A. I. Abou-Aly

CeSn3, a strongly mixed valent material

Abstract Ce in CeIn 3− x Sn x is found to be trivalent for x x > 1.8. In the mixed valence regime, specific heat, susceptibility and resistivity depend on the number of f electrons, n f , in the manner prescribed by recent theories but only if n f = 0.4 for pure CeSn 3 .

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.

Resistivity of the Ce(Rh1−yPty)2 system

The electrical resistivities of Ce(Rh1−yPty)2 samples, and of La(Rh1−yPty)2 samples have been measured from 2 to 300 K. The data suggest that an evolution takes place from antiferromagnetic crystal field split trivalent Ce behavior for pure CePt2 to Kondo Lattice behavior with diminishing crystal field effects for 0.5 < y < 1 to mixed valence behavior for y < 0.5. Comparisons are made to the behavior observed in other systems such as Ce(Pd1−xRhx)3, Ce(Pd1−yAgy)3 and Ce(Sn1−yIny)3.

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.

Effect of the partial replacement of Ca by alkaline element Na on Tl-1223 superconductor

We have investigated the effect of Na substitution at Ca sites on the lattice parameters, electrical resistivity, magnetic susceptibility and thermopower coefficient for TlBa2Ca2-xNaxCu3O9-δ; with 0 ≤ x ≤ 0.4. The lattice parameters elongate with increasing the Na-content. A little enhancement in the superconducting transition temperature Tc has been observed as x increases from 0 to 0.05 and then it depresses gradually for x > 0.05. This observation was attributed to the fact that Na has converted the Tl- 1223 phase from over-doped regime to under-doped regime which is in conformity with the thermopower results, that found to change from negative (over-doped regime) to positive (under-doped regime). The inter-grain critical current density as function of Na has been also reported from ac magnetic susceptibility measurements.

Effect of cooling rate and strontium doping on the formation of (Hg, Tl)-1234 phase

Superconductor samples of nominal composition Hg1-xTlxBa2Ca3Cu4O10+δ (0.3≤x≤1.0) are prepared at ambient pressure using a closed quartz tube at 850 °C. X-ray powder diffraction for the prepared samples is carried out and the results show that the structure of this system is a tetragonal. The lattice parameters a and c are calculated, and the data indicate that a is not affected by the substitution of Tl3+ into Hg2+, whereas c decreases as the Tl content increases. The superconductivity is investigated using the electrical resistance and ac magnetic susceptibility measurements. All the samples have a superconducting behaviour except when x = 0.3. To improve the superconducting properties of this system, the cooling rate for the sample with x = 0.7 is studied; also the replacement of Ca by Sr for both x = 0.3 and x = 0.5 have been investigated. The excess conductivity for x = 0.3 shows that the dimensionality is changed from two-dimensional in the high-temperature region to three-dimensional in the mean field region.

Synthesis and characterization of the Indium-doped Tl-1223 phase

Superconductor of type Tl1 − xInxBa2(Ca0.9Y0.1)2Cu3O9 − δ for x = 0, 0.1, 0.2, 0.3 and 0.5 were synthesized using stoichiometric amount of Ba2(Ca0.9Y0.1)2Cu3O7 + δ precursor, Tl2O3 and In2O3 in a tube furnace at 870°C. The samples were characterized using the x-ray powder diffraction and the scanning electron microscope (SEM) whereas the composition of these samples were determined by micro-probe analysis. The transition temperature Tc for as-synthesized (Tl, In)-1223 compound, determined from the electrical resistance measurements, varied from 122 K for x = 0 to 100 for x = 0.6 These results indicate that the addition of indium decrease the transition temperature of Tl-1223 phase. This is because the addition of indium changes the Tl-1223 phase to the over-doped region. The argon annealing for some of these samples were studied. The effect of external applied magnetic field on the stage of transition is reported. Our data show that the transition width is increased by the increasing of the external applied magnetic field. The samples are more affected by the magnetic field with increasing of indium content.

Comparative studies between the influence of single- and multi-walled carbon nanotubes addition on Gd-123 superconducting phase

The effect of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) addition on the phase formation and the superconducting properties of GdBa2Cu3O7−δ phase has been studied. Therefore, composite superconductor samples of type (CNTs)x GdBa2Cu3O7−δ, 0.0 ≤ x ≤ 0.1 wt.% have been synthesized by a standard solid-state reaction technique. The samples have been characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results of XRD show an enhancement in the phase formation up to 0.06 wt.% and 0.08 wt.% for SWCNTs and MWCNTs, respectively. SEM and TEM reveal that CNTs form an electrical network resulting in well-connected superconducting grains. The electrical properties of the prepared samples have been examined by electric resistivity and I–V measurements, and their results reinforce the XRD, SEM and TEM. Consequently, both Tc and Jc improve as the addition percentage increases up to 0.06 wt.% and 0.08 wt.% for SWCNTs and MWCNTs, respectively.

Electrical resistivity of GdInxSn3-x below TN

Abstract Electrical resistivity measurements are used to determine that GdIn x Sn 3- x samples are antiferromagnetic with T N varying linearly from 20 K for GdSn 3 ( x = 0) to 46 K for GdIn 3 ( x = 3). Pure GdSn 3 and GdIn 3 samples show Fisher-Langer-like resistivity behavior while intermediate concentration samples evolve to Suezaki-Mori type behavior. It is shown that this behavior can be qualitatively understood in terms of varying the relative strenght of the spin fluctuation and superzone energy gap contributions to the resistivity which appear in the Suezaki-Mori theory of the resistivity of an antiferromagnetic metal.

Superconducting parameter determination for (Co0.5Zn0.5Fe2O4)x/Cu0.5Tl0.5-1223 composite

The addition of magnetic Co0.5Zn0.5Fe2O4 nanoparticles to the superconducting Cu0.5Tl0.5-1223 phase has been used to investigate the electrical resistivity behavior of the composite above the superconducting transition temperature Tc. This was studied according to the opening of spin gap and fluctuation conductivity. The results indicated that the pseudogap temperature (T*) and superconducting fluctuation temperature (Tscf) change by increasing the addition of Co0.5Zn0.5Fe2O4 nanoparticles. It was found that T* is related to hole carrier concentration P and it also depends on the antiferromagnetic fluctuation affected by magnetic nanoparticles. The excess-conductivity analysis showed four different fluctuation regions started from high temperature up to Tc, and they were denoted by short wave (sw), two-dimensional (2D), three-dimensional (3D), and critical (cr) fluctuations. The crossover temperature between 3D and 2D (T3D–2D) in the mean field region was decreased by increasing the addition of Co0.5Zn0.5Fe2O4 nanoparticles, in accordance with the decrease in Tscf with x. The coherence length at 0 K along c-axis ξc(0), effective layer thickness of the 2D system d, and inter-layer coupling strength J were estimated as a function of Co0.5Zn0.5Fe2O4 nanoparticle addition. Moreover, the thermodynamics, lower and upper critical magnetic fields, as well as critical current density have been calculated from the Ginzburg number NG. It was found that the low concentration of Co0.5Zn0.5Fe2O4 nanoparticles up to x = 0.08 wt% improves the superconducting parameters of Cu0.5Tl0.5-1223 phase. On the contrary, these parameters were deteriorated for (Co0.5Zn0.5Fe2O4)x/Cu0.5Tl0.5-1223 composite with x > 0.08 wt%.