Structural Changes in Liquid Lithium under High Pressure

Abstract

We have experimentally studied the effect of compression on the structure of liquid lithium (Li) by multiangle energy dispersive X-ray diffraction in a large-volume cupped-Drickamer-Toroidal cell. The structure factors, s(q), of liquid Li have been successfully determined under an isothermal compression at 600 ± 30 K and at pressures up to 11.5 GPa. The first peak position in s(q) is found to increase with increasing pressure and is showing an obvious slope change starting at ∼7.5 GPa. The slope change is interpreted as a structural change from bcc-like to fcc-like local ordering in liquid Li. At pressures above 8.7 GPa, the liquid Li becomes predominantly fcc-like up to the highest pressure of 11.5 GPa in this study. The observed structural changes in liquid Li are consistent with the recently determined melting curve of Li.

Liquid structure under extreme conditions: high-pressure x-ray diffraction studies

“…The value of Q 1 in the liquid S(Q) increases gradually under compression and above 8.7 GPa is consistent with the position and p-evolution of the fcc-111 reflection. This indicates a gradual mixing of bcc-like to fcclike local ordering takes place under compression, with fcclike ordering becoming dominant in the vicinity of the melting curve maximum and underlying solid-state bcc-fcc transition [398]. As for Cs and Rb liquids discussed above, a recent MD simulation study of liquid K predicts a continuous transition between 10 and 20 GPa (above the melting curve maximum, see figure 17) from a metallic liquid to an 'electride' structure (in which electrons are localised in interstitial regions) accompanied by a reduction in coordination number [400].…”

“…XRD measurements of lighter alkali liquids are more challenging due to their weaker scattering signals and higher chemical reactivity. Shu et al [398] recently overcame these difficulties to measure the structure of liquid lithium (Li) by multi-angle ED-XRD under isothermal compression to 11.5 GPa using a LiF cylindrical capsule in a cupped-Drickamer-toroidal cell assembly in the PE-cell at the APS. At ambient-p, the first peak in S(Q) of liquid Li coincides with reflections expected for both bcc-Li (110) and fcc-Li (111) phases [399].…”

Overview of HPCAT and capabilities for studying minerals and various other materials at high-pressure conditions

“…Another example of PE capabilities is demonstrated by recent measurements of the structure of liquid lithium at high pressure (Shu et al 2020a). Major challenges in experimentally determining the structure of liquid lithium include the weak signals in X-ray scattering and its inherent chemical reactivity.…”