Syntheses and structures of compounds with YBaCo4O7-type structure

More than 20 different isostructural (YBaCo4O7-type, P6(3)mc, a = 6.3-6.4, c = 10.1-10.3 Angstrom) compounds in the system RBaX4O7 (R = Ca, Y, In, Dy-Lu, X = Co, Al, Zn, Fe) have been synthesised through solid-state reaction and characterised using either X-ray single crystal or powder diffraction data. The R atom occupies an octahedral space in the close-packed oxygen lattice, the X atoms form together with oxygen a defect wurtzite like net of tetrahedra, and the Ba replaces one of the oxygen in the close packing ending up in an anticuboctahedral 12-coordination. Unit cell expansions, especially in the ab-plane, are seen with the presence of Zn2+ and larger rare-earth (RE) ions at the same time as Al3+ causes the c-axis to shrink. The distribution of Al, Co, Fe and Zn at the two crystallographic X positions is discussed. It was possible to conclude, from displacement parameters, that one certain oxygen position has significantly lower freedom to move than the others, which might affect the materials properties since the very same oxygen is also part in the metal-oxygen-metal bridge with the angle best suited for magnetic super-exchange coupling. (C) 2004 Elsevier SAS. All rights reserved.