Strong growth orientation dependence of strain relaxation in epitaxial (Ba,Sr)TiO3 films and the resulting dielectric properties

Abstract

The growth orientation dependence of strain relaxation and the dielectric properties were investigated for (001)- and (111)-epitaxial (Ba,Sr)TiO3 films. The films were deposited on SrRuO3/SrTiO3 and SrTiO3 substrates using rf magnetron sputtering. The residual strain was found to be remarkably different between the two orientations, although these lattice mismatches are identical; the strain relaxation of the (001)-epitaxial films is significantly slower than that of the (111)-epitaxial films and is promoted only when the growth rate is very low (≤5 nm/h). The observed orientation dependence is discussed with the surface energy for both growth orientations, which influences the growth mode of the films. Due to the large contrast of the strain in the (001)- and (111)-epitaxial films, the paraelectric to ferroelectric phase transition temperature of the (001)-epitaxial films is much higher than that of unstrained bulks, while the (111)-epitaxial films show a phase transition temperature corresponding to that of unstrained bulks regardless of the growth rates.