Crystal structures and reference powder patterns of BaR2ZnO5 (R = La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, and Tm)

Reference x-ray powder patterns and the crystal structures of the lanthanide compounds, BaR2ZnO5, in which R = La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, or Tm were determined by the x-ray Rietveld refinement technique. A structural trend was confirmed for this series of compounds. The compounds with smaller ionic radii (R = Sm, Eu, Gd, Dy, Ho, Y, Er, or Tm) are isostructural to the orthorhombic green phase (BaY2CuO5). The lattice parameters for compounds with R = Tm to Sm range from a = 7.01855(9) angstrom to 7.20452(14) angstrom, b = 12.25445(17) angstrom to 12.5882(2) angstrom, and c = 5.6786(14) angstrom to 5.81218(11) angstrom, respectively. R is sevenfold coordinated inside a monocapped trigonal prism. These prisms share edges to form wave-like chains parallel to the long b-axis. The BaR2ZnO5 compounds which contain larger size R (La and Nd) crystallize in the tetragonal space group 14/mcm. The lattice parameters are a = 6.90982(10) and c = 11.5977(2) angstrom for BaLa2ZnO5, and a = 6.75979(5) angstrom and c 11.54560(12) angstrom for BaNd2ZnO5. The structure consists of ZnO4 tetrahedra (instead of planar CuO4 groups as found in BaR2CuO5) with 10-fold coordinated bicapped square prismatic Ba and 8-fold coordinated bicapped trigonal prismatic R ions between them. The reference x-ray powder patterns will be submitted to the Powder Diffraction File (PDF)