Direct Piezoelectric Coefficient Research Articles

A Chiral B−N Adduct as a New Frontier in Ferroelectrics and Piezoelectric Energy Harvesting

AbstractWithin the burgeoning field of electronic materials, B−N Lewis acid‐base pairs, distinguished by their partial charge distribution across boron and nitrogen centers, represent an underexplored class with significant potential. These materials exhibit inherent dipoles and are excellent candidates for ferroelectricity. However, the challenge lies in achieving the optimal combination of hard‐soft acid‐base pairs to yield B−N adducts with stable dipoles. Herein, we present an enantiomeric pair of B−N adducts [R/SC6H5CH(CH3)NH2BF3] (R/SMBA‐BF3) crystallizing in the polar monoclinic P21 space group. The ferroelectric measurements on RMBA‐BF3 gave a rectangular P‐E hysteresis loop with a remnant polarization of 7.65 μC cm−2, a value that aligns with the polarization derived from the extensive density‐functional theory computations. The PFM studies on the drop‐casted film of RMBA‐BF3 further corroborate the existence of ferroelectric domains, displaying characteristic amplitude‐bias butterfly and phase‐bias hysteresis loops. The piezoelectric nature of the RMBA‐BF3 was confirmed by its direct piezoelectric coefficient (d33) value of 3.5 pC N−1 for its pellet. The piezoelectric energy harvesting applications on the sandwich devices fabricated from the as‐made crystals of RMBA‐BF3 gave an open circuit voltage (VPP) of 6.2 V. This work thus underscores the untapped potential of B−N adducts in the field of piezoelectric energy harvesting.

A Chiral B-N Adduct as a New Frontier in Ferroelectrics and Piezoelectric Energy Harvesting.

Within the burgeoning field of electronic materials, B-N Lewis acid-base pairs, distinguished by their partial charge distribution across boron and nitrogen centers, represent an underexplored class with significant potential. These materials exhibit inherent dipoles and are excellent candidates for ferroelectricity. However, the challenge lies in achieving the optimal combination of hard-soft acid-base pairs to yield B-N adducts with stable dipoles. Herein, we present an enantiomeric pair of B-N adducts [R/SC6H5CH(CH3)NH2BF3] (R/SMBA-BF3) crystallizing in the polar monoclinic P21 space group. The ferroelectric measurements on RMBA-BF3 gave a rectangular P-E hysteresis loop with a remnant polarization of 7.65 μC cm-2, a value that aligns with the polarization derived from the extensive density-functional theory computations. The PFM studies on the drop-casted film of RMBA-BF3 further corroborate the existence of ferroelectric domains, displaying characteristic amplitude-bias butterfly and phase-bias hysteresis loops. The piezoelectric nature of the RMBA-BF3 was confirmed by its direct piezoelectric coefficient (d33) value of 3.5 pC N-1 for its pellet. The piezoelectric energy harvesting applications on the sandwich devices fabricated from the as-made crystals of RMBA-BF3 gave an open circuit voltage (VPP) of 6.2 V. This work thus underscores the untapped potential of B-N adducts in the field of piezoelectric energy harvesting.

Nanoscale Study of the Polar and Electronic Properties of a Molecular Erbium(III) Complex Observed via Scanning Probe Microscopy

We successfully synthesized millimeter-sized single crystals of the molecular erbium(III) complex Er(acac)3(cphen), where acac = acetylacetonate and cphen = 5-chloro-1,10-phenanthroline. The novelty of this work stems from the exhaustive examination of the polar and electronic properties of the obtained samples at the macro-, micro-, and nanoscale levels. The single crystal X-ray diffraction method demonstrates the monoclinic (noncentrosymmetric space group P21) crystallographic structure of the synthesized samples and scanning electron microscopy exhibits the terrace–ledge morphology of the surface in erbium(III) crystals. By using the piezoelectric force microscopy mode, the origin of the polar properties and the hyperpolarizability in the synthesized samples were assigned to the internal domain structure framed by the characteristic terrace–ledge topography. The direct piezoelectric coefficient (~d33) was found to be intensely dependent on the local area and was measured in the range of 4–8 pm/V. A nanoscale study using the kelvin probe force and capacitance force (dC/dz) microscopy modes exposed the effect of the Er ions clustering in the erbium(III) complex. The PFM method applied solely to the Er ion revealed the corresponding direct piezoelectric coefficient (~d33) of about 4 pm/V. Given the maximum piezoelectric coefficient in the erbium(III) complex at 8 pm/V, we highlight the significant importance of the spatial coordination between the lanthanide ion and the ligands. The polar coordination between the lanthanide ion and the nitrogen and oxygen atoms was also corroborated by Raman spectroscopy supported by the density functional theory calculations. The obtained results can be of paramount importance for the application of molecular erbium(III) complex crystals in low-magnitude magnetic or electric field devices, which would reduce the energy consumption and speed up the processing switching in nonvolatile memory devices.

