Local Piezoelectric Properties Research Articles

Structure, Microstructure, and Properties of Modified Ceramics (Na,Sr)0.5Bi0.5TiO3

Single-phase ceramic samples of new compositions (Na1 – хSrх)0.5Bi0.5TiO3 (x = 0–0.5), including those modified by additives of SiO2 and ZnO oxides, have been obtained by solid-phase synthesis. The crystal structure and microstructure of these samples, as well as their dielectric, nonlinear optical, and local piezoelectric properties, have been studied. The formation of a perovskite-type phase with a pseudocubic unit cell in all synthesized samples and an increase in the cell volume as a result of partial substitution of perovskite structure cations are established. A decrease in the temperature of ferroelectric phase transitions (confirmed by the methods of dielectric spectroscopy and laser second-harmonic generation) to the tetragonal paraelectric phase is revealed. Remanent piezoelectric hysteresis loops are obtained for the synthesized samples in the polarization switching mode; this result confirms the occurrence of ferroelectric polarization switching.

Investigation on degree of non-ergodicity and local piezoelectric properties in Na0.5Bi0.5TiO3–BiFeO3–PbTiO3 system

Knowledge of the statics and dynamics of ferroelectric domains is of immense importance since they are directly correlated with macroscopic polarization and strain. For the present work, piezoresponse force microscopy (PFM) is used to afford insight into field-induced phase transitions and local switching properties of a (1–2x)Na0.5Bi0.5TiO3–xBiFeO3–xPbTiO3 system for compositions, x = 0.01, 0.03, 0.05, and 0.07. Rietveld analysis of x-ray diffraction data reveals crystallization of the compound in single and dual phases in the chosen compositions. Upon the application of a local electric field, a phase transition from relaxor to normal ferroelectric (FE) is observed for all samples. A decrease in degree of non-ergodicity is realized within this composition range, which is found by analyzing the stability of field-induced ferroelectric domains. The field-induced FE domains for lower concentrations of x are found to be irreversible and a reversible nature was found for higher values of x. In addition, spatial variations of local switching parameters are investigated with the help of switching spectroscopic-PFM and a maximum local d33 was found for compositions having dual phases.

Peculiarities of Modified Ceramics (Na0.5Bi0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3

Single-phase ceramic samples with new compositions (1 – x – у)(Na0.5Bi0.5)TiO3–хBaTiO3–у(K0.5Na0.5)NbO3 (x = 0.05, у = 0–0.15) modified with ZnO and GeO2 additions were obtained by solid-phase synthesis. Their crystal structure, microstructure, and dielectric and local piezoelectric properties were studied. A phase with a perovskite structure with a pseudocubic unit cell was found to form in all of the synthesized samples; it was shown that the unit cell volume increased as a result of the partial replacement of base cations by complex additive cations. The ferroelectric phase transitions were confirmed by dielectric spectroscopy. Residual piezoelectric hysteresis loops were obtained for the synthesized samples in the polarization switching spectroscopy mode, which confirmed the switching of ferroelectric polarization.

Li diffusion and surface segregation in K0.5Na0.5NbO3 films grown by Pulsed Laser Deposition

Potassium Sodium Niobate has recently raised particular attention in the field of piezoelectric perovskites thanks to its remarkable piezoelectric properties and high Curie temperature. Previous works have shown that slight Lithium (Li) doping can improve the piezoelectric properties and reduce leakage of stoichiometric K0.5Na0.5NbO3 (KNN). In this paper, evidence is provided that this is not the case for thin films synthesized by Pulsed Laser Deposition, at growth temperature high enough to induce the (001) orientation on a Pt(111) /TiO2/SiO2/Si template. The high mobility of alkali ions leads to Li surface segregation and high non-uniformity of Li doping over the film thickness. This is accompanied by a degradation of KNN thin film electrical properties upon Li doping, with an increase in leakage currents by up to one order of magnitude which impedes a macroscopic piezoelectric characterization. On the other hand, local piezoelectric properties investigated by Piezoresponse Force Microscopy are unchanged upon doping. The results clearly point out the critical issues regarding the growth method to obtain a uniform doping of KNN with light elements such as Li. Due to the high mobility of this species, sizable migration phenomena can be thermally activated in physical vapor deposition processes with high thermal budget, ultimately hampering the envisaged benefits of Li on piezoelectric response.

