Lanthanide(III) Nitride Bismuthides M2NBi (M = La–Nd) and Their Potential as Topological Insulators

Abstract

AbstractFour lanthanide(III) nitride bismuthides of the new class M2NBi (M = La–Nd) have been synthesized by the reaction of the respective lanthanide metal (M) with caesium azide (CsN3), elemental bismuth (Bi), the corresponding lanthanide trichloride (MCl3), and caesium chloride (CsCl) as flux in evacuated silica tubes for 7 days at 900 °C. The M2NBi compounds crystallize tetragonally in the space group P4/nmm with Z = 2 with the lattice parameters a = 480.61(4) pm, c = 948.34(9) pm (M = La), a = 475.48(4) pm, c = 938.76(9) pm (M = Ce), a = 471.80(4) pm, c = 929.51(9) pm (M = Pr), and a = 468.13(4), c = 921.08(9) pm (M = Nd). As the main structural feature of the crystal structures, ∞2{[NM2]3+} layers of condensed nitride‐centered square pyramids of M3+ cations dominate. These pyramids, in which the base is built of (M1)3+ and the top of terminal (M2)3+ cations (t), are connected by all four basal edges (e) to form a two‐dimensional network according to ∞2{[N(M1)e4/4(M2)t1/1]3+} that is separated by square double layers of Bi3– anions. Both crystallographically independent M3+ cations bear two types of anions (N3– and Bi3–) as ligands. (M1)3+ is coordinated in the shape of a square antiprism by four N3– and four Bi3– anions, and (M2)3+ is surrounded by a distorted octahedron consisting of one N3– and five Bi3– anions. The Bi3– anions reside in capped square antiprisms of nine M3+ cations. The partial density of states (PDOS) and the band structure of La2NBi show that this compound has to be considered as a zero‐band‐gap semiconductor with a nontrivial topology and a high potential as a topological insulator.