PbTiO3 thin films were epitaxially grown on (001) KTaO3 single crystal substrates by metalorganic chemical vapor deposition. The coherent epitaxial growth introduced a large in-plane tensile strain to the PbTiO3 film. This tensile strain increased TC and directed the polarization to one of the in-plane ⟨100⟩ axes below TC, resulting in the formation of perfect a1/a2/a1/a2 domain structure. We found that the polar distortion is appreciably suppressed in such a1/a2/a1/a2 domain structure while TC is enhanced due to the strain.

The authors grew (001)- and (001)∕(100)-oriented epitaxial PbTiO3 films with various thicknesses on (100)SrTiO3 substrates. They used x-ray diffraction to measure the angles between surface normal [001] of (001)-oriented domains and [100] of (100)-oriented domains. The angles were found to be approximately 3.6° when the film thickness exceeded 1100nm. This value is consistent with the value obtained by a geometric calculation for strain-free PbTiO3. This result suggests that thick epitaxial PbTiO3 films grown on (100)SrTiO3 substrates have a fully strain-relaxed structure.

(100)/(001)-oriented tetragonal Pb(Zr,Ti)O3 (PZT) films, which were thicker than 2 µm, were epitaxially grown on SrRuO3-covered (100)Si, (100)KTaO3, (100)SrTiO3, and (100)CaF2 substrates by metal organic chemical vapor deposition. The volume fraction of the (001)-orientation almost linearly increased as the thermal strain increased during the cooling process from the deposition temperature to the Curie temperature. Consequently, perfectly (001)-oriented, i.e., polar-axis-oriented, thick films were obtained on CaF2 substrates with a remanent polarization of 71 µC/cm2. This approach to grow polar-axis-oriented PZT thick films enabled the intrinsic piezoelectricity of PZT itself to be clarified, and has potential in novel applications.

Epitaxial Pb(Zr,Ti)O3 (PZT) thick films of 2.0–3.0 μm thickness were grown at 600 °C on (100)cSrRuO3∥(100)SrTiO3 and (100)cSrRuO3∥(100)LaNiO3∥(100)CaF2 substrates by pulsed-metal organic chemical vapor deposition. All films showed (100) and/or (001) orientations with tetragonal symmetry. It was found that there is an almost linear relationship between the estimated thermal strain from the deposition temperature to the Curie temperature and the volume fraction of (001) orientation in the mixture of (100) and (001) orientations for the films on both substrates. Consequently, the perfectly (001)-oriented, i.e., polar-axis-oriented, PZT thick films were obtained on CaF2 with the Zr/(Zr+Ti) ratio from 0.20 to 0.40. Moreover, the lattice parameter of a- and c-axes and their ratio (c/a) of those polar-axis-oriented films were almost the same as the reported data for the powder, suggesting that the large strain is not remaining in those films. The relative dielectric constant (εr) of the polar-axis-oriented Pb(Zr0.35Ti0.65)O3 thick film on CaF2 was 180 at 1 kHz, which is lower than that of (100)/(001)-oriented thick films on SrTiO3 but almost agrees with the theoretically calculated value for the c-axis of PZT single crystals. Well saturated polarization-electric-field hysteresis loops with a good square shape were observed for the polar-axis-oriented thick films, and the saturation polarization and the coercive field values were 74 μC/cm2 and 64 kV/cm, respectively. These data clearly show that the electrical properties of the polar-axis-oriented epitaxial thick films are similar to the theoretical predictions for PZT single crystals.

(100)/(001)-oriented epitaxial PbTiO3 films thicker than 1 μm were grown on various types of substrates by chemical vapor deposition. The domain structures of these films with different volume fractions of (001) were investigated. Domain structures, consisting of (100)/(001)-oriented domains, were observed regardless of the type of substrate. However, the tilting angles of the a- and c-domains from the surface normal linearly changed with the volume fraction of the (001) orientation. These results suggest that the volume fraction of the (001) orientation is crucial in identifying the domain structure of PbTiO3 thick films.