Structure of the liquid and the crystal of the phase-change materialSnSe2: First-principles molecular dynamics

Abstract

First-principles molecular dynamics simulations are used to study the structural properties of liquid and crystalline SnSe 2. We reproduce the experimental structure factor with confidence and fully describe the pair-correlation functions and the local structure of the liquid. It is shown that, unlike other group IV chalcogenides such as GeSe 2 , SnSe 2 does not display tetrahedral ordering in the liquid and contains a large amount of fivefold tin atoms with selenium atoms lying in an equatorial plane and at the edges of the polyhedra. A certain number of homopolar defects are found whose rate is substantially lower however than in GeSe 2. Compared to the crystalline system the density in the liquid decreases by 8.5%, which is accompanied by a decrease in the atomic coordination. Local distortions as found in typical phase-change materials are present in SnSe 2 .

Design Rules for Phase‐Change Materials in Data Storage Applications

“…Moreover, the average number of valence electrons per atom was identified as an order parameter, with the octahedral‐to‐tetrahedral transition occurring at a threshold of about 4.25. Micoulaut et al46 noted that an isoelectronic exchange can also impact the occurrence of tetrahedral coordination as they changed the stoichiometry from SnSe 2 to GeSe 2 , although this preserves the number of valence electrons 47. Furthermore, an alternation between atomic species (e.g., ABAB) is observed in phase‐change materials, resembling features of the crystalline structures as discussed later 32.…”

Ultrathin SnSe2 Flakes Grown by Chemical Vapor Deposition for High‐Performance Photodetectors

“…[ 11 ] It has been proposed that SnSe 2 can rapidly and reversibly switch from the amorphous to the crystalline state under laser heating, which leads to signifi cant changes in the optical refl ectivity and thus provides bright potential for data storage applications. [ 13 ] However, most studies have been reported on thick SnSe 2 fi lms obtained by radio-frequency (RF) magnetron sputtering, [ 14 ] or molecular beam epitaxy (MBE) deposition. [ 15 ] Recently reported mechanical exfoliated SnSe 2 crystals demonstrated that it has a high carrier mobility of 8.6 cm 2 V −1 s −1 in ambient environment, [ 16 ] superior to many other reported 2D materials.…”

Pressure-Stabilized Tin Selenide Phase with an Unexpected Stoichiometry and a Predicted Superconducting State at Low Temperatures

“…Under further compression, SnSe transforms to the B2 structure (P m3m space group) and this phase was found to exhibit a superconducting transition at low temperatures above 58 GPa [7]. SnSe 2 is also a layered semiconductor with a hexagonal CdI 2 -type crystal structure (P3m1 space group) [8]. From X-ray diffraction (XRD), it was found that SnSe 2 , which is important for photoelectric applications [9], shows a second polytype with a space group of R3m [10].…”