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were prepared, and their dielectric properties were studied in a broad range of the measurement conditions. In the ferroelectric state, the presence and the change of configuration of the domains determined both the dynamic dielectric nonlinearity and the polarization hysteresis. In thin-film relaxors, the orientation of the randomly interacting dipoles in a random field was responsible for the dynamic dielectric nonlinearity, while the observed hysteresis was suggested to arise due to connection between the applied field and the relaxation times of both the dipoles and the internal field. In thin-film (Ba,Sr)TiO 3 , the hightemperature dielectric hysteresis was found to be relaxorlike.

Epitaxial multilayers and superlattices of Ba0.8Sr0.2TiO3 and Ba0.4Sr0.6TiO3 were grown by pulsed laser deposition on MgO substrates using a La0.5Sr0.5CoO3 bottom electrode. The epitaxial relations, crystal perfection, and strains were studied by x-ray diffraction at room temperature. Pseudomorphic growth of superlattices was demonstrated for the period as large as 62unit cells. The obtained in-plane strain was consistent with that theoretically expected. Low-frequency functionality was found to depend on strain, period, and amount and quality of interfaces.

Low-frequency dielectric response of epitaxial multilayers and superlattices of Ba 0.8 Sr 0.2 TiO 3 :Ba 0.4 Sr 0.6 TiO 3 with a period 4-500 unit cells grown by pulsed laser deposition on La 0.5 Sr 0.5 CoO 3 / MgO is experimentally studied. The response is analyzed as a function of temperature, frequency, applied field, superlattice period, and epitaxial strain. Analysis reveals diffuse phase transitions with the existence of a glasslike state similar to those in thin-film BaTiO 3 and ͑Ba, Sr͒TiO 3 . The detected evolution of relaxation time spectra with decreasing period is suggested to contribute to the corresponding increase in permittivity. The importance of system dynamics for the analysis of microstructure and polarization in epitaxial superlattices of ͑Ba, Sr͒TiO 3 is discussed.Epitaxial thin-film multilayers and superlattices of BST80/20 and BST40/60 with a La 0.5 Sr 0.5 CoO 3 ͑LSCO͒ bottom electrode layer and a Ba 0.6 Sr 0.4 TiO 3 ͑BST60/40͒ buffer layer were grown on MgO ͑001͒ substrates. 19 The number of

In epitaxial films of perovskite ferroelectrics, functionality can be controlled by size-strain-surface effects. Experimental evidence of such a possibility is demonstrated in epitaxial heterostructures of BaTiO 3 thin films and of (Ba,Sr)TiO 3 superlattices grown by pulsed laser deposition on La 0.5 Sr 0.5 CoO 3 /MgO (001). In epitaxial BaTiO 3 films, temperature of phase transition is shown to be a function of in-plane biaxial strain and film thickness. In epitaxial (Ba,Sr)TiO 3 superlattices, the dielectric permittivity, tunability, and temperature of phase transition are shown to be a function of strain and superlattice period. The technological and principal problems limiting nanoscale engineering of ferroelectric functionality are also discussed.