Abstract
Lithium—the lightest alkali metal exhibits unexpected structures and electronic behavior at high pressures. Like the heavier alkali metals, Li is bcc at ambient pressure and transforms first to fcc (at 7.5 GPa). The post-fcc high-pressure form Li-cI 16 (at 40-60 GPa) is similar to Na-cI 16 and related to more complex structures of heavy alkalis Rb-oC52 and Cs- oC84. The other high pressure phases for Li (oC88, oC40, oC24) observed at pressures up to 130 GPa are found only in Li. The different route of Li high-pressure structures correlates with its special electronic configuration containing the only 3 electrons (at 1s and 2s levels). Crystal structures for Li are analyzed within the model of Fermi sphere-Brillouin zone interactions. Stability of post-fcc structures for Li are supported by the Hume-Rothery arguments when new diffraction plains appear close to the Fermi level producing pseudogaps near the Fermi level and decreasing the crystal energy. The filling of Brillouin-Jones zones by electron states for a given structure defines the physical properties as optical reflectivity, electrical resistivity and superconductivity. To understand the complexity of structural and physical properties of Li above 60 GPa it is necessary to assume the valence electron band overlap with the core electrons and increase the valence electron count under compression.
Highlights
Recent high pressure studies of the structure and properties of elements under high pressure bring considerable revision to what has been known previously
The ambient pressure bcc structure undergoes distortions and superlattice formation leading to the creation of a new 24-planes Brillouin zone that accommodates the Fermi sphere with the ~90% filling by electron states
It is considered a close structural relationship of the alkali metal structures Li-oP24, Na-oP8 and K-oP8 with the binary alloy phase AuGa-oP8. The latter phase is related to the family of the Hume-Rothery phases that is stabilized by the Fermi sphere–Brillouin zone interaction where a decrease in the electronic band structure energy occurs due to the contact of the Fermi sphere and Brillouin zone planes
Summary
Recent high pressure studies of the structure and properties of elements under high pressure bring considerable revision to what has been known previously (see review papers [1,2,3] and references therein). The group-I elements of the Periodic table from Li to Cs at normal conditions are related to the free electron metals and adopt the body-centered cubic (bcc) structure. They transform under pressure to the face-centered cubic (fcc) structure and at significant compression to open and complex structures. The post-fcc high-pressure form Li-cI16 (at 40-60 GPa) [5] is similar to Na-cI16 and related to more complex structures of heavy alkalis Rb-oC52 and Cs-oC84. For heavier alkali metals all changes in structure and properties usually are accounted by the conversion of valence electrons from s to d states [13], with the upper empty d-band moving downward on compression and overlapping with the s-band. The electronic energy contribution is suggested as a cause for the formation of complex crystal structures and changes the physical properties
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
