The Phase Change Due to Oxygen Content in the LnBa₂Cu₃O_y Compound Systems (Ln=Tm, Gd, Sm)

Abstract

The phase change due to oxygen content y (7> y >6) was investigated for TmBa 2 Cu 3 O y (TBC), GdBa 2 Cu 3 O y (GBC) and SmBa 2 Cu 3 O y (SBC) by means of X-ray diffraction and electrical resistivity. The phase boundary between orthorhombic and tetragonal phases moved toward the oxygen-rich side when the system changed as TBC→YBa 2 Cu 3 O y (YBC)→GBC→SBC. The plateau in the critical temperature T c was observed in the intermediate region of 6.7> y >6.4 for each system, supporting the existence of an orthorhombic-II phase. It seemed to exhibit a system dependence, i.e., a decrease in T c in the order of TBC, YBC, GBC and SBC.