Intergrowth Compounds in the Zn-Rich Zn−Pd System: Toward 1D Quasicrystal Approximants

A series of γ-brass related structures in the Zn-rich portion of the Zn−Pd phase diagram (ca. 80 at % Zn) is investigated using single-crystal diffraction and tight-binding electronic-structure calculations. Earlier research identified regular arrays of inversion antiphase domains (IAPDs) over a narrow composition range but did not report any characteristic superstructure(s) over the same range. Single-crystal X-ray diffraction allowed for the identification of lattice constants for six “phases” in Zn 1 - x Pd x (0.15 < x < 0.25), and refinements of two crystal structures indicate two important potential building blocks for the intermediate compositions, one of these being the cubic γ-brass structure. A Farey tree construction is described that accounts for the observed long-period superlattice and provides a possible algorithm for targeting one-dimensional, quasiperiodic phases in this and related systems. Tight-binding electronic-structure calculations on the two limiting structures for this region of the Zn−Pd phase diagram suggest a relationship between structure and bonding in these complex intermetallic systems.