RE BCO mixtures with large difference in rare-earth ion size: superconducting properties of chemical solution deposition-grown Yb _{1− x} Sm _x Ba ₂ Cu ₃ O _{7− δ} films

Abstract

The main objective of this work was to study the superconducting properties of RE BCO films with a mixture of rare-earth ( RE ) ions with large difference in ion size, in particular Sm 3+ and Yb 3+ . These Yb 1− x Sm x Ba 2 Cu 3 O 7− δ films have been successfully prepared for the first time by chemical solution deposition following the extremely low-fluorine route, which allows reducing the fluorine content by 93% with respect to standard full trifluoroacetate solutions. On the one hand, critical temperature T c remains stable at approximately 90 K with Sm content up to x = 0.5 where T c starts to increase towards the values of pure SmBCO films of approximately 95 K. On the other hand, the critical current densities J c of the pure SmBCO films are the largest at 77 K, where the influence of a higher T c is very relevant, while at lower temperatures and low fields, the mixed films reach larger values. This demonstrates that mixing rare-earth elements RE in RE Ba 2 Cu 3 O 7− δ causes a change in the pinning properties of the films and reveals the importance of selecting adequate RE BCO compounds according to the temperature and magnetic field region of a desired application.

Microstructure, pinning properties, and aging of CSD-grown SmBa2Cu3O7−δ films with and without BaHfO3 nanoparticles

“…Consequently, while keeping the water vapour, i.e. the dew point T dew constant at 19 • C, we varied T crys at two oxygen partial pressures, which were promising from former studies [12] taking into account that the optimum partial pressure decreases with increasing RE ion size [17,62]. The lower oxygen partial pressure of 50 ppm yielded higher critical temperatures and self-field critical current densities compared to 150 ppm, figure 6.…”

“…In order to improve and optimize the current carrying capabilities of REBCO films and coated conductors for a certain application with a specific range in temperature and magnetic field, artificial pinning centres have to be introduced [2]. Besides mixing RE elements [17], transition metal doping [11], adjusting the stacking fault (SF) density [18] (here YBCO), multilayering and adjusting the Sm-Ba ratio [19], surface decoration [20], and irradiation [21], the best-investigated method is probably the insertion of non-superconducting nanoparticles (for reviews see [22][23][24]), such as perovskites or occasionally pyrochlores [25]. For SmBCO, the former has been intensively investigated by Yoshida et al on PLDgrown films [26].…”

Analytical electron microscopy study of the composition of BaHfO3 nanoparticles in REBCO films: the influence of rare-earth ionic radii and REBCO composition

“…Atomic disorder in such mixed-REE films can result in point defects leading to effective low- T pinning. 17–20 Point defects are assumed to arise from REE-Ba cation exchange 3,21,22 or locally introduced strain due different ionic radii of various REEs. 23 However, the fabrication of mixed-REE films is often more complicated than single-REE films since each REE typically has a different set of optimal fabrication parameters.…”