Pressure effects on the martensitic transformation in metallic lithium

High-resolution neutron-diffraction experiments have been performed on polycrystalline lithium-7 metal over a temperature and pressure range of 45 to 300 K and 1 bar to 6.5 kbar. The partial transition from the bcc phase to the 9R(Sm type) phase occurred at approximately 90 K at 6.5 kbar, about 15 K higher than the similar transition at 1 bar. On warming at 6.5 kbar, the 9R phase transformed to the fcc phase over a narrow temperature range near 140 K. Above 175 K only the bcc phase was present. Single-crystal measurements confirm the 9R to fcc transition even at atmospheric pressure.