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Recently, in ferroelectric materials, there have been many experimental efforts to find out more intriguing topological objects and their functionalities, such as conduction property. Here we investigated ferroelectric domain structures and related topological defects in the (111)-oriented epitaxial tetragonal PbZr0.35Ti0.65O3 thin film. Systematic piezoresponse force microscopy measurements revealed that the field-induced polarization switching can form thermodynamically stable superdomain structures composed of nano-sized stripe subdomains. Within such superdomain structures, we observed the exotic equilateral triangular in-plane flux-closure domains composed of three stripe domain bundles with 120/120/120 degrees of separation. The conductive-atomic force microscopy measurements under vacuum showed that some vertices have significantly higher conductivity compared to other surrounding regions. This work highlights electric field-driven polarization switching and unique crystallographic symmetry (here, three-fold rotational symmetry) can generate exotic ferroelectric domain structures and functional topological defects, such as conductive vertices.

A 30-nm-thick epitaxial tetragonal (100)/(001) Pb(Zr0.22Ti0.78)O3 (PZT) thin film was grown at 600 °C on (001) KTaO3 (KTO) single-crystal substrate by metalorganic chemical vapor deposition. The a/c domain structure in the PZT film was analyzed in detail at room temperature by synchrotron x-ray diffraction (XRD) and piezoresponse force microscopy techniques. The temperature dependence of the crystal structure was investigated by XRD reciprocal space mapping and in-plane grazing incidence XRD. The PZT films were grown on KTO substrates under compressive strains from 700 °C to room temperature. This compressive strain gave rise to a perfect (001) orientation below a Curie temperature (TC) of ∼520 °C. An in-plane a-axis lattice parameter for the c domain kept the same value as that of the substrate lattice up to 350 °C despite the ferroelectric transition. Nucleation of the a domain started at around 350 °C. The formation of the a domain released the strain for the in-plane a-axis lattice parameter, as confirmed by in-plane analysis of the crystal structure. The results revealed that the in-plane average surface area of the PZT unit cell continued to match that of the KTaO3 substrate from 700 °C to room temperature, regardless of the domain structure evolution.

The electric field–temperature phase diagrams of three bismuth sodium titanate-based relaxor ferroelectrics are reported, namely 0.94(Na1/2Bi1/2TiO3)–0.06(BaTiO3), 0.80(Na1/2Bi1/2TiO3)–0.20(K1/2Bi1/2TiO3) and 0.75(Na1/2Bi1/2TiO3)–0.25(SrTiO3). Relaxor behavior is demonstrated by temperature-dependent dielectric permittivity measurements in the unpoled and poled states, as well as by the field-induced phase transition into a ferroelectric phase from the relaxor phase. From temperature-dependent thermometry measurements, we identified the threshold electric field to induce the ferroelectric phase and obtained the released latent heat of the phase transition. We determined the nonergodic and ergodic relaxor phase temperature range based on the absence or presence of reversibility of the relaxor to ferroelectric transition. For all three compositions, the electric field–temperature phase diagram was constructed and a critical point was identified. The constructed electric field–temperature phase diagrams are useful to find optimum operational ranges of ferroelectrics and relaxors for electromechanical and electrocaloric applications.

Reversible electric-field induced domain switching in ferroelectric thin films gives rise to a large electromechanical coupling. Despite extensive in situ studies confirming a dominant contribution from domain switching, the speed of the domain wall motion had not been discussed enough. In this study, we performed time-resolved measurement of lattice elongation and non-180\ifmmode^\circ\else\textdegree\fi{} domain switching for an epitaxial rhombohedral $(111)/(11\overline{1})$-oriented ($\mathrm{Pb}(\mathrm{Z}{\mathrm{r}}_{0.65}\mathrm{T}{\mathrm{i}}_{0.35}){\mathrm{O}}_{3}$ film under nanosecond electric field pulses by means of synchrotron x-ray diffraction. Both lattice elongation and non-180\ifmmode^\circ\else\textdegree\fi{} domain switching due to a 200-ns electric pulse were directly observed from the shift of the 222 diffraction position toward a lower angle and the change in the integrated intensity ratio of 222 to $22\overline{2}$ peaks, respectively. The non-180\ifmmode^\circ\else\textdegree\fi{} domain switching also results in an increase of the switchable polarization. Following the removal of the electric field, it is seen that the non-180\ifmmode^\circ\else\textdegree\fi{} domain back switching from 222 to $22\overline{2}$ is sluggish compared to the relaxation of the field-induced lattice strain. This is different from the (100)/(001)-oriented tetragonal epitaxial $\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_{3}$ films, in which no obvious delay was detected. These results show the importance of the direct time-resolved response observation of the crystal structure change with the application of a high-speed electric pulse field to understand the frequency dispersion of the ferroelectric and piezoelectric responses of $\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_{3}$ films.

