Interface Nuclei in the Y-Ag-Zn System: Three Chemical Pressure-Templated Phases with Lamellar Mg 2 Zn 11 - and CaPd 5+ x -Type Domains.

The interface nucleus approach was recently presented as a framework for understanding and predicting the emergence of modular intermetallic phases, i.e., complex structures derived from the assembly of units from simpler parent structures. Here, we present the synthesis and crystal structures of three new modular intermetallics in the Y-Ag-Zn system that support this strategy: YAg 2.79 Zn 2.80 ( I ), YAg 2.44 Zn 3.17 ( II ), and YAg 2.71 Zn 2.71 ( III ). Each of these structures is derived from an intergrowth of slabs of the Mg 2 Zn 11 and CaPd 5+ x types, with the chief differences being in the thickness and degree of disorder within the CaPd 5+ x -type domains. The merging of the parent structure domains is facilitated by their sharing a common geometrical unit, a double hexagonal antiprism. The use of this motif as an interface nucleus mirrors its role in another family of structures: an intergrowth series combining the CaCu 5 and Laves phase structure types, as in the PuNi 3 -type phase YNi 3 . However, there is a key difference between the two series. While in the CaCu 5 /Laves intergrowths, the interface between the parent structures arises perpendicular to the interface nucleus's unique (hexagonal) axis, in the Mg 2 Zn 11 /CaPd 5+ x -type intergrowths revealed here, the interfaces run parallel to this axis. Using CP analysis of the Mg 2 Zn 11 /CaPd 5 +x -type parent structures, we trace this behavior to the different directions of high-CP compatibility of the interface nuclei in the Mg 2 Zn 11 /CaPd 5+ x and CaCu 5 /Laves structure type pairs. In this way, the Y(Ag/Zn) 5+ x phases highlight the role that interface nuclei play in directing the domain morphologies of modular intermetallic phases.