Ac Electrical Resistivity Measurements Research Articles

High Temperature Superconductors (${\rm Y}_{1-x}{\rm Nd}_{x}$ )Ba2Cu3O7-δ Obtained by Acetate Method

Bulk ceramic samples with chemical composition (Y 1-x Nd x )Ba 2 Cu 3 O 7-δ , where x = 0, 0.1, 0.2, 0.5, and 1 were sintered by a proposed acetate method. The samples were then submitted to structural characterization by X-ray diffraction with crystal structure refining using the Rietveld method. AC electrical resistivity measurements from ambient temperatures down to 4.2 K were performed, as well as magnetic measurements of magnetic moment as function of temperature and magnetic hysteresis loop. Results have shown superconductivity with critical temperatures of about 91 and 60 K for pure YBa 2 Cu 3 O 7-δ (x = 0) and pure NdBa 2 Cu 3 O 7-δ (x = 1) samples, respectively. Scanning electron microscopy images were also analyzed, revealing a regular parallel-piped grain shape. The proposed method showed as an advantage to reduce the grinding time without any considerable degradation on structural or superconducting properties of pure YBa 2 Cu 3 O 7-δ (x = 0) or pure NdBa 2 Cu 3 O 7-δ ( x = 1), as related to samples prepared by a conventional solid state route.

AC electrical resistance measurements of PdH x samples versus composition x

A brief introduction on the transport properties of PdH x system will be presented. The resistance ratio method is the most frequent technique used to measure the interstitial loading of hydrogen atoms into palladium. Using this technique a series of AC electrical resistance measurements of PdH x , demonstrating a stoichiometric values x > 1 obtained by electrochemical method at room temperature and pressure is presented. A full description of the used electrochemical method for preparing the samples PdH x with composition x > 1 and the analysis to determine the achieved composition will be presented. Conclusions on the electrical resistance of PdH x versus composition x and correlated physical phenomena have been done. In particular, these studies show the importance of the electrochemical processes efficiency. In order to have an accurate calculation of x value, precise efficiency amplitude estimation is needed. Our analysis underline the systematic underestimation of the x value in the well known PdH x relative electrical resistance versus x at room temperature as reported in literature.

Plasma assisted in situ laser deposition of Y 1Ba 2Cu 3O 7−x superconducting thin films with laser heating and annealing

Single-chamber laser processing of high temperature Y 1Ba 2Cu 3O 7−x thin films on SrTiO 3 (100), ZrO 2(100) and MgO(100) substrates was carried out using plasma assisted in situ laser deposition. The films were deposited by XeCl excimer laser ablation at substrate temperatures as low as 450–550°C. A dc oxygen plasma at a partial pressure of up to 200 mtorr forced oxygen incorporation during the film growth at a low substrate temperature. The problem of firing and maintaining the discharge was solved by appropriate electrode geometry. Direct cw CO 2 laser irradiation of the substrate surface and excimer laser plume were used to reduce the density of particulates. The films were characterized by: X-ray diffraction, four-point probe ac electrical resistivity measurements, SEM and XMA. A T c onset of ∼88–90 K and J c ∼ 7 × 10 5 A cm −2 at 4.2 K were measured.

Upper critical magnetic fields of Bi 2Sr 2CuO 6 single crystals

The upper critical magnetic fields of Bi 2Sr 2CuO 6 single crystals with the applied magnetic fields H parallel to the ab-plane, H c2( ab), and perpendicular to the ab-plane, H c2( c), have been determined from the AC electrical resistivity measurements up to 8 T. Both H c2( ab) and H c2( c) exhibit positive curvature as a function of temperature T for H c2≤2 T which is much pronounced in H c2( ab). The initial slopes (−d H c2/d T) Tc0 determined from the linear portion of the H c2 versus T curves have the values of 5.0 T/K for H c2( ab) and 1.6 T/K for H c2( c. Both H c2( ab) and H c2( c) data can be fitted very well by the conventional Werthamer, Helfand, Hohenberg and Maki (WHHM) theory in the minimum paramagnetic limit ( λ so=∞) using the experimental values of the initial slopes (−d H c2/d T) Tc0 and T c's and indicates an ordinary type superconductivity in this system. The value of the anisotropic ratio obtained from the H c2( T) data and the (−d H c2/d T) Tc0 data is about 3.3.

