Host-Atom-Driven Transformation of a Honeycomb Oxide into a Dodecagonal Quasicrystal

Dodecagonal oxide quasicrystals (OQCs) have so far been limited to a few elemental systems, with no general formation mechanism established. Here, we demonstrate a versatile approach to OQC formation via a host-atom-induced transformation of a metal-oxide honeycomb network. Adsorption of Ba, Sr, or Eu onto the honeycomb layer triggers its reorganization into a dodecagonal tiling, as revealed by low-energy electron diffraction and scanning tunneling microscopy. Full conversion occurs when 73% of the honeycomb rings are occupied. Kelvin probe and UV photoelectron spectroscopy show a linear decrease in work function with increasing host coverage, followed by a sharp increase upon quasicrystal formation due to reduced host dipoles. This transformation mechanism enables the fabrication of structurally precise OQCs, including a new Eu-Ti-O phase that extends the field to lanthanide quasicrystals, forming a 2D grid of localized magnetic moments. The method might offer a more general route to explore lattice-matched substrates for epitaxial growth and may be adapted to other 2D honeycomb materials such as graphene, hexagonal ice, and silica, paving the way for engineered aperiodic systems beyond transition metal oxides.