Zr‐Al‐C MAX Phases Stabilized by Carbon Vacancies

ABSTRACT Extreme service environments demand the engineering of innovative high‐performance materials, with high purity as a critical design requirement. Zirconium‐based MAX phases are touted for their radiation tolerance, favorable neutronics, and liquid metal compatibility. Accordingly, they are proposed as highly promising candidates to replace corrosion‐sensitive zircalloy coatings for accident‐tolerant fuels in Gen‐III/Gen‐IV nuclear reactors. However, their potential has never materialized due to their poor synthesizability and thus low purity. The inevitable and poorly understood competing formation of ZrC during synthesis severely compromises their thermomechanical integrity and radiation response. This work combines complementary insights into theoretical phase stability and experimental synthesizability of and . Carbon vacancies are predicted to adversely affect stability, whereas moderate (5–10 at.%) carbon deficiency improves stability. Reactive spark plasma sintering /Al/C powder mixtures of varying stoichiometry validated these trends: only forms substantially when using stoichiometric or carbon‐excessive feedstocks, whereas formation is highly sensitive to carbon‐deficient feedstocks: carbon‐stoichiometric or ‐excessive (25 at.%) feedstocks do not yield appreciable quantities of . Defect engineering thus emerges as a powerful alternative strategy for enhancing MAX phase stability and synthesizability without compromising their chemical integrity, opening new avenues for their design and application.