Crystallization of supercooled liquid antimony: A density functional study

Abstract

Crystallization of liquid antimony has been studied at 600 K using six density functional/molecular dynamics simulations with up to 882 atoms and three scenarios: one completely disordered sample that did not crystallize even after 570 ps, four with fixed crystalline slab templates, and one with a fixed crystalline seed. Crystallization proceeded layer-by-layer in most cases and was rapid (∼36 m/s) with templates and somewhat slower with the seed. The seed simulation shows an unusual percolation asymmetry where the crystallite grows faster in the direction normal to the zigzag planes. Changes in pair distribution functions, bond angle distributions, ring statistics, nearest-neighbor distances, and cavity volumes were monitored. Diffusion plays a minor role in the process, and the evolution of bond lengths and ring statistics supports the bond-interchange model introduced to explain the rapid crystallization of Sb-rich phase change materials.

Mechanism of amorphous phase stabilization in ultrathin films of monoatomic phase change material

“…DFT molecular dynamics simulations have shown indeed that Sb crystallizes very fast in the presence of a crystalline Sb boundary with growth velocity of about 36 m s −1 at 600 K while no sign of crystal nucleation was detected on the time scale of half a ns at the same temperature. 41 In fact, crystal nucleation does occur on the time span of a DFT-MD run, but only in the temperature range 300-500 K as reported in ref. 42 and 43. In agreement with previous DFT results, [41][42][43][44] homogeneous crystal nucleation in the supercooled liquid was not observed in NN-MD simulation on a ns time scale above 600 K. Supercritical nuclei appear instead on the time scale of 1-15 ns in the temperature range 300-450 K, but not below 300 K, as we discuss in more details later on.…”

“…41 In fact, crystal nucleation does occur on the time span of a DFT-MD run, but only in the temperature range 300-500 K as reported in ref. 42 and 43. In agreement with previous DFT results, [41][42][43][44] homogeneous crystal nucleation in the supercooled liquid was not observed in NN-MD simulation on a ns time scale above 600 K. Supercritical nuclei appear instead on the time scale of 1-15 ns in the temperature range 300-450 K, but not below 300 K, as we discuss in more details later on. Therefore, in order to explore the crystallization speed in a wide temperature range, we consistently studied the crystal growth at a preformed crystal/amorphous interface which is also believed to be close to the experimental situation realized in the device of ref.…”

Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

“…The (average) mean‐square displacement (msd) is in the context of PCMs particularly used in ab‐initio molecular dynamics (AIMD) simulations to derive atomic mobilities, which then via the Stokes‐Einstein relation can be related to viscosities. [ 169–171 ] So, there must be a kind of relation between the msd used in PCM research and the msd introduced in Equation . However, we have to be careful mixing msd acting on different length and time scales.…”

Local Structural Origin of the Crystallization Tendency of Pure and Alloyed Sb

“…Here, information on the kinetics of pure Sb could not be obtained due to its extreme tendency to crystallize. Ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) have shown that pure Sb can crystallize very rapidly in the presence of crystalline Sb boundaries, with an extremely high growth velocity of ≈36 m s −1 at T = 600 K . Such a crystallization speed is much greater than that of Ge 2 Sb 2 Te 5 .…”