Theoretical study on superconductivity of metal-intercalated boron carbon compounds

In recent years, two-dimensional (2D) superconducting materials have garnered significant interest due to their unique properties and potential applications. Here, we conducted thermodynamic and dynamic stability studies on 51 metal-intercalated hexagonal boron carbon (h-BC) compounds, and ultimately identified 22 stable compounds. Among these 22 compounds, 18 materials are metals, while the remaining 4 materials include 1 semiconductor ( $$\hbox {MgB}_{2}\hbox {C}_{2}$$ MgB 2 C 2 ) and 3 semimetals ( $$\hbox {TiB}_{2}\hbox {C}_{2}$$ TiB 2 C 2 , $$\hbox {ZrB}_{2}\hbox {C}_{2}$$ ZrB 2 C 2 , and $$\hbox {HfB}_{2}\hbox {C}_{2}$$ HfB 2 C 2 ). The possible superconductivity of eighteen metals is studied by solving the Allen–Dynes modified McMillan equation to estimate their superconducting transition temperature ( $$T_{c}$$ T c ). The highest $$T_{c}$$ T c is observed in $$\hbox {KB}_{2}\hbox {C}_{2}$$ KB 2 C 2 ( $$T_{c}$$ T c = 53.47 K), followed by $$\hbox {NaB}_{2}\hbox {C}_{2}$$ NaB 2 C 2 ( $$T_{c}$$ T c = 48.30 K), while the lowest $$T_{c}$$ T c is in $$\hbox {AlB}_{2}\hbox {C}_{2}$$ AlB 2 C 2 ( $$T_{c}$$ T c = 0.04 K). Due to the high $$T_{c}$$ T c of alkali metal intercalation compounds, this work mainly focuses on them. For alkali metal intercalation compounds, we found that the $$T_{c}$$ T c rises with the increase of the main group atomic number, mainly due to the degree of metalization of the $$\sigma $$ σ -bonding band at the Fermi level. Another important reason is the softening of the phonon spectrum. These findings enrich the family of 2D superconductors, providing new theoretical insights for experimental synthesis and opening research ideas for 2D superconducting electronic devices. Graphical abstract