Interpretation of the semiconducting and metallic phases in the sodium titanium bronze Na1–xTi4O8

Abstract

AbstractThe electron transfer process is systematically examined in Na1–xTi4O8 as a direct consequence of cation‐anion orbital overlaps. The critical interatomic distance below which the overlap occurs is presumed to be nearly 0.195 nm. On the basis of distortions present in the octahedra of the host lattice, it is shown that molecular‐type orbitals can be imagined in the semiconducting state orthogonally to the infinite chains of octahedra. In the metallic state two infinite ‐TiO‐ chains with transverse correlations are considered as conveying the collective d‐electrons. The occurrence of a Peierls distortion is discussed and excluded. An additional deformation modulation of Ti atoms is proposed, triggered by the fundamental modulation of the interstitial site occupation. The model can describe, in terms of molecular‐type orbitals, the electrical and magnetic behaviour with varying temperature and Na content.