Predicted novel insulating electride compound between alkali metals lithium and sodium under high pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11672274, 11274281, and 11174214), the China Academy of Engineering Physics Research Projects (Grant Nos. 2012A0101001 and 2015B0101005), the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics

Abstract

The application of high pressure can fundamentally modify the crystalline and electronic structures of elements as well as their chemical reactivity, which could lead to the formation of novel materials. Here, we explore the reactivity of lithium with sodium under high pressure, using a swarm structure searching techniques combined with first-principles calculations, which identify a thermodynamically stable Li–Na compound adopting an orthorhombic oP8 phase at pressure above 355 GPa. The formation of Li–Na may be a consequence of strong concentration of electrons transfering from the lithium and the sodium atoms into the interstitial sites, which also leads to open a relatively wide band gap for LiNa-oP8. This is substantially different from atoms sharing or exchanging electrons in common compounds and alloys. In addition, lattice-dynamic calculations indicate that LiNa-oP8 remains dynamically stable when pressure decompresses down to 70 GPa.