Local Stability to Periodicity in the EuMg5+x Type: Chemical Pressure, Disordered Channels, and Predicted Superstructure in YZn5.225

Abstract

AbstractA central theme in the structural chemistry of intermetallic phases is that complex structures can be derived from variations on simpler ones. This is vividly demonstrated by the variety of structure types that can be connected to chemical pressure (CP)‐driven transformations of the simple CaCu5 type. In this Article, we investigate an intriguing addition to this family: the EuMg5‐type intermetallics, as exemplified by YZn5. As expected from the large negative CPs around the cations in CaCu5‐type structures, YZn5 exhibits tightened coordination environments around the cations. However, it also contains an unusually inhomogeneous atomic packing, particularly in channels running between the Y atoms along c. Our structural reinvestigation of YZn5 reveals a disordered occupation pattern of Zn atoms within these channels, consistent with the EuMg5+x type, a disordered variant of the EuMg5 type. DFT‐CP analysis indicates that the transition from the CaCu5 type to the YZn5+x structure indeed creates more compact Y environments, but strong tensions remain within the Zn sublattice. These include CP features on the channel walls that provide a mechanism for the communication of structural information between the channels and favorable cooperation in their occupation patterns. Based on these results, a structural model is proposed that explains an earlier observation of superstructure reflections in the diffraction patterns of ErZn5 corresponding to a √3×√3×3 supercell.