On the “coloring problem” in YMgZn and related phases

During exploration in the Y–Mg–Zn system for quasicrystal approximants, three new phases, YMg1−xZn1+x (0 ⩽ x ⩽ 0.17) adopting the hexagonal ZrNiAl structure type, have been discovered. In these structures, the elements are completely ordered to minimize both the site energies and the bond energies as calculated by tight-binding calculations. Evaluation of the electron density in YMgZn suggests that Mg–Zn and Y–Zn bonding coupled with maximizing the Zn⋯Zn separations is the main factor influencing the atomic arrangements. Analysis of the electronic density of states of YMgZn indicates an optimized bonding situation for eight valence electrons per formula unit, e.g., as in YMgGa. Subsequently, YMgAl, YMgGa, and YMgIn were successfully prepared and structurally characterized. Their structures show relationships to both densely-packed structures common for intermetallics as well as three-dimensional networks common for valence compounds.