Theoretical insights into lattice dynamics and thermal transport properties of lead-free quadruple halide perovskite Cs4CuSb2Cl12

Abstract

In spite of extensive studies of halide perovskites, little attention has been paid to lattice dynamics and thermal transport properties of halide perovskite Cs₄CuSb₂Cl₁₂ so far. In this work, we systematically investigate the structural, mechanical, and lattice dynamics and thermal transport properties for lead-free quadruple halide perovskite Cs₄CuSb₂Cl₁₂ in the monoclinic phase using state-of-the-art first-principles methods. Scrutiny of the crystal structure reveals that Cs atoms are located inside the over-sized cage-like structure CsCl₁₂, while Cu (Sb) atoms are tightly filled into the octahedral Cu(Sb)Cl₆, expecting a role of atomic rattler for the Cs atoms. We carry out anharmonic lattice dynamics calculations at finite temperature based on self-consistent phonon theory, finding that monoclinic Cs₄CuSb₂Cl₁₂ is dynamically stable at elevated temperature. Moreover, we find that the Cs atomic rattlers result in lattice anharmonicity and severely scatter heat-carrying acoustic and low-energy optical phonons, consequently leading to a low phonon group velocity and extremely short phonon lifetime. We then calculate the temperature-dependent lattice thermal conductivity κ_l of monoclinic Cs₄CuSb₂Cl₁₂ using a unified theory of thermal transport for both crystals and glasses, demonstrating an extremely low κ_l of 0.27, 0.36 and 0.14 W m⁻¹ K⁻¹ at 300 K along x-, y- and z-axes. Moreover, it is found that nano-structuring can further suppress the κ_l by half. Strong lattice anharmonicity is again confirmed from the Grüneisen parameter calculation and temperature dependence of κ_l ∝ T^−0.72. In addition, the elastic constant calculation demonstrates that monoclinic Cs₄CuSb₂Cl₁₂ is mechanically stable with a brittle nature. Our work highlights theoretical insights into the lattice dynamics and thermal transport properties of monoclinic Cs₄CuSb₂Cl₁₂.