Anharmonicity and Ultra-Low Thermal Conductivity in Lead-Free Halide Double Perovskites

Abstract

The lead-free halide double perovskite class of materials offers a promising venue for resolving issues related to toxicity of Pb and long-term stability of the lead-containing halide perovskites. We present a first-principles study of the lattice vibrations in Cs${}_2$AgBiBr${}_6$ , the prototypical compound in this class, and show that the lattice dynamics of Cs${}_2$AgBiBr${}_6$ is highly anharmonic, largely in regards to tilting of AgBr${}_6$ and BiBr${}_6$ octahedra. Using an energy and temperature dependent phonon spectral function, we then show how the experimentally observed cubic-to-tetragonal phase transformation is caused by the collapse of a soft phonon branch. We finally reveal that the softness and anharmonicity of Cs${}_2$AgBiBr${}_6$ yield an ultra-low thermal conductivity, unexpected of high symmetry cubic structures.

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• Anharmonic lattice dynamics in large thermodynamic ensembles with machine-learning force fields: CsPbBr${}_3$ a phonon-liquid with Cs rattlers
• Role of polyhedron unit in distinct photodynamics of zero-dimensional organic-inorganic hybrid tin halide compounds
• Static and Dynamic Disorder in Formamidinium Lead Bromide Single Crystals
• Thermal Conductivity of CaSiO${}_3$ Perovskite at Lower Mantle Conditions
• Multiple lattice instabilities and complex ground state in Cs${}_2$AgBiBr${}_6$
• Mode-coupling theory of lattice dynamics for classical and quantum crystals
• Ineffectiveness of Formamidine in Suppressing Ultralow Thermal Conductivity in Cubic Hybrid Perovskite FAPbI3
• Unique Hierarchical Rotational Dynamics Induces Ultralow Lattice Thermal Conductivity in Cyanide-bridged Framework Materials
• The thermodynamics of CaSiO3 in Earth's lower mantle
• Local structural disorder in crystalline materials
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