Synthesis, crystal structure, magnetic and electronic properties of the caesium-based transition metal halide Cs3Fe2Br9

Abstract

The diversity of halide materials related to important solar energy systems such as CsPbX₃ (X = Cl, Br, I) is explored by introducing the transition metal element Fe. In particular a new compound, Cs₃Fe₂Br₉ (space group P6₃/mmc with a = 7.5427(8) and c = 18.5849(13) Å), has been synthesized and found to contain 0D face-sharing Fe₂Br₉ octahedral dimers. Unlike its isomorph, Cs₃Bi₂I₉, it is black in color, has a low optical bandgap of 1.65 eV and exhibits antiferromagnetic behavior below T_N = 13 K. Density functional theory calculations shed further light on these properties and also predict that the material should have anisotropic transport characteristics.