A First Principles Study of Structural, Mechanical, Phonon, Optoelectronic, and Thermoelectric Properties of MnX ₂ O ₄ (X = Al, Cr) Spinels for Photovoltaic and Thermoelectric Applications

This study investigates the physical properties of the spinel oxides MnAl 2 O 4 and MnCr 2 O 4 using the modified Becke–Johnson potential (mBJ). The stability was also evaluated based on tolerance ( τ ) factor and formation energy (Δ H ) calculations. Positive frequencies are observed in phonon dispersion spectra of both spinels confirming their dynamical stability. Mechanical stability is assured by the Born stability criteria. Both spinels exhibit ferromagnetic ordering, as confirmed by the integral values of their magnetic moments, and display semiconducting behavior according to the accurate mBJ calculations. Analysis of optical conductivity exhibits a high conductivity in the ultraviolet (UV) range, thus proving to be appropriate for photovoltaic devices, specifically for UV detection and solar cell devices. MnAl 2 O 4 and MnCr 2 O 4 have thermoelectric (TE) characteristics indicating that their low thermal conductivity alongside optimal Seebeck values forms the basis for excellent figure of merit (ZT) values very close to unity at 300 K. Their equilibrium between thermal and electronic transport characteristics suggests that both would perform well within respective TE temperature ranges. These results establish MnAl 2 O 4 and MnCr 2 O 4 as multifunctional candidates for optoelectronic and energy‐conversion technologies.