DFT study on the structural, mechanical, electronic, optical and thermodynamic properties of recently synthesized MAX Phase compounds A3InC2 (A= Zr, Hf) under ambient and elevated pressure

Very recently the In-based MAX phases A(3)InC(2) (A= Zr, Hf) have received great attraction for their exceptional physical properties. Here, the physical properties of A(3)InC(2) (A= Zr, Hf) have been studied at ambient and high pressure using the density functional theory (DFT) and CASTEP code. The generalized gradient approximation (GGA) has been used to optimized the crystal structures of A(3)InC(2) (A= Zr, Hf) whereas the good agreement between the optimized and experimental lattice parameters is observed. Structural and mechanical stability of these phases at zero and high pressure is ensured from the negative formation enthalpy and elastic constants data. Positive phonon dispersion curves ensure the dynamical stability of the studied phases. The high bulk modulus and Young's modulus ensure the possible industrial applications of A(3)InC(2) (A= Zr, Hf). Brittle nature of Zr2InC2 and Hf2InC2 is confirmed from Pugh ratio and Poisson's ratio analysis up to 20 GPa and 40 GPa respectively but these phases are shifted towards ductile nature after 20 GPa and 40 GPa pressure. The increase in machinable index with pressure enhanced the damage tolerant characteristics and probable industrial applications of A(3)InC(2) (A= Zr, Hf). Metallic nature of compounds A(3)InC(2) (A= Zr, Hf) is confirmed from band structure calculations. Several optical functions such as dielectric function, refractive index, optical conductivity, absorption, reflectivity and loss function are studied using the Kramers-Kronig relation. High reflectivity in the low energy region confirm the barrier coating like characteristics of A(3)InC(2) (A= Zr, Hf). The quasi-harmonic Debye model is used to investigate the thermal properties of A(3)InC(2) (A= Zr, Hf) where very high melting temperature and extremely low (<1.0) thermal conductivity ensured that these phases have probable applications in thermal barrier coating materials (TBC).