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We report on the correlated investigation between piezoelectric properties and crystalline structure of PbZr0.52Ti0.48O3 (PZT) films under different oxygen pressures in the process of pulsed laser ...

The polarization hysteresis loops and the dynamics of domain switching in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT), antiferroelectric PbZrO3 (PZ) and relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films deposited on Pt/Ti/SiO2/Si substrates were investigated under various bipolar electric fields during repetitive switching cycles. Fatigue behavior was observed in PZT thin films and was accelerated at higher bipolar electric fields. Degradation of energy storage performance observed in PZ thin films corresponds to the appearance of a ferroelectric state just under a high bipolar electric field, which could be related to the nonuniform strain buildup in some regions within bulk PZ. Meanwhile, PLZT thin films demonstrated fatigue-free in both polarization and energy storage performance and independent bipolar electric fields, which are probably related to the highly dynamic polar nanodomains. More importantly, PLZT thin films also exhibited excellent recoverable energy-storage density and energy efficiency, extracted from the polarization hysteresis loops, making them promising dielectric capacitors for energy-storage applications.

The dielectric properties, tunability and figure-of-merit (FOM) of relaxor Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films have been investigated. Dielectric measurements indicated that the dielectric constant (at zero-bias field), tunability and FOM are enhanced as the film thickness increases, which are mainly attributed to the presence of an interfacial layer near the film-electrode interface. Experimental results illustrated that a slight reduction is observed in both dielectric constant and tunability (−2%) in a wide-frequency range (10 kHz–1 MHz), meanwhile, the FOM value decreases significantly (−17%) with increasing frequency, arising from the higher dielectric loss value. The 1000-nm PLZT film shows the largest tunability of 94.6% at a maximum electric-field of 1450 kV/cm, while the highest FOM factor is 37.6 at 1000 kV/cm, due to the combination of medium tunability (88.7%) and low dielectric loss (0.0236). All these excellent results indicated that the relaxor PLZT films are promising candidates for specific applications in microwave devices.

The microstructure, ferroelectric, electric-field breakdown strength, and energy-storage properties of relaxor Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films grown on flexible Ti foils using pulsed laser deposition were systematically investigated. Low temperature deposited PLZT thin films showed very slim polarization hysteresis loops with a high difference between maximum and remanent polarizations and low remanent polarization through modulating the film structure with a small columnar-grain size. An ultrahigh recoverable energy density (Ureco) of 40.9 J/cm3, excellent energy efficiency (η) of 80.2% and large breakdown strength (EBD) of 3000 kV/cm were achieved in a PLZT film deposited at the low temperature of 480 °C. More importantly, this film shows excellent charge-discharge cycling endurance with a small variation of both Ureco and η values (less than 3%) after 1010 cycles and good thermal stability under a wide operating temperature range from room temperature to 200 °C. These results indicate that the relaxor PLZT films deposited on thin Ti foils, even at low temperature, are a promising strategy to enhance energy-storage performance for pulse-power energy-storage systems with broad temperature range applications, especially in applications where the device weight is critical (lightweight) due to the thin and low density of Ti foils.

Relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films with a thickness of 1.2 μm were deposited on LaNiO3-buffered Ca2Nb3O10-nanosheet/Si. It was revealed how structural modification of a PLZT film, fabricated using pulsed laser deposition under various ablation rates, can be used to tune its energy-storage performance and piezoelectric-strain. A highest unipolar piezoelectric-strain of 0.71% with extremely low strain-hysteresis of 1.9% and corresponding normalized-strain of 142 pm/V under an electric field of 500 kV/cm were observed in the film deposited at an ablation rate of 50 Hz, and such film consists of vertical columnar-structure. Whereas, the film deposited at a low ablation rate of 10 Hz with dense-structure had the higher recoverable energy-storage density (50.2 J/cm3) and energy-storage efficiency (82.2%) due to the larger electric-breakdown strength (3150 kV/cm). The strongly improved performance by choosing an appropriate film structure is important for practical applications in pulse-power energy-storage as well as for the development of piezo-driven microelectromechanical-systems.

Functional oxides on silicon have been the subject of in-depth research for more than 20 years. Much of this research has been focused on the quality of the integration of materials due to their intrinsic thermodynamic incompatibility, which has hindered the flourishing of the field of research. Nevertheless, growth of epitaxial transition metal oxides on silicon with a sharp interface has been achieved by elaborated kinetically controlled sequential deposition while the crystalline quality of different functional oxides has been considerably improved. In this Research Update, we focus on three applications in which epitaxial ferroelectric oxides on silicon are at the forefront, and in each of these applications, other aspects of the integration of materials play an important role. These are the fields of piezoelectric microelectromechanical system devices, electro-optical components, and catalysis. The overview is supported by a brief analysis of the synthesis processes that enable epitaxial growth of oxides on silicon. This Research Update concludes with a theoretical description of the interfaces and the possibility of manipulating their electronic structure to achieve the desired coupling between (ferroelectric) oxides and semiconductors, which opens up a remarkable perspective for many advanced applications. © 2021 Author(s).

Polarization fatigue, i.e., the loss of polarization of ferroelectric capacitors upon field cycling, has been widely discussed as an interface related effect. However, mechanism(s) behind the development of fatigue have not been fully identified. Here, we study the fatigue mechanisms in Pt/PbZr0.52Ti0.48O3/SrRuO3 (Pt/PZT/SRO) capacitors in which all layers are fabricated by pulsed laser deposition without breaking the vacuum. With scanning transmission electron microscopy, we observed that in the fatigued capacitor, the Pt/PZT interface becomes structurally degraded, forming a 5 nm–10 nm thick non-ferroelectric layer of crystalline ZrO2 and diffused Pt grains. We then found that the fatigued capacitors can regain the full initial polarization switching if the externally applied field is increased to at least 10 times the switching field of the pristine capacitor. These findings suggest that polarization fatigue is driven by a two-step mechanism. First, the transient depolarization field that repeatedly appears during the domain switching under field cycling causes decomposition of the metal/ferroelectric interface, resulting in a non-ferroelectric degraded layer. Second, this interfacial non-ferroelectric layer screens the external applied field causing an increase in the coercive field beyond the usually applied maximum field and consequently suppresses the polarization switching in the cycled capacitor. Our work clearly confirms the key role of the electrode/ferroelectric interface in the endurance of ferroelectric-based devices.

