Experimental and Theoretical Investigations of Out-of-Plane Ordered Nanolaminate Transition Metal Borides: M 4 CrSiB 2 (M = Mo, W, Nb).

We report the synthesis of three out-of-plane chemically ordered quaternary transition metal borides ( o -MAB phases) of the chemical formula M ₄ CrSiB ₂ (M = Mo, W, Nb). The addition of these phases to the recently discovered o -MAB phase Ti ₄ MoSiB ₂ shows that this is indeed a new family of chemically ordered atomic laminates. Furthermore, our results expand the attainable chemistry of the traditional M ₅ SiB ₂ MAB phases to also include Cr. The crystal structure and chemical ordering of the produced materials were investigated using high-resolution scanning transmission electron microscopy and X-ray diffraction by applying Rietveld refinement. Additionally, calculations based on density functional theory were performed to investigate the Cr preference for occupying the minority 4 c Wyckoff site, thereby inducing chemical order.