High-resolution X-ray diffraction reciprocal space mapping (HRXRD-RSM) was applied for the structural characterization of epitaxial BiFeO3 thin film grown on SrRuO3-coated (001) SrTiO3 single crystal substrate with a variety of film thicknesses ranging from 15 to 500 nm. Distinguishing monoclinic structure from rhombohedral or tetragonal structures was accomplished with a set of HRXRD-RSMs measured for several hkl diffraction conditions. The BiFeO3 thin films showed both monoclinic and tetragonal structures depending on film thickness. Tetragonal structure was observed for film thicknesses below 50 nm and was highly strained due to epitaxial strain, while films with film thickness thicker than 50 nm showed monoclinic structure. No BiFeO3 thin films showed bulk rhombohedral structure. This structural change in BiFeO3 thin film may play an important role in the enhanced ferroelectricity observed.
Remanent polarizations (Pr) of 200-nm-thick epitaxial Pb(Zr0.35,Ti0.65)O3 (PZT) thin films deposited on (001), (110), and (111) SrTiO3 (STO) substrates coated with SrRuO3 (SRO) were compared to the domain configurations that were precisely and quantitatively characterized by high-resolution x-ray diffraction reciprocal space mapping (HRXRD-RSM). (001)/(100), (101)/(110), and (111) oriented domains were obtained for films grown on (001), (110), and (111) STO substrates coated with SRO, respectively. HRXRD-RSM showed that the films grown on (001) and (110) STO substrates mainly consisted of (001) and (101) domains, although they also included about 32% and 25% of (100) and (110) domain, respectively. Tilt growths in the domains were found except for the (001) domain. The tilt growths in the (100), (101), and (110) domains were attributed to the geometrically induced tilt by the 90° domain that had {101} domain walls. On the other hand, the tilt in the (111) domain was attributed to the misfit strain relaxation by introducing tilt growth in the domain but not due to the 90° domain. The Pr ratios of films having different domain configurations were well explained by the estimated Pr ratios from the volume fractions of the domains, based on the assumption that the 90° domain was not reoriented by the externally applied electrical field and did not contribute to the measured Pr values. This indicates that the 90° domain is strongly pinned in epitaxial 200-nm-thick PZT films and the 180° domain switching is the dominant contribution to the total remanent polarization.
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.
Two-dimensional X-ray diffraction (XRD 2 ) was applied to the in-plane strain evaluation of the piezoelectric microcantilever fabricated from the (001)-/(100)-oriented Pb(Zr 0:52 ,Ti 0:48 )O 3 film deposited on a (001) c LaNiO 3 /(111) Pt/TiO 2 /SiO 2 /Si/ SiO 2 /(001) Si substrate under the applied voltage. In-plane lattice parameters were estimated using XRD 2 results with two different diffractions originated from PZT, surface normal 002/200 diffractions at ¼ 0 and 45 rotated 101/110 diffractions from surface normal ( ¼ 45 ). The out-of-plane and in-plane lattice parameters were linearly increased and decreased by increasing the applied voltage, regardless of the a-and c-axes. A significant 90 -domain rotation from the a-domain to the cdomain was not observed in the microcantilever. The calculated transverse piezoelectric constants (d 31 ) based on the in-plane strain, curvature, and z-displacement indicated similar values of about À140 AE 10 pm/V. This result shows that the in-plane lattice strain mainly contributed to the displacement of the cantilever.
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