Advanced quantum mechanical insights into bulk orthorhombic Mg 3 CrN 4 for high-temperature thermoelectric energy conversion and UV optoelectronic applications

Abstract This study uses first-principles density-functional theory (FP-LAPW/WIEN2k) in conjunction with semiclassical Boltzmann transport to study bulk Mg 3 CrN 4 with orthorhombic Pmn 2 1 symmetry. The optimized structure, which has an equilibrium volume of around 2,300 a.u. 3 and a bulk modulus of about 74 GPa, indicates considerable incompressibility and is mechanically stable ( a = 12.85 Å, b = 11.11 Å, c = 10.00 Å). Strong Cr-d/N-p hybridization results in a direct bandgap of about 3.6 eV, according to spin-polarized electronic structure simulations that correct for the well-known GGA gap underestimate. Charge-density maps show mixed ionic–covalent bonding. There is noticeable anisotropy in the optical spectra: the real part of the dielectric function turns negative in certain UV ranges, the absorption rises sharply above 2 eV with strong UV activity, the reflectivity stays below about 35 %, and the optical conductivity shows strong peaks around 5–6 eV (=9 × 10 3 Ω −1 cm −1 ), indicating intense interbond transitions. Thermoelectric transport, when subjected to a constant- τ approximation, exhibits almost symmetric electron-hole behavior around μ = 0. Its spin dependence is distinct, and its σ / τ and κ e / τ are negligible at the intrinsic chemical potential but greatly boosted with p- or n-type doping. Mg 3 CrN 4 has the potential to be a multifunctional nitride that combines UV-active optoelectronic response with promising high-temperature thermoelectric performance. Such performance is demonstrated by the calculated Figure of merit, which reaches ZT = 1.0–1.1 at 1,000–1,200 K. We should validate this experimentally and pursue additional band-edge engineering for energy-conversion applications.

Hali tarjima qilinmagan