Synthesis, crystal structure, and magnetic properties of ordered perovskites Sr 2LnTaO 6 (Ln = lanthanides)

Abstract

A series of Sr 2LnTaO 6 (Ln=lanthanides except for La, Ce, and Pr) has been prepared by a standard ceramic method and their crystal structure has been determined by powder X-ray diffraction using the Rietveld analysis method. The crystal symmetry of their oxides is monoclinic (space group P2 1/ n) with an ordered arrangement of Ln and Ta ions. Magnetic susceptibility measurements show that these compounds are paramagnetic down to 5 K. The 151 Eu Mössbauer spectrum for Sr 2EuTaO 6 indicates that the Eu ion is in the trivalent state. The symmetry of the Eu site is distorted from the octahedral symmetry, and its spin–orbit coupling constant is determined to be 342 cm −1. In the Yb compound, the energy levels in the octahedral crystal field splitting are determined to be E Γ 7− Γ 6 =1324 and E Γ 8− Γ 6 =391 cm −1 by calculating the magnetic susceptibility.