Remarkable decrease in lattice thermal conductivity of transition metals borides TiBby dimensional reduction.

Two-dimensional transition metals borides TiBhave excellent magnetic and electronic properties and great potential in metal-ion batteries and energy storage. The thermal management is important for the safety and stability in these applications. We investigated the lattice dynamical and thermal transport properties of bulk-TiBand its two-dimensional (2D) counterparts based on density functional theory combined with solving phonon Boltzmann transport equation. The Poisson's ratio of bulk-TiBis positive while it changes to negative for monolayer TiB. We found that dimension reduction can cause the room-temperature in-plane lattice thermal conductivity decrease, which is opposite the trend of MoS, MoSe, WSeand SnSe. Additionally, the room temperature thermal conductivity of mono-TiBis only one sixth of that for bulk-TiB. It is attributed to the higher Debye temperature and stronger bonding stiffness in bulk-TiB. The bulk-TiBhas higher phonon group velocity and weaker anharmonic effect comparing with its 2D counterparts. On the other hand, the room temperature lattice thermal conductivity of mono-TiBis two times higher than that of mono-TiB, which is due to three-phonon selection rule caused by the horizontal mirror symmetry.