Truncated Lorch‐window method revealing the off‐octahedral Ge in nanocrystalline Ge₂Sb₂Te₅

Abstract

Traditional Lorch‐window technique was modified to the truncated Lorch‐window through various truncation ranges to apply the Lorch‐window functions. The terminal ripples in radial distribution functions (RDFs) were weakened and the shoulder peak at 2.6 Å in crystalline Ge2Sb2Te5 (GST) was revealed by the indication of the off‐octahedral Ge. The Cs‐corrected high resolution transmission electron microscopy image and the corresponding simulations suggest that the off‐octahedral Ge atoms are indeed in the tetrahedral symmetry. These results indicate that the complex structural details in the intermediate phase of GST other than simple rock‐salt structure though the quantified information, such as the accurate atomic positions of the off‐octahedral Ge need being further clarified in the future. These results also reveal the significance of high‐Q signals in revealing the structures in short range order.Left (a): Original reduced interference function F(Q) (black) and truncated F(Q) data. Right (b): Corresponding RDF curves. L‐12 (red half‐solid triangle) represent the data with a truncation range of 12 Å−1, and L‐16 (open square) for the truncation range of 16 Å−1. magnified image

Long-range crystal-lattice distortion fields of epitaxial Ge-Sb-Te phase-change materials

“…Several proposed models agree on well‐ordered Te sublattice and a mixture of Sb, Ge, and vacancies on the other sublattice. In addition to that some of recent studies have shown the different chemical nature of Ge atom and the importance in the GST might form a heterogeneous structural picture that might envision a fast switching arising from a partial bonding rearrangement.…”

Modelling the phase‐transition in phase‐change materials

“…In addition, Lang et al showed that the local tetrahedral configuration of Ge is unstable in the crystalline environment (although there has been recent controversy on this topic, see Refs. 7–9). Bichara et al 10 found octahedral units in the liquid phase, whereas Caravati et al 11 found both tetrahedral and octahedral atomic environments in amorphous GST.…”

Toward structural/chemical cotailoring of phase‐change Ge–Sb–Te in a transmission electron microscope

“…Great efforts have been made to chemically/structurally tailor material toward multifunctional practicing. Ge 2 Sb 2 Te 5 chalcogenide is one of the prototype materials for phasechange random access memory (PRAM; Sun et al, 2006;Wuttig et al, 2006;Zhang et al, 2007;Song et al, 2008;Zhang et al, 2008;Liu et al, 2012;Wuttig, 2012;Yamada, 2012). Considering that Ge 2 Sb 2 Te 5 locates in the theoretical pseudo-binary (GeTe) m (Sb 2 Te 3 ) n homologous series (Eom et al, 2006;Silva et al, 2008), it is of great interests to experimentally separate the two components.…”