KP15: Natural van der Waals material with ultra-low thermal conductivity and excellent thermoelectric performance

Abstract

Recently, a natural van der Waals material KP15 has been successfully synthesized and reported to possess obvious anisotropy, high carrier mobility, and stable chemical properties. Herein, through combining Boltzmann transport equation and first-principles calculations, we systematically investigate the electronic and phononic transport properties and thermoelectric (TE) performance of KP15. Our calculations show that KP15 exhibits obvious anisotropic lattice thermal conductivity with extremely low intertube thermal conductivity of 1.49 W/mK at room temperature. Such low thermal conductivity is mainly originated from the intrinsic weak intertube interactions and beneficial for the TE performance. Meanwhile, KP15 also hosts evident anisotropic electronic transport properties and relatively high Seebeck coefficients over a wide range of carrier concentrations. Based on the electronic relaxation time obtained from the deformation potential theory, the TE conversion efficiency of KP15 is evaluated, and the thermoelectric figure of merit could approach as high as 1.40 at 700 K along the c-axis under n-type doping. The findings presented in this work indicate that KP15 has extremely low intertube thermal conductivity and excellent TE performance, which will stimulate further experimental exploration of similar alkali metal phosphating systems and more van der Waals materials.