Magnetic properties and structural transitions of orthorhombic fluorite-related compounds Ln3MO7 (Ln=rare earths, M=transition metals)

Abstract

Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln 3 MO 7 (Ln = rare earths, M = transition metals) were investigated. In this study, we prepared a series of molybdates Ln 3 MoO 7 (Ln = La ~ Gd). They crystallize in an orthorhombic superstructure of cubic fluorite with space group P2 1 2 1 2 1 , in which Ln 3+ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). All of these compounds show a phase transition from the space group P2 1 2 1 2 1 to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility measurements from 1.8 to 400 K and specific heat measurements from 0.4 K to 400 K. Gd 3 MoO 7 shows an antiferromagnetic transition at 1.9 K.Measurements of the specific heat for Sm 3 MoO 7 and the analysis of the magnetic specific heat indicate a "two-step" antiferromagnetic transition due to the ordering of Sm magnetic moments in different crystallographic sites, i.e., with decreasing temperature, the antiferromagnetic ordering of the 7-coordinated Sm ions occur at 2.5 K, and then the 8-coordinated Sm ions order at 0.8 K. The results of Ln 3 MoO 7 were compared with the magnetic properties and structural transitions of Ln 3 MO 7 (M = Nb, Ru, Sb, Ta, Re, Os, or Ir).3

Photoluminescence properties of a new orange–red‐emitting Sm3+–La3SbO7 phosphor

“…This type of structure allows a wide variety of chemical substitutions at the R and M sites (3+ and 4+ or 2+ and 5+ combinations of valence, as well as oxygen vacancies). The R sites can accommodate all the rare earth ions together with yttrium and have an ordered, defect‐fluorite superstructure . For antimonate compounds, Hinatsu et al reported the detailed crystal structure and magnetic properties of ternary Ln 3 SbO 7 (Ln = rare earths).…”

Studies on phase transitions of rare earth tantalates (Sm₁₋<i>_xLn_x</i>)₃TaO₇ (<i>Ln</i> = Nd, Eu) with fluorite-related structure

“…7),12) On the other hand, Ln 3 MoO 7 compounds which crystallize in the orthorhombic structure with space group P2 1 2 1 2 1 at room temperature transform to the space group Pnma when they are heated above the transition temperature. 43) For any Ln 3 MO 7 compounds, their phase transition temperatures increase with decreasing Ln ionic radius. 9),12),13),31), 43) As for M = Ta compounds, crystal structures and magnetic properties for Ln 3 TaO 7 (Ln = La, Pr, Nd, SmLu) were reported.…”

Color - Tunable Phosphors in Weberite Type System, La3 SbO7 :Bi3+ , Eu3+ for Near-UV LED Applications

“…Thus it creates one oxygen vacancy per fluorite cell. Here cation ordering occurs at the metal site and the oxide‐vacancy occurs at anion site, because of the significant difference in ionic radii of Ln 3+ and M 5+ cation . Photoluminescence properties of Eu 3+ doped R 3 SbO 7 (R=La, Gd, Y) and Sm 3+ doped La 3 SbO 7 were studied by Wang et al .…”

“…Here cation ordering occurs at the metal site and the oxide-vacancy occurs at anion site, because of the significant difference in ionic radii of Ln 3 + and M 5 + cation. [10] Photoluminescence properties of Eu 3 + doped R 3 SbO 7 (R = La, Gd, Y) and Sm 3 + doped La 3 SbO 7 were studied by Wang et al [11] and Li et al [12] respectively. It is reported that this compound has high chemical and thermal stability as well as lattice stiffness.…”