Chemical nature of colossal dielectric constant of CaCu3Ti4O12 thin film by pulsed laser deposition

Epitaxial CaCu(3)Ti(4)O(12) thin films grown by pulsed laser deposition were studied in the as-deposited and oxygen annealed state. The first one exhibited the usual transition from dielectric to colossal dielectric behavior upon increasing the temperature to above 100 K. This transition disappeared after annealing at 900 degrees C in air. The two states significantly differ in their x-ray photoelectron spectra. The state of colossal dielectric constant corresponds to a bulk material with considerable amounts of Cu(+) and Ti(3+), combined with Cu species enrichment at the surface. The annealed state exhibited a nearly stoichiometric composition with no Cu(+) and Ti(3+). The previously observed p-type conduction in the as-deposited state is thus related to oxygen vacancies compensated by the point defects of Cu(+) and Ti(3+). (c) 2008 American Institute of Physics.