Dynamical stability, vibrational, and optical properties of anti-perovskite A3BX (Ti3TlN, Ni3SnN, and Co3AlC) phases: A first principles study

We have investigated various physical properties including phonon dispersion, thermodynamic parameters, optical constants, Fermi surface, Mulliken bond population, theoretical Vickers hardness, and damage tolerance of anti-perovskite A(3)BX phases for the first time by employing density functional theory methodology based on the first principles method. Initially, we assessed nine A(3)BX phases in total and found that only three phases (Ti3TlN, Ni3SnN, and Co3AlC) are mechanically and dynamically stable based on the analysis of computed elastic constants and phonon dispersion along with phonon density of states. We revisited the structural, elastic, and electronic properties of the compounds to judge the reliability of our calculations. The absence of bandgap at the Fermi level characterizes the phases under consideration as metallic in nature. The values of Pugh ratio, Poisson's ratio, and Cauchy factor have predicted the ductile nature associated with strong metallic bonding in these compounds. A high temperature feasibility study of the phases has also been performed using the thermodynamic properties, such as the free energy, enthalpy, entropy, heat capacity, and Debye temperature. The Vickers hardness of the compounds is estimated to be similar to 4 GPa, which is comparable to many well-known MAX phases, indicating their reasonable hardness and easily machinable nature. The static refractive index n(0) has been found around similar to 8.0 for the phases under study that appeals as a potential candidate to design optoelectronics appliances. The reflectivity is found above 44% for the Ti3TlN compound in the energy range of 0 eV-14.8 eV, demonstrating that this material holds significant promise as a coating agent to avoid solar heating.