Structural, Elastic, Electronic, Magnetic, and Thermoelectric Characteristics of MgEu2X4 (X = S, Se) Spinel Compounds: Ab-Initio Calculations

The structural, elastic, electronic, magnetic, and thermoelectric properties of MgEu2X4 (X = S and Se) spinel compounds are investigated computationally. Calculations are performed using the full-potential linearized augmented plane wave (FP-LAPW) method within the Perdew, Burke, and Ernzerhof generalized gradient approximation (PBE-GGA), GGA + U, and modified Becke-Johnson (mBJ-GGA) approximations. The band structure and density of states results from the three exchange-correlation approximation methods (mBJ, GGA + U, and PBE) show that these spinel compounds are fully spin-polarized. Also, they possess a half-metallic character in the spin-down channel with a direct bandgap (Gamma-Gamma) of about 3.44, 2.712, and 2.472 eV for MgEu2S4 and 2.89, 2.285, and 2.017 eV for MgEu2Se4, respectively. The formation of both compounds is energetically favorable based on the results of the total energy and cohesive energy calculations. Furthermore, the two compounds are chemically and mechanically stable, as concluded from cohesive energy and elastic calculations. The elastic calculations reveal that both spinel compounds are ductile materials. The ionic bonds are predominant. The quasi-harmonic model has also been used to investigate the influences of temperature and pressure on thermal characteristics. The thermoelectric behavior is studied using the BoltzTraP code. Both systems show good thermoelectric properties for the spin-down channel.