Stabilizing MoB2 with HCP structure in (MoxHf(1‒x)/5Zr(1‒x)/5Ta(1‒x)/5V(1‒x)/5Nb(1‒x)/5)B2 via a high-entropy strategy

The properties of molybdenum diboride are intricately tied to its crystal structure, which includes two distinct phases, α-MoB₂ and β-MoB₂. The α-MoB₂ exhibits superior electrical and catalytic properties, akin to those of graphite due to the similar HCP structure. Nevertheless, the transformation between α-MoB₂ and β-MoB₂ is complicated and the formation of α-MoB₂ remains challenge due to higher Gibbs free energy. The MoB₂ powder synthesized through boro/carbothermal reduction in this study suggests the β phase, transforming into α-MoB₂ completely via a high-entropy strategy. It founds that the introduction of high-entropy diborides (HEB) effectively inhibits the grain growth of samples, resulting in a significant enhancement in their hardness. The potential for the formation of a single-phase between MoB₂ and HEB is associated with Pauling electronegativity difference, δ_χP. Furthermore, the formation of a single-phase solid solution was found to contribute to the improvement in the fracture toughness of the samples. This work presents a novel strategy for stabilizing α-MoB₂, offering valuable insights into understanding phase-transition behavior in MoB₂ and the solid solubility in multi-component ceramics.