Clathrate structure of YB3C3 for high-performance thermoelectrics with superior mechanical properties

Exploring high-performance thermoelectric materials with improved mechanical properties is important for broadening the application scope and the assembly requirement of stable devices. This work presents an effective strategy to discover hard thermoelectric material by inserting foreign atoms in the rigid covalent framework. We demonstrate this in boron-carbon clathrate VII structure, showing a promising candidate for highly efficient thermoelectric energy conversion, especially with Y atom filled in the cage, with a peak zT of 0.73 at 1,000 K. The ab initio calculations indicate that YB3C3 system has low lattice thermal conductivity of 4.5 W/(m·K) at 1,000 K due to the strong rattling of encaged Y atom. The strongly covalent framework provides highly degenerate band structures consisting of heavy and light electron pockets, which can maintain high carrier mobility arising from small effective mass and thus large group velocity. Consequently, high power factor can be achieved in YB3C3 for both electron and hole doping. In addition, it exhibits well mechanical properties and a Vickers hardness of 23.7 GPa because of the strong covalent boron-carbon framework. This work provides a novel avenue for the search of high-performance thermoelectric materials with excellent mechanical properties, based on boron-carbon clathrate structure.