Ferroelastic domain switching significantly affects piezoelectric properties in ferroelectric materials. The ferroelastic domain switching and the lattice deformation of both a-domains and c-domains under an applied electric field were investigated using in-situ synchrotron X-ray diffraction in conjunction with a high-speed pulse generator set up for epitaxial (100)/(001)-oriented tetragonal Pb(Zr0.4Ti0.6)O3 (PZT) films grown on (100) c SrRuO3//(100)KTaO3 substrates. The 004 peak (c-domain) position shifts to a lower 2θ angle, which demonstrates the elongation of the c-axis lattice parameter of the c-domain under an applied electric field. In contrast, the 400 peak (a-domain) shifts in the opposite direction (higher angle), thus indicating a decrease in the a-axis lattice parameter of the a-domain. 90° domain switching from (100) to (001) orientations (from a-domain to c-domain) was observed by a change in the intensities of the 400 and 004 diffraction peaks by applying a high-speed pulsed electric field 200 ns in width. This change also accompanied a tilt in the angles of each domain from the substrate surface normal direction. This behaviour proved that the 90° domain switched within 40 ns under a high-speed pulsed electric field. Direct observation of such high-speed switching opens the way to design piezo-MEMS devices for high-frequency operation.

The temperature evolution of polar order in an A-site complex perovskite (Bi1/2K1/2)TiO3 (BKT) has been investigated by measurements of dielectric permittivity, depolarization current, and stress-stain curves at elevated temperatures. Upon cooling from high temperatures, BKT first enters a relaxor state and then spontaneously transforms into a ferroelectric state. The analyses of temperature and frequency dependence of permittivity have revealed that polar nanoregions of the relaxor phase appear at temperatures higher than 560 ◦C, and also that their freezing at 296 ◦C triggers the spontaneous relaxor-ferroelectric transition.We discuss the key factors determining the development of long-range polar order in A-site complex perovskites through a comparison with the relaxor (Bi1/2Na1/2)TiO3. We also show that application of biasing electric fields and compressive stresses to BKT favors its ferroelectric phase, resulting in a significant shift of the relaxor-ferroelectric transition temperature towards higher temperatures. Based on the obtained results, electric field-temperature and stress-temperature phase diagrams are firstly determined for BKT.

The microstructure of an epitaxial PbTiO3 thick film was investigated by using transmission electron microscopy (TEM). An analysis of bright-field TEM (BFTEM) images revealed the existence of displacements along the [00 direction of PbTiO3. High-resolution TEM (HRTEM) observation indicated that stacking faults parallel to the (001) plane of PbTiO3 are formed in the thick film. Local strain fields around the stacking faults were quantified by geometric phase analysis of the HRTEM image. The measured strain suggested the presence of a pair of extrinsic and intrinsic stacking faults. The distance between an extrinsic stacking fault and an intrinsic one corresponds to two unit cells along the [00 direction of PbTiO3. The formation of these stacking faults is considered to be associated with the strain relaxation of the film.

Changes in crystal structure and ferroelectric properties are investigated for (100)/(001)-oriented epitaxial PbTiO3 thin films grown on CaF2 substrates by metal organic chemical vapor deposition. In this work, PbTiO3 films, with thickness ranging from 60 to 2000 nm, presented volume fraction of (001)-oriented c-domain higher than 90%. Hence, the residual strain is smaller compared to films deposited on widely investigated SrTiO3 substrates. Additionally, more than 60 μC/cm2 remnant polarization is obtained for all film thickness ranges, and the estimated spontaneous polarization taking into account c-domain volume fraction is about 80 μC/cm2 regardless of film thickness, in good agreement with reported values for the single crystal.

The growth mechanism of large-size domains in PbTiO3/SrTiO3 heteroepitaxial thin films was examined using annular bright field (ABF) – scanning transmission electron microscopy and geometric phase analysis (GPA). {101} domain walls surrounded 90° domains. The large 90° domain grows by the coalescence of the nano-size domains of less than 5 nm width. A strain map obtained from the GPA of ABF-STEM image showed that 90° domains interacted elastically and attractively with edge dislocations at PbTiO3/SrTiO3 interface through simple shear strain.

