Crystal structure of DyBa2Cu4O8: A new 77 K bulk superconductor

Single-crystal x-ray diffraction data from DyBa₂Cu₄O₈ are used to confirm the structure of RBa₂Cu₄O₈ (R=Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Tm), all of which have been synthesized in bulk and display substantial Meissner diamagnetism. The structure is orthorhombic, space group Ammm, with a=3.846 3(3), b=3.872 6(3), and c=27.237(2) Å. Copper-oxygen layers parallel to (001) are dimpled as in the 1-2-3 structure. Unique copper-oxygen strips parallel to (100) have copper in distorted square-planar coordination. Magnitudes of oxygen anisotropic thermal vibrations are significantly less than in the 1-2-3 structure; thus the oxygen content of 1-2-4 is expected to be significantly more stable.