Computational exploration of chemically ordered and disordered M-sites in M'2M''B2 and M'4M''B3 compounds

Abstract

Boron-based materials are highly desirable for their promising mechanical properties, rendering them ideal for various industrial applications. In this study, we capitalize on the advantage of the two unique metal sites in the V₃B₂ (4h and 2a) and Cr₅B₃ (16h and 4c) prototype structures. These two sites are further considered when alloying between two different metals, M' and M'', forming novel B-based ternary M'₂M''B₂ and M'₄M''B₃ compounds. A high-throughput phase stability search encompassing a total of 2738 compositions with M' and M'' being occupied systematically with Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hf, Tl, and Pb was further performed. The thermodynamic phase stability of the simulated materials was assessed by evaluating the formation enthalpy, ∆H_cp. Additionally, simulated disordered metals were further considered in systems with compounds identified as stable or close to stable. In total, 56 ternary phases were identified as stable when considering a configurational entropy contribution at 2000 K. 32 out of the 56 predicted stable phases displayed a preference for chemical order whereas 24 favored disorder of M' and M''. Initial synthesis attempts of the predicted stable Ta2MoB2 compound were made, showing indications for presence ordered Ta₂MoB₂ or disordered (Ta_0.667Mo_0.333)₃B₂.