The nonlinear response of a ferroic to an applied fi eld has been studied through the phenomenological Rayleigh Law for over a hundred years. Yet, despite this, the fundamental physical mechanisms at the nanoscale that lead to macroscopic Rayleigh behavior have remained largely elusive, and experimental evidence at small length scales is limited. Here, it is shown using a combination of scanning probe techniques and phase fi eld modeling, that nanoscale piezoelectric response in prototypical Pb(Zr,Ti)O 3 fi lms appears to follow a distinctly non-Rayleigh regime. Through statistical analysis, it is found that an averaging of local responses can lead directly to Rayleigh-like behavior of the strain on a macroscale. Phase-fi eld modeling confi rms the twist of the ferroelastic interface is key in enhancing piezoelectric response. The studies shed light on the nanoscale origins of nonlinear behavior in disordered ferroics.

Raman scattering spectra and ferroelectric properties of epitaxial tetragonal Pb(Zr, Ti)O3 were investigated for polar axis-oriented thin films with various Zr/(Zr + Ti) ratios and by changing the ratios from 0 to 0.50 at different measurement temperatures. The chosen films in the thickness range of 1–2 μm present the advantage of showing small residual strain. The E (TO) modes were successfully isolated using cross-polarization configurations, while A1 (TO) and B1 modes were activated using parallel polarization configurations. Systematic changes in Raman peak positions were observed with changes in the Zr/(Zr + Ti) ratios at different measurement temperatures. It was found in both cases that the tetragonal distortion (c/a-1) and the value of square of spontaneous polarization (Ps2) linearly increased with increasing ω2[A1(1TO)], where a and c are the lattice parameters of a and c-axes. This indicates that monitoring A1(1TO) mode is efficient as a characterization method of ferroelectricity. It can also be used as a novel nondestructive process check or reliability assessment technique during fabrication of microelectromechanical systems (MEMS) using piezoelectric materials.

The ferroelectric domain structure of PbTiO3(PTO) films was investigated by using transmission electron microscopy (TEM). In the film with PTO/SrTiO3(STO) structure, 180º domains are formed near the SrTiO3(STO) substrate and the domain length of 180º domains is 100 nm. However, 180º domains are not formed in the film with Pt/PTO/SrRuO3(SRO)/STO structure. These results show that 180º domains are formed in order to minimize depolarizing field energy, and that the domain length of 180º domains is determined by the competition among the depolarizing field energy, domain wall energy, Coulomb interaction and elastic interaction.

Epitaxial (La0.07Sr0.93)SnO3 [LSSO] films were deposited on CaF2 substrates by pulse laser deposition. The (1 0 0)c orientation of LSSO films was observed only on (1 1 0)CaF2, whereas (1 1 0)c orientation was found on (1 1 1)CaF2 and (1 0 0)CaF2. (0 0 1) polar axis oriented tetragonal Pb(Zr0.35Ti0.65)O3 films were grown on the fabricated (1 0 0)cLSSO∥(1 1 0)CaF2 by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr0.35Ti0.65)O3∥(1 0 0)cLSSO∥(1 1 0)CaF2 stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm.

(100)-epitaxial SrTiO3 thin films having biaxial compressive strains up to -1.60% were grown on lattice mismatched substrates. Two phase transitions induced by the coupled instabilities (antiferrodistortive and ferroelectric) in SrTiO3 were revealed in a common set of samples investigated at temperatures from 8 to 600 K by CuK alpha and synchrotron x-ray diffractions and by UV-Raman spectroscopy. It is shown that the in-plane compressive strain in SrTiO3 significantly increases the transition temperature between cubic and tetragonal-antiferrodistortive phases and furthermore precipitates a ferroelectric polar phase at lower temperatures. The strain-temperature phase diagram based on the measurements shows a cubic-to-antiferrodistortive transition temperature that is substantially higher than predicted within a phenomenological Landau-Ginsburg-Devonshire treatment. In contrast the transition to the ferroelectric polar phase is found to be close to the temperature predicted, with the consequence that there is no crossing of the two phase transitions for temperatures up to 600 K.