Morphological properties of ZnO nanostructures doped with Ag and Li for piezoelectric applications

The development of a facile method to obtain materials with piezoelectric properties, through a green synthesis, as an alternative to lead-free materials, was the main objective of this work. Piezo active materials were grown by chemical methods on two types of metal substrates: Pt/Ti/SiO2/Si and the Ti foil. Ag and Li-doped ZnO nanostructures were prepared by hydrothermal method at low temperature on metallic substrates which were previously covered with ZnO seed layer deposited by spin coating sol-gel method. The newly prepared materials were covered with a polymer layer and were morphological characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The piezoelectric properties were estimated by measuring the direct piezoelectric coefficient d33. The test results show that the doped ZnO nanostructures synthesized using a green route exhibit a piezoelectric response so the established method can be considered a promising approach for obtaining piezoelectric materials on large surfaces. Piezo active nanostructures could be of interest for integration into piezoelectric devices.

Simultaneous high-frequency measurement of direct and inverse transverse piezoelectric coefficients of thin films using longitudinal vibration

Simultaneous high-frequency measurement of direct and inverse transverse piezoelectric coefficients of thin films using longitudinal vibration

A combination of large unipolar electrostrain and d33 in a non-ergodic relaxor ferroelectric

One of the important requirements for piezoelectric materials for use as high strain actuators is that they exhibit large unipolar electrostrain with minimum hysteresis. While large unipolar electrostrain >1% is generally achievable in good quality single crystals, most polycrystalline piezoelectric show low values < 0.4%. Unipolar electrostrain 0.5%–0.7% in polycrystalline piezoelectrics has often been reported in Na0.5Bi0.5TiO3-based compositions at the non-ergodic ergodic boundary. Not amenable to poling, such materials exhibit almost nearly zero direct piezoelectric coefficient (d33 ∼ 0 pC/N) and cannot be simultaneously used as a sensor. In this paper, we report a combination of large unipolar electrostrain of ∼0.6% with small strain hysteresis of 25% in a Sn-modified relaxor ferroelectric system PbTiO3–Bi(Ni1/2Zr1/2)O3. It exhibits d33 ∼ 340 pC/N, which is stable up to 130 °C, and large signal converse piezoelectric coefficient d33* ∼ 1200 pm/V. A combination of large d33 and d33* in the same material makes it an important candidate for simultaneous use as a sensor and high strain actuators. X-ray diffraction study in situ with the electric field suggests that large electrostrain with low strain hysteresis in this system is because of the increased reversible switching of the field stabilized tetragonal ferroelastic domains.

High output performance of piezoelectric energy harvesters using epitaxial Pb(Zr, Ti)O3 thin film grown on Si substrate

For a high power density in piezoelectric energy harvesters, both a large direct piezoelectric coefficient (e31,f) and a small relative permittivity constant (εr,33) are required. This study proposed an energy harvesting device made of an epitaxial Pb(Zr, Ti)O3 (PZT) thin film grown on a Si substrate. The epitaxial PZT thin film is deposited on the Si substrate by RF magnetron sputtering. The epitaxial PZT thin film grown on Si substrate has a εr,33 constant of 318. The output voltage as a function of input displacement was measured using a shaker to evaluate the direct e31,f coefficients and energy harvester output characteristics. According to the figure of merit defined as (e31,f)2/ε0εr,33, the epitaxial PZT/Si cantilever is 32 GPa. At a resonant frequency of 373 Hz under an acceleration of 11 m/s2, the epitaxial PZT/Si cantilever has a high output power of 40.93 μW and power density of 108.3 μW/cm2/g2 without any damage, which is very promising for high power energy harvester applications.