Local piezoelectric properties of perforated ferroelectric barium–strontium titanate films

Objectives. Focused ion beam etching remains one of the most common methods for fabricating 2D photonic crystals and structures based on functional materials. This technique is quite well developed for semiconductors. But at the same time, the change in the properties of ferroelectric materials under the action of a focused ion beam, including parameters of distribution and switching of the polarization state under the action of an electric field, remains poorly studied. The purpose of this work is to determine the local piezoelectric parameters in perforated ferroelectric films of barium strontium titanate (Ba0.8Sr0.2TiO3) with ordered vertical air channels fabricated by focused ion beam etching.Methods. Experimental studies were conducted using piezoresponse force microscopy under applied electric field in planar geometry.Results. It is shown that the perforation of a ferroelectric film leads not only to the formation of significant inhomogeneities in the piezoelectric response distribution in the structure, but also to the noticeable increase in the magnitude of both the vertical and lateral components of the piezoresponse near the perforation holes. The calculation results showed that the greatest enhancement is observed for the lateral component of the piezoresponse: from 5 pm/V for a nonperforated film to 65 pm/V in the perforated area.Conclusions. The most probable mechanism for such a change in properties is the influence of a disturbed layer that occurs at the boundary and the inner surface of vertical air channels. The properties of this layer are due to two factors: amorphization of the structure as a result of the focused ion beam etching and the appearance of pinned domain states near the hole, leading to the formation of the complex piezoresponse distribution both at the hole boundary and in the gap between the perforations. The information obtained is important for understanding the peculiarities of the formation of local piezoelectric and ferroelectric responses in photonic crystals fabricated by focused ion beam etching, as well as for finding ways to control their state when an external electric field is applied.

Robust Piezoelectric Coefficient Recovery by Nano-Inclusions Dispersion in Un-Poled PVDF–Ni0.5Zn0.5Fe2O4 Ultra-Thin Films

This work aimed to study the influence of the hybrid interface in polyvinylidene fluoride (PVDF)-based composite thin films on the local piezoelectric response. Our results provide evidence of a surprising contradiction: the optimization process of the β-phase content using nano-inclusions did not correspond to the expected nanoscale piezoelectric optimization. A large piezoelectric loss was observed at the nanoscale level, which contrasts with the macroscopic polarization measurement observations. Our main goal was to show that the dispersion of metallic ferromagnetic nano-inclusions inside the PVDF films allows for the partial recovery of the local piezoelectric properties. From a dielectric point of view, it is not trivial to expect that keeping the same amount of the metallic volume inside the dielectric PVDF matrix would bring a better piezoelectric response by simply dispersing this phase. On the local resonance measured by PFM, this should be the worst due to the homogeneous distribution of the nano-inclusions. Both neat PVDF films and hybrid ones (0.5% in wt of nanoparticles included into the polymer matrix) showed, as-deposited (un-poled), a similar β-phase content. Although the piezoelectric coefficient in the case of the hybrid films was one order of magnitude lower than that for the neat PVDF films, the robustness of the polarized areas was reported 24 h after the polarization process and after several images scanning. We thus succeeded in demonstrating that un-poled polymer thin films can show the same piezoelectric coefficient as the poled one (i.e., 10 pm/V). In addition, low electric field switching (50 MV/m) was used here compared to the typical values reported in the literature (100–150 MV/m).

