Crystal structures and magnetic properties of ordered perovskites Ba2LnNbO6 (Ln = lanthanide elements)

A series of double-perovskite oxides Ba(2)LnNbO(6) (Ln = lanthanide elements) were synthesized. Their powder X-ray diffraction measurements and Rietveld analysis show that they are monoclinic with space group P2(1)/n and that Ln(3+) and Nb5+ ions are structurally ordered. Although the average Ln-O bond length increases with the ionic radius of Ln(3+), the average Nb-O bond length is nearly constant for all the Ba(2)LnNbO(6). Magnetic susceptibility measurements show that they are paramagnetic down to 2 K. The Eu-151 Mossbauer spectrum for Ba2EuNbO6 indicates that the Eu ion is in the trivalent state and a quadrupole interaction exists in this compound. Both the magnetic susceptibility and the electron paramagnetic resonance (EPR) spectrum measurements show that the Gd3+ ion is in the S-8(7/2) state. In addition, the anisotropic EPR spectrum indicates that the six oxygen coordination around the Gd3+ ion has no longer a perfect octahedral symmetry. (C) 1999 Academic Press.