L. A. Klinkova, V. I. Nikolaychik, N. V. Barkovsky, V. K. Fedotov, A. F. Shevchun
ABSTRACT
The composition and structure of ceramic samples of Eu2Ba3Cu5Oy (Eu‑235) oxide of a tetragonal and orthorhombic structure were studied by X-ray diffraction (XRD) and chemical analysis, electron diffraction, elemental analysis (EA), and high-resolution electron microscopy (SEMM) in a transmission electron microscope (TEM). According to XRF data, samples annealed in air at a temperature of 1213 K and additionally in an oxygen atmosphere (P (O2) = 101 kPa, 723 K) are single-phase. However, according to EA data in TEM, these samples are inhomogeneous in the cationic composition, which corresponds to the process of disproportionation of 3Eu2Ba3Cu5Oy → Eu3Ba4Cu7Oy (Eu‑347) + Eu3Ba5Cu8Oy (Eu‑358). On the curve of the temperature dependence of the magnetic susceptibility = f (T) of the rhombic sample Eu‑235 with a diamagnetic response at Tc = 80 K, two more are observed at Tc = 40 and 30 K, indicating the presence of three superconducting phases. The tetragonal and rhombic Eu‑235 samples according to the STEM images are nanostructured and consist of coherently fused domains 2–5 nm in size.
KEYWORDS:
oxide Eu2Ba3Cu5Oy, disproportionation, nanostructure, superconductivity.