Temperature dependence of electrical conductivity in systems with large polarons and bipolarons

Conductivity increase with temperature at constant carrier concentration is accustomed in systems of small polarons. We demonstrate it can occur in systems with large (bi)polarons at their transition into delocalized states. Calculated temperature dependence of conductivity demonstrates good consent with experiments on BaTiO3, TiO2, and superconducting cuprates in normal state. (C) 2001 Elsevier Science B.V. All rights reserved.