The amorphous to crystalline transformation proceeds atmoderately elevated temperature (˜473 K) which shows thatGe15Sb85 nanoparticles are a good candidate forphase-change memory applications in terms of long data retention time.
Chalcogenide ternary compounds Ge2Sb2Te5 (GST) are well-known phase-change materials that exhibit fast structural transition between amorphous and crystalline phases. Metastable (m-)GST, its crystalline phase, is a distorted NaCl structure with 4(b) sites occupied by 40% Ge, 40% Sb, and 20% vacancies. Atomic configuration of 4(b) sites, especially the distribution of vacancy, is known to be crucial not only for phase-change process but also to the electrical transition such as Anderson localization. Despite its significance, consensus on the 4(b)-site configuration is yet to be established. In this talk, we present the effect of vacancy ordering in m-GST on material properties. We calculated energetics of m-GST for various vacancy configurations using first-principles calculations and tight-binding method. For quantitative analysis of the relationship between vacancy distribution and energetic stability, we established a set of parameters that quantify the degree of vacancy disorder in m-GST to identify key structural features that govern the system’s energy and electrical conductivity. Correlation between annealing temperature and vacancy ordering of m-GST was also investigated using molecular dynamics simulations.
Phase-change Ge–Sb–Te (GST) nanoparticles have been in ..
Phase-change memory materials have stimulated a great deal of interest although the size-dependent behaviors have not been well studied due to the lack of method for producing their nanoscale structures. We report the synthesis and characterization of GeTe and Sb2Te3 phase-change nanowires via a vapor−liquid−solid growth mechanism. The as-grown GeTe nanowires have three different types of morphologies: single-crystalline straight and helical rhombohedral GeTe nanowires and amorphous curly GeO2 nanowires. All the Sb2Te3 nanowires are single-crystalline.