Shock-synthesized quasicrystals

Abstract

Impact-processing of planetary materials and laboratory-shock experiments are of great interest. During these extreme processes a hypervelocity shock wave generates extremely high pressure and high temperature for exceptionally short times (micro-and nanoseconds) and provides favourable conditions for the formation of peculiar structures. In a recent IUCrJ article, Hu et al. (2020) report the shock synthesis of an unusual material, the icosahedral Al 62 Cu 31 Fe 7 quasicrystal (QC), which was previously identified in the Khatyrka meteorite (Bindi et al., 2016). QCs are a unique type of material, which are characterized by sharp diffraction features and possess symmetry elements that apparently are inconsistent with the conventional rules of crystallography. In particular, the first Al 86 Mn 14 alloy QC to be recognized has icosahedral symmetry featuring among other things fivefold rotation axes (Shechtman et al., 1984). The appearance of these unconventional rotations triggered exciting discussions right from the first report [reviewed in Prodan et al. (2017) and https://paulingblog.wordpress.com/tag/quasicrystals/]. On the one hand, Shechtman and colleagues presented QCs as a new type of crystalline material, in which atoms are repeated according to a quasiperiodic translation (Lifshitz, 2003). The interpretation of the QCs' structure was also approached with the so-called Amman tiling, the 3D equivalent of the 2D Penrose tiling (Lord et al., 2000). On the other hand, Pauling insisted that no crystallographic rules were violated and considered QCs as multiply twinned cubic structures (e.g. Pauling, 1985). Although it turned out that Pauling's interpretation did not hold, recently Prodan et al. (2017) reported that QCs could in fact be interpreted as multiply twinned structures, considering the unit cell of the primitive golden rhombohedra, and demonstrated that 'tiling' and 'multiple twinning' are fully compatible with each other. However, this interpretation requires the occurrence of equal size twin domains, which is uncommon in nature. In either way, the crystallographic identity of QCs seems to be still debated. Since their discoveries, over a hundred QCs have been described from syntheses. In contrast, only a few studies report QCs from natural materials and, in fact, all have been associated with Khatyrka meteorite. So far three new QC types have been described from this meteorite: the i-phase I with composition of Al 63 Cu 24 Fe 13 , officially named icosahedrite (Bindi et al., 2009); the d-phase with composition of Al 71 Ni 24 Fe 5 , referred to as decagonite (Bindi et al., 2015); and the i-phase II with Al 62 Cu 31 Fe 7 composition (Bindi et al., 2016). However, this list perhaps can be extended with additional extraterrestrial phases (personal communication with Luca Bindi). In either way, to date three natural QCs are known from the Khatyrka meteorite. In meteorite research the mineral assemblage can aid understanding of the formation condition of an associated phase; however, the proper interpretatio...

Spiers Memorial Lecture: Mechanochemistry, tribochemistry, mechanical alloying – retrospect, achievements and challenges

“…150 Recently, quasicrystals were also obtained by another type of mechanical action, by shock waves, with implications for their origin in asteroid collisions. 151–157…”