plastic deformation (EPD) model, and proportional specimen resistance (PSR) model. The load independent (true) microhardness of (Bi1.8Pb0.4)Sr2Ca2.1−xHoxCu3.1O10+δ superconducting samples showed identical behavior to that of the PSR model.

Structural, Optical and Room Temperature Magnetic Study of Mn-Doped ZnO Nanoparticles

Undoped and Mn-doped ZnO nanoparticles (Zn1−xMnxO), with nominal weight percentages (0.00≤x≤0.10), have been synthesized by co-precipitation technique. The synthesized nanoparticles are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV) and Fourier transform infrared spectroscopy (FTIR). From XRD analysis, the compound ZnMnO3 is formed for x≥0.05 with cubic structure (a=8.3694A) and its concentration increases with x. Moreover, XRD analysis reveals the wurtzite hexagonal crystal structure for ZnO. The lattice parameters (a and c) of Zn1−xMnxO are calculated and they increase with the doping concentration of Mn as a consequence of the larger ionic size of Mn2+ ions compared to Zn2+ ions. The crystallite size is calculated for all the samples using Debye–Scherrer’s method (SSM), Williamson–Hall methods (UDM, USDM and UDEDM) and Size-Strain Plot method (SSP), and the results are in good agreement with TEM. The presence of functional groups and the chemical bonding is confirmed by FTIR spectra that shows a peak shift between undoped and doped ZnO. The energy bandgap (Eg) is calculated for different concentrations of Mn (0.00≤x≤0.10) by using the UV-visible optical spectroscopy, between 300nm and 800nm, showing a noticeable drop in Eg with x. At room temperature, the magnetization of the samples reveals the intrinsic ferromagnetic (FM) behavior of undoped ZnO, ferromagnetic behavior of ZnxMn1−xO (0.01≤x≤0.03) and the co-existence of ferromagnetic and paramagnetic behavior for ZnxMn1−xO (0.05≤x≤0.10). This ferromagnetism is decreased for the doped samples as a consequence of antiferromagnetic coupling between Mn ions. The two samples correspond to x=0.01 and x=0.10, tend to be superparamagnetic because of the formation of single domain particles as a consequence of small particle size. x=0.03 shows an optimum value of Mn concentration for maximum saturation magnetization and the best ferromagnetic nature.

Effect of ZnO Nano-Oxide Addition on the Superconducting Properties of the (Bi.Pb)2223 Phase

The major limitation of Bi-system superconductor applications is the intergrain weak links and weak flux pinning capability producing low critical current density of the Bibased phases. In order to enhance these characteristics and other superconducting properties, effective flux pinning centers are introduced into high temperature superconductors. In this work, different weight percentages of ZnO nano oxide were introduced at the final stage of the Bi1.8Pb0.4Sr2Ca2Cu3O10-y superconductor preparation process. Phase characterization was completed by X-ray diffraction (XRD). Exact constitution of the samples was determined using particle induced X-ray emission (PIXE). Granular and microstructure were investigated using scanning electron microscopy (SEM). Electrical resistivity as function of the temperature was carried to evaluate the relative performance of samples, and finally, E-J characteristic curves were obtained at 77K. Using 0.4 ZnO weight percentage, the electrical and granular properties were greatly enhanced, indicating more efficient pinning mechanisms. A critical current density of 949 A/cm2 was obtained which represents more than twice the value obtained for the pure sample (Jc= 445 A/cm2).

Magnetoresistance studies of Tl-1223 phase substituted by scandium

Superconducting samples of type TlBa2Ca2-xScxCu3O9-δ with x = 0.0, 0.025, 0.05, 0.1, and 0.2 have been prepared via solid-state reaction technique. The effect of weak magnetic fields up to 4.4 kG on the electrical resistivity of the prepared samples has been studied to investigate the flux motion for this phase. The results reveal a slight shift in the superconducting transition temperature Tc and an increase in the superconducting transition width ΔT with increasing magnetic fields. The experimental data fit well with the thermally activated flux creep model and the activation energy U(B) shows a power law dependence on magnetic field as B. Also, the transition width is related to the magnetic field according to the relation ΔT α Bn. The values of β and n are strongly dependent on the Scandium-content. The temperature and magnetic field dependence of the activation energy U(B, T) is found to be U(B, T) ~ ΔT B-η, where η = β + n. The critical current density Jc(0) and the upper critical field Bc2(0) are calculated, from the above measurements, as a function of Scandium-content. Finally the electronic thermal conductivity κe, estimated from Wiedemann-Franz law, is reported at different applied magnetic fields for the prepared samples.