Structural signature and transition dynamics of Sb₂Te₃ melt upon fast cooling

Abstract

Crystalline Sb2Te3 is widely studied due to its important applications in memory materials and topological insulators. The liquid and amorphous structures of this compound as well as the dynamics upon quenching, however, are yet to be fully understood. In this work, we have systematically studied the dynamical properties and local structure of Sb2Te3 at different temperatures using ab initio molecular dynamics simulations. The calculated structure factors agree well with the experimental results. The atomic number density and mean-squared displacement as a function of temperature clearly indicate three states as the temperature decreases, namely, melt, undercooled liquid and glass state, respectively. By analyzing the chemical environments and bond-angle distribution functions, we demonstrate that the most probable short-range motifs in the Sb2Te3 system are defective octahedrons, and they are connected with each other via four-fold rings. This interesting structural feature may be responsible for the high fragility and easy phase transition upon glass forming that is applied in memory devices.

Temperature dependence of structural, dynamical, and electronic properties of amorphous Bi2Te3: an ab initio study

“…Previous studies have pointed out that the 4-fold rings ABAB are the basic structural elements for fast phase transition in PCMs [37][38][39][40], which could reduce the stochasticity of nucleation [41]. In our previous work for amorphous Sb 2 Te 3 , we found that these defective octahedrons are connected with each other via 4-fold rings [18]. Highly coordinated (such as 6-fold and 5-fold) octahedrons can provide more structural sites for forming 4-fold ring; therefore, less distorted octahedral motifs in amorphous Bi 2 Te 3 are more conducive to the formation of these 4-fold rings.…”

“…The comparison of the primitive rings for Bi 2 Te 3 and Sb 2 Te 3 at 300 K are computed in figure 6. Similar to glassy state Sb 2 Te 3 [18], 4-fold rings in Bi 2 Te 3 are the dominant structural motif among these n-fold rings, the fraction of which is even larger than Sb 2 Te 3 . Previous studies have pointed out that the 4-fold rings ABAB are the basic structural elements for fast phase transition in PCMs [37][38][39][40], which could reduce the stochasticity of nucleation [41].…”

“…However, systematic theoretical studies at the atomic level about the structures and properties of Bi 2 Te 3 during a rapid cooling process is still far from complete. In a previous work, we have studied the structural transformation of Sb 2 Te 3 from liquid to amorphous upon fast cooling [18]. Results show that most short-range motifs in the Sb 2 Te 3 system are defective octahedrons.…”

Optical Properties and Local Structure Evolution during Crystallization of Ga16Sb84 Alloy

“…The programming speed (i.e., the phase-change rate) can reach sub-nanoseconds, much faster than any other memory device 6 . Due to the exceptional performance, phase-change materials (PCMs) have been intensively studied since their invention in the 1960s 7 , and since then various PCMs have been discovered, such as Ge-Te 8–11 , Sb-Te 12–15 , and Ge-Sb-Te 16–21 .…”

Local structure origin of ultrafast crystallization driven by high-fidelity octahedral clusters in amorphous Sc0.2Sb2Te3

“…[10][11][12] As for the amorphous Sb 2 Te 3 , Sb and Te atoms are mostly in defective octahedral sites. 13,14 Due to this similarity of local structures between the crystalline and amorphous states, the two phases can transform to each other without long atomic diffusion. To further improve the performance of Sb 2 Te 3 , researchers managed to add some other elements (such as Al, 15 In, 16 Ag, 17 and Ti 18 ) to Sb 2 Te 3 .…”