Crystal Structures and Magnetic Properties of Ordered Perovskites Ba2LnNbO6 (Ln=Lanthanide Elements)

A series of double-perovskite oxides Ba2LnNbO6 (Ln=lanthanide elements) were synthesized. Their powder X-ray diffraction measurements and Rietveld analysis show that they are monoclinic with space group P21/n and that Ln3+ and Nb5+ ions are structurally ordered. Although the average Ln–O bond length increases with the ionic radius of Ln3+, the average Nb–O bond length is nearly constant for all the Ba2LnNbO6. Magnetic susceptibility measurements show that they are paramagnetic down to 2 K. The 151Eu M?ssbauer 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 8S7/2 state. In addition, the anisotropic EPR spectrum indicates that the six oxygen coordination around the Gd3+ ion has no longer a perfect octahedral symmetry.