Polaron relaxation and non-ohmic behavior in CaCu3Ti4O12 ceramics with different cooling methods

Structure, defects, non-ohmic behavior and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics with furnace-cooled and water-quenched methods have been systemically investigated. Cooling methods make an influence on reoxidation process and cause changes of electric properties in grains and at grain boundaries. SEM–EDS provides detailed imaging information about Cu-rich phase on the fracture of CCTO ceramics which is explained by the reoxidation reaction during cooling. Morphologies of the water-quenched sample show very small grains floating in bigger grains; whereas they reveal that many grains are surrounded by an exfoliated sheet of Cu-rich phases in the furnace-cooled sample. The polaron relaxation associated with Ti3+ ions and oxygen vacancies occurs at low temperatures, and more Ti3+ ions are remained in the water-quenched sample. The Schottky barrier height (I–V, non-ohmic behavior) associated with the reoxidation of grain boundaries can be modified by cooling method.