Three-dimensional carbon Archimedean lattices for high-performance electromechanical actuators

We propose three-dimensional carbon (3D-C) structures based on the Archimedean lattices (ALs) by combining $sp^2$ bonding in the polygon edges and $sp^3$ bonding in the polygon vertices. By first-principles calculations, four types of 3D-C ALs: (4, $8^2$), (3, $12^2$), ($6^3$), and ($4^4$) 3D-Cs are predicted to be stable both dynamically and mechanically among 11 possible ALs. Depending on the index of ALs, the 3D-C ALs show distinctive electronic properties: the (4, $8^2$) 3D-C is an indirect bandgap semiconductor, the (3, $12^2$) 3D-C is semimetal, while the ($6^3$) and ($4^4$) 3D-Cs are metals. Considering the structural deformation due to the changes in their electronic energy bands, we discuss the electromechanical properties of the 3D-C ALs as a function of charge doping. We find a semiconductor-to-metal and semimetallic-to-semiconductor transitions in the (4, $8^2$) and (3, $12^2$) 3D-Cs as a function of charge doping, respectively. Moreover, the (3, $12^2$) 3D-C exhibits a $sp^2$-$sp^3$ phase transformation at high charge doping, which leads to a huge 30% irreversible strain, while the reversible strain in the (4, $8^2$) 3D-C is up to 9%, and thus they are quite promising for electromechanical actuators.