POLARONS IN TRANSITION-METAL OXIDES

Abstract

The polaron concept is of importance primarily for current carriers in transition-metal oxides which are semiconductors by virtue of added impurities (Li//2O in NiO) or excess metal (e. g. , in TiO//2). The carrier (a hole in NiO, an electron in TiO//2) then moves in a narrow band formed primarily from the d-orbitals of the transition-metal ion. It is thought that the d- orbitals overlap not directly but via the 2p-orbitals of the oxygen, and that the band width may be 0. 1 ev upwards. Large and small polarons discussed. Carrying a charge cloud with it increases the electron effective mass (mp).