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

Synthesis of new fluorite-related rare earth oxides LnLn 0 2 MO 7 (Ln, Ln 0 5 rare earths; M 5 Nb, Sb, Ta), their structures and magnetic properties by calorimetry measurements Abstract New fluorite-related quaternary rare earth oxides LnLn 0 2 MO 7 (Ln = Nd, Gd, Tb; Ln 0 = Lu and Y; M = Nb, Sb, Ta) were prepared. They crystallize in an orthorhombic superstructure of cubic fluorite with space group C222 1 . The results of the Rietveld analysis indicate that there exists some disordering of the Ln and Ln 0 atoms at the eight-coordinate site and the seven-coordinate site. These compounds are paramagnetic down to 1.8 K except for TbLu 2 SbO 7 . Magnetic susceptibility measurements show that TbLu 2 SbO 7 antiferromagnetically orders at 3.0 K. Specific heat measurements also show a k-type anomaly at the same temperature. The analysis of the magnetic specific heat for TbLu 2 SbO 7 indicates that the magnetic transitions are due to the ground doublet state of Tb 3? ions.