title: Structure of Rb-III: novel modulated stacking structures in alkali metals.
abstract: The crystal structure of Rb-III, stable between 13 and 17 GPa, has been determined from quasi-single-crystal x-ray diffraction data. It is orthorhombic, space group C222(1), with 52 atoms in the unit cell, and has an 8-10-8-8-10-8 stacking of 8- and 10-atom layers. The recently reported 84-atom structure of Cs-III can be understood as an 8-8-10-8-8-8-8-10-8-8 stacking of the same layers. These represent a new class of modulated elemental structures.
authors.affiliation: Department of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelmes
authors.forename: M I
authors.initials: MI
authors.lastname: McMahon
authors.forename: J S
authors.initials: JS
authors.lastname: Loveday
authors.forename: S
authors.initials: S
authors.lastname: Rekhi