Jc Of Films Research Articles

Temperature dependence of critical currents in REBCO thin films with artificial pinning centers

Conventionally, δTc type (order parameter modulation) and δl type (mean free path modulation) pinning mechanisms have been proposed to explain the temperature dependence of the flux pinning of superconducting materials. According to previous studies, it is assumed that the temperature dependence of Jc of REBa2Cu3O7 (REBCO, RE = Y, Gd, Sm, etc) films without artificial pinning centers (APCs) is δl type, but it is unidentified when APCs are introduced into the films. In this paper, GdBCO thin films doped with BaHfO3 (BHO) deposited on LaAlO3 substrates by pulsed laser deposition were studied. A target exchange method was used to alternately ablate two targets of pure GdBCO and BHO for introducing nanorods as APCs into GdBCO films. Since the insulative BHO acts as a strong pinning center, the δTc pinning mechanism is expected for the temperature dependence of Jc of these thin films. However, the experimental results showed that the Jc of the films with BHO nanorods was determined by the δl pinning mechanism over a wide temperature range. In order to explain these unexpected results, we examined the pinning mechanism by nanorods based on a resultant pinning force model.

Nanostructural Defects and Critical Current Densities in High-Quality <inline-formula> <tex-math notation="TeX">$\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{CaCu}_{2}\hbox{O}_{8+{\rm X}} $</tex-math></inline-formula> Epitaxial Thin Films Prepared by MOCVD

Nanostructural defects were investigated by transmission electron microscopy in c-axis-oriented epitaxial Bi 2 Sr 2 CaCu 2 O 8+X (Bi2212) thin films with high T c (R = 0) ≥ 83 K and high transport critical current density ofJ c >10 10 A/m 2 at 10 K. We observed misfit dislocations at twin boundaries, dislocations associated with stacking faults parallel to the a-b plane, and antiphase boundaries. We compared the magnetic-field dependent J c values at various temperatures in two Bi2212 films. About 110-nm-thick film A showed lower J c than ~280-nm-thick film B at low temperatures (≤ 20 K) or in low magnetic fields (≤ 0.1 T). However, the J c of film B decreased more rapidly in high magnetic fields, leading to a crossover of the two J c -B curves at temperatures of 30 K and above. This is probably because film B contained a higher density of antiphase boundaries, which caused stronger pinning and higher J c values at low temperatures but may have caused enhanced thermally activated motion of pancake vortices that eventually resulted in lower Jc values in high magnetic fields at moderate temperatures.

Single crystals and thin film growth in Bi(Pb)-SrCaCuO system by the flux method

Abstract A part of the Bi2O3-SrO-CaO-CuO-system phase diagram was investigated and the primary crystallization of layered crystals-heteropolytype 2201 and 2212 phases with maximal contents (up to 50%) was determined. It was shown that the primary crystallization concentration region of the layered crystals is narrowed with the introduction of 0.20–0.25 PbO to the melt. However, the amount of 2212 phase is increased to 80–95% and beyond at this time. Crystals of Bi2.05Pb0.13Sr2.07Ca1.12Cu2O x , with TCo ⋍ 80–83 K and Jc ⋍ 104 A/cm2 at 77 K, are obtained by melt cooling. Blocking textured films of Bi-Pb-Sr-Ca-Cu-O with 2–5 μm width on LaGaO3 and NdGaO3 substrates were obtained by liquid phase epitaxy, using KCl and optimal melt compositions. In such compositions phase 2212 with TCo ⋍ 78–80 K is crystallized. However, the obtained films contain 20–10% of 2201 and La3+-ions, and therefore they had TCo  77 K. Possible ways of increasing TCo and Jc of films under synthesis by LPE are proposed.

High Field Properties of Superconducting Nb3Ge Films Prepared by Chemical Vapor Deposition

The superconducting critical current densities Jc of Nb3Ge films prepared by chemical vapor deposition have been investigated in magnetic fields parallel and perpendicular to the film plane up to above 20 T. The Jc and its field dependence are strongly influenced by any change in the microstructure of films deposited at different deposition temperatures Td. Films deposited at a low Td of 800°C exhibit a high Jc below 20 T and show a slight difference between parallel and perpendicular field dependences of Jc. As Td is increased to 900°C, the Jc of films is appreciably lowered over the entire field range and the difference between two field dependences of Jc is remarkably enlarged. The upper critical field Hc2 of these films has been obtained by extrapolating the Kramer plot of Jc1/2H1/4 versus H to J1/2cH1/4=0, and were estimated to range from 28 to 31 T at 4.2 K.