Structural, dielectric, ferroelectric, and electromechanical performance of Mn modified (BaCa)(ZrTi)O3 ceramics

Lead-free (Ba0.85Ca0.15)(Zr0.1Ti0.9)1-xMnxO3 [x = 0.01,0.02,0.03,0.04,0.05] ceramics were prepared by conventional solid-state reaction method. The structural evaluation was analyzed by the X-ray diffraction and Rietveld refinement, which illustrate that all the compositions exhibit dual phase crystal structure i.e., tetragonal + orthorhombic with space group P4mm+ Amm2. The surface morphology was studied using the scanning electron microscope and it is found that Mn doping modifies the grain size. The temperature and frequency-dependent dielectric study show that the dielectric constant reduces with an increase in Mn content. The lowering of the Curie temperature is also observed with an increase in Mn doping percentage. A well-saturated ferroelectric loop is obtained for all compositions with a reduction in the remnant polarization and coercive electric field. The direct piezoelectric coefficient was measured by the quasi-static method for all the compositions. The elastic compliances and piezoelectric and coupling parameters of all the compositions were calculated using the resonance and anti-resonance technique. The figure of merit concerning energy harvesting was calculated using the parameters obtained from the resonance and anti-resonance measurement. The high value of elastic, piezoelectric, and coupling parameters makes the composition suitable for harvesting application.

Self-powered, high sensitivity printed e-tattoo sensor for unobtrusive arterial pulse wave monitoring

Self-powered, highly unobtrusive, low-cost and accurate arterial pulse wave monitoring devices need to be developed to enable cost-efficient monitoring of entire cardiovascular disease risk groups. We report the development of a scalable fabrication process for a highly unobtrusive piezoelectric ultra-thin (t ~ 4,2 µm) e-tattoo arterial pulse wave sensor which utilizes only transparent and biocompatible polymer-based materials. The ferroelectric performance of the ultra-thin P(VDF-TrFE) material layer is optimized through the use of crosslinked PEDOT:PSS electrodes; this results in ~70 % and ~34 % improvements in remanent polarization (Pr) and coercive field (Ec), respectively, when compared to the sensors with pristine PEDOT:PSS electrodes. The ultra-thin form factor enables access to the high bending mode sensitivity of the P(VDF-TrFE) material layer; the maximum sensitivity value achieved in uniaxial and multiaxial bending is ~1700 pC N-1, which is ~50 times higher than the measured normal mode sensitivity. The increased sensitivity is linked to a specific set of direct piezoelectric coefficients using combination of experimental results, statistical analysis and finite element modeling. Finally, the accuracy of the e-tattoo sensor is demonstrated in the non-invasive measurement of radial artery pulse wave by comparing the signal to that obtained with reference device from 7 study subjects.

Highly (00l)-textured BiFeO3 thick films integrated on stainless steel foils with an optimized piezoelectric performance

Piezoelectric BiFeO3 films were successfully prepared on 304 stainless steel (SS) foils via RF-magnetron sputtering at 450 °C. By adopting a LaNiO3/Pt/Ti tri-layer bottom electrode, a predominant (100)-orientation and a better crystalline morphology were achieved in the BiFeO3 film, resulting in better ferroelectric and dielectric properties targeted for piezoelectric applications than those directly grown on SS or LaNiO3/SS. These properties include a large remnant polarization (Pr~68 μC/cm2), a large coercive field (Ec~241 kV/cm) and a sizable self-bias (Ebi~ 158 kV/cm), as well as a low dielectric constant and a reduced dielectric loss (εr≤200 and tan δ ≤ 0.026 in 1 kHz-1 MHz). Based on this optimal BiFeO3-SS heterostructure, large converse and direct transverse piezoelectric coefficients |e31,f| ~ 1.7 C/m2 and 1.07 C/m2 were achieved in prototype piezoelectric actuator and energy harvester structures, respectively. These results suggest that BiFeO3-SS heterostructures have a great potential for applications in lead-free, metal-based piezoelectric micro-electro- mechanical systems (piezo-MEMS).

