The Hume-Rothery electron concentration rule studied through interference phenomena in a series of cP12 compounds with either a true gap or pseudogap across the Fermi level

Abstract

ABSTRACTAmong binary MX2-type cP12 compounds with space group , there are many compounds with either a true gap or pseudogap at the Fermi level. They are grouped into two with respect to the total valence electrons per atom (VEC), the first being at 14/3, while the second at 20/3. The ratio of the number of itinerant valence electrons per atom e/a over VEC is used as a measure to evaluate a drastic change in the electronic structure from the nearly free electron-like to the tight binding-like. The Full-potential Linearized Augmented Plane Wave (FLAPW) band calculations were performed to study to what extent the value of e/a can be well defined. We claim that the Hume-Rothery electron concentration rule holds for As2Si, P2Si and MgTe2, where the ratio above is higher than 90%. For compounds with M = Fe, Ru and Os and X = S, Se and Te, where the ratio is between 60 and 70%, the discussion based on a large Brillouin zone is still meaningful but the validity of Hume-Rothery electron concentration rule is judged to be marginal. The value of e/a is lowered below 20% and the Hume-Rothery electron concentration rule fails in MgO2 and O2Os.