Complex Structural Disorder in the Zintl Phases YbMnSb and YbMnSb.

A systematic investigation of the ternary system Yb-Mn-Sb led to the discovery of the novel phase YbMnSb. Its crystal structure was characterized by single-crystal X-ray diffraction and found to be complex and highly disordered. The average YbMnSb structure can be considered to represent a defect modification of the CaLiMgSb type and to crystallize in the tetragonal 4/ space group (No. 136) with four formula units per cell. The structural disorder can be associated with both occupational and positional effects on several Yb and Mn sites. Similar traits were observed for the structure of the recently reported YbMnSb phase (monoclinic space group 2/, No. 15), which was reevaluated as part of this study as well. In both structures, distorted Sb octahedra centered by Yb atoms and Sb tetrahedra centered by Mn atoms form disordered fragments, which appear as the hallmark of the structural chemistry in this system. Discussion along the lines of how difficult, and important, it is to distinguish YbMnSb from the compositionally similar binary YbSb and ternary YbMnSb compounds is also presented. Preliminary transport measurements for polycrystalline YbMnSb indicate high values of the Seebeck coefficient, approaching 210 μV K at 600 K, and a semiconducting behavior with a room-temperature resistivity of 114 mΩ cm.