The LEDs lighting device with phosphor ingredient (pcLEDs) is among the most common lighting methods in recent years and evaluated by chromatic uniformity and lighting capacity. Therefore, we introduce the phosphor particles that can improve the scattering efficiency (SEPs) to apply in pcLEDs at 8500 K correlated color temperature (CCT) with the expectation to produce better pcLEDs by enhancing both quantity and quality of emitted light. Combining various materials such as CaF 2 and SiO 2 with yellow Y 3 Al 5 O 12 :Ce 3+ phosphor composition in the pcLEDs simulation created by the LightTools program is the mechanism of this research. The simulated pcLEDs are tested and the results will be verified with Mie-scattering theory. The observation of the simulation leads to the conclusion about the scattering coefficients of SEPs at 455 nm and 595 nm wavelengths. The calculation showed that CaF 2 is better for color homogeneity yet suffer from luminous flux deficiency as the concentration gets higher. On the other hand, SiO 2 is the scattering enhancement material that can maintain high luminous flux regardless of its concentration.

Color uniformity is one of the essentials for the on-going development of WLED. To achieve a high color uniformity index, increasing the scattering events within the phosphor layers was reported to be the most efficient method and in this article, ZnO is the chosen material to apply in this method. After analyzing the scattering properties through the scattering cross-section 𝐶𝑠𝑐𝑎(𝐷,𝜆), scattering coefficient 𝜇𝑠𝑐𝑎(𝜆) and scattering phase function 𝜌(𝜃,𝜆), the which outcomes comfirm that ZnO can enhance the scattered light in the phosphor layers. Moreover, the findings from the study of ZnO concentration from 2% to 26% suggest that color uniformity also depends on the fluctuation of ZnO concentration, therefore, to control color uniformity the focus should be implied on both size and concentration of ZnO. The experimental results from this research show that the luminous flux of WLED is at the peak if the concentration of ZnO is at 6%, and when the concentration of ZnO is at 18% and has 100 nm particles size, the ΔCCT reaches the lowest level. The final choice should be based on the desired characteristic of WLEDs, however, if the WLED need to excel in both luminous flux and ΔCCT then 6% ZnO concentration with particles size from 100 nm-300 nm is the optimal choice.

The impact of polarization effects induced by a ferroelectric layer on the on-state performance of ferroelectric gate AlGaN/GaN HEMTs has been studied by using experiments and extensive TCAD simulations. Stress-free and high quality crystalline (111) lead-zirconate-titanate ($\mathrm{P}\mathrm{b}(\mathrm{Z}\mathrm{r}_{x}\mathrm{T}\mathrm{i}_{1-x})\mathrm{O}_{3}$ or PZT) films on top of GaN have been successfully obtained by adopting a single magnesium-oxide (MgO) monolayer as a buffer layer. By adjusting the zirconium composition (x) of PZT, solely the spontaneous polarization in PZT is varied. In addition a onedimensional electrostatic model has been derived showing the impact of the polarization in the ferroelectric gate on the 2DEG sheet density and threshold voltage ($V_{\mathrm{T}\mathrm{H}}$), which is in good agreement with TCAD simulations. The experimental data show for $x=0.20$ a minimum on-resistance $(R_{\mathrm{O}\mathrm{N}})$ of $\sim 9.7\mathrm{k}\Omega$ and for $x=0.52$ a minimal $V_{\mathrm{T}\mathrm{H}}$ of ~-3.3V. The results are important for providing a guide line to optimize ferroelectric gate AlGaN/GaN HEMTs.

Origins of polarization fatigue in ferroelectric capacitors under electric field cycling still remain unclear. Here, we experimentally identify origins of polarization fatigue in ferroelectric PbZr0.52Ti0.48O3 (PZT) thin-film capacitors by investigating their fatigue behaviours and interface structures. The PZT layers are epitaxially grown on SrRuO3-buffered SrTiO3 substrates by a pulsed laser deposition (PLD), and the capacitor top-electrodes are various, including SrRuO3 (SRO) made by in-situ PLD, Pt by in-situ PLD (Pt-inPLD) and ex-situ sputtering (Pt-sputtered). We found that fatigue behaviour of the capacitor is directly related to the top-electrode/PZT interface structure. The Pt-sputtered/PZT/SRO capacitor has a thin defective layer at the top interface and shows early fatigue while the Pt-inPLD/PZT/SRO and SRO/PZT/SRO capacitor have clean top-interfaces and show much more fatigue resistance. The defective dielectric layer at the Pt-sputtered/PZT interface mainly contains carbon contaminants, which form during the capacitor ex-situ fabrication. Removal of this dielectric layer significantly delays the fatigue onset. Our results clearly indicate that dielectric layer at ferroelectric capacitor interfaces is the main origin of polarization fatigue, as previously proposed in the charge injection model.

Thin PbZrO3 (PZO) antiferroelectric films with (001)-preferred orientation were deposited on SrRuO3/Ca2Nb3O10-nanosheet/Si substrates using pulsed laser deposition. Variation of the deposition temperature was found to play a key role in the control of the microstructure and strongly influence the energy storage performance of the thin film. The critical phase switching field, where the aligned antiferroelectric (AFE) domains start to transform into the ferroelectric (FE) state, decreased with increasing temperature. On the other hand, the content of the FE phase in the AFE PZO thin films increased with increasing deposition temperature. A large recoverable energy-storage density of 16.8 J/cm3 and high energy-storage efficiency of 69.2% under an electric field of 1000 kV/cm were achieved in the films deposited at 525 °C. This performance was due to the high forward switching field and backward switching field values and the low difference between these two fields. Moreover, the PZO thin films showed great charge-discharge cycling life with fatigue-free performance up to 1010 cycles and good thermal stability from room temperature to 100 °C.

