Characterization of REBa₂Cu₃O_7−X (RE = Gd, Ho) nanostructures, fabricated by a simple technique

Highlights: • REBa₂Cu₃O_7−X nanostructures was synthesized by sol–gel method assisted by ultrasonic irradiation. • Different solvents with different vapor pressures were used to achieve different morphologies. • The effect of ultrasound wave was studied on the morphology, particle size and superconducting properties. • Behavior of the magnetic susceptibility of the nanoparticles was studied in different strengths. - Abstract: Simple citrate sol–gel method assisted by ultrasonic irradiation has been employed to fabricate REBa₂Cu₃O_7−X (RE123) (RE = Gd, Ho) nanostructures. The elevated temperature and pressure due to the sudden collapsing the bubbles with a high stability and energy in the ultrasonic procedure gave rise to a clear variation in the morphology, however compared with the bulk samples, the ultrasound waves had no significant effect on the onset critical temperature of the prepared nanoparticles (about 91.4 K). Changes of the magnetic susceptibility with temperature were found to be independent of the applied field strength, probably due to the elimination of the weak links in the products. The influence of various solvents with different vapor pressures and so different destruction powers, including methanol, toluene, 1-butanol, and 1-hexanol, was also studied on the morphology and particle size of the products. The crystalline size of the Ho123 was calculated 32.38 nm, according to the Williamson–Hall plot, in agreement with the TEM images. Using the Rietveld method, the lattice parameters of Ho123 nanoparticles were obtained to be slightly smaller than that of Gd123