Newly synthesized Pb-based 312 MAX phases M3PbC2 (M = Zr and Hf): A First-principles study

Abstract

The MAX phases' unique mixture of ceramic and metallic features makes them appealing for various technological uses. Zr3PbC2 and Hf3PbC2, two Pb-based MAX phases, were recently synthesized experimentally. The physical properties, such as structural properties as well as electronic, mechanical, hardness, thermal, and lastly, the optical properties of M3PbC2 (M = Zr and Hf) have been investigated using density functional theory (DFT) and analogized with those of other 312 MAX phases. The optimized cell volume and computed lattice constants match the experimental values. The calculated band structure certifies the metallic character, and DOS calculations confirmed the dominant contribution to conductivity from the Zr-4d and Hf-5d states. The stiffness constant (Cij) proved the mechanical stability of these compounds. The mechanical behavior of the studied compounds was explored by calculating the elastic moduli, hardness parameters, and fracture toughness, which are also compared to those of the 312 MAX phases. The tightly bound M–C covalent bonds within the crystal give these compounds high stiffness. The Mulliken population (both atomic and bond) was calculated to explore the bonding characteristics within them and the Vickers hardness of the titled phases. The degree of elastic anisotropy present within phases has been analyzed by calculating different indices. The phonon dispersion curves and phonon DOS (PHDOS) were computed to check the dynamical stability of the phases. Thermodynamic potential functions were calculated from the PHDOS. The thermal parameters were also studied, including the Debye temperature, melting temperature, Grüneisen parameter, and minimum thermal conductivity (Kmin). A thorough computation and analysis of the vital optical constants was done to explore their potential in diverse fields. The titled compounds are suitable for use as thermal barrier coating (TBC) materials and coating materials to prevent solar heating.