DIMORPHISM AND MAGNETIC-PROPERTIES OF DY2BACOO5

A new green Dy2BaCoO5 oxide has been prepared at 1300-degrees-C in an argon flow. X-Ray diffraction data reveal that it crystallizes with the Sm2BaCuO5 structure type, space group Pnma and lattice parameters a = 12.3375(4) angstrom, b = 5.7250(2) angstrom and c = 7.0880(2) angstrom. When the synthesis is carried out at a lower temperature of 910-degrees-C, the previously reported brown Dy2BaCoO5 oxide is obtained with the Nd2BaNiO5 structure type, space group Immm and lattice parameters a = 3.7475(3) angstrom, b = 5.8039(4) angstrom and c = 11.5082(7) angstrom. A tentative model relating the two structure types is given. Magnetic susceptibility data reveal a very different behaviour of the two oxides, which has been explained by taking into account their structures. At low temperature antiferromagnetic ordering has been observed in both the cobalt and dysprosium sublattices and the estimated Neel temperatures are 10.4 and 4.5 K for the Immm and Pnma forms of Dy2BaCoO5 respectively.