THE GROWTH-PROCESS AND CERTAIN FERROELECTRIC PROPERTIES OF HETEROEPITAXIAL (BA1-XSRX)TIO3/MGO(001) THIN-FILMS

Heteroepitaxial (Ba0.85Sr0.15)TiO3 and (Ba0.6Sr0.4)TiO3 thin films of thickness from 20 to 1200 nm were obtained on the (001) planes of MgO single crystals of thickness 0.5 mm by the method of r.f. sputtering of stoichiometric targets. Depending on the sputtering conditions, insular or layer-by-layer growth of the heteroepitaxial films was observed. Large planar mechanical stresses (sigma(11) = sigma(22)) act in these thin films owing to the misfit of lattice parameters of the substrate (a(s)) and the thin film (a(f) < a(s); sigma(11)o = sigma(22)o = sigma(o) > 0) and also to the difference in coefficients of thermal expansion of the substrate (lambda(s)) and the thin film (lambda(f) < lambda(s); sigma(11)t = sigma(22)t = sigma(t) < 0). In the case of films of of thickness d(f) less-than-or-equal-to 20 nm tensile stresses are found (sigma(o) > 0), while in films of thickness d(f) > 20 nm compressive stresses occur (sigma(t) < 0). The nature of the domain structure of the thin films and also their dielectric, piezoelectric and electro-optical properties thus depend on the sign of sigma.