Effect of Ti concentration on the growth of chemically-ordered regions of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ epitaxial thin films

(1-x)Pb(Mg_1/3Nb_2/3)O₃xPbTiO₃ (PMNPT) (x = 01) epitaxial thin films with high crystallinity have been prepared by using metallo-organic decomposition (MOD) processes at a temperature half of the crystallization temperature of the corresponding bulk crystals. X-ray diffraction patterns show that Ti-poor and Ti-rich PMNPT thin films have perovskite-type structure with a single phase of pseudocubic and/or tetragonal phase, respectively. The morphotropic phase boundary (MPB) is located around x = 0.6. Chemically-ordered regions (CORs), where Mg and Nb ions at B-sites show 1:1 ordered structure in the 111 directions, are clearly detected by using aberration-corrected high angle annular dark field-scanning transmission electron microscopy (HAADFSTEM) images taken along the 110 directions, while it is difficult to analyze the detailed structure of the CORs by the electron or X-ray diffraction methods owing to the small volume. It showed that the density of COR rapidly decreases with increasing the Ti concentration, keeping the size of each COR, which infers that the COR may vanish at the Ti composition less than MPB. STEM analysis around the film/substrate interface shows the elastic interaction between CORs and local strain fields would be weak.