In search of chemical clues: Single-crystal structural studies of PrBa2Cu3O6 and PrBa2Cu3O7

摘要: Abstract Complete refinements of single-crystal X-ray diffraction intensity data for two tetragonal PrBa 2 Cu 3 O 6 crystals and detwinned orthorhombic 7 crystals, along with a more precise refinement YBa , have confirmed that the praseodymium compounds are strictly isostructural yttrium congeners. Crystallographic available superconducting RBa analogs (R=Y, rare earth) were used to establish overall structural trends as function lanthanide size. In comparison these trends, present results obtained indicate no markedly unusual features; crystallographic behavior Pr corresponds trivalent ion. However, subtle anomalies in x system revealed by detailed comparisons systems oxygen content. The axial CuO bond distance is unusually short both indicating stronger chemical linkage chains planes compared systems. Trends bond-valence sums polyhedral volumes about R 3+ suggest increased spatial extension 4f-orbitals (as neighboring Nd ) mediates strong interactions manifold capable inhibiting superconductivity. retention superconductivity 1.85 Ce 0.15 CuO 4 may arise from significant crystal-chemical differences between T′ — -type structures: structure features (1) layers bonded only Pr, not Cu, (2) larger volume greater isolation 4f-orbitals.