The Formation and Motion of Small Polarons

Abstract

In this paper I shall endeavor to qualitatively discuss some essential aspects of the theory of the formation and motion of small polarons. This theory has been developed with the view of applying it to materials which are often classified as low-mobility insulators. T i cally, the mobilities involved are substantially less than 1 cm2 /V-sec.In these circumstances electrical transport is, for the most part, discussed in terms of phonon-assisted hops (tunneling events) rather than in terms of scattering events. Specific situations to which the theory has been applied2 d include ththe motion of holes in the ionic crystals MnO1, NbO2, 2,3 and UO2,4 and the motion of electrons in the molecular crystals orthorhombic sulfur5 (S8) and realgar (AS4S4).6 In addition, the theory may also be applied to noncrystalline systems such as the vanadate glasses. However, the following discussion will be concerned solely with the generic features of the theory of small polarons and not with the detailed application to specific systems.