Synthesis and investigation of Sr-containing 223 and 1222 complex oxides in the R-Sr-Ce-Cu-O system (R = Pr, Nd, Sm-Gd, Dy-Yb and Y)

Abstract An extended family of layered complex copper oxides has been synthesized in the system R 2 O 3 -SrO-CeO 2 -CuO (R = Pr, Nd, Sm-Gd, Dy-Yb and Y). The compounds were studied by X-ray powder diffraction, electron microscopy and EDS analysis. Eu 1.6 Sr 1.8 Ce 0.6 Cu 3 O 8.6 ( a = 3.8439 (2) A, c = 28.09 (1) A) and Y 1.5 Sr 1.8 Ce 1.0 Cu 2.7 O 8.6 ( a = 3.8160 (7) A, c = 29.120 (5) A), belonging to two structural groups of 223- and 1222-type, respectively, were chosen for Rietveld structure refinement. Their structures can be described as 14-layered stackings along the c -axis. The compounds with larger lanthanides (R=Pr-Gd) are isostructural with Ba-containing 223 phases, e.g. (R,Ba) 2 (R, Ce) 2 Cu 3 O 8+δ . Among the synthesized compounds only the ones with R=Sm and Eu have been shown to be superconductors ( T c =30 and 36 K, respectively) after high-pressure oxygen treatment (120 atm). 1222 phases with smaller rare earth elements (R=Dy-Yb and Y) differ from 223 phases in composition and lattice parameters, having structures which are more similar to (Pb, Cu)-1222, e.g. (Pb, Cu) (Eu, Ce) 2 (Sr, Eu) 2 Cu 2 O 8+δ . Compounds of 1222-type did not become superconducting even when treated with high-pressure oxygen.