CuO4 Superconductor Research Articles

A study of the microstructure and the critical current density of La1.85Sr0.15CuO4 superconductor

The irreversible magnetization, the critical current density and the microstructure of the high-temperature superconductor La1.85Sr0.15CuO4 are compared. Direct observations by transmission electron microscopy (TEM) revealed two orthogonal arrays of extended screw-type dislocations (2 to 5 × 1011 lines per cm2) parallel to the crystallographic directions 〈100〉 and 〈010〉, respectively. These dislocations are dissociated into partial bound stacking faults. Microanalysis showed that Sr concentration around the dislocation cores is about 10% lower than that of the matrix. Measurements of the hysteresis cycle, M(H,T), at various angular orientations (θ.∅) of the field H with respect to the crystalline directions show no detectable correlation between the directions of the dislocations and the critical current density. This suggests that the anisotropy of the critical current density is first of all controlled by the intrinsic properties of the material rather than by the anisotropy of the dislocation structure.

Phonons and Specific Heat of electron High Tc Nd1.85Ce0.15CuO4 Superconductor

Abstract A simple Born model has been seen to explain reasonably well the optical and neutron data available for the Nd 1.85 Ce 0.15 CuO 4 high — T c oxide superconductor. The high frequency phonon bands reveal highly two-dimensional behaviour. Planar dispersions are significant for the different layers. The lattice specific heat in the low temperature region shows a non-Debye behaviour i.e., a variation different from a T 3 — one.

Composition dependence of transition temperature in new superconductors: La2 −x (Ba, Sr) x CuO4

We have investigated the variation of transition-temperature and coupling parameter with the composition concentration in La2 −x (Ba, Sr) x CuO4 superconductors using a formulation developed on the basis of an idea of pairing of charge carriers by exchange of both acoustic plasmons and phonons. Reasonably good agreement is found between the recent experimental results and our theoretical results on the superconducting transition temperature.

Temperature dependence of electrical resistivity in (La1−Y)1.85Sr0.15CuO4 superconductors

Abstract In the (La 1- x Y x ) 1.85 Sr 0.15 CuO 4 compound system, a K 2 NiF 4 -type single phase was found up to x =0.10. For 0.15≦ x ≦1.0, extra phase appeared and the tetragonal phase changed into orthorhombic one for x ≧0.3. The onset temperature of the transition from superconducting to normal states was increased a little, but the offset one was lowered with increasing the content, x , up to x =0.5. For 0.5 x ≦1, the superconducting state was not observed.

EVIDENCE FOR A POSSIBLE ORDER-DISORDER TRANSITION IN THE JOSEPHSON JUNCTION LATTICE OF A GRANULAR La1.85Sr0.15CuO4 SUPERCONDUCTING OXIDE

We present a detailed low field susceptibility study of a sintered La1.85Sr0.15CuO4 superconductor. We find that two critical temperatures should be considered in order to explain our observations. The lower one is characteristic of an order-disorder transition in the Josephson Junction lattice and scales as H .55. Moreover, it is inferred that field cooled data do not give the true bulk Meissner effect.

Properties of La1.8Sr0.2CuO4 superconductors

Critical current, critical field, and carrier density measurements have been made on bulk samples of La1.8Sr0.2CuO4 to assess the potential of such oxide superconductors for practical applications. The importance of preparing samples in a high oxygen pressure was documented. The upper critical field at T=0 was estimated to be 530 kOe. From magnetization hysteresis loops, critical current densities were determined between 0 and 60 kOe. At 60 kOe, the values were 2×103 A/cm2 at 4.2 K and 4×102 A/cm2 at 18 K in samples that exhibited characteristics of weak flux pinning. The effective carrier density at 48 K was 1×1021 cm−3, approximately half of the expected upper limit. A set of microscopic superconducting parameters has been derived from transition temperature, resistivity, and upper and lower critical field measurements made on a single specimen.