Abstract
Complex crystal symmetry variation is observed for the oxygenated PrBa 2− x La x Cu 3O 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 2Cu 3O 7 or CuBa 2PrCu 2O 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 2Cu 3O 6.88 to 2.8 K for PrBa 1.3La 0.7Cu 3O 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.
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