Computational exploration of CsZrX3 (X = Cl, Br) halide perovskites: a DFT and BoltzTraP2 approach toward opto-spintronics and thermoelectric applications.

Abstract

Lead-free halide perovskites have attracted significant interest owing to their potential applications in advanced optoelectronic, spintronic, and energy-conversion devices. This study presents a comprehensive first-principles investigation of the structural, electronic, magnetic, mechanical, optical, thermoelectric, and phonon dispersion properties of cubic CsZrX3 (X = Cl, Br) perovskites using density functional theory (DFT) and semiclassical Boltzmann transport theory. Spin-polarized electronic-structure calculations reveal half-metallic behavior, characterized by a metallic majority-spin channel and an insulating minority-spin channel. The minority-spin band gaps are 5.52 and 4.50 eV for CsZrCl3 and CsZrBr3, respectively while both compounds exhibit a total magnetic moment of approximately 2.00 µ B per formula unit, primarily arising from the Zr 4d states. Phonon dispersion calculations confirm the dynamical stability of both compounds, as indicated by the absence of imaginary phonon frequencies throughout the Brillouin zone. Both compounds satisfy the Born mechanical stability criteria and exhibit Pugh ratios of 2.30 and 2.29 for CsZrCl3 and CsZrBr3, respectively, indicating a ductile tendency according to the adopted criterion. The calculated Debye temperatures are 251.13 and 198.24 K, whereas the estimated melting temperatures are 1116.16 and 1032.42 K, respectively. Their optical responses feature relatively high static dielectric constants and refractive indices, along with pronounced ultraviolet absorption. The transport coefficients are strongly dependent on temperature and chemical potential, as shown by semiclassical Boltzmann transport simulations. At 900 K, the maximum power factors reach 6.9 × 10-3 and 6.6 × 10-3 W m-1 K-2 for CsZrCl3 and CsZrBr3, respectively, when a constant relaxation time of τ = 10-14 s is assumed. The combination of integer magnetic moments, dynamical and mechanical stability, favorable optical characteristics, and thermoelectric performance suggests that CsZrX3 (X = Cl, Br) may be of interest for further investigation as multifunctional lead-free halide perovskites for potential spintronic, optoelectronic, and energy-related applications.

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