Synthesis of new fluorite-related rare earth oxides Ln $${\text{Ln}}_{2}^{\prime }$$ Ln 2 ′ MO7 (Ln, Ln′ = rare earths; M = Nb, Sb, Ta), their structures and magnetic properties by calorimetry measurements

Abstract

New fluorite-related quaternary rare earth oxides Ln $${\text{Ln}}_{2}^{\prime }$$ MO7 (Ln = Nd, Gd, Tb; Ln′ = Lu and Y; M = Nb, Sb, Ta) were prepared. They crystallize in an orthorhombic superstructure of cubic fluorite with space group C2221. The results of the Rietveld analysis indicate that there exists some disordering of the Ln and Ln′ atoms at the eight-coordinate site and the seven-coordinate site. These compounds are paramagnetic down to 1.8 K except for TbLu2SbO7. Magnetic susceptibility measurements show that TbLu2SbO7 antiferromagnetically orders at 3.0 K. Specific heat measurements also show a λ-type anomaly at the same temperature. The analysis of the magnetic specific heat for TbLu2SbO7 indicates that the magnetic transitions are due to the ground doublet state of Tb3+ ions.