Search results for "memory materials"

Density functional/molecular dynamics simulations of phase-change materials

2013

Nucleus-driven crystallization of amorphous Ge2Sb2Te5: A density functional study

2012

Early stages of nucleus-driven crystallization of the prototype phase change material Ge2Sb2Te5 have been studied by density functional/molecular dynamics simulations for amorphous samples (460 and 648 atoms) at 500, 600, and 700 K. All systems assumed a fixed cubic seed of 58 atoms and 6 vacancies. Crystallization occurs within 600 ps for the 460-atom system at 600 and 700 K, and signs of crystallization (nucleus growth, percolation) are present in the others. Crystallization is accompanied by an increase in the number of “ABAB squares” (A: Ge, Sb, B: Te), and atoms of all elements move significantly. There is no evidence of cavity movement to the crystal-glass interface, as suggested rece…

Structure and dynamics in amorphous tellurium and Te-n clusters: A density functional study

2012

Density functional/molecular dynamics simulations have been performed on amorphous tellurium (a meltquenched sample of 343 atoms at 300 K) and on Te clusters with up to 16 atoms. The former extend our calculations on liquid Te at 560, 625, 722, and 970 K [Phys. Rev. B 81, 094202 (2010)]. We discuss trends in structures (including those of other group-16 elements), electronic densities of states, and vibration frequencies. Chain structures are common in S and Se, but the chains in amorphous Te are short, and branching sites with threefold-coordinated atoms are common. The energy difference between two- and threefold local coordination depends sensitively on the exchange-correlation functiona…