The microstructure and electrical properties of Ba0.6Sr0.4TiO3 thin films have been investigated. Nanometer-sized domains, ranging from 8 to about 30 nm, were observed by piezoresponse force microscopy (PFM). The critical size, below which only single domains exist, is found to be about 31 nm. The film exhibits ferroelectric behavior characterized by polarization hysteresis loop and capacitance-voltage curve. (c) 2005 Elsevier B.V. All rights reserved.