Domain structure of epitaxial PbTio3 thin films: Effects of substrate selection and film thickness

The status of strain relaxation related with the formation of crystallographic twin domains in epitaxial PbTiO3 thin films grown on various substrates such as MgO (001), KTaO3(100), and SrTiO3 (001) was extensively analyzed using synchrotron X-ray diffraction. Each system showed the characteristic domain structures depending on a thermo-elastic interaction between the film and the substrate as reflected in the value of c/a ratio. Perfectly c-axis oriented PbTiO3 films were obtained on SrTiO3 (001) substrates, while the films grown on KTaO3 (100) showed a-domain dominant structures with only a bit amount of c-domains embedded in matrix a-domains. Thickness dependence of the domain structure was also characterized for the films grown on MgO (001), in which degree of c-axis orientation, α, increased as a function of film thickness within a few tens of nm region and exhibited a saturation value of ∼0.75 above a certain critical film thickness.