TITLE : Glass-like Thermal Conductivity in Single Crystal of Layered Metal Halides

ABSTRACT :

As the periodic atomic arrangement of a crystal is made to a disorder or glassy-amorphous system by destroying the long-range order, the value of lattice thermal conductivity, kL, decreases, and its fundamental characteristics change. Disordered atomic arrangement severely limits the phonon mean free path in a material, however, it can also have a deteriorating effect on the charge carrier transport. Therefore, the realization of ultralow and unusual glass-like kL in a crystalline material is challenging but it holds the key to many applications like in thermoelectricity, thermal barrier coatings and hot phonon bottleneck in optoelectronics.[1, 2] Herein, I will be talking about achieving an ultralow value (~0.20 W/m.K at room temperature) and unusual glass-like temperature dependence (2-400 K range) of kL in a large single crystal of layered halide perovskite. Soft acoustic phonons with low cut-off frequency (20 cm-1) are responsible for the low sound velocity in layered halide and makes the structure elastically soft with low bulk and shear moduli. While a strong anharmonicity originates from the low energy and localized rattling-like vibration of Cs atoms, synchrotron X-ray pair-distribution function analysis evidences the presence of a local structural distortion in the Bi-halide octahedra. We have proposed that the hierarchical chemical bonding and low energy vibrations, from selective sublattice in the crystalline inorganic halide perovskites, open an exciting platform for thermal transport research, which is intriguing from lattice dynamical aspects as well as have potential applications.

MEETING DETAILS :

Speaker: Prof. Kanishka Biswas

Venue: A1-NKN

Date and Time: May 5th, 2022, 12:00 PM