Phase formation and superconductivity in REBaSrCu3−x(PO4)xOy (0 ≤ x ≤ 0.3)

TLDR: Oxy-anion substituted phases of the composition REBaSrCu 2.8 (PO 4 3− ) 0.2 O y have been synthesized as discussed by the authors, and single phase formation is achieved only for the larger rare earths (La → Ho and Y) and all the phases crystallize in the tetragonal 123 structure.

Abstract: Oxy-anion (PO 4 3− ) substituted phases of the composition REBaSrCu 2.8 (PO 4 ) 0.2 O y have been synthesized. Single phase formation is achieved only for the larger rare earths (La → Ho and Y) and all the phases crystallize in the tetragonal 123 structure. IR studies confirm the presence of a phosphate group in the structure. The total oxygen content (including that associated with the oxy-anion PO 4 3− ) has been found to be in the range 7.01 to 7.10 per formula unit. Except for RE = La, Nd, Yb and Lu, all the phases exhibit superconductivity and the T c,zero values vary from 18 to 38 K. The T c,zero increases with decreasing size of RE 3+ . ErBaSrCu 3 O 7 is multiphasic and single phase formation is achieved for the first time by phosphate substitution at the copper site. Single phase formation is encountered for x = 0.10 and 0.15 with T c,zero values of 54 and 37 K respectively.