Phononic transport in 1T prime-MoTe2: anisotropic structure with an isotropic lattice thermal conductivity

TL;DR

This study uses first-principles calculations to reveal that 1T prime MoTe2 exhibits highly anisotropic structure but nearly isotropic lattice thermal conductivity, influenced by phonon properties and structural factors.

Contribution

It provides the first detailed analysis of phononic transport and thermal conductivity in 1T prime MoTe2, highlighting the role of phonon mean free paths and anisotropic structure.

Findings

1T prime MoTe2 has low and nearly isotropic lattice thermal conductivity (~13 W/mK).

Phonons with mean free paths less than 300 nm contribute to 80% of thermal conductivity.

The material's anisotropic structure results in a lower sound velocity compared to 1H phase.

Abstract

Molybdenum ditelluride (MoTe2) is an unique transition metal dichalcogenide owing to its energetically comparable 1H and 1T prime phases. This implies a high chance of coexistence of 1H-1T prime heterostructures which poses great complexity in the measurement of the intrinsic lattice thermal conductivities (kappa). In this work, via first-principles calculations, we examine the lattice-wave propagation and thermal conduction in this highly structurally anisotropic 1T prime MoTe2. Our calculation shows that the 1T prime phase has a sound velocity of 2.13 km/s (longitudinal acoustic wave), much lower than that of the 1H phase (4.05 km /s), indicating a staggered transmission of lattice waves across the boundary from 1H to 1T prime phase. Interestingly, the highly anisotropic 1T prime MoTe2 shows nearly isotropic and limited kappa_L of 13.02 W/mK, owing to a large Gruneisen parameter of acoustic flexural mode, heavy masses of Mo and Te elements and a low phonon group velocity. Accumulative kappa_L as a function of mean free path (MFP) indicates phonons with MFP less than ~300 nm contribute 80% of kappa_L and an inflection point at ~600 nm. Our results will be critical for understanding of the size dependent kappa_L of nanostructured 1T prime MoTe2.