Frequency-dependent PFM signal induced by surface adsorbates

Piezoresponse force microscopy (PFM) is an indispensable tool for investigating local piezoelectric and ferroelectric properties by detecting the electromechanical strain response to an applied voltage on a surface. The PFM technique is highly sensitive to the surface state of a sample, such as surface adsorption and surface potential, which could lead to the misinterpretation of the quantitative value of PFM signal as well as the presence of ferroelectricity. In this study, we observed a frequency-dependent PFM signal generated by surface adsorbates. However, the surface adsorbates can be removed by sample cleaning albeit the cleaning induced a significant change in surface potential. Thus, correct evaluation of the effective piezoelectric coefficient was realized by cleaning the sample and ruling out the electrostatic contribution. This work demonstrates that one should be careful to consider the effect of adsorbates and the electrostatic effect to correctly evaluate the piezoelectric coefficient.

Textured K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> Thin Films by Aqueous Chemical Solution Deposition on SrTiO<sub>3</sub> Substrates for MEMS Applications

Na0.5K0.5NbO3 (KNN) thin films were fabricated on (100) oriented SrTiO3 substrates by spin coating a stable environmentally friendly aqueous KNN precursor. Homogeneous films with an average grain size down to 60 nm were observed after heat treatment at 900 °C. The high degree of texture was confirmed by XRD. The intensity of the KNN (100) reflection for films on (100) oriented substrates increased with increasing sintering temperature up to 900 °C. The ferroelastic and piezoelectric properties of the film was confirmed by PFM. Local piezoelectric properties of selected films will be discussed in relation to the processing conditions, microstructure and orientation of the substrate.

Influence of A-site doping on properties of lead-free KNN-based perovskite ceramics

Influence of A-site doping with Li+, Ag+, and K+ cations on structure, microstructure, dielectric, ferroelectric, and local piezoelectric properties of potassium niobate (K0.5Na0.5)NbO3 ceramics was studied. Changes in the unit cell parameters correlated with ionic radii changes. Correlations between dielectric and piezoelectric properties were confirmed. The highest effective local d33 piezoelectric coefficient values were observed in Ag+-doped compositions prepared by the sol-gel method.

Phase transitions, dielectric and piezoelectric properties of [(Na0.5Bi0.5)1-xLix]TiO3 (x = 0 – 0.1) ceramics

The effect of substitution of lithium cations in the sublattice A of sodium bismuth titanate on the parameters of the crystal structure, microstructure, dielectric and local piezoelectric properties of ceramics [(Na0.5Bi0.5)1-xLix] TiO3 with x = 0 ÷ 0.1 has been studied. Modified samples have been characterized by phase transitions manifesting themselves in the form of peaks of permittivity near ∼600 K. An increase in the value of the piezoelectric coefficient d33 at x ≥ 0.08 has been established, which correlates with an increase in the value of dielectric permittivity at room temperature.

Manganese-doping enhanced local heterogeneity and piezoelectric properties in potassium tantalate niobate single crystals.

Ion doping, an effective way to modify the nature of materials, is beneficial for the improvement of material properties. Mn doping exhibits gain of piezoelectric properties in KTa1-x Nb x O3 (KTN). However, the impact mechanism of Mn ions on properties remains unclear. Here, the effects of Mn doping on local heterogeneity and piezoelectric properties in KTN are studied. The electric field-induced strain of Mn-doped KTN is ∼0.25% at 10 kV cm-1, 118% higher than that of pristine KTN. Meanwhile, as a result of Mn doping, the dielectric permittivity was tripled and the ferroelectricity was modified. The changes in A1(2TO), B1 + E(3TO) and E(4TO) vibrations characterized by Raman spectra indicate increased local polarization, weak correlation of dipoles and distorted lattices in Mn-doped KTN, respectively. First-principles calculations demonstrate stronger local heterogeneity introduced by Mn dopants, which weakens the dipole correlations and reduces domain sizes. As a result, the decreased domain sizes, combined with the larger ratio of lattice parameters c and a of the Mn-contained portion, are responsible for the higher piezoelectricity. This work reveals the impact on properties of KTN from Mn dopants and the prominent role of local heterogeneity in improving piezoelectricity, being valuable for the optimization and design of material properties.

