Abstract
Physical properties of lithium under extreme pressures continuously reveal unexpected
features. These include a sequence of structural transitions to lower symmetry phases,
metal-insulator-metal transition, superconductivity with one of the highest elemental
transition temperatures, and a maximum followed by a minimum in its melting line. The
instability of the bcc structure of lithium is well established by the presence of a temperaturedriven
martensitic phase transition. The boundaries of this phase, however, have not been
previously explored above 3 GPa. All higher pressure phase boundaries are either
extrapolations or inferred based on indirect evidence. Here we explore the pressure
dependence of the martensitic transition of lithium up to 7GPa using a combination of
neutron and X-ray scattering. We find a rather unexpected deviation from the extrapolated
boundaries of the hR3 phase of lithium. Furthermore, there is evidence that, above B3GPa,
once in fcc phase, lithium does not undergo a martensitic transition.
