| Abstrakt: |
The possible emergence of superconductivity in layered metal boride carbide compounds MB2C2(M = Sc, Y, Be, Ca) was investigated using density functional theory calculations upon the topology of a boron–carbon network and the nature of the metal. ScB2C2and YB2C2show metallic and superconductive properties with low critical temperatures (Tcs). The semiconducting BeB2C2compound may show superconductivity upon carrier doping with a high Tcof 47.8 K by hole doping─comparable to the structurally related MgB2superconductor─but with a low Tcby electron doping. In contrast, the semiconducting CaB2C2compound is predicted to be a superconductor by hole and electron doping but with low Tcs. These differences arise from the spatial distribution of electrons at the Fermi level. For compounds with low Tcs, electrons at the Fermi level are localized primarily on B and C π states perpendicular to the BC layers, experiencing minimal influence from atomic oscillations and resulting in weak electron–phonon interactions. Conversely, for a high Tc, electrons are found in σ-bonding states, leading to strong electron–phonon interactions. Electrons at the Fermi level in boron–carbon σ-bonding states seem to be a prerequisite to expect high Tcsuperconductivity in this kind of compound. |
