Martensitic phase transformation of single-crystal lithium from bcc to a9R-related structure

Abstract

A neutron elastic- and inelastic-scattering study of single-crystal bcc lithium was performed above and below the martensitic phase transformation in the vicinity of 75 K. The transformation is abrupt and the bcc lattice partially transforms to a 9R-related (Sm-type) structure. The 9R ${\mathrm{c}}^{\mathrm{*}}$ and ${\mathrm{a}}^{\mathrm{*}}$ axes of this variant are nearly along the [110] and [11¯0] bcc directions, respectively. The (10L) and (20L) 9R reflections were broadened and shifted from their ideal positions compared to the (00L) 9R reflections, indicative of numerous stacking faults. On warming, the sample reverts back to a single crystal with the same bcc orientation.