a- and b-axis-oriented (Bi3.25Nd0.75− x Eu x )Ti3O12 (BNEuT, x = 0–0.75) films of 3.0 µm thickness were fabricated on conductive Nb:TiO2(101) substrates containing 0.79 mass % Nb by high-temperature sputtering at 650 °C, and their structural and piezoelectric characteristics were investigated. The room-temperature remanent polarization (2P r) and effective piezoelectric coefficient (d 33) values for the BNEuT films exhibited maxima of 87 µC/cm2 and 15 pm/V, respectively, at x = 0.10, which were approximately 1.3 times larger than those (2P r = 65 µC/cm2 and d 33 = 12 pm/V) of the nondoped (Bi3.25Nd0.75)Ti3O12 (BNT) nanoplate. The BNEuT film with x = 0.10 had a high a-axis orientation judging from the X-ray diffraction measurement and the observation of the phase image by piezoresponse force microscopy. It is shown that adequate Eu3+ doping of BNT nanoplates produces a larger displacement magnitude of the octahedra than that in the nondoped BNT nanoplate, resulting in an improvement of piezoelectric properties in addition to the ferroelectricity.

a- and b-axis-oriented (Bi3.25Nd0.75 - x Eu x )Ti3O12 (BNEuT, x = 0–0.75) films of 3.0 µm thickness were fabricated on conductive Nb:TiO2(101) substrates containing 0.79 mass % Nb by high-temperature sputtering at 650 °C, and their structural and ferroelectric characteristics were investigated. All the films had a mostly single-phase orthorhombic structure, with high degrees of a- and b-axis orientations of 99.0–99.8%. The lattice parameters (a-, b-, and c-axis lengths) and the calculated orthorhombic lattice distortion decreased monotonically with increasing Eu content. The microstructure of BNEuT films with x = 0–0.50 was nanoplate-like, whereas that of films with x≥0.60 was significantly more bulk-like. The real room-temperature remanent polarization (2P r *), taking the porosity between the nanoplates into account, had a maximum value of 2P r * = 87 µC/cm2 at x = 0.10, which was approximately 1.3 times larger than that (65 µC/cm2) of the nondoped BNT film. It is shown that lattice distortion caused by rotation of octahedra in the a–b plane due to the Eu substitution plays a significant role in the improvement of ferroelectricity.

Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (BNEuT-0.1) films with a-and b-axis orientations and thicknesses of 1.8-2.3 µm were sputter-deposited on conductive Nb:TiO 2 (101) substrates containing 0.79 mass % Nb. The deposition temperature was fixed at 650 °C, and the sputtering gas pressure was varied from 0.4 to 5.0 Pa in order to examine its effect on the structural, ferroelectric and piezoelectric properties of the films. The films were found to have a mostly single-phase orthorhombic structure, with a high degree of a-and b-axis orientations (93-98%). The films had a nanoplate microstructure, with the plates being aligned along the [100]/[010] direction, and porosities of 15-25%. A maximum room-temperature remanent polarization (2P r ) of 93 µC/cm 2 was obtained for a sputtering gas pressure of 5.0 Pa. All the films were strongly a-axis oriented, according to the results of X-ray diffraction measurements and vertical amplitude images in piezoresponse force microscopy. The optimal sputtering gas pressure for heteroepitaxial growth of BNEuT-0.1 nanoplates with a high degree of a-axis orientation of 96.5%, a maximum orthorhombicity of 0.0017, a comparatively large remanent polarization of 2P r = 66 µC/cm 2 , and a high porosity of 24% was found to be 0.4 Pa.

Sr 2 Bi 4 Ti 5 O 18 (SBTO) films with a-and b-axis orientations, and thicknesses of 0.9-1.2 µm were sputter-deposited on conductive Nb:TiO 2 (101) substrates containing 0.79 mass % Nb. The deposition temperature was varied from 575 to 700 °C under a fixed gas pressure of 0.4 Pa, and the structural and ferroelectric characteristics of the films were investigated. SBTO films deposited at 625-700 °C had a mostly single-phase orthorhombic structure, with a high degree of a-and b-axis orientations [α (h00)/(0k0) ] of 99.0-99.8%. In addition, the full width at half maximum of the (200) diffraction peak was 0.69-0.86°, which indicated good crystallinity. SBTO films deposited at 625-650 °C had a nanoplate-like microstructure with the plates aligned along the [010] direction. The real room-temperature remanent polarization ð2P Ã r Þ, taking the porosity between the nanoplates into account, exhibited a maximum of 40 µC/cm 2 at 650 °C. Thus, the optimal deposition temperature for heteroepitaxial growth of SBTO nanoplates with a high α (h00)/(0k0) of ;99.0% and excellent ferroelectric properties on conductive Nb:TiO 2 substrates is 650 °C under a gas pressure of 0.4 Pa.