Abstract Scope |
The discovery of quasicrystals forced solid-state chemists to revisit basic assumptions about crystallinity, bonding, and materials stability. A fundamental question emerges: Are quasicrystals thermodynamically stable? Density functional theory is often used to evaluate thermodynamic stability, but quasicrystals are aperiodic and cannot be simulated using periodic boundary conditions. Here, we present a new technique to directly calculate the bulk and surface energies of quasicrystals in DFT. We compute the energies of finite sized quasicrystal nanoparticles with increasing sizes, and then fit the bulk and surface energies of the nanoparticles using a Gibbs-Thomson relationship. Using this technique, we evaluate the Tsai-type ScZn and YbCd icosahedral quasicrystals, whose structures have previously been resolved with atomistic resolution. We find that the ScZn and YbCd quasicrystals are bulk metastable but have low surface energies, which drives a size-dependent phase stability crossover at the nanoscale. Moreover, we show that when undercooling from the melt, the low surface energies of these quasicrystals drive their preferential nucleation over a wide region in the Temperature-Composition phase diagram. |