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

Abstract

We report on the synthesis of computationally predicted out-of-plane chemically ordered transition metal borides labeled o-MAB phases, Ta4M″SiB2 (M″ = V, Cr), and a structurally equivalent disordered solid solution MAB phase Ta4MoSiB2. The boride phases were prepared using solid-state reaction sintering of the constituting elements. High-resolution scanning transmission electron microscopy along with Rietveld refinement of the powder-X-ray diffraction patterns revealed that the synthesized o-MAB phases Ta4CrSiB2 (98 wt % purity) and Ta4VSiB2 (81 wt % purity) possess chemical ordering with Ta preferentially residing in the 16l position and Cr and V in the 4c position, whereas Ta4MoSiB2 (46 wt % purity) was concluded to form a disordered solid solution. Density functional theory (DFT) calculations were used to investigate the dynamic stability, elastic properties, and electronic density states for the MAB phases, confirming the stability and suggesting the borides based on Cr and Mo to be stiffer than those based on V and Nb.