Potential Semiconducting and Superconducting Metastable Si3C Structures under Pressure

Si3C is predicted to take on a diamond type structure (space group: I (4) over bar 2d), at P = 1 atm, consistent with the experimental results on a cubic Si0.75C0.25 alloy. This structure is computed to be a semiconductor with a direct band gap of about 1.3 eV, within the desired values. Under pressure, Si3C may transform to metastable metallic R (3) over barm-2 and R (3) over barm-3 structures at about 2S and 250 GPa, respectively. Both are layered structures with six-coordinate Si and unusual six-coordinate carbon atoms. The R (3) over barm-1 and R (3) over barm-2 structures are both estimated to be superconductors with T-c of a few Kelvin. This is the first time that superconductivity in undoped silicon carbides is calculated.