Crystallographic studies and X-ray diffraction patterns of Ba5R8Zn4O21 by Rietveld refinements

The structure of the Ba5R8Zn4O21 series (R=lanthanides) was investigated us ing X-ray Rietveld refinements. The compounds were successfully prepared fo r R=Eu, Gd, Dy, Ho, Er, Tm, and Yb. Ba5R8Zn4O21 crystallizes in the tetrago nal space group I4/m; for R=Yb to Eu, a ranges from 13.635 02(5) to 13.960 62(9) Angstrom, c from 5.658 46(3) to 5.784 83(5) Angstrom, and V from 1051 .987(8) to 1127.459(14) Angstrom (3). The Zn2+ ions adopt a fivefold distor ted square pyramidal coordination. The seven-coordinate R3+ reside in monoc apped trigonal prisms. These prisms share edges, and form layers stacked al ong the c axis. There are two types of BaO polyhedra: bicapped square prism s (BaO10), and irregular BaO10 polyhedra. For larger R, Ba5R8Zn4O21 was not stable, and tetragonal BaR2ZnO5(La,Nd) and orthorhombic BaR2ZnO5(SM) phase s were observed instead. (C) 2001 International Centre for Diffraction Data .