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Ultralow Thermal Conductivity in Chain-like TlSe Due to Inherent Tl+ Rattling
journal contribution
posted on 2019-12-13, 20:44 authored by Moinak Dutta, Shidaling Matteppanavar, Matukumilli V.
D. Prasad, Juhi Pandey, Avinash Warankar, Pankaj Mandal, Ajay Soni, Umesh V. Waghmare, Kanishka BiswasUnderstanding the mechanism that correlates phonon transport
with
chemical bonding and solid-state structure is the key to envisage
and develop materials with ultralow thermal conductivity, which are
essential for efficient thermoelectrics and thermal barrier coatings.
We synthesized thallium selenide (TlSe), which is comprised of intertwined
stiff and weakly bonded substructures and exhibits intrinsically ultralow
lattice thermal conductivity (κL) of 0.62–0.4
W/mK in the range 295–525 K. Ultralow κL of
TlSe is a result of its low energy optical phonon modes which strongly
interact with the heat carrying acoustic phonons. Low energy optical
phonons of TlSe are associated with the intrinsic rattler-like vibration
of Tl+ cations in the cage constructed by the chains of
(TlSe2)nn–, as evident in low
temperature heat capacity, terahertz time-domain spectroscopy, and
temperature dependent Raman spectroscopy. Density functional theoretical
analysis reveals the bonding hierarchy in TlSe which involves ionic
interaction in Tl+–Se while Tl3+–Se
bonds are covalent, which causes significant lattice anharmonicity
and intrinsic rattler-like low energy vibrations of Tl+, resulting in ultralow κL.