In-plane polarization contribution to the vertical piezoresponse force microscopy signal mediated by the cantilever “buckling”

Rigorous experimental/theoretical approach to measure and to minimize in-plane piezoresponse contribution to the vertical piezoresponse force microscopy (PFM) signal is presented. In-plane piezoresponse mediated by the cantilever “buckling” is shown to affect apparent vertical PFM signal being of the same order of magnitude as a true out-of-plane piezoresponse. Decoupling of these two contributions based on simple mathematical procedure is demonstrated. Row PFM data are analyzed as a function of the laser beam focus position on the cantilever allowing suppression of “buckling” contribution and, hence, measurement of only out-of-plane piezoresponse component. This approach can be used for the accurate recovery of the piezoresponse displacement vector, what is of paramount importance for the reconstruction of the domain structures and quantitative characterization of the polarization distribution and local piezoelectric properties in ferroelectric materials.

Dielectric and local piezoelectric properties of lead-free KNN-based perovskite ceramics

Influence of cation substitutions in (K0.5Na0.5)NbO3–Ba(Li2/5W3/5)O3 ceramics on structure parameters, microstructure, dielectric, ferroelectric and local piezoelectric properties have been studied. Depending on solid solutions compositions, changes in structure parameters and effective d33 piezoelectric coefficient and other properties were observed.

Local piezoelectric properties in Na-flux GaN bulk single crystals

The local piezoelectricity of a Na-flux GaN crystal grown on a multipoint-seed-GaN template is investigated using piezoresponse force microscopy. The piezoresponse is critically dependent on two types of growth regions that are dominantly formed in the Na-flux GaN crystal: the c-growth sector (cGS), which is grown on top of the point-seed GaN surface with a growth front of (0001) planes, and the facet-growth sector (FGS), which is grown on the side of cGS with {101¯1} facets. Quantitative analyses reveal the GaN surface displacements at cGS that result from the piezoresponses increase with the applied AC voltage: the measured values well reflect the piezoelectric constant of d33 in GaN. The piezoresponses at the FGS and the boundary between the cGS and FGS are less sensitive than that at the cGS. A combination of cathodoluminescence and multiphoton excitation photoluminescence techniques clarifies that a local reduction of the piezoresponse observed in cGS is attributed to microscale FGSs that exist randomly in cGS. The dependence of the piezoresponse on the growth regions is quantitatively discussed from three possible viewpoints that potentially affect the polarization properties of GaN: residual strain, local crystallographic tilting, and inherent carrier distribution. As a result, a carrier screening effect is the most probable candidate to induce reduction of the piezoresponse in the FGSs of GaN crystals.

Structure, ferroelectric and local piezoelectric properties of KNN-based perovskite ceramics

Structure, microstructure, dielectric, ferroelectric, and local piezoelectric properties of perovskite ceramics in the systems (1-x)(K0.5Na0.5)NbO3 – x(Bi0.5Na0.5)TiO3 (x = 0 ÷ 0.1) and (1-x)(K0.5Na0.5)NbO3 – x(Bi0.5Na0.5)ZrO3 (x = 0.01 ÷ 0.05) have been studied. Improvement of dielectric parameters and effective d33 piezoelectric coefficient was obtained in compositions with x = 0.03 and 0.05, correspondingly.

Microstructure and Properties of Lead-Free Perovskite Ceramics on the Base of KNN Perovskite

The influence of LiSbO3 on the structure, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K0.5Na0.5)NbO3 ceramics has been studied. Changes in unit cell parameters correlated with ionic radii changes and high effective local d33 piezoelectric coefficient values were observed depending on solid solutions compositions.

