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 (Γ–Γ) 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.
Born effective charges Zi, β α *, dielectric tensors εα,βand the dynamic stability for AgMgF3 and KMgF3 compounds were treated based on the harmonic and quasi-harmonic theory implemented in phonopy code. The band gap for both compounds as well as the effective masses of electrons and holes are calculated at different pressures using the TB-mBJ (GGA) approximation within the framework of the density functional theory. Furthermore, absorption coefficient, refractive index, extinction coefficient, reflectivity, and optical conductivity, for both compounds were calculated. On the other hand, we studied the nature of atomic bonds by the topological distribution of the charge density as well as computing the effective charge of each atom based on the Quantum Theory of Atoms in Molecules (QTAIM) as implemented in Bader code, therefore the ionic type for bonds was explored. The mechanical stability was verified after calculating the elastic behavior at the equilibrium ground-state for both compounds. Thermal properties such as heat capacity at constant volume, entropy, Debye temperature, and thermal expansion coefficient are treated depending on the quasi-harmonic model. They are examined under both pressure and temperature influences. The thermoelectric properties of the compound AgMgF3 showed a high figure of merit (ZT) reached 0.75 at a temperature of 300 K if it was doped with a concentration of 1021 cm-3 of n-type.
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