High-temperature X-ray diffraction measurements of fluorite-related rare earth antimonates Ln3SbO7 (Ln=Nd, Tb) and their magnetic properties

Abstract

Ternary rare-earth antimonates Ln3SbO7 (Ln=rare earths) were prepared, and their structures were determined by X-ray diffraction measurements. They crystallize in an orthorhombic superstructure of cubic fluorite (space group Cmcm for Ln=La, Pr; Ccmm for Ln=Sm–Dy), in which Ln3+ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated). For Ln=Nd, two phases with the Cmcm and Ccmm space groups coexist at room temperature. When the temperature was increased, the Nd3SbO7 compound transformed into a single phase with the space group Cmcm. Through magnetic susceptibility measurements, an antiferromagnetic transition was observed at 3.0K (Ln=Nd) and 7.8K (Ln=Tb). Analysis of the magnetic specific heat for Tb3SbO7 indicates that the 8-coordinated Tb ions magnetically orders at 7.8K, and with furthermore decreasing temperature, the 7-coordinated Tb ions shows antiferromagnetic ordering at 3.0K.