Ab Initio Study of the Physical Properties of Cs-Based Double Perovskites Cs2 AX6 (A = Ge, Mn; X = Cl, I)
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Date
2024-04-15
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Abstract
Device applications in magnetic media, spintronics, oxygen membranes, sensors, etc., are some of the
uses of ferrite materials. In this work, we have studied the structural, electronic, magnetic, mechanical,
and thermoelectric properties of Cs-based double perovskites Cs2 AX6 (A = Ge, Mn; X = Cl, I), using
Quantum Espresso with generalized gradient approximation Perdew–Burke–Ernzerhof and Perdew–
Burke–Ernzerhof in solids exchange–correlation functionals. The band structure results show that
Cs2 GeCl6 and Cs2 MnCl6 are semiconductors with direct band gaps. However, there are bands crossing
observed for Cs2 GeI6 from the conduction band minimum to the valence band maximum, indicating
the metallic nature of the material. Moreover, Cs2 MnI6 has magnetic properties; it exhibits a metal-
lic nature in the spin-up state and a semiconductor nature in the spin-down state, suggesting that it
can be used in spintronics applications. The calculated total magnetic moment of Cs2 MnCl6 is 3.0µB
(for both Perdew–Burke–Ernzerhof and Perdew–Burke–Ernzerhof in solids), while for Cs2 MnI6 , the
calculated total magnetic moments are 3.02µB and 3.06µB , for Perdew–Burke–Ernzerhof and Perdew–
Burke–Ernzerhof in solids exchange–correlation functionals, respectively. The results of the mechanical
properties calculations show that Cs-based double perovskites Cs2 AX6 (A = Ge, Mn; X = Cl, I) are
mechanically stable. Cauchy’s pressure and Poisson’s, Frantsevich’s, and Pugh’s ratios of the studied
materials confirm that Cs2 MnCl6 is brittle, while the remaining studied double perovskite materials
are ductile. Electrical conductivity, thermal conductivity, Seebeck coefficients, power factor, and figure
of merit are the thermoelectric parameters analyzed in this study. Seebeck coefficients, electrical con-
ductivity, and power factor increase with the rise in temperature, and Cs2 MnX6 (X = Cl, I) double
perovskite materials have higher values of electrical conductivity than Cs2 GeX6 (X = Cl, I). All the
studied materials have positive type conductivity due to their positive Seebeck coefficient values.