Giant electromechanical response viaferroelastic domain switching is achieved in epitaxial (001) ferroelectric tetragonal (T) PbZr0.3Ti0.7O3/rhombohedral (R) PbZr0.55Ti0.45O3 bilayers, grown on La0.67Sr0.33MnO3 buffered SrTiO3 substrates. X-ray diffraction and transmission electron microscopy show that the domain structure of the T films is tuned as a function of its thickness, from a fully a1/a2-domains (30 nm thick T layer) to a three domain stress-free c/a1/c/a2 polytwin state (100 nm thick T layer). A large switchable polarization is found up to 65 μC cm−2. Quantitative piezoelectric force microscopy reveals enhanced piezoelectric coefficients, with d33 coefficients ranging from 250 to 350 pm V−1, which is up to seven times higher than the nominal PbZrxTi1−xO3 thin film values. These are attributed to the motion of nanoscale ferroelastic domains. Fatigue testing proves that these domains are reversible and repeatable up to 107 cycles. In-situ X-ray synchrotron measurements reveal that the ferroelastic domain switching is promoted by a pulsating strain effect imposed by the R layer. The study reports a fundamental understanding of the origin of giant piezoelectric coefficients in epitaxial ferroelectric bilayers.

(100)/(001)-oriented epitaxial lead titanate (PbTiO3) films with various thicknesses were grown on (100) KTaO3 substrates by pulsed metal–organic chemical vapor deposition. The change of crystal structure with film thickness and deposition temperature was investigated. The paraelectric phase of 50 and 1000 nm-thick films had a tensile strain of 0.5% and almost 0% at 700 °C, respectively. The phase change temperature from the paraelectric phase to the ferroelectric phase, the Curie temperature (Tc), increased with the in-plane strain of the paraelectric phase; that is, Tc increased with decreasing film thickness. In contrast, room-temperature tetragonal distortion decreased as the film became thinner. This study reveals the effect of in-plane tensile strain in (100)/(001)-oriented epitaxial PbTiO3 films with higher Tc and smaller tetragonal distortion at room temperature.

Understanding the dynamic behavior of interfaces in ferroic materials is an important field of research with widespread practical implications, as the motion of domain walls and phase boundaries are associated with substantial increases in dielectric and piezoelectric effects. Although commonly studied in the macroscopic regime, the local dynamics of interfaces have received less attention, with most studies limited to domain growth and/or reversal by piezoresponse force microscopy (PFM). Here, spatial mapping of local domain wall-related relaxation in a tensile-strained PbTiO3 thin film using time-resolved band-excitation PFM is demonstrated, which allows exploring of the field-induced strain (piezoresponse) as a function of applied voltage and time. Through multivariate statistical analysis on the resultant 4-dimensional dataset (x,y,V,t) with functional fitting, it is determined that the relaxation is strongly correleated with the distance to the domain walls, and varies based on the type of domain wall present in the probed volume. Phase-field modeling shows the relaxation behavior near and away from the interfaces, and confirms the modulation of the z-component of polarization by wall motion, yielding the observed piezoresponse relaxation. These studies shed light on the local dynamics of interfaces in ferroelectric thin films, and are therefore important for the design of ferroelectric-based components in microelectromechanical systems.

Epitaxial rhombohedral Pb(Zr0.65Ti0.35)O3films with (100) and (110)/(10-1) and (111)/(11-1) orientations were grown on various kinds of singlecrystal substrates having different thermal expansion coefficient. Volume fractions of (110) and (111) orientations in respective (110)/(10-1) and (111)/(11-1)-oriented films were almost linearly increased with increasing thermal strain, εthermal, applied to the films that wasgenerated under the cooling process after the deposition from the growth temperature to the Curie temperature.Observed saturationpolarization (Psat)was changed linearly with the volume fractions of (110) and (111) orientations, in the same manner asthe volume fractions of (001) and (101) orientations in (001)/(100) and (101)/(110) oriented tetragonal Pb(Zr,Ti)O3 filmsreported previously. These results showed that the volume fraction of the non-180o domains Pb(Zr,Ti)O3films of both tetragonal and rhombohedral symmetriescan be manipulated by εthermal, which brings possibly to control the Psat value.

