Electronic origin of melting T-P curves of alkali metals with negative slope and minimum

TL;DR

This paper explains the unusual melting behavior of alkali metals under pressure by analyzing electron energy level transformations and Fermi sphere-Brillouin zone interactions, revealing the electronic origins of their complex T-P melting curves.

Contribution

It introduces an electronic structure-based model to understand the negative slope and minimum in alkali metals' melting curves under pressure.

Findings

Melting curves show initial increase then decrease with pressure.

Electron energy level overlap explains complex melting behavior.

Fermi sphere-Brillouin zone interaction accounts for observed phenomena.

Abstract

Group I elements - alkali metals Li, Na, K, Rb and Cs - are examples of simple metals with one s electron in the valence band. Under pressure these elements display unusually complex structural behaviour transforming from close-packed to low symmetry open structures. Unexpectedly complex form was found for melting curves of alkalis under compression with initial increasing in accordance to Lindemann criterion and further decreasing to very low melting point. To understand complex and low symmetry structures in compressed alkalis a transformation of the electron energy levels was suggested which involves an overlap between the valence band and outer core electrons. Within the model of the Fermi sphere - Brillouin zone interaction one can understand the complex melting curve of alkalis.