Crystal structures and magnetic properties of ordered perovskites Ba(2)LnNbO(6) (Ln = lanthanide elements)

A series of double-perovskite oxides Ba(2)LnNbO(6) (Ln = lanthanide element s) were synthesized. Their powder X-ray diffraction measurements and Rietve ld 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 b ond 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 susceptibili ty measurements show that they are paramagnetic down to 2 K. The Eu-151 Mos sbauer spectrum for Ba2EuNbO6 indicates that the Eu ion is in the trivalent state and a quadrupole interaction exists in this compound. Both the magne tic susceptibility and the electron paramagnetic resonance (EPR) spectrum m easurements show that the Gd3+ ion is in the S-8(7/2) state. In addition, t he anisotropic EPR spectrum indicates that the six oxygen coordination arou nd the Gd3+ ion has no longer a perfect octahedral symmetry. (C) 1999 Acade mic Press.