Different incommensurate composite crystal structure for Sc-II

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 GPa, the shortest distance between guest atoms is similar to 2.7 angstrom, comparable to the average host-host distance of 2.8 angstrom. This differs from the structure proposed recently [H. Fujihisa , Phys. Rev. B 72, 132103 (2005)] which has a body-centered guest structure, with anomalously short guest-guest distances.