Absence of precursor effects above the martensitic transformation in a virgin crystal of Li metal

Measurements of the short-wavelength ${\mathrm{\Sigma }}_4$ phonons in a virgin crystal of Li metal at 293, 200, 100, and 80 K show a slight softening of the phonons with a decrease in temperature, as observed in some other alkali metals, contrary to all the other phonon branches measured in high-symmetry directions. Theoretical anharmonicity calculations predict this anomalous behavior even for Rb, which does not undergo a transformation. Diffuse scattering measurements in the vicinity of the (110) and (200) reflections at 200, 100, and 80 K did not reveal any unusual changes. There is an overall increase in the background as the temperature was decreased, which is attributed to the Debye-Waller factor associated with the large spin-incoherent scattering. The widths of the phonon groups also decreased as the temperature was lowered. These and other neutron-scattering measurements, along with ultrasonic attenuation studies fail to give evidence for precursor effects of the 9R transformation in virgin crystals of lithium metal.