Strong Anharmonicity at the Origin of Anomalous Thermal Conductivity in Double Perovskite Cs2 NaYbCl6

Cappai, Antonio

First

Methodology

;Melis, Claudio

Second

Methodology

;Marongiu, Daniela

Methodology

;Quochi, Francesco

Methodology

;Saba, Michele

Methodology

;Congiu, Francesco

Methodology

;He, Yihui;Slade, Tyler J;Kanatzidis, Mercouri G;Colombo, Luciano

Last

Conceptualization

2023-01-01

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Abstract

Anomalous thermal transport of Cs2 NaYbCl6 double-halide perovskite above room temperature is reported and rationalized. Calculations of phonon dispersion relations and scattering rates up to the fourth order in lattice anharmonicity have been conducted to determine their effective dependence on temperature. These findings show that specific phonon group velocities and lifetimes increase if the temperature is raised above 500 K. This, in combination with anharmonicity, provides the microscopic mechanism responsible for the increase in lattice thermal conductivity at high temperatures, contrary to the predictions of phonon transport theories based on solely cubic anharmonicity. The model accurately and quantitatively reproduces the experimental thermal conductivity data as a function of temperature.