Piezoelectric D31 Coefficients Research Articles

Longitudinal and transverse piezoelectric effects of ferroelectret metamaterials with positive and negative Poisson's ratios

A theoretical model has been developed to express the longitudinal and transverse piezoelectric effects in ferro/piezoelectrets. This model is an extension of the classic model based on layer-dielectric structures that focuses on the longitudinal piezoelectric effect. The improved model reveals that the relation between the longitudinal piezoelectric d33 coefficient and the transverse piezoelectric d31 coefficient is associated with Poisson's ratio μ13 (or μ31) and Young's moduli Y1 and Y3. The polarity of the two coefficients is opposite for materials with a positive Poisson's ratio as normally observed in conventional piezoelectric materials, and the same for materials with a negative Poisson's ratio, i.e., auxetic materials. The experimental results available in the literature and obtained from ferroelectret metamaterials with a honeycomb cross-sectional structure and two-dimensional (2D) symmetric structure, called 2D ferroelectret metamaterials, designed and prepared in this study reasonably agree with theoretical predictions. This study not only extends the scope of the metamaterials by inducing the concept of ferroelectret metamaterials but also provides a strategy for designing ferroelectrets with designable properties.

Ultralight and sensitive ferroelectret films with a human skin-like texture

Biologically inspired by natural skin, polypropylene (PP) ferroelectret films with a human skin-like texture, featuring lightweight, light transmittance, small thickness, stretchability, as well as significant longitudinal and transverse piezoelectric activity, are prepared with a simple procedure, and their piezoelectric properties are characterized. The mechanical structure of the fabricated ferroelectret films is of a double-level cellular structure with distributed tight junctions and dipolar charges deposited on the opposite inner walls of cells. The preliminary results show that the area density, light transmittance, and thickness of the films are 3.5 g/m2, 80%, and 10–20 μm, respectively. A quasi-static piezoelectric d33 coefficient of a few thousand pC/N at 3.4 kPa and a dynamic piezoelectric d31 coefficient of −40 pC/N at a frequency of 80 Hz and a stress of 20 kPa are achieved. The improved piezoelectric performance seems mainly owing to the reduction of the elastic modulus for the double-level structure and the enhancement of charges in deep traps in very thin cell walls. The sound pressure level, generated by an ultrasonic emitter made of the PP ferroelectret film, is about 87 dB at 46 kHz as driven by a voltage of 20 V (peak to peak voltage). An ultra-thin tactile sensor based on the fabricated films can localize positions and detect the track and moving speed of applied force. These results indicate that the cost-efficient films may extend the applications of ferroelectrets in flexible electronics.

Excellent piezoelectric properties and high Tc in Fe2O3-doped PMW-PNN-PZT ceramics

In this work, in order to develop piezoelectric ceramics sintered at low temperature with high piezoelectric d31 coefficient, Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)0.09(Zr0.5Ti0.5)0.88O3 ceramics were fabricated as a function of the amount of Fe2O3 addition using a conventional mixed oxide method. The microstructure, dielectric and piezoelectric properties were systematically investigated as a function of amount of Fe2O3 addition. At the sintering temperature of 920 °C, the excellent values of density = 7.94 (g/cm3), piezoelectric coefficient (d31) = 246 pC/N, planar electromechanical coupling coefficient (kp) = 0.69, mechanical quality factor (Qm) = 213, dielectric constant (εr) = 2,682 and high Curie temperature =366 °C were obtained from the ceramics doped with 0.3 wt% Fe2O3, respectively.

High piezoelectric d31 coefficient and high Tc in PMW-PNN-PZT ceramics sintered at low temperature

In this study, in order to develop piezoelectric ceramics with high piezoelectric d31 coefficient and high Curie temperature (Tc), Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)0.09(Zr0.5Ti0.5)0.88O3 ceramics doped with sintering aids were fabricated using a columbite precursor method. The crystal structure, dielectric and piezoelectric properties were investigated as a function of calcination temperature. At the sintering temperature of 920°C, the optimal values of density=7.83(g/cm3), piezoelectric coefficient(d31)=263pC/N, piezoelectric coefficient(d33)=620pC/N, planar electromechanical coupling coefficient (kp)=0.689, mechanical quality factor (Qm)=100, dielectric constant(εr)=2524 and Curie temperature (Tc)=340°C were obtained from the ceramics with the two step calcination temperature of 1st=1130°C, 2nd=780°C, respectively, for haptic actuator application.

