title: Kinetic origin of divergent decompression pathways in silicon and germanium.
abstract: Silicon and germanium transform from diamond to β-tin structure under compression, but upon decompression they turn into metastable BC8 Si and ST12 Ge phases, respectively, instead of returning to the lowest-enthalpy diamond structure. Here we explore by first-principles calculations the atomistic mechanism underlying this intriguing phenomenon. We identify a body-centered tetragonal structure in I4(1)/a (C(4h)(6)) symmetry as a precursory state of the BC8 Si phase formed via a double cell bond-rotation mechanism with a low kinetic barrier. Kinetics also play a central role in selecting the decompression pathway in Ge via a trinary cell bond-twisting reconstruction process toward the ST12 Ge phase. In both cases, transformation back to energetically more favorable diamond structure is inhibited by the higher enthalpy barrier. These results explain experimental findings and highlight the kinetic origin of the divergent decompression pathways in Si and Ge.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. wjt@aphy.iphy.ac.cn
authors.forename: Jian-Tao
authors.initials: JT
authors.lastname: Wang
authors.forename: Changfeng
authors.initials: C
authors.lastname: Chen
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mizuseki
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kawazoe