Achieving Large Switchable Polarization and Enhanced Piezoelectric Response in BiFeO3‐PbTiO3 Solid Solution Ceramics

AbstractPerovskite materials based on BiFeO3‐PbTiO3 (BFPT) solid solutions are promising for various applications thanks to the extremely large spontaneous polarization (Ps) and existence of multiferroic morphotropic phase boundary. For applications in piezoelectric and memory devices, complete switching of Ps is needed, which is hard to achieve practically. In this work, a simple modified mixed‐oxide reaction method is developed allowing to prepare Dy‐ and Sm‐modified BFPT ceramics with significantly improved properties. The MPB compositions demonstrate well‐saturated ferroelectric hysteresis loops with large switchable remanent polarization of 60 µC cm−2 and enhanced piezoelectric properties with a large‐signal piezoelectric coefficient d33* = 214 pm V−1 and a direct piezoelectric coefficient d33 = 128 pC N−1, which is one and a half times larger than the best d33 value reported for the BFPT ceramics so far. The Curie temperature reaches 539 °C, suggesting a potential for high‐temperature applications. The domain structure is studied by piezoresponse force microscopy. It is found that the enhanced dielectric/piezoelectric properties are mainly due to polarization rotation/extension (intrinsic) mechanism, while the extrinsic contributions of the interphase and domain walls are virtually absent. The strategies for improvement of properties of BFPT and related materials are proposed.

One simple approach, two remarkable enhancements: Manipulating defect dipoles and local stress of (K, Na)NbO3-based ceramics

Although the composition-driven multi-phase coexistence strategy has been widely used to modify the piezoelectric properties of potassium sodium niobate ((K, Na)NbO3, KNN) based ceramics, the trade-off between long-range ferroelectric ordering and chemical additives-induced disorder hinders the further improvement of piezoelectricity and makes the electric field-induced strain temperature-dependent. Herein, to resolve two issues, we proposed a new concept, that is, manipulating defect dipoles and local stress of a pre-constructed multi-phase coexistence through controlling zirconium (Zr) content. We validated the new concept by designing 0.96(K0.4Na0.6)Nb0.955Sb0.045O3-0.04(Bi0.5Na0.5)Zr(1+x)O3 ceramics. In samples with Zr deficiency (i.e., x=-0.1), we obtained high retention of 91% in normalized unipolar strain (Suni) over the temperature range of 30-160 °C, even under low electric fields of 10-20 kV/cm, superior to those of other representative KNN-based ceramics. In samples with slight Zr excess (i.e., x=0.07), we achieved an increase in direct piezoelectric coefficient (d33) and converse piezoelectric coefficient (d33*) by 12% and 25%, respectively, in comparison with that at x=0. The enhanced temperature stability stems from the released domain walls that are pinned by defect dipoles, and the increased d33 (and d33*) originates from the synergetic contributions of the multi-phase coexistence, increased grain size, and stabilization of the ZrO2 secondary phase. Therefore, our new concept would benefit the composition design and performance improvement of KNN-based ceramics in the future.

Piezoelectric unimorph microcantilevers for measuring direct and converse piezoelectric coefficients

In this study, we propose a new piezoelectric measurement method using unimorph microcantilevers to evaluate precise values of direct and converse piezoelectric coefficients for piezoelectric microelectromechanical system applications. We fabricated unimorph microcantilevers comprising 3-μm-thick polycrystalline Pb(Zr,Ti)O3 (PZT) thin films on a 20-μm-thick silicon (Si) layer. The converse piezoelectric coefficient was measured as |e31,f| = 3.9–5.8 C/m2, which was in good agreement with the measurement results of PZT thin films without microfabrication. The direct piezoelectric properties of the PZT microcantilevers were measured at the resonance frequency of each microcantilever, and |e31,f| was ∼2 C/m2, which was consistent with previous reports on the piezoelectric properties of a PZT thin film on Si. Since the measurement results included the effects of the stress condition and microfabrication damage, the measurement method of this study can evaluate the actual piezoelectric coefficient of piezoelectric properties in microdevice structures.

