Ab Initio Study on the Effect of Au Layers on Phase Stability, Chemical Bonding, Elastic, and Thermal Properties of Ti ₄ Au <i> _n </i> C ₃ ( <i>n</i>  = 1–3)

ABSTRACT The recently synthesized Ti 4 Au 3 C 3 with a unique gold trilayer stacking offers a promising model to explore the influence of noble metal layers on phase stability, chemical bonding, and elastic and thermal properties. In this work, these properties are investigated by first‐principles simulations for Ti 4 Au 3 C 3 as well as hypothetical Ti 4 AuC 3 and Ti 4 Au 2 C 3 , thereby clarifying their MAX‐phase characteristics and enabling assessment of potential future applications. Increasing the Au‐layer count from a monolayer (Ti 4 AuC 3 ) through a bilayer (Ti 4 Au 2 C 3 ) to a trilayer (Ti 4 Au 3 C 3 ) significantly affects both the elastic behavior and finite‐temperature thermal properties. Analyses of bond stiffness and related mechanical indicators suggest lower damage tolerance for Ti 4 Au 3 C 3 than for Ti 4 Au 2 C 3 and Ti 4 AuC 3 . Also including the contribution from electronic excitation, their heat capacity and thermal expansion are predicted by quasi‐harmonic approximations, with near‐room‐temperature heat capacities of approximately 154, 179, and 206 J·mol −1 ·K −1 , and average linear thermal expansion coefficients of 10.10 × 10 −6 , 12.45 × 10 −6 , and 18.02 × 10 −6 K −1 for Ti 4 AuC 3 , Ti 4 Au 2 C 3 , and Ti 4 Au 3 C 3 over 300–1000 K, respectively. This work offers quantitative guidance for A‐layer engineering of Au‐containing MAX phases and a method to tune the properties of MAX phases for potential engineering applications.