Electronic properties of new Ca(Al$_x$Si$_{1-x})_2$ and Sr(Ga$_x$Si$_{1-x})_2$ superconductors in crystalline and nanotubular states

The band structure of new layered (AlB$_2$ type) Ca(Al$_x$Si$_{1-x})_2$ and Sr(Ga$_x$Si$_{1-x})_2$ superconductors is studied by the first-principle full-potential LMTO method. It has been shown that the superconducting properties of ternary silicides are due to the high density of (Ca,Sr)d states at the Fermi level, whereas the growth of $T_C$ in going from Sr(Ga$_x$Si$_{1-x})_2$ to Ca(Al$_x$Si$_{1-x})_2$ is associated with the increase in phonon frequencies due to the decrease in atomic masses. Simulations are performed for the electronic properties of hypothetical $(11,11)$ and $(20,0)$ CaAlSi and SrGaSi nanotubes. In going from the crystalline to the nanotubular state, the silicide systems retain metal-like properties. The template and «film rolling» techniques can be used for obtaining silicide nanotubes.