We unravel crystallization processes across the scales.
- Multistep nucleation pathways
- Dynamics and stabilization of quasicrystals
- Dislocations in complex metallic alloys
Multistep nucleation pathways
The transformation from a fluid to a crystal can be complicated and involve one or more precursors. Such multistep crystallization pathways occur in many chemical and physical systems, and the driving force for the appearance of the precursors has been explained by unique characteristics of the interactions among the system’s building blocks. We investigated multistep crystallization pathways in hard particles, where interaction is dictated solely by building-block shape and thus entropy. We categorized multistep crystallization pathways based on the dimension of the prenucleation motifs and discuss possible comparisons to other crystallization processes.
Sangmin Lee, Erin G. Teich, Michael Engel, Sharon C. Glotzer
Entropic Colloidal Crystallization Pathways via Fluid-Fluid Transitions
and Multidimensional Pre-Nucleation Motifs
Proceedings of the National Academy of Sciences 116, 14843-14851 (2019)
Dynamics and stabilization of quasicrystals
A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. Shortly after the discovery of quasicrystals in 1982, it was proposed that the atoms are not fully trapped in a single local equilibrium position but can chose dynamically between several minima. Elementary excitations are called phason flips and the associated collective motions are phason modes. We established the existence of phason flips in simulation and proved that the entropy contribution of phason modes is sufficient to stabilize random tiling quasicrystals over similar approximant crystals.
Kobi Barkan, Michael Engel, Ron Lifshitz
Controlled Self-Assembly of Periodic and Aperiodic Cluster Crystals
Physical Review Letters 113, 098304 (2014)
Alexander Kiselev, Michael Engel, Hans-Rainer Trebin
Confirmation of the Random Tiling Hypothesis for a Decagonal Quasicrystal
Physical Review Letters 109, 225502 (2012)
Entropic Stabilization of Tunable Planar Modulated Superstructures
Physical Review Letters 106, 095504 (2011)
Michael Engel, Masahiro Umezaki, Hans-Rainer Trebin, Takashi Odagaki
Dynamics of Particle Flips in Two-Dimensional Quasicrystals
Physical Review B 82, 134206 (2010)
Dislocations in complex metallic alloys
Complex metallic alloys, characterized by large unit cells, are interesting because they show unusual physical behaviors and properties. One such property is the appearance of metadislocations. These line defects involve a reorganization of the material in an extended region around the dislocation core. We developed a geometric theory and derived an optimized crystal structure with ab initio methods for the description of metadislocations in Al-Pd-Mn alloys.
Benjamin Frigan, Alejandro Santana, Michael Engel, Daniel Schopf, Hans-Rainer Trebin, Marek Mihalkovic
Low-Temperature Structure of ξ’-Al-Pd-Mn Optimized by Ab Initio Methods
Physical Review B 84, 184203 (2011)
Michael Engel, Hans-Rainer Trebin
A Unified Projection formalism for the Al-Pd-Mn Quasicrystal Ξ-Approximants and their Metadislocations
Philosophical Magazine 85, 2227-2247 (2005)