Effect of Halogen Ions on the Low Thermal Conductivity of Cesium Halide Perovskite

Abstract

The lattice dynamics of CsSnX 3 (X = Cl, Br, and I) and CsPbI 3 , which are low-thermal-conductivity materials, are investigated using first-principles phonon calculations. Because of the strong lattice anharmonicity and the accompanying instability of high-temperature cubic phases, the self-consistent phonon theory, which can incorporate the effect of lattice anharmonicity at a mean-field level, is applied in this study. The calculated lattice thermal conductivity reproduced a low thermal conductivity, as shown experimentally, owing to the short phonon lifetime due to the incoherent scattering contribution of Cs atoms. The halogen ion dependence on thermal conductivity reveals that CsSnCl 3 exhibits an anomalous lattice thermal conductivity that is as low as that of CsSnBr 3 . This indicates that the lattice dynamics cannot be explained merely in terms of the atomic mass of the compounds. The low thermal conductivity of CsSnCl 3 is caused by the exceptionally short phonon lifetime; further, a bonding analysis suggests that covalent bonding contributes significantly to the unusual anharmonicity of CsSnCl 3 .

Pressure effects on the anomalous thermal transport and anharmonic lattice dynamics of CsX (X = Cl, Br, and I)

“…12 It was reported that the k L of CsSnCl 3 is lower than that of CsSnBr 3 , which originates from the short phonon lifetimes in CsSnCl 3 . 13 The k L of CaO was also found to be lower than that of CaS, whereas the k L of CaO exceeds that of CaS under a compressive strain of over 2%. 14 In this work, the anharmonic lattice dynamics of CsX is investigated to elucidate the pressure dependence of k L of CsX, as well as the unexpected higher k L of CsI.…”

“…The third-order force constants were extracted based on the compressive sensing approach using the least absolute shrinkage and selection operator (LASSO) technique, 15,17 which was often used for strongly anharmonic materials. 13,18,19 The third-order force constants were extracted from the following LASSO equation:…”

“…The third-order force constants were extracted based on the compressive sensing approach using the least absolute shrinkage and selection operator (LASSO) technique, 15,17 which was often used for strongly anharmonic materials. 13,18,19 The third-order force constants were extracted from the following LASSO equation:where A and F are the displacement matrix and force vector, respectively. The A − F datasets were obtained by the following procedures: first, ab initio molecular dynamics (AIMD) simulations in the canonical ensemble (NVT) were performed using 4 × 4 × 4 supercells of CsX for 4 ps with a time step of 2 fs at 300 K; then for 40 atomic configurations equally spaced in time, all the atoms were displaced by 0.1 Å in random directions to include anharmonic terms up to the sixth order when fitting Φ ; finally, the atomic forces of these configurations were calculated based on density functional theory (DFT), and the A − F datasets were constructed.…”

Photothermally Enhanced Photoresponse of Bismuth Halide Perovskite by Phonon Scattering

“…As reported, lead-based halide perovskites possess ultra-low thermal conductivities (0.37, 0.51, and 0.73 W m −1 K −1 for MAPbI 3 , 12 MAPbBr 3 , 13 and MAPbCl 3 , 14 respectively) that are closely related to the atomic structure, 15 atomic disorder, crystal anharmonic vibration, crystal structure, and electron pair. 16 The control in thermal conductivity can also be achieved by tuning the proportion of halogens 17 in tin-based perovskites 18 such as CsSnBr 3−X I X , which possesses an ultralow thermal conductivity of 0.32 W m −1 K −1 due to strong phonon scattering. Meanwhile, two-dimensional Ruddlesden− Popper perovskites such as BA 2 MA n−1 Pb n I3 n+1 (n = 1−7) have been demonstrated to alter n to exhibit lower thermal conductivity than MAPbI 3.…”

First-Principles Phonon Quasiparticle Theory Applied to a Strongly Anharmonic Halide Perovskite

“…The first-order self-consistent phonon (SC1) theory is one of the most successful methods, which determines the renormalized phonon frequencies by the variational principle applied to the first-order cumulant expansion of the Helmholtz free energy [16,17]. Since the SC1 theory can, to a large extent, remedy the negative frequency problems of the harmonic approximation, it has been actively employed in first-principles calculations of phononrelated physics of anharmonic materials, including thermal transport [13,[18][19][20][21], phonon-limited mobility [22], bandgap renormalization [23,24], thermal expansion [25,26], and conventional superconductivity [7,12,27]. While these studies clearly demonstrate the advantage of the SC1 theory over the quasiharmonic theory and purely perturbative approaches, the quantitative accuracy of SC1 is still inadequate for strongly anharmonic materials.…”