A crystal chemical approach to superconductivity. II. An analysis of local bond-valence distribution in inorganic compounds

Abstract

A crystal chemical approach to superconductivity based upon a bond-valence sum analysis of inorganic compounds is extended by an analysis of local bond-valence distribution. The notions of stoichiometric and structural valence together with Pauling’s rule of equal distribution of valences among the ligands of a given atom allow to provide a characterization for the strength of bonds which is used to define structurally distinguished bond paths. Combinations of these paths represent infinite units of strongly overlapping orbitals. Such units are assumed to be the conducting units in superconductors. A large number of crystal-structure data determined at ambient temperature and pressure has been analyzed including data of chalcogenides and pnictides as well as cuprates. It is shown that infinite units of strongly overlapping orbitals always exist in compounds which become superconducting on cooling with or without applied pressure and/or by doping. As a consequence, a systematic search for potential unconventional superconductors in inorganic crystallographic databases seems to be promising.