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

Abstract

Inspired by the recent discovery of Ti4MoSiB2, a quaternary phase with out-of-plane chemical order that we denote o-MAB, we perform an extensive first-principles study to explore attained chemical order and...

Experimental and Theoretical Investigations of Out-of-Plane Ordered Nanolaminate Transition Metal Borides: M4CrSiB2 (M = Mo, W, Nb)

“…In addition, when comparing the lattice parameters, a and c (Table S5) of the o -MAB phases Mo 4 CrSiB 2 , W 4 CrSiB 2 , and Nb 4 CrSiB 2 , with their ternary counterparts, Mo 5 SiB 2 , W 5 SiB 2 , and Nb 5 SiB 2 , a noticeable reduction of the lattice parameters is shown for the o -MAB phases due to the replacement of M in Wyckoff position 4c with a smaller element, Cr. Although the ternary Cr 5 SiB 2 is theoretically predicted to be unstable, this work clearly shows the possibility to incorporate Cr in ternary T2 phases when the A element is Si and the occupied site is 4 c , to form out-of-plane chemically ordered phases with the chemical formula M 4 CrSiB 2 (M = Mo, W, Nb).…”

“…30,31 Similarly, by adding Ti to Mo 5 SiB 2 (a T2 phase) in a ratio of Ti:Mo equal to 4:1, out-of-plane chemical ordering was established, creating the o-MAB phase Ti 4 MoSiB 2 , 32 while using the molten salt (ZnCl 2 ) method resulted in the conversion of Ti 4 MoSiB 2 to single sheets of 2D TiO x Cl y . 32 Recently, a systematic theoretical approach was implemented by Dahlqvist et al 33 to predict the stability of o-MAB phases in the form of M 4 M′AB 2 with M from Groups 3 to 9 and A = Al, Si, P, Ga, Ge. Guided by this and previous work, 32,33 we present herein the synthesis and characterization of three novel o-MAB phases: Mo 4 CrSiB 2 , W 4 CrSiB 2 , and Nb 4 CrSiB 2 , overcoming the challenge of including Cr in Sibased T2 MAB phases.…”

“…32 Recently, a systematic theoretical approach was implemented by Dahlqvist et al 33 to predict the stability of o-MAB phases in the form of M 4 M′AB 2 with M from Groups 3 to 9 and A = Al, Si, P, Ga, Ge. Guided by this and previous work, 32,33 we present herein the synthesis and characterization of three novel o-MAB phases: Mo 4 CrSiB 2 , W 4 CrSiB 2 , and Nb 4 CrSiB 2 , overcoming the challenge of including Cr in Sibased T2 MAB phases. Chemical ordering is confirmed, and Cr is found to reside in Wyckoff position 4c.…”

Computational prediction of novel MAB phases

“…An initial idea is to apply the combined framework to similar compositions, such as 𝑀 𝐴B , in hopes of expanding the family of quaternary MAB phases. Any low energy structure is further motivated to be included within a large screening study by combining different metals for potential stable phases, similar to previous proposed strategies [87]. Alternative properties which would be interesting to consider within future projects are the effects of vacancies and the entropy effects within disordered systems.…”

Computationally Driven Discovery of Quaternary Tantalum-Based MAB-Phases: Ta4M″SiB2 (M″ = V, Cr, or Mo): Synthesis, Characterization, and Elastic Properties

“…18 These quaternary MAB phases can either be o-MAB phases with out-of-plane chemical order or disordered solid solutions. 18 Notably, the study predicted 35 o-MAB phases as well as 121 solid solutions, showing that alloying is a fruitful pathway for expanding the concept of T2 phases to include novel elemental combinations. To date, Mo 4 TiSiB 2 is the only member of the o-MAB phases to be experimentally reported; 17 accordingly, there is a need to develop experimental approaches to also realize other members of this o-MAB phase family.…”