Mechanical and piezoelectric performance of cross-linked polypropylene films treated with extending

Commercially available cross-linked polypropylene (XPP) foam sheets exhibit strong piezoelectric effect after proper mechanical modification and polarization. Such electromechanical property in XPP is due to the specific space charge distribution and void structure, and this kind of electro-active materials is named piezoelectrets or ferroelectrets. Owing to the unique features such as low cost, small acoustic impedance, flexibility, weight light, piezoelectret films could be applied in air-borne acoustic and ultrasonic transducers, wearable flexible electronic devices, micro-energy harvesters, and so on. In this paper, the mechanical and piezoelectric performance of XPP films, with a gel fraction of 50% and treated by extending, is investigated. The results show that the Young׳s module of XPP in the thickness direction decreases from 4.9MPa to 0.54MPa by the increasing extending ratios from 0% to 100%. The quasi–static piezoelectric d33 and d32 coefficients are 420 and 0.4pC/N for the samples with an extending ratio of 100%, respectively. Piezoelectric d31 coefficients of about 2.4pC/N are obtained in the films with a treatment of an extending ratio of 20%. This value is larger than the films without treatment, which could be due to the reduction of Young׳s modulus in longitudinal direction. After an annealing at 70°C for 24h, the d33 coefficients in XPP films decrease to 43% of the initial values, showing an improved thermal stability comparing with normal polypropylene piezoelectret films. The enhancement of thermal stability in XPP films could be associated with the cross-linked molecular network.

Inkjet printed micropump actuator based on piezoelectric polymers: Device performance and morphology studies

All inkjet printed piezoelectric actuators based on poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF–TrFE)) for applications as pump actuators in microfluidic lab-on-a-chip systems (LOC) are manufactured and investigated in terms of their morphology and actuator performance. Furthermore, a pump demonstrator with an all-printed P(VDF–TrFE) actuator is characterized here for the first time. The actuators are manufactured in a fully additive and flexible way by successive inkjet printing of a P(VDF–TrFE) film sandwiched between two silver electrodes on a polyethylene terephthalate (PET) substrate. Different from most current micropumps where actuator elements are fabricated separately, no additional joining step is required in the manufacturing approach employed here. Actuator performance is investigated by measurements of piezoelectric d31 coefficients as well as remanent polarization Prem for different thermal treatments of the as-printed P(VDF–TrFE) films. A strong dependence of the device performance on the annealing temperature is found with maximum values for d31 and Prem of approximately 10pmV−1 and 5.8μCcm−2, respectively. Morphology investigations of the printed films by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) indicate an increased degree of crystallinity of the piezoelectric β-phase for samples annealed at temperatures above 110°C, which coincides with improved device performance. A basic pumping function with pump rates of up to 130μLmin−1 is demonstrated, which is promising for future applications in LOC. Furthermore, the process chain and characterization presented here can be employed to design and manufacture also other P(VDF–TrFE)-based devices and allows the combination with additional printed on-chip functionalities in future LOC.

Evaluation of transverse piezoelectric coefficient of ZnO thin films deposited on different flexible substrates: a comparative study on the vibration sensing performance.

We report on the systematic comparative study of highly c-axis oriented and crystalline piezoelectric ZnO thin films deposited on four different flexible substrates for vibration sensing application. The flexible substrates employed for present experimental study were namely a metal alloy (Phynox), metal (aluminum), polyimide (Kapton), and polyester (Mylar). ZnO thin films were deposited by an RF reactive magnetron sputtering technique. ZnO thin films of similar thicknesses of 700 ± 30 nm were deposited on four different flexible substrates to have proper comparative studies. The crystallinity, surface morphology, chemical composition, and roughness of ZnO thin films were evaluated by respective material characterization techniques. The transverse piezoelectric coefficient (d31) value for assessing the piezoelectric property of ZnO thin films on different flexible substrates was measured by a four-point bending method. ZnO thin films deposited on Phynox alloy substrate showed relatively better material characterization results and a higher piezoelectric d31 coefficient value as compared to ZnO films on metal and polymer substrates. In order to experimentally verify the above observations, vibration sensing studies were performed. As expected, the ZnO thin film deposited on Phynox alloy substrate showed better vibration sensing performance. It has generated the highest peak to peak output voltage amplitude of 256 mV as compared to that of aluminum (224 mV), Kapton (144 mV), and Mylar (46 mV). Therefore, metal alloy flexible substrate proves to be a more suitable, advantageous, and versatile choice for integrating ZnO thin films as compared to metal and polymer flexible substrates for vibration sensing applications. The present experimental study is extremely important and helpful for the selection of a suitable flexible substrate for various applications in the field of sensor and actuator technology.

