  S-band metals such as alkali and alkaline earth metals do not undergo a
superconducting transition (SCT) at an ambient pressure, but their
high-pressure phases do. In contrast, room temperature stable electride
electride (C12A7:e-) in which anionic electrons in the crystallographic
sub-nanometer-size cages have high s-character exhibits SCT at 0.2-0.4K at an
ambient pressure. In this paper we report that crystal and electronic structure
of C12A7:e- are close to those of the high pressure superconducting phase of
alkali and alkaline earth metals and the SCT of both materials is induced when
electron nature at Fermi energy (EF) switches from s- to sd-hybridized state.
