Domains in Ultrathin Ferroelectric Films with Metallic and Semiconducting Electrodes

Abstract

We discuss ferroelectric phase transitions into single- and multidomain states in very thin films using continuous theory. In a typical case of BaTiO3 film with SrRuO3 electrodes the homogeneous states remains ferroelectric down to 2.5 nm, same thickness as in ab-initio modeling, whereas the actual critical thickness is determined by the existence of the domains that may exist in films just 0.8 nm thick. Nonlinear screening by carriers in semiconducting electrodes could have made the phase transition first order, but this Batra transition in monodomain state does not happen since it is preempted by domain formation. The results do not depend on whether or not the screening carriers may be present in the ferroelectric itself.