Structures and magnetic properties of new fluorite-related quaternary rare earth oxides LnY2TaO7 and LaLn2RuO7 (Ln=rare earths)

• New fluorite-related quaternary rare earth oxides Ln′Ln″2MO7 have been prepared.
• All compounds LnY2TaO7 (Ln=La–Dy) are paramagnetic down to 1.8 K.
• LaTb2RuO7 shows two magnetic anomalies at 10 and 17 K.

New fluorite-related quaternary rare earth oxides LnY2TaO7 (Ln=La–Dy) and LaLn2RuO7 (Ln=Eu–Tb) have been prepared. They crystallize in an orthorhombic superstructure of cubic fluorite with space groups C2221 and Cmcm, respectively. The results of the Rietveld analysis for LnY2TaO7 (Ln=La–Dy) indicate that there exists no structural ordering of the Ln and Y ions at the eight-coordinate 4b site and the seven-coordinate 8c site, but the larger Ln ions occupy the eight-coordinate 4b site rather than the seven-coordinate 8c site, with increasing the Ln ionic radius. On the other hand, the results of the Rietveld analysis for the X-ray diffraction profiles of LaTb2RuO7 showed that La and Tb atoms are almost situated at the eight-coordinated site (4a site) and seven-coordinated site (8g site), respectively, i.e., cation ordering occurs on the 4a and 8g sites.All compounds LnY2TaO7 (Ln=La–Dy) are paramagnetic down to 1.8 K. On the other hand, LaTb2RuO7 shows an antiferromagnetic transition at 17 K. In addition, another magnetic anomaly has been found at 10 K. Analysis of the magnetic specific heat for LaTb2RuO7 indicates that the magnetic transitions at 10 and 17 K are due to the magnetic ordering of Tb3+ and Ru5+ ions, respectively.

Two magnetic anomalies have been observed in the temperature dependence of ∂(χT)/∂T for LaTb2RuO7. It is discussed that the anomalies at 10 and 17 K are due to the magnetic ordering of Tb3+ and Ru5+ ions, respectively.Figure optionsDownload as PowerPoint slide