Polymorphic Transitions in Metallic Halides

Abstract

An x-ray powder analysis of RbI made at 4500 kg/${\mathrm{cm}}^2$ pressure and room temperature shows the crystal form of RbI to be body-centered cubic under these conditions. The lattice constant is 4.33${}_5{}^{}{}_{}{}^{}\mathrm{A}$. The volume change from the face-centered lattice which is stable below 4000 atmospheres is 0.037 ${\mathrm{cm}}^3$ per gram. This is about 0.009 ${\mathrm{cm}}^3$ per gram greater than Bridgman's piston displacement value and the difference may be significant.