We report the energy-storage performance and electric breakdown field of antiferroelectric PbZrO3 (PZ) and relaxor ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) single films, as well as PLZT/PZ and PZ/PLZT heterolayered films grown on SrRuO3/Ca2Nb3O10–nanosheet/Si substrates using pulsed laser deposition. These films show the highly textured (001) orientation. The ‘square’ hysteresis loop with very sharp electric field–induced antiferroelectric–ferroelectric (AFE–FE) phase transition is observed for the PZ/Si film, meanwhile the heterolayerd PLZT/PZ/Si and PZ/PLZT/Si films show the ‘slanted’ hysteresis loops with gradual phase transition. Moreover, the electric field-induced AFE-FE phase transition in the hererolayered films is occurred at lower applied electric fields (~275 kV/cm) than that in the PZ/Si (~425 kV/cm), due to the presence of the PLZT layers in the heterolayered films. Owing to the dense structure in PLZT layer, the large electric breakdown strength of 2000 and 1825 kV/cm, and then the high recoverable energy-storage density of 28.8 and 23.8 J/cm3, respectively, are obtained for the PLZT/Si and PZ/PLZT/Si films.

Thin relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films were deposited on Si substrates using Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) nanosheets as the growth template layer and SrRuO3 (SRO) as the base electrode layer, using pulsed laser deposition. XRD and cross-sectional SEM results show that the structure of the PLZT layers changes from very dense with (001)-orientation to columnar with (110)-orientation for CNOns and TiOns, respectively. The recoverable energy-storage density (Ureco) is nearly proportional to the critical electric breakdown field (EBD), which increases with PLZT film thickness. A very high Ureco value of 58.4 J cm-3 and energy-storage efficiency (η) of 81.2% were obtained at an EBD of 3400 kV cm-1 for the 1000 nm thick PLZT film on CNOns/Si, significantly higher than for the film on TiOns/Si (Ureco = 44.0 J cm-3 and η = 59.6% for EBD = 2800 kV cm-1). This excellent energy storage performance in the PLZT/SRO/CNOns/Si is due to the dense film structure and nearly hysteresis-free relaxor behavior. These results are important for improving the performance of relaxor-ferroelectric thin films for high-power capacitor applications.

Dissipative particle dynamics computations were used to study the interaction between two carbon nanotubes (CNTs) stabilized with a polymer in an aqueous solution. The calculated interaction forces quantitatively described the steric effects of the adsorbed polymer on CNT agglomeration. It was found that the repulsive peak depended on the orientation of the CNTs relative to each other. A general equation describing the forces between polymer-stabilized CNTs was established, and its parameters were evaluated based on the results of the simulations. The procedure can be extended to other adsorbed molecules, like surfactants or biomolecules.

Carbon nanotube suspensions in water can be stabilized with the use of surfactants. However, when a suspension is exposed to harsh conditions, the surfactants might detach from the carbon nanotube (CNT) surface leading to CNT agglomeration and precipitation. In order to explore temperature effects on the suspension, the surfactant adsorption isotherms of an ionic surfactant (alkylpropoxy sulfate, alfoterra 123-8s) and a nonionic surfactant (secondary alcohol ethoxylate, tergitol 15-s-40) on a CNT are obtained at various temperatures using dissipative particle dynamics (DPD) simulations. The effects of shear stresses, such as those experienced by the CNT–surfactant suspension when it passes through pumps, are also explored by applying different levels of constant shear on the suspension. It is seen that there is good agreement between the DPD results and the Langmuir model for the adsorption of both alfoterra and tergitol on CNTs. The detachment of the surfactant from the nanotubes occurs with the detachme...

Perovskite-type lead-free Bi[Formula: see text](Na[Formula: see text]K[Formula: see text](Ti[Formula: see text]Zrx)O3 (BNKT-[Formula: see text]Zr) ferroelectric films (with [Formula: see text] from 0.00 to 0.05) were synthesized on Pt/Ti/SiO2/Si substrates via chemical solution deposition. The influence of Zr[Formula: see text] concentration on the microstructures, ferroelectric and energy-storage properties of the prepared films was investigated in detail. It showed that the BNKT-[Formula: see text]Zr films possessed rhombohedral and tetragonal symmetries in morphotropic phase boundary when a small amount of Zr[Formula: see text] was added. Ferroelectric and energy-storage properties of the films investigated at an applied electric field of 600[Formula: see text]kV/cm were significantly enhanced with appropriate Zr[Formula: see text] concentration. The remnant polarization ([Formula: see text]), maximum polarization ([Formula: see text]) and [Formula: see text]–[Formula: see text] values at [Formula: see text] reached the highest values of 18.1[Formula: see text][Formula: see text]C/cm2, 42.0[Formula: see text][Formula: see text]C/cm2 and 24.0[Formula: see text][Formula: see text]C/cm2, respectively. Thanks to the strong enhancement in [Formula: see text] and the large [Formula: see text]–[Formula: see text] value, the highest recoverable energy-storage density gets the value of 4.6[Formula: see text]J/cm3 for the 2[Formula: see text]mol.% Zr[Formula: see text]-doped BNKT film. These obtained results indicate that the appropriate Zr[Formula: see text]-doped BNKT films have many application potentials in the advanced capacitors.

Epitaxial (PbMg1/3Nb2/3O3)2/3-(PbTiO3)1/3 (PMN-PT) films with different out-of-plane orientations were prepared using a CeO2/yttria stabilized ZrO2 bilayer buffer and symmetric SrRuO3 electrodes on silicon substrates by pulsed laser deposition. The orientation of the SrRuO3 bottom electrode, either (110) or (001), was controlled by the deposition conditions and the subsequent PMN-PT layer followed the orientation of the bottom electrode. The ferroelectric, dielectric and piezoelectric properties of the (SrRuO3/PMN-PT/SrRuO3) ferroelectric capacitors exhibit orientation dependence. The properties of the films are explained in terms of a model based on polarization rotation. At low applied fields domain switching dominates the polarization change. The model indicates that polarization rotation is easier in the (110) film, which is ascribed to a smaller effect of the clamping on the shearing of the pseudo-cubic unit cell compared to the (001) case.

Normal-ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) and relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin-films are deposited on SrRuO3-covered SrTiO3/Si substrates. An ultrahigh recoverable energy-storage density (Ureco) of 68.2 J/cm3 and energy efficiency (η) of 80.4% are achieved in the PLZT thin-films under a large breakdown strength (EBD) of 3600 kV/cm. These values are much lower in the PZT thin-films (Ureco of 10.3 J/cm3 and η of 62.4% at EBD of 1000 kV/cm). In addition, the remanent polarization (Pr) and dielectric-constant are also investigated to evaluate the breakdown strength in thin-films. Polar nano-regions (PNRs) are created in the PLZT thin-films to enable relaxor behavior and lead to slim polarization loops along with very small Pr. The excellent operating temperature of energy-storage performance and also the breakdown strength obtained in the PLZT thin-films are mainly ascribed to the presence of PNRs. Moreover, both PZT and PLZT thin-films exhibit superior performance up to 1010 times of charge-discharge cycling.

