Crystal structure and microstructure of epitaxial Pb(Zr,Ti)O₃ films consisting of mixed phases with tetragonal and rhombohedral symmetries grown on (100)_cSrRuO₃//(100)SrTiO₃ substrate by metalorganic chemical vapor deposition

(100)-/(001)-oriented epitaxial Pb(Zr,Ti)O₃(PZT) films with various Zr/(Zr + Ti) ratios and film thicknesses were grown on (100)_cSrRuO₃//(100)SrTiO₃substrates at 600 °C by metalorganic chemical vapor deposition. Their crystal structure and microstructure consisting of particularly mixed phases with tetragonal and rhombohedral symmetries were investigated in detail. Films with the mixed phases with tetragonal and rhombohedral symmetries were ascertained at a Zr/(Zr + Ti) ratio of around 0.50 at a thickness of more than 200 nm from x-ray diffraction (XRD) analysis, while no mixed phase region was observed for 50 nm thick film. The relative volume fraction of the tetragonal cdomain decreased with increasing film thickness for 2-μm-thick films with mixed phases, while the tetragonal adomain and rhombohedral domain increased. These mixed phases were ascertained to have originated from the same cubic PZT grown above Curie temperature from results obtained by temperature-dependent high-resolution XRD reciprocal space mapping. The transmission electron microscopy images clearly revealed that the microstructure of the film gradually changed along the film thickness, despite the fact that the film was very uniform. Tetragonal phases were dominant in the bottom region (near the interface with the substrate) of the film, while rhombohedral phase was dominant in the upper region (near the surface), which was also ascertained by cross-sectional Raman analysis. In addition, the tetragonal a/cdomain was wider in the bottom region than that in the upper region of film with mixed phases. These data clearly demonstrate that both the crystal structure and microstructure changed along the film thickness.