Structural phase transitions and the effect on Pr anomalous ordering for the PrBa2-xLaxCu3O7+y system

[[abstract]]Complex crystal symmetry variation is observed for the oxygenated PrBa2-xLaxCu3O7+y system (0⩽x⩽1, -0.12⩽y⩽0.39). Powder X-ray Rietveld analysis indicates that the crystal structure changes from the PrBa2Cu3O7 or CuBa2PrCu2O7 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 TN(Pr) decreases monotonically from 18 K for PrBa2Cu3O6.88 to 2.8 K for PrBa1.3La0.7Cu3O7.24. The increasing Pr-O bond length with decreasing TN indicates that Pr ordering is closely correlated with the wave function overlap between Pr-4f orbital and O-2pπ orbital in the CuO2 bi-layers[[fileno]]2010102010213[[department]]物理