BiVO4 is a promising light harvester for the construction of photoanode for solar-driven water splitting, but it suffers from low charge mobility and slow oxygen evolution reaction kinetics. Herein, we report on a novel strategy using AgOx (e.g. Ag2O and AgO) nanoparticles as hole collectors to boost the BiVO4 photoanode to its best photocatalytic performance. AgOx helps to boost the charge transfer efficiency at the BiVO4/electrolyte interface up to 93%, being much higher than 40% achieved for a bare BiVO4 photoanode. AgOx also contributes to improving the photostability of BiVO4 by offering an efficient quenching of the photogenerated holes, which are harmful to the BiVO4, e.g. causing an oxidative dissolution of V. In a pH 7 phosphate buffer electrolyte and under 1 sun illumination, the best BiVO4/AgOx photoanode generates a photocatalytic current density of 4.65 mA/cm2 at 1.23 V vs. reversible hydrogen electrode. It represents a 2.3-fold improvement of activity in comparison to a bare BiVO4 without AgOx decoration. The current BiVO4/AgOx can be placed among the top-tier photoanodes for solar water splitting made of BiVO4 light harvester.

Relaxor ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films have been epitaxially grown via pulsed laser deposition on SrRuO3/SrTiO3 single crystal with different orientations. The high recoverable energy-storage density and energy-storage efficiency in the epitaxial PLZT thin films are mainly caused by the coexistence of relaxor and antiferroelectric-like behaviors. The recoverable energy-storage density of 12.03, 12.51 and 12.74 J/cm3 and energy-storage efficiency of 86.50, 88.14 and 88.44%, respectively, for the PLZT(001), PLZT(011) and PLZT(111) thin films measured at 1000 kV/cm. The high energy density and high efficiency indicate that the relaxor epitaxial PLZT(111) thin film is a promising candidate for high pulsed power capacitors.

Pb(Zr0.52Ti0.48)O3 (PZT) films with (001) orientation were deposited on Pt(111)/Ti/SiO2/Si(100) substrates using pulsed laser deposition. Variation of the laser pulse rate during the deposition of the PZT films was found to play a key role in the control of the microstructure and to change strongly the piezoelectric response of the thin film. The film deposited at low pulse rate has a denser columnar microstructure, which improves the transverse piezoelectric coefficient (d31f) and ferroelectric remanent polarization (Pr), whereas the less densely packed columnar grains in the film deposited at high pulse rates give rise to a significantly higher longitudinal piezoelectric coefficient (d33f) value. The effect of film thickness on the ferroelectric and piezoelectric properties of the PZT films was also investigated. With increasing film thickness, the grain column diameter gradually increases, and also the average Pr and d33f values become larger. The largest piezoelectric coefficient of d33f = 408 pm V–1 was found for a 4-μm film thickness. From a series of films in the thickness range 0.5–5 μm, the z-position dependence of the piezoelectric coefficient could be deduced. A local maximum value of 600 pm V–1 was deduced in the 3.5–4.5 μm section of the thickest films. The dependence of the film properties on film thickness is attributed to the decreasing effect of the clamping constraint imposed by the substrate and the increasing spatial separation between the grains with increasing film thickness.

Dissipative Particle Dynamics (DPD) simulations were used to investigate the conformation of polyvinyl pyrrolidone (PVP) grafted on carbon nanotubes (CNT) and the physical adsorption of the PVP under shear flow. The behavior of PVP on the surface of CNTs was illustrated after the physical adsorption of PVP on the CNT reached equilibrium in an aqueous medium. It was found that PVP molecules prefer to adsorb on the CNT surface and to occupy an “island” area. To examine the structure of CNT-PVP under shear flow, equilibrium CNT-PVP particles were released into Couette and Poiseuille flows. Depending on the shear rate, the polymer could be in one of three configurations: adsorbed, shear-affected and separated. Additionally, the conformation of the polymer was influenced. Average values of the end-to-end distance and the radius of gyration were found to increase when the shear force increases.

We report on the correlated investigation between crystal structures, field-induced phase transition, and energy storage properties of both polycrystalline and epitaxial antiferroelectric PbZrO3 (PZO) films grown by pulsed laser deposition on Si and SrTiO3 substrates. The structural characterization revealed the polycrystalline structure of the PZO films on Pt/Si and the epitaxial relationship between the films and the SrTiO3/Si and SrTiO3 substrates. Different to normal ferroelectric fi lms, the polycrystalline PZO films show similar polarization loops but with a higher maximum polarization, resulting in a larger energy storage density under the same conditions. Due to the larger electric breakdown strength (2800 kV/cm), however, the epitaxial PZO films grown on SrTiO3/Si have a higher recoverable energy storage density (24.9 J/cm3) than those on Pt/Si (23.4 J/cm3 at 2500 kV/cm) and on SrTiO3 (22.0 J/cm3 at 2550 kV/cm). Additionally, the introduction of SrRuO3 oxide-electrode improves the endurance performance of energy storage properties of the films on STO/Si by suppressing the formation of the dead layer between the film and the electrode. In this way, applications based on PZO films would be more easily integrated on Si and open the way to develop high-power commercial energy storage systems.

Relaxor ferroelectric thin films show excellent energy-storage performance for pulse-power applications. In this study, La-doped Ba1-xLax(Zr0.25Ti0.75)O3 (BLZT, x = 0–8%) thin films were grown on LaNiO3 buffered Ca2Nb3O10-nanosheet/Si substrates. BLZT thin films indicate prominently increasing relaxor behavior with increasing La-doping concentration, which is conducive to obtaining a very slim polarization hysteresis loop with a low remanent polarization and a high breakdown strength. As a result, BLZT thin films with 5 mol.% La-doping simultaneously exhibit a great 72.2 J/cm3 recoverable energy-storage density and a large 78.6% energy-storage efficiency under a high 3.8 MV/cm breakdown strength. These results present a promising environmentally friendly candidate for the next generation of advanced energy-storage capacitor applications.

