Variation of anomalous Pr ordering and crystal symmetry for the oxygenated system

Structural, transport, magnetic, calorimetric, and neutron data were reported for the oxygen-annealed (Formula presented) or 1212-type (Formula presented) system (Formula presented) Powder x-ray Rietveld analysis indicates that due to subtle oxygen distribution in the (Formula presented) plane for these oxygenated cuprates, two structural symmetry transitions were observed, from orthorhombic (Formula presented) (CuO chain) O(I) phase (space group Pmmm) for (Formula presented) to tetragonal 1212 T phase (Formula presented) for (Formula presented) and then to a different type of orthorhombic 1212 O(II) phase (Cmmm) for (Formula presented) Resistivity data indicate that Pr-in-Ba is not favorable for metallic state and no superconductivity can be detected for these insulating cuprates. Magnetic-susceptibility, heat-capacity, and neutron-diffraction data show that, regardless of the structural transitions, the anomalous Néel temperature (Formula presented) decreases monotonically and smoothly from 18 K for (Formula presented) to 2.5 K for (Formula presented) with the same c-axis antiferromagnetic Pr spin alignment. The increasing Pr-O bond length observed with decreasing (Formula presented) indicates that this unusual Pr magnetic ordering is closely correlated with the wave-function overlap between (Formula presented) orbital and eight (Formula presented) orbital in the (Formula presented) bilayer.