Ordered Superstructure of InSb-IV

The crystal structure of InSb phase IV has been determined at 5 GPa using angle-dispersive powder-diffraction techniques. The proposed solution is a site-ordered orthorhombic superstructure, spacegroup Cmcm, composed of six NaCl-like planes stacked along the c axis and alternately displaced approximately ±0.1b. Two of the planes are flat, and the others are slightly puckered due to a small relative displacement of the In and Sb atoms along the c axis. The results add a remarkably complex example to growing evidence that (generally much simpler) Cmcm-type structures are common to most of the more ionic II-VI and III-V semiconductors under pressure.