Comparative Ab-Initio Investigation of Structural, Electronic, Mechanical, Thermoelectric and Thermophysical Properties of MnAs Polymorphs

Intermetallic compounds are ordered solid-state metallic alloys which are widely used in aerospace, energy and electronic industries, and are crucial for high-temperature structural components in aircraft engines. The present study investigates MnAs intermetallics via ab-initio structural, electronic, mechanical, thermoelectric and thermophysical properties using density functional theory (DFT) with PBEsol exchange–correlation functional. This investigation was centered on the tetragonal (Tetr), hexagonal (hcp), and cubic (cP) phases of MnAs. The novelty of this investigation lies in its thermoelectric analysis, which has not yet been reported in scientific literature. Our computed lattice parameters of and (for Tetr phase), and (for hcp phase), and (for cP phase) aligns well with experiment and existing theoretical data, indicating the validity of the study. The negative formation energy and binding energy analysis showcases the structural stability of the calculations. The electronic density of states calculations revealed zero band gap energy as an indication that all three phases are metallic conductors. The obtained elastic constants for the Tetr, hcp, and cP phases of MnAs satisfy the Born mechanical stability criteria, suggesting that all three phases are mechanically stable. Significantly, the mechanical analysis from BH/GH ratio and Poisson’s ratio exhibited ductility, which confirms the electronic DOS results of the three phases as metals. Also, while they all exhibit anisotropic character, the highest resistant to deformation is found in Tetr and hcp phases. Furthermore, the investigated thermoelectric (TE) transport properties recorded maximum power factors of 4.4 x 1011 W.cm−1.K−2.s−1 (Tetr phase), 7.2 x 1011 W.cm−1.K−2.s−1 (hcp phase), and 9.4 x 1011 W.cm−1.K−2.s−1 (cP phase) all at 800 K respectively. Moreover, our finding suggests that the registered high Seebeck coefficient S and minimum thermal conductivity displayed by the cP phase at 300 K makes this phase a promising candidate for TE applications. The thermophysical assessment of the Debye temperature, entropy, free energy, internal energy, heat capacity, and acoustic sound velocities of Tetr, hcp, and cP compounds of MnAs are also discussed.