Finite-Temperature Dynamics of Elemental Electrides Under Extreme Conditions

Crystalline alkali metals generally exhibit near free-electron behavior at ambient conditions. For sodium at high pressures of above 200GPa, a deviation from such a metallic behavior was found in the insulator hP4 electride phase[1]. We investigated the temperature-induced changes in such systems using density functional theory. For the solid phase, the closure of the band gap with increasing temperature was explored through a comparison between the time scales for electron–phonon and phonon–phonon interactions. However, the more-intriguing aspect has been the observation of a metallic state, upon melting of Na-hP4, with coalescent dynamic electron bubbles rather than a conventional uniform electron gas. In essence, the emphasis of this work is to highlight the differences between the dynamics of the electride phases of pure elements, e.g., Na-hP4, vis-à-vis non-electride phases, e.g. Na-tI19, under thermal effects.

[1] Y. Ma et al., Nature 458, 182 (2009).