Quaternary aluminum silicides grown in Al flux: RE5Mn4Al(23-x)Si(x) (RE = Ho, Er, Yb) and Er44Mn55(AlSi)237.
Four novel intermetallic silicides, RE5Mn4Al(23-x)Si(x) (x = 7.9(9), RE = Ho, Er, Yb) and Er44Mn55(AlSi)237, have been prepared by reaction in aluminum flux. Three RE5Mn4Al(23-x)Si(x) compounds crystallize in the tetragonal space group P4/mmm with the relatively rare Gd5Mg5Fe4Al(18-x)Si(x) structure type. Refinement of single-crystal X-ray diffraction data yielded unit cell parameters of a = 11.3834(9)-11.4171(10) Å and c = 4.0297(2)-4.0575(4) Å with volumes ranging from 522.41(5) to 528.90(8) Å(3). Structure refinements on single-crystal diffraction data show that Er44Mn55(AlSi)237 adopts a new cubic structure type in the space group Pm3n with a very large unit cell edge of a = 21.815(3) Å. This new structure is best understood when viewed as two sets of nested polyhedra centered on a main group atom and a manganese atom. These polyhedral clusters describe the majority of the atomic positions in the structure and form a perovskite-type network. We also report the electrical and magnetic properties of the title compounds. All compounds except the Ho analogue behave as normal paramagnetic metals without any observed magnetic transitions above 5 K and exhibit antiferromagnetic correlations deduced from the value of their Curie constants. Ho5Mn4Al(23-x)Si(x) exhibits a ferromagnetic transition at 20 K and an additional metamagnetic transition at 10 K, suggesting independent ordering temperatures for two distinct magnetic sublattices.
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Nicholas P
NP
Calta
Mercouri G
MG
Kanatzidis