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MM: Fachverband Metall- und Materialphysik

MM 21: Transport in Materials: Diffusion, Conduction of Charge or Heat I

MM 21.5: Talk

Tuesday, March 19, 2024, 11:15–11:30, C 264

Role of anharmonicity in the lattice dynamics and thermal transport of different phases of KNbO₃ — •Niloofar Hadaeghi, Chen Shen, and Hongbin Zhang — Institute of Materials Science, Technical University of Darmstadt, Darmstadt, Germany

The KNbO₃ material, with its intriguing properties, has always been considered as a great (lead-free) candidate in the energy storage applications. However, despite the significant interest in its cubic, tetragonal, and orthorhombic phases, investigation of their lattice dynamics and lattice thermal transport have remained challenging, due the unstable phonon modes in the harmonic phonon dispersion bands. Here, utilizing self-consistent phonon theory and compressive sensing techniques, we explore the significant role of quartic anharmonicity in the renormalization of the harmonic interatomic force constants and hardening of the lattice modes in the temperature dependent phonon bands and density of states in the three phases. Moreover, the lattice thermal conductivity (LTC), along with the phonon lifetimes are studied for the three phases. The achieved results are in a good agreement with experimental values, where the lower experimental values are due to the higher different types of scattering related to the poly-crystalline nature in the experiment. For instance, the calculated result at 1000 K is 1.45 W/m.K for the cubic phase, where the experimental value is 1.2 W/m.K. The values of LTC at 300 K are as 4.2 W/m.K for the cubic, 7.3 W/m.K for the tetragonal and 7.8 W/m.K for the orthorhombic phases.

Keywords: Anharmonicity; Lattice dynamics; temperature dependent phonon bands