First-principles calculations of structural, elastic, electronic and transport properties of vanadium-doped zirconium lead carbide max phase

Abstract

First-principles calculations have been used to systematically investigate the structural, electronic, elastic, thermodynamic, and transport properties of Zr2PbC MAX phase and its alloys. The V-based alloys (VxZri-x)2PbC, 0 < x < 1 were synthesized by substituting V on the M-site of the MAX phase at a concentration of 0.25, 0.50, 0.75, and 1.00 respectively. Within the density functional theory (DFT), density functional perturbation theory (DFPT), and Boltzmann transport theory, the generalized gradient approximation (GGA: PBE, PBEsol, PW91), the local density approximation (LDA: PZ) exchange-correlation functionals, and the plane-wave pseudopotential method were used. The examined materials crystallized into a hexagonal shape of space group P63/mmc in relaxed and optimized configurations. The calculated electronic bands and density of states show that the studied MAX phases are conductors. The elastic constants show that all studied materials are mechanically stable based on the Born stability criteria for hexagonal crystals, and structurally stable based on the total minimum energy of the relaxed structures. The 100 % replacement of the Zr atoms shows a significant increase in the Seebeck coefficient and the thermoelectric figure of merit of the terminal MAX phase (V2PbC). Structurally all the studied materials are hard, brittle, and of high directional anisotropy. Calculated properties have been compared with available experimental data and are in good agreement. All four alloys show a significant increase in the electronic, elastic and thermodynamic properties with a decrease in the lattice parameters as the V concentration increases. The terminal alloy V2PbC has a lower total energy compared to the Zr2PbC. The transport properties have been calculated in a temperature range of 200 to 800 K by applying GGA (PBE). For the material at 800 K, a rapid decrease in the thermal conductivity with a slow decrease in electrical conductivity leads to an increase in the figure of merit.