Structural Diversity and Electron Confinement in Li₄N: Potential for 0-D, 2-D, and 3-D Electrides

Abstract

In pursuit of new lithium-rich phases and potential electrides within the Li-N phase diagram, we explore theoretically the ground-state structures and electronic properties of LiN at P = 1 atm. Crystal structure exploration methods based on particle swarm optimization and evolutionary algorithms led to 25 distinct structures, including 23 dynamically stable structures, all quite close to each other in energy, but not in detailed structure. Several additional phases were obtained by following the imaginary phonon modes found in low-energy structures, as well as structures constructed to simulate segregation into Li and LiN. The candidate LiN structures all contain NLi polyhedra, with n = 6-9. They may be classified into three types, depending on their structural dimensionality: NLi extended polyhedral slabs joined by an elemental Li layer (type a), similar structures, but without the Li layer (type b), and three-dimensionally interconnected NLi polyhedra without any layering (type c). We investigate the electride nature of these structures using the electron localization function and partial charge density around the Fermi level. All of the structures can be characterized as electrides, but they differ in electronic dimensionality. Type-a and type-b structures may be classified as two-dimensional (2-D) electrides, while type-c structures emerge quite varied, as 0-D, 2-D, or 3-D. The calculated structural variety (as well as detailed models for amorphous and liquid LiN) points to potential amorphous character and likely ionic conductivity in the material.

First-Principles Prediction of New Electrides with Nontrivial Band Topology Based on One-Dimensional Building Blocks

“…Both of these electrides offer high electron-donating powers as reflected in the Pinacol coupling reaction [14], ammonia synthesis [15], and trifluoromethylation [16]. In particular, Ca 2 N serves as a prototypical material for binary [17][18][19][20] layered electrides using computational searches based on a database [21] and evolutionary algorithms [22][23][24], which provided possible electride candidates and design principles [21][22][23][24].…”

“…Once a new electride is found, the most straightforward extension for the next electride is to combinatorially change its elements but retain its crystal symmetry. Since its rediscovery as a two-dimensional electride, many electrides with anti-CdCl 2 structures have been suggested [22][23][24]. So far, however, those electrides, either experimentally synthesized or theoretically predicted, are in a limited class with respect to crystal symmetry and chemical groups.…”

Carbon nanotube-based black coatings

“…In addition, the use of a support catalyst is highly sensitive to the material used, which crystalline face 90 is used if growing on sapphire, how it is deposited 91 and how it is treated post-deposition. 92 Catalyst poisoning is another issue which limits the eventual height to which one can grow vertically aligned carbon nanotubes. It is believed that amorphous carbon growth leads to the eventual termination of the growth of the nanotubes on the metal catalyst site.…”

Theoretical study of a novel organic electride with large nonlinear optical responses

“…Therefore, molecular electrides have also attracted great attention from researchers devoted to the development of new NLO materials, in particular, organic second‐order NLO materials with potential applications in ultrafast modulators and switches, [18] laser frequency conversion devices, surface and interface characterization tools, and biological and chemical sensors [19,20] . Recently, the definition of electride has been extended from solids [7] to liquids [21,22] and even to molecular electrides in gas (theoretical model) [23] . Although many organic molecular electrides have been theoretically designed, [24–31] unfortunately, they have not been successfully synthesized yet.…”