Ultralow lattice thermal conductivity in type-I Dirac MBene TiB₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• MBenes, a novel class of 2D transition metal borides, are gaining attention.
• Transport studies in these 2D materials are scarce but crucial for understanding their properties.

Purpose of the Study:

• To investigate the layer-dependent electronic and transport properties of the TiB2 MBenes system.
• To explore the impact of layer number on electronic structure, thermal conductivity, and thermoelectric performance.

Main Methods:

• Utilizing Boltzmann transport theory combined with ab-initio density functional theory calculations.
• Examining the electronic band structure, including Dirac cone characteristics.
• Calculating anisotropic room-temperature and high-temperature lattice thermal conductivity.
• Assessing electronic transport coefficients and thermoelectric figure of merit (ZT).

Main Results:

• Monolayer (ML) TiB2 MBenes exhibit a Dirac-semimetallic character, while bilayers (BL) display type-II Weyl metallic behavior due to altered Dirac cones.
• Anisotropic lattice thermal conductivity was observed, with ultralow values at high temperatures attributed to phonon scattering and Dirac states.
• Monolayer TiB2 MBenes show a promising room-temperature thermoelectric figure of merit (ZT) of 1.71, significantly higher than the 0.38 for bilayers.

Conclusions:

• The number of layers critically influences the electronic and transport properties of TiB2 MBenes.
• TiB2 MBenes possess ultralow thermal conductivity, making them suitable for thermoelectric applications.
• Monolayer TiB2 MBenes demonstrate excellent potential for room-temperature thermoelectric energy conversion.