Abstract
Ternary intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, and Ho) have been prepared by arc-melting followed by annealing at 800 °C. All the compounds belong to the Tb117Fe52Ge112 structure type (space group Fm 3 ¯ m) characterized by a complex giant cubic unit cell with a ~ 30 Å. The single-crystal structure determination of Y- and La-containing compounds reveals a significant structural disorder. A comparison of these and earlier reported crystal structures of R117Co52+δSn112+γ suggests that more extensive disorder occurs for structures that contain larger lanthanide atoms. This observation can be explained by the need to maintain optimal bonding interactions as the size of the unit cell increases. Y117Co56Sn115 exhibits weak paramagnetism due to the Co sublattice and does not show magnetic ordering in the 1.8–300 K range. Ho117Co55Sn108 shows ferromagnetic ordering at 10.6 K. Both Pr117Co54Sn112 and Nd117Co54Sn111 exhibit antiferromagnetic ordering at 17 K and 24.7 K, respectively, followed by a spin reorientation transition at lower temperature.
Highlights
Intermetallics with giant unit cells (GUC) that contain hundreds and thousands of atoms represent one of the most interesting topics in the structural inorganic chemistry
In the Al-Cu-Ta system [11,12], Al56.6 Cu3.9 Ta39.5 crystallizes in the F43m space group with the unit cell volume around 93,000 Å3, but a slight compositional change leads to another phase, Al55.4 Cu5.4 Ta39.1, which exhibits a more complicated crystal structure and has the largest intermetallic unit cell reported to date, with the volume around 365,000 Å3
We have previously reported the magnetic properties of several R117 Co52+δ Sn112+γ materials (R = Sm, Tb, Dy) [23], suggesting that the magnetic phase transitions arise solely due to the Properties
Summary
Intermetallics with giant unit cells (GUC) that contain hundreds and thousands of atoms represent one of the most interesting topics in the structural inorganic chemistry. Typical representatives of GUC intermetallics include clathrate compounds [4], Zintl phases [5], Frank-Kasper phases [6,7], Nowotny chimney-ladder phases [8,9], and quasicrystals and their approximants [10]. The realm of these materials can be expanded by slight variation of the compositions that can lead to the expansion of the existing isostructural systems and to the formation of new crystal structures. In the Al-Cu-Ta system [11,12], Al56.6 Cu3.9 Ta39.5 crystallizes in the F43m space group with the unit cell volume around 93,000 Å3, but a slight compositional change leads to another phase, Al55.4 Cu5.4 Ta39.1 , which exhibits a more complicated crystal structure and has the largest intermetallic unit cell reported to date, with the volume around 365,000 Å3
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