Stabilization of the elusive or non-existent “YbMnPt” phase by chemical heterogeneity: The pseudo-ternary phases Eu0.28Yb0.72MnPt and YbCd0.13Mn0.87Pt with TiNiSi type structure

The ternary RE-Mn-Pt systems (RE = rare-earth metal) have remained surprisingly vacant. Our attempts to stabilize hypo-thetical equiatomic “REMnPt” phases that are isovalent to RECdPt were found to be extremely challenging. However, us-ing metal fluxes synthesis approaches, two quasi-ternary phases Eu0.28Yb0.72MnPt and YbCd0.13Mn0.87Pt, with stoichi-ometries at the vicinity of the elusive “YbMnPt” phase, were obtained by reacting mixtures of the elements at high tem-perature with large excess of Eu and Cd, respectively. The two title compounds crystallize in the orthorhombic TiNiSi type structure (space group, Pnma), according to single crystal X-ray diffraction data, with Eu/Yb or Cd/Mn atomic mixing at the corresponding atomic sites. Noteworthy, the two phases feature Mn (3d5) linear zigzag chains with very similar Mn–Mn distances of 2.97 Å, longer than the sum of Mn covalent radii (2.74 Å), but non-negligeable. The Mn chains also interact strongly with the surrounding Pt atoms to form the polyanionic {MnPt} framework. The rare-earth metals Yb and Eu are arguably divalent and, we could surmise that the apparent non-existence of the pristine “YbMnPt” phase can be ascribed to geometric frustrations as it can be the result of packing mismatched between the cationic and anionic sublat-tices. Hence, partial isovalent substitutions at either Yb position by larger Eu atom or at Mn position by larger Cd atom may be necessarily to optimize the atomic packing. Our findings further demonstrate that chemical heterogeneity can be vital for the stability of certain classes of elusive materials in general.