Lead-free Bi0.5(Na0.8K0.2)0.5TiO3 (abbreviated as BNKT) films have been synthesized via a sol-gel technique on Pt/Ti/SiO2/Si substrates, and the dependence of the physical properties in BNKT films were investigated as a function of the crystallization temperature. The BNKT films were annealed at different temperatures (600, 650, 700, and 750°C) for 60 min in the air. The results of this study showed that the optimal crystallization temperature is 700°C. At this, the BNKT films exhibited a single perovskite phase structure and high-dense surface. Besides, the remanent (Pr) and maximum (Pm) polarization reached their highest values of 9.2 µC/cm2 and 30.6 µC/cm2, respectively. All the films showed a weak ferromagnetic behavior with the maximum saturated magnetization (Ms) of 2.1 emu/cm3. These values are equivalent to the highest Pr and Pm values in previous reports on lead-free films.

Thin film capacitors of the lead-free (K0.5Na0.5)NbO3 (KNN) with (100) orientation were grown on Pt/Ti/SiO2/SOI (silicon-on-insulator) substrates by pulsed laser deposition. The films are pure phases and do not show other crystal orientations. The remnant polarization Pr, saturation polarization Psat, longitudinal d33,f and transverse (d31,f and e31,f) piezoelectric coefficients of the KNN films were determined (Pr=12.6 µC/cm2, Psat=25.0 µC/cm2, d33,f=58 pm/V, d31,f=−42 pm/V and e31,f=−5.6 C/m2). These values are well comparable with the highest values reported for lead-free films of different compositions and therefore these KNN films form a potential alternative to PZT films in lead-free MEMS applications.

The layered perovskite-type niobate KCa2Nb3O10 and its derivatives show advantages in several fields, such as templated film growth and (photo)catalysis. Conventional synthesis routes generally yield crystal size smaller than 2 μm. We report a flux synthesis method to obtain KCa2Nb3O10 crystals with significantly larger sizes. By using different flux materials (K2SO4 and K2MoO4), crystals with average sizes of 8 and 20 μm, respectively, were obtained. The KCa2Nb3O10 crystals from K2SO4 and K2MoO4 assisted synthesis were protonated and exfoliated into monolayer nanosheets, and the optimal exfoliation conditions were determined. Using pulsed laser deposition, highly (001)-oriented piezoelectric stacks (SrRuO3/PbZr0.52Ti0.48O3/SrRuO3, SRO/PZT/SRO) were deposited onto Langmuir-Blodgett films of Ca2Nb3O10- (CNO) nanosheets with varying lateral nanosheet sizes on Si substrates. The resulting PZT thin films showed high crystallinity irrespective of nanosheet size. The small sized nanosheets yielded a high longitudinal piezoelectric coefficient d33 of 100 pm/V, while the larger sized sheets had a d33 of 72 pm/V. An enhanced transverse piezoelectric coefficient d31 of -107 pm/V, an important input parameter for the actuation of active structures in microelectromechanical systems (MEMS) devices, was obtained for PZT films grown on CNO nanosheets with large lateral size, while the corresponding value on small sized sheets was -96 pm/V.

Flow of water past an array of single-walled carbon nanotubes (SWNTs) is simulated in this work to determine the interaction parameters of carbon nanotubes (CNTs) and water using Dissipative Particle Dynamics (DPD). For this flow configuration, results from molecular dynamics simulations by Walther et al. are available and can be used for validation (Phys. Rev. E, 2004, 062201). The hydrodynamic properties for SWNT (32, 0) with diameter of 2.5 nm were determined in different Reynolds number flows. A set of appropriate DPD parameters was found so that the drag coefficients of the CNT agreed well with the Stokes–Oseen analytical solution and the fluid slip length on the CNT wall was comparable with the Walther et al. results. It was also found that it is feasible to apply these parameters in longer length and time scales by increasing the number of water molecules grouped into each DPD bead and still maintain the hydrodynamic properties of CNTs as well as their hydrophobic surface character.

Epitaxial ferroelectric Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) thin films were fabricated on silicon substrates using pulsed laser deposition. Depending on the buffer layers and perovskite oxide electrodes, epitaxial films with different orientations were grown. (110)-oriented PZT/SrRuO 3 (and PZT/LaNiO 3 ) films were obtained on YSZ-buffered Si substrates, while (001)-oriented PZT/SrRuO 3 (and PZT/LaNiO 3 ) were fabricated with an extra CeO 2 buffer layer (CeO 2 /YSZ/Si). There is no effect of the electrode material on the properties of the films. The initial remnant polarizations in the (001)-oriented films are higher than those of (110)-oriented films, but it increases to the value of the (001) films upon cycling. The longitudinal piezoelectric d 33 ,f coefficients of the (110) films are larger than those of the (001) films, whereas the transverse piezoelectric d 31 ,f coefficients in the (110)-films are less than those in the (001)-oriented films. The difference is ascribed to the lower density (connectivity between grains) of the former films.

The relaxor ferroelectric Pb 0.9 La 0.1 (Zr 0.52 Ti 0.48 )O 3 (PLZT) thin films were deposited using pulsed laser deposition, and their microstructures, break-down field strengths and energy storage performances were investigated as a function of the buffer layer and electrode. A large recoverable energy-storage density ( U reco ) of 23.2 J/cm 3 and high energy-storage efficiency ( η ) of 91.6% obtained in the epitaxial PLZT film grown on SrRuO 3 /SrTiO 3 /Si are much higher than those in the textured PLZT film ( U reco = 21.9 J/cm 3 , η = 87.8%) on SrRuO 3 /Ca 2 Nb 3 O 10 -nanosheet/Si and the polycrystalline PLZT film ( U reco = 17.6 J/cm 3 , η = 82.6%) on Pt/Ti/SiO 2 /Si, under the same condition of 1500 kV/cm and 1 kHz, due to the slim polarization loop and significant antiferroelectric-like behavior. Owing to the high break-down strength (BDS) of 2500 kV/cm, a giant U reco value of 40.2 J/cm 3 was obtained for the epitaxial PLZT film, in which U reco values of 28.4 J/cm 3 (at BDS of 2000 kV/cm) and 20.2 J/cm 3 (at BDS of 1700 kV/cm), respectively, were obtained in the textured and polycrystalline PLZT films. The excellent fatigue-free properties and high thermal stability were also observed in these films.