Effect of post-deposition annealing on transverse piezoelectric coefficient and vibration sensing performance of ZnO thin films

The present experimental study investigates the influence of post-deposition annealing on the transverse piezoelectric coefficient (d31) value of ZnO thin films deposited on a flexible metal alloy substrate, and its relationship with the vibration sensing performance. Highly c-axis oriented and crystalline ZnO thin films were deposited on flexible Phynox alloy substrate via radio frequency (RF) reactive magnetron sputtering. ZnO thin film samples were annealed at different temperatures ranging from 100°C to 500°C, resulting in the temperature of 300°C determined as the optimum annealing temperature. The crystallinity, morphology, microstructure, and rms surface roughness of annealed ZnO thin films were systematically investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM), respectively. The piezoelectric d31 coefficient value was measured by 4-point bending method. ZnO thin film annealed at 300°C was highly c-axis oriented, crystalline, possesses fine surface morphology with uniformity in the grain size. This film showed higher d31 coefficient value of 7.2pmV−1. A suitable in-house designed and developed experimental set-up, for evaluating the vibration sensing performance of annealed ZnO thin films is discussed. As expected the ZnO thin film annealed at 300°C showed relatively better result for vibration sensing studies. It generates comparatively higher peak output voltage of 147mV, due to improved structural and morphological properties, and higher piezoelectric d31 coefficient value.

All inkjet-printed piezoelectric polymer actuators: Characterization and applications for micropumps in lab-on-a-chip systems

Digital printing technologies are promising as future manufacturing approaches due to their capabilities of highly flexible and additive material deposition on various substrates. In this contribution, all inkjet-printed piezoelectric polymer actuators are presented based on polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) and electrodes printed from silver nanoparticle dispersions. The target application for the actuators described here are membrane pumps for microfluidic lab-on-a-chip (LOC) systems. For the first time, all-inkjet-printed P(VDF-TrFE) actuators are reported and the corresponding piezoelectric d31 coefficient is measured. For manufacturing the actuators, a low-cost procedure is employed that consists of only three inkjet printing and post-processing steps where moderate thermal treatments (Tmax=130°C) are combined with plasma sintering. The processing is therefore compatible with a wide range of temperature sensitive polymer substrates, completely additive and highly flexible. A sandwich-like structure of a piezoelectric P(VDF-TrFE) layer between two silver electrodes is inkjet-printed onto a polyethylene terephthalate (PET) substrate. When a voltage is applied across the piezoelectric layer, the reverse piezoelectric effect will lead to a bending deflection of this unimorph structure. The piezoelectric d31 coefficients are found to be approximately 7 to 9pmV−1, which allows the generation of significant actuator deflections. For the application in a micropump, flow rates of several 100μLmin−1 are anticipated, which is promising for LOC applications. Most current micropumps are based on actuator elements that are fabricated separately and mounted on a passive membrane. By using all inkjet-printed actuators, as presented here, the joining step is avoided and the benefits of low-cost printed devices are added to the well-developed processing approaches for microfluidic chips.

Relaxor behavior of K0.5La0.5Bi2Nb2O9 ceramics

K 0.5 La 0.5 Bi 2 Nb 2 O 9 , a relaxor, was synthesized and the structural studies confirmed it to be an n=2 member of the Aurivillius oxides. The 12{h00} and 12{hk0} types of superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein Ea=0.04eV, Tf=428K,and ωo=1010Hz. The diffuseness parameter γ=2.003 established the relaxor nature and it was attributed to the A-site cationic disorder. The piezoelectric d31 coefficient was 0.5pC∕N at 300K and 2pC∕N at 480K.

Interferometric Measurement of the Temperature Dependence of Piezoelectric Coefficients for PZN-8%PT Single Crystals

Piezoelectrically induced displacements were measured by a laser interferometric method in the temperature range 150 K–333 K for two domain-engineered 0.92Pb(Zn1/3Nb2/3)-0.08PbTiO3 single crystals poled in the [001]-direction. Assuming an effective tetragonal symmetry, we determined the piezoelectric d31 coefficient by measuring the displacement on (100) and (110) crystal faces. Coefficient d31 = −1280 pC/N was calculated for the [100]-direction at room temperature. Its value is reduced to −550 pC/N at 210 K. Piezoelectric coefficient d31 measured on a second sample in the [110]-direction exhibited a smaller value than the previous one, only about –555 pC/N at room temperature and –360 pC/N at 190 K. Different domain structures in both samples might be the possible reason for this difference. Temperature dependence of piezoelectric coefficient d33 was also investigated. The effect of aging is also discussed. The domain configuration in crystals was observed by optical microscopy.

Temperature behavior of the complex piezoelectric d31 coefficient in modified lead titanate ceramics

Piezoelectric properties of modified lead titanate ceramics were investigated in an effort to explain the large electromechanical anisotropy observed in these materials. While the thickness coupling factor is approximately constant with temperature, the planar coupling factor becomes zero near room temperature, probably indicating a change in sign of the piezoelectric d 31coefficient. It is shown that for an accurate description of the electromechanical behavior of modified lead titanate ceramics, all material constants relevant for the planar coupling mode ( s 11, ε 33 d 31) must be taken as complex. Possible contributions to the complex d 31 are discussed.