Different incommensurate composite crystal structure for Sc-II

Abstract

The long uncertain crystal structure of the high-pressure phase of scandium, Sc-II, is found to have an incommensurate composite structure comprising a body-centered host structure and a $C$-face-centered guest structure. At $23\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, the shortest distance between guest atoms is $\ensuremath{\sim}2.7\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, comparable to the average host-host distance of $2.8\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. This differs from the structure proposed recently [H. Fujihisa et al., Phys. Rev. B 72, 132103 (2005)] which has a body-centered guest structure, with anomalously short guest-guest distances.