Due to its physical properties gallium-nitride (GaN) is gaining a lot of attention as an emerging semiconductor material in the field of high-power and high-frequency electronics applications. Therefore, the improvement in the performance and/or perhaps even extension in functionality of GaN based devices would be highly desirable. The integration of ferroelectric materials such as lead-zirconate-titanate (PbZrxTi1-xO3) with GaN has a strong potential to offer such an improvement. However, the large lattice mismatch between PZT and GaN makes the epitaxial growth of Pb(Zr1-xTix)O-3 on GaN a formidable challenge. This work discusses a novel strain relaxation mechanism observed when MgO is used as a buffer layer, with thicknesses down to a single unit cell, inducing epitaxial growth of high crystallinity Pb(Zr0.52Ti0.48)O-3 (PZT) thin films. The epitaxial PZT films exhibit good ferroelectric properties, showing great promise for future GaN device applications.

Piezoelectric lead-zirconate-Titanate (PZT) thin films were deposited on 4-inch (111)Pt/Ti/SiO2/Si(001) wafers using large-Area pulsed laser deposition (PLD). This study was focused on the homogeneity in film thickness, microstructure, ferroelectric and piezoelectric properties of PZT thin films. The results indicated that the highly textured (001)-oriented PZT thin films with wafer-scale thickness homogeneity (990 nm ± 0.8%) were obtained. The films were fabricated into piezoelectric cantilevers through a MEMS microfabrication process. The measured longitudinal piezoelectric coefficient (d 33f = 210 pm/V ± 1.6%) and piezoelectric transverse coefficient (e 31f = -18.8 C/m2 ± 2.8%) were high and homogeneity across wafers. The high piezoelectric properties on Si wafers will extend industrial application of PZT thin films and further development of piezoMEMS.

This paper treats processing sequence induced changes on PZT. Two kinds of metal-PZT-metal capacitors are compared. The top surface and sidewall of PZT in one kind of capacitor is directly bombarded by energetic particles during ion milling process, whereas PZT in the other kind of capacitor is not. The polarity of plasma charging may depend on the ion milling parameters and influence the self-poling of virgin PZT capacitors. Direct ion bombardment induces a significant decrease of PZT permittivity. The PZT reliability (both RVS and TDDB) at positive voltage worsens because of bombardments of energetic particles; whereas the PZT reliability at negative voltage is not influenced. It indicates that the process induced positively charged defects present in the upper part of the capacitor structure initiate the dielectric breakdown.

Antiferroelectric PbZrO3 (PZO) thin-films were fabricated by pulsed laser deposition (PLD) and sol-gel techniques to investigate the effect of antiferroelectric-ferroelectric (AFE-FE) phase transition on the energy storage performance. The (100)-oriented PLD thin-films have a square-double polarization-electric field (P-E) hysteresis loop with a sharp-phase transition and the (111)-oriented sol-gel thin-films have a slanted P-E loop with a diffused-phase transition. The difference in the phase transition fields between PLD and sol-gel thin-films could be attributed to their difference in crystalline orientations. In this case, the antipolar AFE phase is along the [110]-direction of the original tetragonal-cell under zero electric-field, while the antipolar AFE phase switches into the polar FE phase under a strong enough electric-field and the tetragonal-cell becomes rhombohedral with the polar direction of [111]. Due to the larger maximum polarization and slimmer P-E loop, the higher recoverable energy-storage (Ureco) of 19.4 J/cm3 and larger energy-efficiency (η) of 70.8%, are achieved in sol-gel thin-films. More importantly, this film shows excellent charge-discharge cycling endurance of both Ureco and η values after 1010 cycles and good thermal-stability under a wide operating temperature. From the viewpoint of applications, the sol-gel method is considered to be a promising approach towards producing low-cost PZO thin-films for high-efficiency energy-storage devices over a broad temperature range.

The energy-storage performance and piezoelectric properties were determined for epitaxial antiferroelectric (AFE) PbZrO3 (PZ), ferroelectric (FE) PbZr0.52Ti0.48O3 (PZT), and relaxor ferroelectric (RFE) Pb0.9La0.1Zr0.52Ti0.48O3 (PLZT) thin films that were deposited on to SrTiO3 buffered Si substrates. The films were investigated by directly measuring the polarization hysteresis loops and piezoelectric strain curves. The square polarization loop with a high remanent polarization and a large piezoelectric coefficient obtained in PZT thin films allow them to be useful for various applications in ferroelectric field effect transistors and/or in MEMS actuators. Meanwhile, there is a jump of about 0.9% in the strain curve of PZ thin films around the field-induced AFE-FE phase transition, which is useful in digital displacement transducers due to a good ON/OFF strain state. The large recoverable energy-storage density, excellent energy-storage efficiency, and low strain hysteresis due to a slim hysteresis loop combine to make PLZT thin films as a potential candidate for a broad range of applications from energy storage to nano-positioning precision systems.

Earlier theoretical reports predicted that the usage of a piezoelectric stressor layer around the FinFET, i.e., the PiezoFET, offers a great potential for steep subthreshold slope devices. For the first time, we analyzed the practical realization of such PiezoFETs comprising a piezoelectric stressor layer, lead–zirconate–titanate (PZT), and aluminum–nitride (AlN) deposited on n-type silicon FinFETs. A high-piezoelectric response in the range of 100 pm/V has been obtained for the PZT PiezoFET evidencing the converse piezoelectric effect in the device. The piezoelectric response for the AlN device was much less (13 pm/V) as expected. Underlying device properties, such as subthreshold swing (SS) and low-field electron mobility have been significantly affected by the presence of the PZT stressor. A 20%–50% change in the mobility and a change in the SS (about 5 mV/decade) have been observed. The change can be attributed to the strain induced reduction of the interface trap density at the ${\rm Si}/{\rm SiO}_{2}$ interface. This strain is partly formed by the bias over the piezoelectric layer, which indicates the converse piezoelectric effect related tunable strain in both the silicon channel and gate oxide.