The Influence of Pressure on Structural, Elastic, Piezoelectric and Dielectric Properties of R3c‐BiAlO3 Based on Ab Initio Calculations

AbstractIn this paper, we deal with a theoretical and predictive study of the influence of the applied pressures on the structural, elastic and piezoelectric properties of the rhombohedral BiAlO3 perovskite (R3c space group) phase by combining both the density functional theory (DFT) and the density functional perturbation theory (DFPT) included in the ABINIT code. The results indicate a decrease in structural cell volume and the elastic constants appear to be more intense as the applied pressure increases. Due to the increase in the direct piezoelectric coefficient (e33) and the decrease of the elastic constant (c33), the converse piezoelectric coefficients (d33) tend to improve with increased pressure applied. At a pressure of 10 GPa, the value of the direct piezoelectric constant reached 6.23 C/m2 which becomes an indirect competitor to lead zirconate titanate (PZT). The dielectric constants and born effective charge at high pressure have been calculated. Our results agree well with the available experimental and theoretical results. Our findings, especially piezoelectricity, can help in various applications of high‐pressure devices such ultrasonic transducer.

Influence of annealing temperature on the existence of polar domain in uniaxially stretched polyvinylidene-co-hexafluoropropylene for energy harvesting applications

The structural and electroactive properties of the as-prepared random copolymer polyvinylidene-co-hexafluoropropylene thin film are explored as a function of thermal treatment at various temperature regions. The thermal treatment of the polymer thin film not only changes the structural conformations that is very natural but establishes a polar domain in the non-polar α-phase. Here, we discover an anomalous temperature-dependent crossover behavior from the non-polar α-phase to an appreciable enhancement in ferroelectric and piezoelectric responses. The maximum unipolar strain (Smax=−5.01%), an ultrahigh value of normalized piezoelectric coefficient (d33∗=−556pm/V), high electromechanical coupling factor (Kp=0.78) factor including the high dielectric constant (ϵ′=23at100Hz) at a relatively low electric field of 900 kV/cm may, therefore, be an effect of the established polar domain for the sample annealed at 105 °C. The direct piezoelectric charge coefficient (d33), a key factor for the performance of a prepared polymer thin film system as an energy harvester, lies in the range of −10±2pC/N. Also, the annealed sample exhibited a persistent polarization after several cumulative cycles of applied stress.

Flexoelectric Poling of Functionally Graded Ferroelectric Materials

AbstractFlexoelectricity is a phenomenon that can yield an electromechanical coupling in all dielectric materials, whereas piezoelectricity presents itself in specially treated (electrically poled) ferroelectric materials. The present study explores the possibility of achieving electrical poling in a material, purely by mechanical means, by virtue of flexoelectricity and thereby harnessing the potential of coexistence of the two phenomena. A theoretical investigation on a functionally graded ferroelectric material sample of square shape with barium titanate and polyvinylidene fluoride as its constituents is conducted in this direction using isogeometric analysis based computational framework. Applied mechanical load on the material results in varying magnitude of electric field inside the material, which in some fraction of the material reaches a magnitude sufficient enough to yield a permanent poling. Simulation results suggest that it is possible to achieve poling of up to 75% of the material volume. This partially poled material is later considered for its contribution in the total electromechanical coupling of the material. The combination of piezoelectric and flexoelectric effects is found to enhance the equivalent piezoelectric coefficient in converse electromechanical (by up to 90%) coupling while a detrimental effect is observed in direct equivalent piezoelectric coefficient (by up to 89%) due to this combination.

Good piezoelectricity of self-polarized thick epitaxial (K,Na)NbO3 films grown below the Curie temperature (240 °C) using a hydrothermal method

Using a hydrothermal method, (K0.88Na0.12)NbO3 films were deposited at 240 °C on (100) cSrRuO3//(100)SrTiO3 substrates. Moreover, without any poling treatment, direct and inverse transverse piezoelectric coefficients, e31,f, near 0 kV/cm were approximately −5.0 C/m2 for the as-deposited film. This value was nearly unchanged following the application of an electric field and poling treatment, suggesting that as-deposited films are almost in a fully self-polarized state without the application of an electric field. As-deposited films with a thickness of up to 22 μm showed constant piezoelectricity without any poling treatment. The films did not crack or peel because of substrates due to the small thermal strain originating from the low deposition temperature. The figures of merit (FOM) for the vibration energy harvester [FOM = e31,f2/(ε0εr)] and sensor [FOM = e31,f/(ε0εr)] were estimated to be good at 32.8 GPa and –5.9 GV/m, respectively, primarily because of the low relative dielectric constant of ∼110. Furthermore, the piezoelectric voltage coefficient g31 [= d31/(ε0εr)] was estimated and demonstrated a high value of 0.073 Vm/N.

