Stabilizing MoB ₂ with HCP structure in (Mo <i> _x </i> Hf _(1‒ <i> _x </i> _)/5 Zr _(1‒ <i> _x </i> _)/5 Ta _(1‒ <i> _x </i> _)/5 V <sub>(

Abstract The properties of molybdenum diboride are intricately tied to its crystal structure, which includes two distinct phases, α‐MoB 2 and β‐MoB 2 . The α‐MoB 2 exhibits superior electrical and catalytic properties, akin to those of graphite due to the similar HCP structure. Nevertheless, the transformation between α‐MoB 2 and β‐MoB 2 is complicated and the formation of α‐MoB 2 remains challenge due to higher Gibbs free energy. The MoB 2 powder synthesized through boro/carbothermal reduction in this study suggests the β phase, transforming into α‐MoB 2 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 MoB 2 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‐MoB 2 , offering valuable insights into understanding phase‐transition behavior in MoB 2 and the solid solubility in multi‐component ceramics.