The crystal structure of Tm_0.76Se (blue phase)

Abstract

Tm0.76Se crystallizes in space group Pnnn, with cell constants a = 7.9591(3) A ̊, b = 7.9524(4) A ̊, c = 11.2513(6) A ̊ and Z = 16. The final residual values obtained are RF = 0.067 and wRF = 0.069 for the 402 unique reflections observed up to 60° 2 - θ with graphite-monochromatized Mo Kα and refined with 20 structural parameters. This compound is a superstructure from the NaCl type with ordering of the cation vacancies with bodycentered orthorhombic lattice, while the collapsing of the anions around the sites with reduced occupations further lowers the symmetry to primitive orthorhombic. © 1987.