Electric-field- and stress-induced phase transformations were investigated in polycrystalline 0.5 mol. % Mn-doped (1−x)(Bi1/2Na1/2)TiO3-x(Bi1/2K1/2)TiO3 (x = 0.1, 0.2). To characterize the effect of electric field and stress on the stability of the ferroelectric and relaxor states, polarization- and current density-electric field curves, as well as the stress-strain response as a function of temperature were characterized. Analogous to the observed electrical behavior, the macroscopic mechanical constitutive behavior showed a closed hysteresis at elevated temperatures, indicating a reversible stress-induced relaxor-to-ferroelectric transformation. The electrical and mechanical measurements were used to construct electric field–temperature and stress-temperature phase diagrams, which show similar characteristics. These data show that a mechanical compressive stress, similarly to an electric field, can induce long-range ferroelectric order in a relaxor ferroelectric.

An approach for probing dynamic phenomena during hysteresis loop measurements in piezoresponse force microscopy (PFM) is developed. Dynamic PFM (D-PFM) necessitates development of 5-dimensional (5D) data acquisition protocols and associated methods for analysis and visualization of multidimensional data. Using a combination of multivariate statistical analysis and phenomenological fitting, we explore dynamic behavior during polarization switching in model ferroelectric films with dense ferroelastic domain structures and in ferroelectric capacitors. In polydomain films, multivariate analysis of the switching data suggests that ferroelectric and ferroelastic components can be decoupled and time dynamics can be explored. In capacitors, a strong correlation between polarization dynamics and microstructure is observed. The future potential of D-PFM for probing time-dependent hysteretic phenomena in ferroelectrics and ionic systems is discussed.

The structural and ferroelectric domain variants of highly-strained BiFeO3 films grown on vicinal LaSrAlO4 substrates were studied by piezoelectric force microscopy and high-resolution X-ray reciprocal space mapping. Through symmetry breaking of the substrate surface, ferroelastic domain variants in the highly-strained MC phase BiFeO3 can be greatly reduced. Single-domain film can be obtained on substrates with large miscut angle, which is accompanied by the reduction of structural variants in the mixed-phase nanodomains. These findings lead to better understanding of the phase evolution and polarization rotation process in the strain-driven morphotropic phase system., Comment: 15 pages, 4 figures

Perfectly (111)-oriented rhombohedral Pb(Zr, Ti)O3 [PZT] films were successfully grown on (111) CaF2 substrates. These films have the polar-axis perpendicular to the substrate surface without non-180o domains. Well saturated polarization (P) –electric field (E) hysteresis loops were observed at various frequencies and temperatures. Temperature dependence of the saturation polarization (Psat.) was in good agreement with the estimated one by Haun et al. using phenomenological approach but did not strongly depend on the measured frequencies. On the other hand, the coercive field (Ec) increased with decreasing temperature and with increasing the measurement frequency.

Lead zirconium titanate, Pb(Zr,Ti)O3 [PZT], have been intensively studied for various ferroelectric applications, and have a renewal interest due to their promising application for microelectromechanical systems (MEMS) because of their outstanding ferroelectric and piezoelectric properties. Remanent polarization (Pr) is the not only most fundamental parameter but also the practical importance for real applications to achieve high density devices. Spontaneous polarization (PS) is the expected maximum Pr value of the materials that depend on the composition, orientation and the crystallinity of Pb(Zr,Ti)O3. Thus, in an academic point of view, lots of efforts have been made to investigate PS value. However, PZT crystals with single domain are hard to be obtained, inducing a lack of direct characterization of PS values using PZT single crystal. This situation is due to c/a/c/a polydomain structure of PZT, where a domain and c domain are respective (100) and (001) oriented domains. This domain structure is the result of relaxation process of stress induced under the growth process of PZT. To achieve this purpose, we switch our idea from growth of the bulky single crystal to epitaxial films with polar axis orientation. In addition, a comprehensive and systematic characterization of ferroelectric properties of PZT films with different volume fraction of polar-axis-oriented domain is investigated. This chapter investigates the thickness and Zr/(Zr+Ti) ratio dependencies of domain structure and ferroelectric properties, and correlates physical properties, namely lattice

The dynamic switching of ferroelastic nanodomains in ferroelectric PbZr0.3Ti0.7O3/PbZr0.7Ti0.3O3 bilayers was investigated. Synchrotron microdiffraction using a high-speed pulse generator reveals that electric field pulses as short as 200 ns can switch the ferroelastic domain. Multiples of random distribution analysis of the field-induced changes in diffraction peak intensities finds a dynamic strain change from 0.2 to 1% with increasing the pulse width. Raman spectroscopy shows considerable decreases in A1(1TO) soft mode intensity after applications of short pulses, confirming the ferroelastic switching. The results demonstrate that ferroelastic domains can indeed move at time scales of the order of hundreds of nanoseconds.

