Out‐Of‐Plane Ordered Laminate Borides and Their 2D Ti‐Based Derivative from Chemical Exfoliation

Abstract

Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M5SiB2 (T2) phases, the finding of a family of laminated quaternary metal borides, M′4M″SiB2, with out‐of‐plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti4MoSiB2, establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti4MoSiB2 and select removal of Si and MoB2 sub‐layers is validated by derivation of a 2D material, TiOxCly, of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of ≈4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.

The effect of strain and pressure on the electron-phonon coupling and superconductivity in MgB2—Benchmark of theoretical methodologies and outlook for nanostructure design

“…For instance, if biaxial tensile or compressive strain in the ab-plane is desired, epitaxial growth along a common c-axis could allow for sandwiching of out-of-plane ordered pure Mg and suitable M (with the flat boron sublayers being spectators in the clustering). This idea is similar to what has recently been experimentally proven to be possible in the work of Dahlqvist et al 66 We also suggest co-deposition with intermediate temperature to allow some, but limited, surface diffusion. This allows for creating 3D intertwined coherent nanostructures or columns that are strained from all directions.…”

Chemical order or disorder – a theoretical stability expose for expanding the compositional space of quaternary metal borides

“…In a recent study we investigated the stability of T2 phases upon metal alloying for M 5 SiB 2 and predicted 11 chemically ordered phases as well as 40 solid solutions to be stable, including the experimentally verified Ti 4 MoSiB 2 . 37 Here we expand the possible chemistries by also considering A = Al, Ga, Ge and P upon metal alloying. We choose to not include A = In and Sn in this study due to the rather large formation enthalpy Δ H cp shown for M 5 InB 2 and M 5 SnB 2 in Fig.…”

“…28 Furthermore, in a most recent study, we synthesized Ti 4 MoSiB 2 , an o -MAB phase with proven out-of-plane chemical order of Ti and Mo, from which we subsequently derived a new 2D material, TiO x Cl y , of high yield and in the form of delaminated sheets. 37 The parent materials needed to realize these 2D materials were obtained through metal alloying of ternary MAB phases. This emphasizes that in our quest for finding novel 2D materials we must explore and enlarge the palette of materials from which they originate.…”

“…All five experimentally reported solid solutions (M 0 0:8 M 00 0:2 ) 5 AB 2 are predicted to be stable here, 35,36,56 as well as the recently discovered Ti 4 MoSiB 2 o-MAB. 37 Noteworthily, the additional 121 solid solution and 35 o-MAB phases are predicted to be stable, mainly for A = Si, P, and Ge, suggesting that metal alloying in T2 phases is a prospective path towards expanding the possible chemistries which, in turn, provide a high tunning potential of these materials. Table 1 summarizes the stable o-MAB and solid solution MAB phase compositions.…”

“…[34][35][36] We have recently shown that metal alloying in Si-based T2 phases holds potential for a range of new compositions, including the discovered out-of-plane ordered Ti 4 MoSiB 2 , called o-MAB. 37 It has been demonstrated that the bonds between the two metallic sites, Ti and Mo, are key to the stability of this specific structure. 38 In the present work we use a systematic theoretical approach to demonstrate the expansion of the possible chemistries for T2 phases, beyond A = Si, both with respect to ternary and quaternary compositions.…”