DFT insights into the electronic structure, mechanical behaviour, lattice dynamics and defect processes in the first Sc-based MAX phase Sc2SnC

Abstract

The ceramic and metallic properties of the MAX phases make them attractive for numerous technological applications. The very recent experimental synthesis of the first scandium (Sc) based MAX phase Sc2SnC is an important addition to the MAX phase family as it further expands the diversity of physical characteristics of this family. Here we employ density functional theory (DFT) calculations to investigate the structural, electronic, mechanical, lattice dynamical properties of Sc2SnC including defect processes to compare with those of existing M2SnC phases. The calculated structural properties are in good agreement with the experimental values. The new phase Sc2SnC is structurally, mechanically and dynamically stable. Sc2SnC is metallic with a mixture of covalent and ionic character. The covalency of Sc2SnC including M2SnC is mostly controlled by the effective valence. Sc2SnC in M2SnC family ranks second in the scale of deformability, softness and machinability. The elastic anisotropy level in Sc2SnC is moderate compared to the other M2SnC phases. Like other members of the M2SnC family, Sc2SnC has the potential to be etched into 2D MXenes and has the potential to be a thermal barrier coating (TBC) material. The hardness and melting point of Sc2SnC, including M2SnC, follows the trend of bulk modulus.

Role of Chalcogen Atoms as an A-Site Element on the Physical Properties of 211 MAX Phases in the Hf–A–B System

“…Furthermore, Poisson's ratio is capable of predicting the nature of chemical bonds between atoms in solids. 44 A fully covalent bond will exist in a crystal if its Poisson's ratio is equal to or less than 0.10. A compound with a Poisson's ratio equal to or greater than 0.33 is expected to be fully metallic-bonded.…”