An electric field–temperature (E-T) phase diagram for a lead-free 0.5 mol. % Mn-doped Bi(Na0.1K0.9)TiO3 ceramics was investigated. The x-ray diffraction, dielectric and polarization measurements revealed relaxor behavior and were used to characterize the stability regions of the non-ergodic relaxor, ergodic relaxor and electric field induced ferroelectric states. As indicated by the polarization–current density profiles, transformation between two electric fields, induced ferroelectric states with opposite polarization direction arise via a two-step process through an intermediate relaxor state. Interplay between the ferroelectric state conversion and intermediate relaxor state is governed by the dynamics of polarization relaxation. The presented E-T phase diagram revealed the effects of the applied electric field and temperature on stability regions. This is of special interest since the Bi0.5(Na0.1K0.9)0.5TiO3 ceramics were proposed as a potential piezoceramic material.

A new orientation control method for depositing (110)-oriented perovskite thin films was demonstrated using a (101)PdO//(111)Pd buffer layer on (100)Si substrates, which is widely used in integrated ferroelectric and dielectric applications. The (101)-oriented PdO was obtained by oxidizing (111)Pd films deposited on a (111)Pt/TiOx/SiO2/(100)Si substrate and (110)-oriented perovskites including SrRuO3 and (Ba0.5,Sr0.5)TiO3 (BST) were obtained on (101)PdO by the RF magnetron sputtering method. Although the BST films deposited at 500 °C were not crystallized, the BST films deposited above 600 °C are fully crystallized and the (110)-orientation is dominant. The (110)-oriented BST thin film showed good dielectric property with high dielectric constant (>600) at 0 kV/cm and high tunability (>50% at ±200 kV/cm). Comparing this dielectric property with those of other oriented BST films, both the dielectric constant and the tunability tend to decrease in the order of (111)-, (100)-, and (110)-preferred orientations.

The effects of bipolar pulse poling on the ferroelastic domain structure and their contribution to the electrical and piezoelectric properties of Pb(Ti0.7Zr0.3)O3 films are investigated. Micro x-ray diffraction measurements clearly show that the volume fraction of the c-domain increases irreversibly as the poling field is increased, leading to changes in the remanent polarization, dielectric constant, and piezoelectric coefficient. Theoretical estimations well explain the changes of remanent polarization and dielectric constant, but the increase in piezoelectric coefficient is much larger than the theoretical estimation. In-situ x-ray diffraction analysis under an electric field reveals that this disagreement is due to the unexpected activation of the ferroelastic domain wall motion. Our results provide new insight into the poling effect on the electric and piezoelectric properties of ferroelectric films.

Lead zirconate titanate, Pb(Zr,Ti)O3 or PZT, is one of the most widely investigated ferroelectric and piezoelectric materials due to its superior properties. However, the intrinsic properties of PZT have not been directly measured due to the lack of fabrication of single crystals even though a basic understanding of intrinsic properties has been of interest developing lead-free piezoelectric materials. We demonstrated the direct observation of the intrinsic piezoelectric property by means of the detection of electric-field induced crystal lattice distortion of thick Pb(Zr0.35Ti0.65)O3 single-crystalline films with single polar-axis orientation and negligible residual strain using the time-resolved X-ray diffraction (XRD) together with the polarization response. Consequently, the effective converse piezoelectric response was experimentally revealed; hence, the electrostrictive coefficient, which is the conversion coefficient between the electrical and mechanical response, was determined. The obtained effective electrostrictive coefficient was 5.2–6.3 × 10−2 m4/C2, which agrees with theoretical prediction.

Ferroelectric properties were investigated for (100), (110), and (111)-single-oriented rhombohedral Pb(Zr0.65Ti0.35)O3 films. Saturation polarization, P sat, was changed by the simple tilting angle of the polar axis from the film surface normal. On the other hand, (100)- and -oriented films prepared on (100) Si substrates showed similar P sat values due to the coexistence of orientation. The coercive field, E c, of rhombohedral Pb(Zr0.65Ti0.35)O3 films was lower than that of tetragonal Pb(Zr0.4Ti0.6)O3 films. (100)-oriented rhombohedral films with SrRuO3 electrodes did not show noticeable degradation in polarization up to 1010 switching cycles. These results show that (100)-oriented rhombohedral Pb(Zr x Ti1− x )O3 film is available to realize the low voltage operated ferroelectric random access memory instead of the present tetragonal Pb(Zr x Ti1− x )O3 films.

