High Critical Current Density and Enhanced Pinning in Superconducting Films of YBa₂Cu₃O_7−δ Nanocomposites with Embedded BaZrO₃, BaHfO₃, BaTiO₃, and SrZrO₃ Nanocrystals

Abstract

Chemical solution deposition (CSD) of YBa2Cu3O7−δ (YBCO) nanocomposites from colloidal precursor solutions containing double metal oxide preformed nanocrystals is a promising, costeffective and reproducible approach to produce superconducting films with high critical current density (Jc) and enhanced pinning. Here, the influence of the preformed nanocrystal composition on the microstructure and superconducting properties of the YBCO nanocomposite films is studied, with a focus on establishing a simple and scalable process to grow nanocomposites that can be transferred to grow nano-added coated conductors. Colloidal stable BaZrO3, BaHfO3, BaTiO3 and SrZrO3 nanocrystals (3-6 nm in diameter) were synthesized and added to an environment-friendly low-fluorine YBCO precursor solution. High-quality superconducting layers were grown on LaAlO3 single-crystal substrates from these four nanocomposite precursor solutions in a single deposition process, without the need of a seed layer, yielding Jc of 4-5 MA/cm² at 77 K in self-field. The different YBCO microstructures produced by the four types of nanocrystals and the resulting microstrain of the films are compared and related with the magnetic-field and angular dependence of Jc. We demonstrate the BaHfO3-containing nanocomposite as the best-performing with a homogeneous distribution of nanoparticles with 7 nm in average diameter and a high density of stacking faults, which leads to some of the best superconducting properties ever achieved via low-fluorine CSD. The Jc exhibits a much smoother decay in applied magnetic fields and a much more isotropic behaviour for non-parallel magnetic fields, and the pinning force is increased by a factor of 3.5 at 77 K and 1 T with respect to the pristine film.

All-chemical YBa2Cu3O7−δ coated conductors with preformed BaHfO3 and BaZrO3 nanocrystals on Ni5W technical substrate at the industrial scale

“…On the other hand, the positive effects of adding nanocrystals are much less pronounced than in the case of single-crystal substrates. In our studies of YBCO nanocomposite films on LaAlO3 [19], the observed Jc(77, sf) were 10% higher in both BHO-and BZO-added YBCO films, and in high fields (>1 T) Jc increased by a factor of three (BHO-added) and two (BZO-added). In the current study, BHO-CC and BZO-CC show a rather moderate increase (~40 and 20%) in Ic at 77 K and high fields (>1 T), which becomes less pronounced (20 and 10% in BHO-CC) or even disappears (in BZO-CC) at 65 and 30 K. Below we discuss the possible reasons for such a modest improvement and possible ways to enhance these positive effects.…”

“…5 mol-%), one would anticipate a much smaller value  ~ 0.37. Note that in 5 mol-% BHO-and BZO-added YBCO films on LaAlO3 substrates, we observed  = 0.33 and 0.38 versus 0.53 in the pristine films [19].…”

“…Because of the overall nonstoichiometric Y1.3Ba1.8Cu3.0Ox composition and unfinished reaction (presence of Ba(O,F)2), it contains rather small (50 to 100 nm) secondary phase particles (Y2O3 and Y2Cu2O5) and a rather large density of SFs (Figure 8). These defects are possibly the major reason why the addition of 5 mol-% BHO or BZO nanocrystals gives smaller effects on the CC templates than on LaAlO3 [19]. Indeed, the microstrain   0.39% in the pristine YBCO-CC is already rather large (compared to 0.08% in the pristine YBCO on LaAlO3) and only slightly increases to   0.45% in BHO-CC and BZO-CC (Table 5).…”

Recent Advances and Challenges in the Development of Radiofrequency HTS Coil for MRI

“…In the experimental results, we observed that the value of B + 1 at which the superconducting material transits from the superconducting state to the dissipative state depends on temperature, but also on the value of the static field. This can be explained by the temperature, field, and field-orientation dependence of the critical current density of the HTS material, as studied by [45], in comparable conditions.…”

“…The phase perturbation was also shown to have a strong temperature dependence (Figure 3B); the amplitude of the perturbation was continuously reduced as the temperature increased. Using a phenomenological model of the coil superconducting diamagnetism, it was shown that these artifacts were caused by a small yet unavoidable misalignment, less than 1°, of the HTS coil in the static field B 0 , and that their temperature dependence mirrored the temperature dependence of the in-plane critical current of YBCO measured in comparable conditions [45].…”