Silver niobate doped lead-free perovskite KNN ceramics

Influence of AgNbO3 doping on structure, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K0.5Na0.5)NbO3 ceramics was studied. Decreased in the unit cell parameters correlated with ionic radii changes. High effective local d 33 piezoelectric coefficient values (800 pm/V) were observed in compositions studied.

Atomic-scale origin of ultrahigh piezoelectricity in samarium-doped PMN-PT ceramics

Designing high-performance piezoelectric materials based on atomic-scale calculations is highly desired in recent years, following the understanding of the structure-property relationship of state-of-the-art piezoelectric materials. Previous mesoscale simulations showed that local structural heterogeneity plays an important role in the piezoelectric property of ferroelectrics; that is, larger structural heterogeneity leads to higher piezoelectricity. In this Rapid Communication, by combining first-principles calculations and experimental characterizations, we explored the atomic-scale origin of the high piezoelectricity for samarium-doped $\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-PT) ceramics, which possesses the highest piezoelectric ${d}_{33}$ of $\ensuremath{\sim}1500\phantom{\rule{0.16em}{0ex}}\mathrm{pC}\phantom{\rule{0.28em}{0ex}}{\mathrm{N}}^{\ensuremath{-}1}$ among all known piezoelectric ceramics. The impacts of various dopants on local structure and piezoelectric properties of PMN-PT ceramics were investigated in terms of the effective ionic radius and cation valence. Our results show that A-site dopants with a valence of 3+ are more effective to produce local structural heterogeneity in PMN-PT when compared with the A-site dopants with a valence of 2+, and a smaller dopant size leads to a larger variation of local structure. According to this study, the outstanding piezoelectricity in Sm-doped PMN-PT ceramics is attributed to the fact that $\mathrm{S}{\mathrm{m}}^{3+}$ is the smallest ions that can entirely go to the A site of PMN-PT rather than the B site. The present work may benefit the design of high-performance piezoelectric materials based on the concept of local structural engineering.

Significance of electrostatic interactions due to surface potential in piezoresponse force microscopy

Piezoresponse force microscopy (PFM) has gradually becomes indispensable tool to investigate local piezoelectric and ferroelectric properties in diverse material systems. However, numerous reports have shown that the PFM signal can originate from several non-piezoelectric origins. Among them, because the electrostatic interaction between the AFM tip/cantilever and sample surface can be readily involved, it can be the most important factor during PFM measurement. In particular, in materials with relatively low piezoelectricity, the situation can be more significant because the PFM signals from weak piezoelectricity can be hidden or buried by the electrostatic interactions. Herein, we examined the significance of the electrostatic interactions induced by the surface potential in PFM. Using piezoelectric and non-piezoelectric materials, we examined how the surface potential-dependent electrostatic interactions can significantly affect the PFM signal. We observed that the electrostatically induced PFM amplitude have a linear relationship with the magnitude of surface potential when the instrumental noise floor is properly considered. Our results demonstrate that electrostatic interactions can be significant and their recognition and minimization are essential during PFM and other AFM-based measurements.

Fabrication of preferentially (001)-oriented Pb(Zr,Ti)O3 films consisting of anisotropic single crystal nanoparticles

Single crystal Pb(Zr,Ti)O3 (PZT) nanoparticles were synthesized via a hydrothermal method using oleic acid. The obtained PZT nanoparticles had a sheet-like structure, and transmission electron microscopy observations revealed that the normal direction of these sheet-like nanoparticles corresponds to the c-axis. PZT films consisting of these nanoparticles were fabricated through the dip-coating method on a Pt/TiOx/SiO2/Si substrate; the sheet-like nanoparticles were aligned with their c-axes parallel to the substrate. Preferentially (001)-oriented PZT film was formed because of the morphology of each single PZT crystal, and this preferential (001)-orientation was maintained even after heat treatment at 600 °C. Local piezoelectric properties were measured via piezoresponse force microscopy with a cantilever as the top electrode, and piezoelectric constant−applied voltage hysteresis loops with high squareness were obtained for the PZT film heated at 600 °C.