First-Principles Study of Three-Dimensional Electrides Containing One-Dimensional [Ba3N]3+ Chains

Abstract

Electrides, a unique type of compound where electrons act as anions, have a high electron mobility and a low work function, which makes them promising for applications in electronic devices and high-performance catalysts. The discovery of novel electrides and the expansion of the electride family have great significance for their promising applications. Herein, we reported four three-dimensional (3D) electrides by coupling crystal structure database searches and first-principles electronic structure analysis. Subnitrides (Ba₃N, LiBa₃N, NaBa₃N, and Na₅Ba₃N) containing one-dimensional (1D) [Ba₃N]³⁺ chains are identified as 3D electrides for the first time. The anionic electrons are confined in the 3D interstitial space of Ba₃N, LiBa₃N, NaBa₃N, and Na₅Ba₃N. Interestingly, with the increase of Na content, the excess electrons of Na₅Ba₃N play two roles of metallic bonding and anionic electrons. Therefore, the subnitrides containing 1D [Ba₃N]³⁺ chains can be regarded as a new family of 3D electrides, where anionic electrons reside in the 3D interstitial spaces and provide a conduction path. These materials not only are experimentally synthesizable 3D electrides but also are promising to be exfoliated into advanced 1D nanowire materials. Furthermore, our work suggests a discovery strategy of novel electrides based on one parent framework like [Ba₃N]³⁺ chains, which would accelerate the mining of electrides from the crystal structure database.

Figure 1

Structure of Ba₃N (a) and NaBa₃N (b) as viewed along the c-axis and Na₅Ba₃N (c) as viewed along the b-axis. A side view of an isolated _∞¹[NBa_6/2] chain is also shown in (a). The green, gray, and orange spheres, respectively, denote Ba, N, and Na atoms.

Figure 2

Computed lattice constants (PBE, PBE-D2, PBE-D3, and PBE-dDsC) versus experimental lattice constants including volume (a), lattice constant a (b), lattice constant b (c), and lattice constant c (d) of Ba₃N, LiBa₃N, NaBa₃N, and Na₅Ba₃N.

Figure 3

ELF for Ba₃N. The isosurface plot (a) and the corresponding map of the (0001) plane at c = 1 (b), the (0001) plane at c = 3/4 (c), and the (112̅0) plane (d).

Figure 4

Calculated band structure (a), PDOS (b), the isosurface and the map of partial charge density of interstitial band 1 (c), band 2 (d), and band 3 (e) of Ba₃N. The bands around the Fermi level, mainly contributed by the interstitial electrons, are highlighted in red, blue, and green lines. In (c–e), the green and gray spheres, respectively, denote Ba and N atoms.

Figure 5

ELF for NaBa₃N-Na. The isosurface plot (a) and the corresponding map of the (0001) plane at c = 1 (b), the (0001) plane at c = 3/4 (c), and the (112̅0) plane (d).

Figure 6

ELF for NaBa₃N. The isosurface plot (a) and the corresponding map of the (0001) plane at c = 1 (b), the (0001) plane at c = 3/4 (c), and the (112̅0) plane (d).

Figure 7

Calculated band structure (a), PDOS (b), the isosurface and the map of partial charge density of interstitial band 1 (c), band 2 (d), band 3 (e), and band 4 (f) of NaBa₃N. The interstitial bands, mainly contributed by the interstitial electrons, are highlighted in bold red, blue, green, and cyan lines. In (c–f), the green, gray, and orange spheres, respectively, denote Ba, N, and Na atoms.

Figure 8

Calculated ELF for Na₅Ba₃N (a), Na₅Ba₃N-2e^– (b), Na₅Ba₃N-4e^– (c), Na₅Ba₃N-6e^– (d), and Na₅Ba₃N-8e^– (e). The isosurface plot (left) and the corresponding map of the (010) plane at c = 3/4 (right). The green, gray, and orange spheres, respectively, denote Ba, N, and Na atoms.

Figure 9

(a) Calculated band structure of Na₅Ba₃N. The Ba-, Na-, and N-related bands are depicted using blue, purple, and red dots. (b) Total and projected DOS of Na₅Ba₃N. (c) Calculated partial charge density for Na₅Ba₃N around the Fermi level (−1.38 eV < E–E_F < 0 eV). The isosurface plot of the partial charge density is set as 0.003 e/ų along the b-axis and the corresponding map of the (010) plane at c = 3/4.