A revolutionary discovery has shaken the world of materials science: a quasicrystal with a unique structure with a periodic approximation has been discovered in samples obtained from an extraterrestrial source. This discovery not only expands our understanding of the fundamental principles of quasicrystal formation, but also opens up new prospects for creating materials with unprecedented properties.
Existing quasicrystals typically exhibit an aperiodic structure with long-range order, violating the translational symmetry characteristic of classical crystals. However, a new quasicrystal discovered in space exhibits an intermediate state between periodicity and quasi-periodicity. Its structure can be approximated by a periodic lattice, which greatly simplifies its mathematical description and modeling.
Introducing Al34Ni9Fe2, the first known natural periodic crystal approximant of decagonite (Al71Ni24Fe5), a unique natural quasicrystal. This quasicrystal is characterized by a periodic arrangement of planes with quasi-periodic atomic order and tenfold symmetry. The new mineral, which has received approval from the International Mineralogical Association (IMA 2018-038), is officially named proxydecagonite, reflecting its belonging to the periodic approximants of decagonite.
Both minerals, decagonite and proxydecagonite, were found in fragments of the Khatyrka meteorite. Proxydecagonite is the first quasicrystalline approximant of the Al-Ni-Fe system discovered in nature. It is known that in this system the decagonal quasicrystalline phase undergoes transformations at a temperature of about 940 °C, decomposing into Al13(Fe,Ni)4, Al3(Fe,Ni)2 and a liquid phase. At temperatures from 800 to 850 °C, Al13(Fe,Ni)4, Al3(Fe,Ni) and Al3(Fe,Ni)2 are formed.
Interestingly, proxydecagonite was not produced in the laboratory. Its formation in a meteorite under extreme pressure and temperature caused by shock waves during a collision suggests its potential thermodynamic stability at high pressure. Structurally, pseudopentagonal symmetrical elements are distinguished, such as pentagonal bipyramids connected by edges and corners to trigonal bipyramids. Importantly, the shortest distance between Ni and Al atoms exceeds the distance between Ni and Ni.
A detailed analysis of the composition and structure of the quasicrystal showed the presence of a unique combination of elements, different from known terrestrial quasicrystals. This indicates the possibility of the existence of completely new mechanisms for the formation of quasicrystalline structures in space conditions.
The discovery of a quasicrystal with a periodic approximation is of great importance for various fields of science and technology. Firstly, this discovery will deepen theoretical knowledge about quasicrystals and their properties. Secondly, the new structure can be used to create materials with unique optical, electronic and mechanical characteristics. Thirdly, the study of the origin of this cosmic quasicrystal can shed light on the processes occurring in distant corners of the Universe. Further research is aimed at a detailed study of the structure and properties of the new quasicrystal, as well as the search for new materials with a similar architecture.
Author: Luca Bindi, Joyce Pham & Paul J. Steinhardt
Institute: Department of Geosciences, University of Florence, Via La Pira, 4, I-50121, Florence, Italy