Ion beam induced atomic mixing kinetics of Te/Cu and Te/Ag

Abstract Ion beam mixing, at room temperature, of Te/Cu and Te/Ag systems induced by 300 keV Kr + irradiation are studied by means of ac electrical resistivity measurements and 2 MeV 4 He + back scattering spectrometry. Electrical resistivity data explained in terms of Riviere and Jaouen model showed that mixing is due to collisional cascade processes only. The effect of the sharp gradient in the ion energy (calculated from TRIM) transferred to target recoils at the Te/Cu (or Te/Ag) interface is correlated with the mixing efficiency calculated from resistivity data. On the other hand, RBS data also showed a large extent of mixing in the Te/Cu system compared to the Te/Ag system. A mixed layer with a nearly uniform composition of Te 0.27 Cu 0.73 and a thickness of approximately 1500 A is obtained after mixing with a fluence of 2.5×10 16 Kr + /cm 2 , while a nonuniform mixed layer has been formed for Te/Ag system after mixing with a fluence of 2.13×10 16 Kr + /cm 2 .

Pressure dependence of the superconducting transition temperature of (Y 1−χPr χ)Ba 2Cu 3O 7−δ compounds; Evidence for 4f electron hybridization

The effect of nearly hydrostatic pressure to 20 kbar on the superconducting transition temperature T c of (Y 1−χPr χ)Ba 2Cu 3 O 7−δ compounds with 0⩽χ⩽0.5 was determined by means of low frequency ac electrical resistivity measurements. The application of pressure to this system reveals striking effects which appear to be associated with the hybridiazation between Pr 4f and valence band states. In this range of pressure P, T c increases with P for 0⩽χ⩽0.2, exhibits a maximum at ∼6 kbar for χ=0.3, and decreases rapidly with P for χ⩾0.4, while the initial rate of increase of T c with pressure (d T c/d P) P=0 , increases with χ for 0⩽χ⩽0.3. These results suggest there is a pressure-induced electronic phase transition at ∼6 kbar foir χ=0.3 that shifts to lower values of P for higher values of χ.

Effect of Oxidizing Atmosphere on Superconductivity in RBa2Cu3−xMxOz

ABSTRACTThe dependence of the superconducting properties of RBa2Cu3−xMxOz (R = Y, Gd, M = Cr, Mn, Fe, Co, Ni, and x = 0.0, 0.025, 0.05, 0.1, 1.0, 3.0) on the oxidizing environment used during the processing (sintering/annealing) of these materials has been investigated. Samples of nominal composition, YBa2Cu3Oz, were prepared from the same starting materials and subjected to two different controlled heat treatments, under both controlled oxygen and ozone atmospheres. Measurements of ac electrical resistance versus temperature indicate that the critical temperatures are increased, and the widths of the superconducting transitions are narrowed for identically heat-treated samples when processed under ozone atmosphere rather than under an oxygen environment. Thermogravimetric analysis data indicate this trend to be correlated with increased oxygen content and thermal stability. This effect is also observable for materials with metal substitution for Cu, although the measured Tc's are generally lower for increased values of x. X-ray powder diffraction analysis showed the materials to be mostly single phase.

Transition from antiferromagnetism to ferromagnetism in the superconducting mixed ternary system (Sm1?x Er x )Rh4B4

The mixed ternary system (Sm1−x Er x )Rh4B4 has been investigated by means of measurements of ac electrical resistance in various applied magnetic fields, ac magnetic susceptibility, and specific heat. The low-temperature superconducting and magnetic transition temperature versus Er concentrationx phase diagram reveals the occurrence of a single transition to long-range magnetic order for all concentrations, changing from antiferromagnetism for SmRh4B4 to ferromagnetism for ErRh4B4 atx ≈ 0.2. The upper critical magnetic field versus temperature curves for various Er concentrations exhibit combined features characteristic of both SmRh4B4 and ErRh4B4, rather than a gradual evolution from one type to the other. A model for such a mixed magnetic system is discussed, and comparisons with other mixed ternary systems are made.

Transport and magnetic properties of layered rare earth disilicides

The layered rare earth (RE) disilicides RE 3Si 5 with RE = Y, Er, Tm, Yb and Lu have been studied by means of ac magnetic susceptibility and ac electrical resistance measurements. Evidence for magnetic orderings have been found at 4.4K, 3.1K and 1.7K for Er 3Si 5 and at 2.1K for Tm 3Si 5. The resistance of Lu 3Si 5 was observed to drop abruptly below 7K, possibly indicating the presence of a superconducting phase. An apparent correlation was noted between the value of the room temperature resistivity and the amount of negative curvature observed in the resistivity above ∼ 50K in these materials.