Abstract
Complex crystal symmetry variation is observed for the oxygenated PrBa 2-x La x Cu 3 O 7+y system (0≤x≤1, -0.12≤y≤0.39). Powder X-ray Rietveld analysis indicates that the crystal structure changes from the PrBa 2 Cu 3 O 7 or CuBa 2 PrCu 2 O 7 1212C-type (C for chain) orthorhombic O(I)-phase (space group Pmmm) to 1212-type tetragonal T-phase (P4/mmm) around x = 0.45, and then to a new 1212-type of orthorhombic O(II)-phase (Cmmm) around x = 0.65. However, regardless of the structural change, anomalous Pr ordering temperature T N (Pr) decreases monotonically from 18 K for PrBa 2 Cu 3 O 6.88 to 2.8 K for PrBa 1.3 La 0.7 Cu 3 O 7.24 . The increasing Pr-O bond length with decreasing T N indicates that Pr ordering is closely correlated with the wave function overlap between Pr-4f orbital and O-2p π orbital in the CuO 2 bi-layers.