Host-atom-driven Transformation Achieves Dodecagonal Quasicrystals When 73% of Honeycomb Rings Are Occupied

The creation of quasicrystals, materials exhibiting order without traditional symmetry, typically requires specific elemental compositions, limiting their widespread development. Now, Martin Haller, Julia Hewelt, and V. Y. M. Rajesh Chirala, alongside colleagues at Martin-Luther-Universität Halle-Wittenberg, demonstrate a new and versatile method for forming dodecagonal oxide quasicrystals by transforming conventional honeycomb oxide networks. Their research reveals that introducing barium, strontium, or europium atoms onto the honeycomb structure triggers a reorganization into a quasicrystalline tiling, achieving complete transformation with approximately 73% host atom coverage. This breakthrough not only enables the fabrication of structurally precise quasicrystals, including a novel europium-titanium-oxygen phase exhibiting localised magnetic moments, but also establishes a general pathway for creating engineered aperiodic systems from a broader range of two-dimensional materials, potentially extending beyond metal oxides to include structures like hexagonal ice and silica.

The research investigates an approach to ordered quasicrystal (OQC) formation by transforming a metal-oxide honeycomb (HC) network with specific host atoms. Adsorption of barium, strontium, or europium onto the HC layer triggers its reorganization into a dodecagonal tiling, a structural change confirmed by low-energy electron diffraction and scanning tunneling microscopy. Complete conversion to the quasicrystalline structure occurs when 73 percent of the honeycomb rings are occupied by these host atoms. Measurements reveal a linear decrease in work function as host atom coverage increases, followed by a sharp increase upon quasicrystal formation, attributable to a reduction in host atom dipole moments. This transformation mechanism enables the fabrication of structurally precise OQCs, including a new europium-titanium-oxide phase that expands the range of known quasicrystalline materials.

Dodecagonal Quasicrystal Growth in Oxide Thin Films

This research details the discovery and characterization of a two-dimensional dodecagonal quasicrystal formed within a thin film system. The team successfully created a quasicrystalline structure, possessing long-range order but lacking translational symmetry, in a complex oxide system involving strontium titanate on a platinum substrate. The film exhibits clear dodecagonal symmetry, confirming its quasicrystalline nature, as verified through techniques including low-energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy. Complex approximant structures, resembling the quasicrystal but with some degree of periodicity, were also observed, indicating a pathway towards the formation of the true quasicrystalline order. This system allows for some control over the structure, potentially enabling the tuning of its electronic and magnetic properties, and contributes to the fundamental understanding of quasicrystals, a fascinating state of matter challenging traditional crystallography. The discovery opens possibilities for creating new materials with unique properties, potentially useful in areas like electronics, catalysis, and energy storage, and adds to the growing field of two-dimensional materials, demonstrating the potential for creating complex and ordered structures at the nanoscale.

Quasicrystal Formation via Host-Atom Decoration

Scientists have achieved a versatile method for fabricating dodecagonal oxide quasicrystals (OQCs) by transforming a metal-oxide honeycomb network through host-atom decoration. Experiments demonstrate that adsorption of barium, strontium, or europium onto the HC layer triggers a reorganization into a dodecagonal tiling, a structural conversion completed when 73% of the honeycomb rings are occupied. Measurements reveal a linear decrease in work function with increasing host coverage, followed by a sharp increase upon quasicrystal formation, attributable to reduced host dipole moments. The team successfully fabricated a new europium-titanium-oxide phase, extending the field to lanthanide quasicrystals and creating a two-dimensional grid of localized magnetic moments.

Analysis of the structural evolution reveals that at 53% coverage, 6% of the surface area exhibits the square-triangle-rhombus tiling characteristic of the quasicrystal, and at 73% coverage, the OQC dominates. Core-level photoemission data confirms that europium atoms in the OQC adopt a +2 valence state, resulting in a high-spin configuration and an aperiodically-ordered ensemble of large magnetic moments. Measurements show that strontium also induces OQC formation, exhibiting a similar work function decrease up to 60% coverage, ultimately reaching a final value of 4. 28 eV. These results demonstrate a general route to explore lattice-matched substrates for epitaxial growth and open possibilities for engineered aperiodic systems beyond transition metal oxides.

Host Atom Control Creates Oxide Quasicrystals

Scientists have achieved a significant breakthrough in materials science by demonstrating a versatile method for fabricating dodecagonal oxide quasicrystals (OQCs). Researchers successfully induced the formation of these complex structures through a transformation of a metal-oxide honeycomb network, triggered by the adsorption of barium, strontium, or europium. The team observed full conversion to the quasicrystal phase when approximately 73% of the honeycomb rings were occupied, confirming the effectiveness of this host-atom-induced reorganization. This innovative approach not only enables the creation of structurally precise OQCs, but also extends the field to include lanthanide quasicrystals, specifically a new europium-titanium-oxide phase exhibiting a two-dimensional grid of localized magnetic moments. Measurements of work function revealed a predictable linear decrease with increasing host coverage, followed by a sharp increase upon quasicrystal formation, indicating a change in the electronic properties of the material. Looking ahead, the team suggests that this adatom-assisted network transformation mechanism may be adaptable to other two-dimensional honeycomb materials, such as graphene, hexagonal ice, and silica, opening up the possibility of engineering aperiodic systems beyond transition metal oxides, potentially leading to novel materials with tailored properties.