The origin of the ferroelectricity of Bi(Mg1/2Ti1/2)O3 films was investigated. Epitaxial Bi(Mg1/2Ti1/2)O3 films with film thicknesses of 50 to 800 nm were grown on (111)cSrRuO3/(111)SrTiO3 substrates by pulsed laser deposition. A Bi(Mg1/2Ti1/2)O3 film was not strongly clamped from the substrate and identified to have rhombohedral symmetry with a = 0.398 nm and α= 89.8°, which was independent of film thickness within 100 to 800 nm. The relative dielectric constant, remanent polarization, and coercive field of the Bi(Mg1/2Ti1/2)O3 films at room temperature were almost constant at about 250, 60 µC/cm2, and 240 kV/cm, respectively, for film thicknesses above 200 nm. These data suggest that Bi(Mg1/2Ti1/2)O3 films are ferroelectric.

In this paper we investigated the intrinsic impact of Bi(Zn 1/2Ti1/2)O3 (BZT) addition on the crystallographic and ferroelectric properties of Pb(Zr 0.4Ti0.6)O3 (PZT) thin films deposited by sol-gel technique. We could emphasis the shrinkage of lattice parameters, leading to a decrease of spontaneous polarization, with increasingly BZT content. This result is coherent with predicted evolution of spontaneous polarization with unit cell tetragonality.

We have studied the strain field around the 90° domains and misfit dislocations in PbTiO3/SrTiO3 (001) epitaxial thin films, at the nanoscale, using the geometric phase analysis (GPA) combined with high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field––scanning transmission electron microscopy (HAADF-STEM). The films typically contain a combination of a/c-mixed domains and misfit dislocations. The PbTiO3 layer was composed from the two types of the a-domain (90° domain): a typical a/c-mixed domain configuration where a-domains are 20–30 nm wide and nano sized domains with a width of about 3 nm. In the latter case, the nano sized a-domain does not contact the film/substrate interface; it remains far from the interface and stems from the misfit dislocation. Strain maps obtained from the GPA of HRTEM images show the elastic interaction between the a-domain and the dislocations. The normal strain field and lattice rotation match each other between them. Strain maps reveal that the a-domain nucleation takes place at the misfit dislocation. The lattice rotation around the misfit dislocation triggers the nucleation of the a-domain; the normal strains around the misfit dislocation relax the residual strain in a-domain; then, the a-domain growth takes place, accompanying the introduction of the additional dislocation perpendicular to the misfit dislocation and the dissociation of the dislocations into two pairs of partial dislocations with an APB, which is the bottom boundary of the a-domain. The novel mechanism of the nucleation and growth of 90° domain in PbTiO3/SrTiO3 epitaxial system has been proposed based on above the results.

The ferroelectric domain structure of a PbTiO3 thin film on (100) SrTiO3 has been investigated by transmission electron microscopy (TEM). Two types of a-domain were found: one extended through the film to the surface and another comprised small a-domains confined within the film. Dark-field TEM (DFTEM) observation revealed that 180° domains formed near the substrate and stopped their growth 100 nm away from the substrate. The DFTEM observation also revealed that 90° domain boundaries had head-to-tail structures. To confirm the polarization direction obtained by experiments, diffracted intensities under a two-beam condition were simulated using the extended Darwin–Howie–Whelan equations. On the basis of the obtained results, a ferroelectric domain structure model of PbTiO3 thin films on SrTiO3 is proposed.

The ferroelectric property, crystal structure, and A1(1TO) soft mode of almost strain-free epitaxial polar axis-oriented tetragonal lead zirconate titanate thick films grown on CaF2 substrates were investigated by changing the Zr/(Zr+Ti) ratio and the temperature. The square of spontaneous polarization (Ps), Ps2, monotonically increased as tetragonal distortion, (c/a)−1, increased where a and c are the lattice parameters of the films and as the square of frequency in A1(1TO), ω2[A1(1TO)], increased. Additionally, the relationships of Ps2, (c/a−1), and ω2[A1(1TO)] were experimentally obtained, which confirmed the Ps value obtained from (c/a−1) and ω[A1(1TO)] without direct polarization measurements.