Dependency of direct and inverse transverse piezoelectric properties on composition in self-polarized epitaxial (KxNa1−x)NbO3 films grown via a hydrothermal method

(KxNa1−x)NbO3 films that were approximately 3 μm in thickness and with various x values were systematically deposited at 240 °C on (100)cSrRuO3//(100)SrTiO3 substrates using a hydrothermal method. Direct and inverse transverse piezoelectric coefficients, e31,f, near 0 kV cm−1 were approximately −5.0 C m−2 for the as-deposited films with a wide range of x values without any poling treatment. A large difference in e31,f value was not observed before or after poling treatment upon applying a positive electric field, suggesting that the as-deposited (KxNa1−x)NbO3 films with x = 0.36–0.88 were almost fully in a self-polarized state. (KxNa1−x)NbO3 films with x = 0.36–0.88 without any poling treatment showed a figure of merit for an energy harvester (FOM = e31,f2/εr) above 0.13, as calculated directly from e31,f. These FOM values are relatively high compared with the reported ones for other lead-free films that have a perovskite structure.

An evaluation method for direct piezoelectric coefficients of thin films using both-ends-hinge-supported unimoprh beams

We have developed a new method for measuring the direct piezoelectric effect of piezoelectric thin films, consisting of both-ends-hinge-supported unimorph beams (BUBs). This method can determine the precise direct transverse piezoelectric coefficient e31,f of arbitrary piezoelectric films by measuring the displacement and the output voltage between the electrodes of the BUBs. We formulated the e31,f values based on the flexure basic formula, and a constitutive equation of electromagnetic field for the BUBs, including measuring systems such as oscilloscopes, which have an arbitrary input impedance. In this study, we were able to obtain a piezoelectric coefficient of a lead zirconate titanate (PZT) thin film on a Si substrate of e31,f = 4.7 Cm−2, regardless of the input impedance of the measurement instrument. Using this method, we then measured the temperature characteristics of e31,f for the PZT thin film. We clearly observed the increase of e31,f , and the relative dielectric constant, with an increase in temperature. We obtained a temperature gradient for of a = 0.01 Cm−2K−1, a value which is in good agreement with previous research. We also measured the time dependences of the e31,f after polling piezoelecric films. The e31,f value decreased over time, and we were able to obtain a logarithmic time gradient for normalized e31,f of p = −0.01, a value consistent with the results of previous studies.

Phase diagram for Bi-site La-doped BiFeO3[sbnd]BaTiO3 lead-free piezoelectric ceramics

Three different series of lead-free ceramics, i.e., (1-y)Bi1.03(1-x)LaxFeO3–yBaTiO3 (y = 0.27, x = 0.00–0.12), (y = 0.30, x = 0.00–0.10), and (y = 0.33, x = 0.00–0.08) are prepared via a conventional solid-state reaction with water quenching. From X-ray diffraction and electrical property measurements, two morphotropic phase boundaries (MPBs) are discovered in all three ceramic systems. The first MPB (MPB-I) appeared between rhombohedral and tetragonal phases, whereas the second MPB (MPB-II) appeared between tetragonal and cubic-like phases. The highest direct piezoelectric coefficients (d33 = 201, 274, and 268 pC/N) are mainly attributed to the typical MPB-I of the rhombohedral and tetragonal phases. However, the highest converse piezoelectric coefficients (d33∗ = 490, 500, and 570 pm/V with Curie temperature > 330 °C) are obtained for compositions near to the MPB-II. A significant enhancement in the dielectric constant at low temperature is associated with the local structural heterogeneity by La3+ doping, which serves as an origin for a high piezoelectric strain response. Based on the crystal structure as well as on the dielectric, ferroelectric, and piezoelectric properties, a phase diagram is constructed for La-doped BiFeO3BaTiO3 ceramics. This phase diagram reveals the relationship between piezoelectric performance and crystal structure.