In this contribution, we report on the compositional dependence of the mechanical and piezoelectric properties of Pb(ZrₓTi₿₋ₓ)O₃ (PZT) thin films fabricated by pulsed laser deposition (PLD). These films grow epitaxially on silicon with a (110) preferred orientation and have excellent piezoelectric properties, which make them outstanding candidates for application in microelectromechanical system devices. Vibrometric measurements on capacitors showed that the effective longitudinal piezoelectric coefficient (d₃₃,f) of 100-nm thick PZT films has a maximum value of 72 pm/V for a composition of $x$ = 0.52. The Young's modulus was determined by measuring the difference in the flexural resonance frequencies of cantilevers before and after the deposition of the PZT thin films. The compositional dependence of the Young's modulus shows an increase in value for the Zr-rich compositions, which is in agreement with the trend observed in their bulk ceramic counterparts. From the obtained dielectric constant and d₃₃,f, we show that the calculated coupling coefficients of the PLD-PZT thin films have higher values for most of the compositions than their ceramic counterparts.

Graphical abstractDisplay Omitted Thin film PZT/LNO stacks on an encapsulated TiN electrode are studied.Promising ferroelectric behavior of these thin film layers is reported.A passive layer adjacent to the electrode is recognized and characterized.The leakage current was described by a diffusion-based model. We realized metal-ferroelectric-metal (MFM) capacitors comprising high-quality ferroelectric lead zirconate titanate (Pb(Zr0.52Ti0.48)O3 or PZT) thin films on an LaNiO3/poly-Si/titanium nitride (TiN)/SiO2 integrated on a 100mm Si wafer. Promising effective piezoelectric coefficient and remnant polarization of 53pm/V and 19.2µC/cm2, respectively, are obtained for the 100nm-PZT/20nm-LNO stack. Further analysis of the samples indicates the presence of a passive layer, possibly near the Ti/PZT interface at the top electrode. A leakage current model has been used to explain the obtained current density-electric field curves. In this model, diffusion limited transport has been assumed in which the injection is interface-controlled. Based on the capacitance and the leakage current measurements, the thickness and dielectric constant values of the passive layer are estimated to be 2.1nm and 23, respectively. The observed apparent low barrier height value of 0.32eV is attributed to ferroelectric polarization related phenomena. A good agreement between measurement and leakage current model is obtained.

A process for the fabrication of piezoelectric membranes with Pb(Zr0.45Ti0.55)O3 (PZT) thin films for micrometer-range actuation and sensing applications has been developed. The films grown by sol-gel on the Pt/Ti/SiO2/SOI (silicon-on-insulator) substrates have similar randomly oriented perovskite phases, but the nearly epitaxial film made by the pulsed laser deposition exhibits a more compact and flat morphology. It is observed that a denser microstructure produced by pulsed laser deposition leads to a significantly higher remanent polarization and piezoelectric coefficient in the capacitor structure, as well as in a much higher piezoelectric membrane displacement, but only a slightly enhancement of the quality factor of the membrane actuator is obtained. The membrane actuator with the epitaxial PZT thin film grown on a SrRuO3/Yttria-Stabilized Zirconia/SOI substrate using pulsed laser deposition shows significantly enhanced piezoelectric membrane displacement and quality factor. The results and discussion in our paper provide a better understanding of the relationship between the microstructure and the thin film properties, which may lead to significant improvements in device performance

We have investigated the growth characteristics and optical constants of thin AlN films made by thermal atomic layer deposition (ALD) from trimethylaluminum (TMA) and ammonia (NH3). We observed the nucleation, closure and growth after closure of the films using atomic force microscopy and in-situ spectroscopic ellipsometry. A fully covered surface was obtained for films with a thickness of about 2 nm. The self-limiting ALD growth was observed at temperatures of 330 and 350◦C with deposition rates of 1.5 and 2.1 Å/cycle, respectively. At 370◦C, thermal decomposition of TMA dominated the growth mechanism, resulting in a fast and non-self-limiting deposition. Low concentrations of oxygen (0.8−2.5%) and carbon (5−7.5%) incorporated into the films were measured. We found that the refractive index increased remarkably with increasing film thickness and growth temperature.

The effect of two poling processes on the ferroelectric and piezoelectric properties of sol–gel and pulsedlaser-deposited Pb(Zr0.45Ti0.55)O3 (PZT) thin films has been investigated as a function of the poling field, poling temperature and poling time. In the case of dc-electric field poling at an elevated temperature (200 °C), the remnant polarization and effective piezoelectric coefficient are found to increase with and saturate at high dc-poling field (400 kV/cm) and long poling time (30 minutes). The room-temperature poling process using ac electric field poling, shows the same trend with poling field but much shorter poling times (100 seconds), with only a slightly lower saturation value of polarization. It is suggested that in room-temperature poling screening charges are merely rearranged, whereas in high temperature poling these charges are largely removed. A much larger improvement in the properties of sol–gel PZT thin films is found, as compared to those deposited using pulsed laser deposition (PLD), indicating that a poling process is required for sol–gel films.

Very good crystallinity and highly c-axis-oriented aluminum nitride (AlN) thin films are sputtered on titanium (Ti) to fabricate thin piezoelectric cantilevers. Raman spectroscopy measurements and X-ray diffraction (XRD) indicate the high quality of these AlN films. A fabrication process, fully CMOS compatible, is developed to realize slender piezoelectric microcantilevers. Actuation enhancement for the AlN piezoelectric cantilevers is achieved by coating the slender beams with a thin PECVD silicon nitride (SiN) layer. Very good linearity and high displacement, up to 19.5 nm for 200 μm long cantilevers and 4.25 nm for 100 μm long cantilevers for 1 V actuation at quasi-static mode, are obtained with a 500 nm SiN top layer. These displacement values are three times larger than our previously reported values for cantilevers without SiN layer coating. This makes these cantilevers, without the need of employing nonstandard metals such as platinum (Pt), very promising for micro/nanoactuators.

The transverse piezoelectric coefficient e31,f and mass-sensitivity were measured on piezoelectric cantilevers based on epitaxial PZT thin-films with film-thicknesses ranging from 100 to 2000 nm. The highest values of e31,f and mass-sensitivity were observed at a film thickness of 500–750 nm, while the observed remnant polarization Pr and longitudinal piezoelectric coefficient d33,f values become saturated with a film thickness of 750–1000 nm. To obtain high performance by making use of its optimal film thickness, PZT thin films with various Zr/Ti ratios from 20/80 to 80/20 were studied. The experimental results indicated that the ferroelectric property reached a highest remnant polarization Pr at a Zr/Ti ratio of 20/80, while the longitudinal piezoelectric coefficient d33,f increased with increasing Zr content and reaches a maximum at a Zr/Ti ratio of 52/48. The findings suggest that the optimal composition for mass-sensitivity and transverse piezoelectric coefficient e31,f was shifted to the tetragonal part of the phase diagram with the Zr/Ti ratios of 45/55 and 40/60, respectively.

Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) metal oxide nanosheets (ns) are used as a buffer layer for epitaxial growth of piezoelectric capacitor stacks on Si and Pt/Ti/SiO2/Si (Pt/Si) substrates. Highly (001)- and (110)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) films are achieved by utilizing CNOns and TiOns, respectively. The piezoelectric capacitors are characterized by polarization and piezoelectric hysteresis loops and by fatigue measurements. The devices fabricated with SrRuO3 top and bottom electrodes directly on nanosheets/Si have ferroelectric and piezoelectric properties well comparable with devices that use more conventional oxide buffer layers (stacks) such as YSZ, CeO2/YSZ, or SrTiO3 on Si. The devices grown on nanosheets/Pt/Si with Pt top electrodes show significantly improved polarization fatigue properties over those of similar devices grown directly on Pt/Si. The differences in properties are ascribed to differences in the crystalline structures and the density of the films. These results show a route toward the fabrication of single crystal piezoelectric thin films and devices with high quality, long-lifetime piezoelectric capacitor structures on nonperovskite and even noncrystalline substrates such as glass or polished metal surfaces.

We investigated the residual stress and Young's modulus of Pb(ZrxTi1 - x)O3 (PZT) thin films with a (110) preferred orientation and a composition x ranging from 0.2 to 0.8. The films are grown by pulsed laser deposition on silicon cantilevers aligned along the and silicon crystal directions. Changes in resonance frequency and static bending of the cantilevers are used to determine the Young's modulus and residual stress respectively. The Young's modulus was found to be in the range of 100-200 GPa. The residual stress is tensile and shows a sharp increase from about 50 to 250 MPa at a composition of x = 0.2 to 0.4. These mechanical parameters clearly depend on the cantilever orientation with respect to the silicon crystal, which we suspect to be linked to the epitaxial growth of the films. The variation in stress with composition can be explained by the difference in thermal expansion between silicon and PZT, if we assume an intrinsic stress of 200-300 MPa to be already present immediately after deposition. Strain calculated from X-ray diffraction data leads to unreasonably high residual stress values, at least one order of magnitude higher than measured by cantilever bending. © 2016 Elsevier B.V. All rights reserved.

Dissipative particle dynamics (DPD) simulations were utilized to investigate the ability of sodium dodecyl sulfate (SDS) to adsorb inside a single-walled, arm-chair carbon nanotube (SWCNT), as well as the effect of surfactant on the properties of water inside the SWCNT. The diameter of the SWCNT varied from 1 to 5 nm. The radial and axial density profiles of water inside the SWCNTs were computed and compared with published molecular dynamics results. The average residence time and diffusivity were also calculated to show the size effect on mobility of water inside the SWCNT. It was found that nanotubes with diameter smaller than 3 nm do not allow SDS molecules to enter the SWCNT space. For larger SWCNT diameter, SDS adsorbed inside and outside the nanotube. When SDS was adsorbed in the hollow part of the SWCNT, the behavior of water inside the nanotube was found to be significantly changed. Both radial and axial density profiles of water inside the SWCNT fluctuated strongly and were different from those in bulk phase. In addition, SDS molecules increased the retention of water beads inside SWCNT (d ≥ 3nm) while water diffusivity was decreased.

This paper reports on the piezoelectric-microelectromechanical system micro-fabrication process and the behavior of piezoelectric stacks actuated silicon cantilevers. All oxide layers in the piezoelectric stacks, such as buffer-layer/bottom-electrode/film/top-electrode: YSZ/SrRuO3/Pb(Zr,Ti)3/SrRuO3, were grown epitaxially on the Si template of silicon-on-insulator substrates by pulsed laser deposition. By using an analytical model and finite element simulation, the initial bending of the cantilevers was calculated. These theoretical analyses are in good agreement with the experimental results which were determined using a white light interferometer. The dependences of the cantilever displacement, resonance frequency and quality factor on the cantilever geometry have been investigated using a laser-Doppler vibrometer. The tip displacement ranged from 0.03 to 0.42 µm V−1, whereas the resonance frequency and quality factor values changed from 1010 to 18.6 kHz and 614 to 174, respectively, for the cantilevers with lengths in the range of 100–800 µm. Furthermore, the effect of the conductive oxide electrodes on the stability of the piezoelectric displacement of the cantilevers has been studied.

This paper presents a reliability study on unpackaged metal-PZT-metal capacitors. Both ramped voltage stress (RVS) and time dependent dielectric breakdown (TDDB) measurements show that environmental humidity dramatically worsens the PZT reliability. Visible breakdown spots on the surface of PZT capacitors are studied in detail. The measurement results indicate that both reversible and irreversible PZT degradation/breakdown happen during TDDB. The dependence of time to breakdown on polarity of applied voltage is argued to relate to the crystal structure of PZT and the stack of the PZT capacitor.

The pulsed laser deposition process of 300nm thick films of Pb(Mg1/3Nb2/3)O3)0.67-(PbTiO3)0.33 on (001)-oriented SrTiO3 was studied by varying deposition pressure, substrate deposition temperature, laser fluence on the target and target-substrate distance. Perovskite phase pure, (001)-oriented, epitaxial smooth films were obtained in a narrow range of deposition parameters. The ferroelectric and dielectric properties of films fabricated within this parameter range still vary significantly. This shows the sensitivity of the system for growth conditions. The best film has a polarization value close to that expected for a (001) poled, stress free single crystal film. All films show deposition conditions dependent variations in the self-bias field. The self-bias is very stable during long cycling for films made at optimum deposition conditions. The piezoelectric coefficients of the films are strongly reduced with respect to bulk single crystal values due to the film clamping. The properties variations are ascribed to changes in the grain boundary properties in which film defects are expected to accumulate. Notably slight off-stoichiometry may cause localized screening charges, affecting specifically the polarization and dielectric constant.