Article pubs.acs.org/IC
Quaternary Aluminum Silicides Grown in Al Flux: RE5Mn4Al23−xSix (RE = Ho, Er, Yb) and Er44Mn55(AlSi)237 Nicholas P. Calta† and Mercouri G. Kanatzidis*,†,‡ †
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
‡
S Supporting Information *
ABSTRACT: Four novel intermetallic silicides, RE5Mn4Al23−xSix (x = 7.9(9), RE = Ho, Er, Yb) and Er44Mn55(AlSi)237, have been prepared by reaction in aluminum flux. Three RE5Mn4Al23−xSix compounds crystallize in the tetragonal space group P4/ mmm with the relatively rare Gd5Mg5Fe4Al18−xSix 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) Å3. Structure refinements on single-crystal diffraction data show that Er44Mn55(AlSi)237 adopts a new cubic structure type in the space group Pm3̅n 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. Ho5Mn4Al23−xSix exhibits a ferromagnetic transition at 20 K and an additional metamagnetic transition at 10 K, suggesting independent ordering temperatures for two distinct magnetic sublattices.
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INTRODUCTION Rare earth-containing intermetallic compounds exhibit a wide variety of interesting structural and physical properties including heavy fermion behavior,1−4 superconductivity,5−7 Kondo physics,8−10 quantum criticality,11−13 and interesting magnetic ordering.14−17 While this diversity of properties is fascinating, prediction of these behaviors remains elusive. Therefore, the availability of new phases via discovery synthesis and their subsequent characterization is of particular importance to intermetallic chemistry, as new compounds can validate existing insights or generate new ones. In recent years, we have explored a number of RE/T/Al/Si systems, where RE is a rare earth element and T is a transition metal, using aluminum flux as a reaction medium.18−24 Flux reactions provide many synthetic advantages, including increased © 2013 American Chemical Society
diffusion of reactants to improve reactivity and single-crystal growth.25−27 These reactions also allow for lower reaction temperature than traditional solid-state techniques or arc melting, providing a route to access kinetically stabilized phases that do not otherwise appear in the phase diagram. Aluminum flux reactions have yielded rare earth transition metal aluminum silicides and germanides with a wide variety of properties. REFe4Al9Si6 (RE = Tb, Er) exhibits exceptionally robust oxidation resistance at high temperature by forming a passivating surface layer of oxide, gaining less than 1% by mass upon heating in air to 900 °C.24 Many compounds in this class magnetically order in some way at low temperature, on the Received: May 3, 2013 Published: August 9, 2013 9931
dx.doi.org/10.1021/ic401659y | Inorg. Chem. 2013, 52, 9931−9940
Inorganic Chemistry
Article
target compound. The resulting ingot was etched in
