Piezotensegritic structures for transducer applications

Piezoelectricity and tensegrity have been coupled into an electrically active device. This concept, hereby known as piezotensegrity, can be used to sense or actuate. A composite sensor has been tested using compression elements stabilized with tensioning bands. The piezoelectric elements are arranged on the face diagonals with perimeter tension bands. Experimental piezoelectric response from this design was 1200 pC/N in air testing with peak hydrostatic response of 700 pC/N. The good device sensitivity as compared to properties of the base piezoelectric material is attributed to the internal arrangement of the piezoelectric elements and the tensioning system. Received: 28 April 1999 / Reviewed and accepted: 6 August 1999     

PZT-epoxy piezoelectric transducers: A simplified fabrication procedure

Composite piezoelectric transducers have been constructed by partially dicing PZT ceramics and back-filling with epoxy. Composites containing 10 to 70 volume percent PZT were prepared with several different rod diameters. Measured dielectric constants ranged from 200 to 1000, longitudinal piezoelectric coefficients d₃₃ from 200 to 350 pC/N, and hydrostatic piezoelectric coefficients d_h from 40 to 80 pC/N. Piezoelectric properties are compared with solid PZT and with 3-1 composites made by extrusion.     

Piezoelectricity of single-and multi-layer cellular polypropylene film electrets

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct-and inverse-piezoelectric d ₃₃ coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d ₃₃ coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets. Translated from Journal of Functional Materials, 2006, 37(2): 207–209 [译自: 功能材料]     

The effects of CuO-doping on dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Ba(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

CuO-doped lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT) and barium zirconate titanate (Ba(Zr_0.07Ti_0.93)O₃, BZT) were prepared via a multi-step solid-state reaction process. The BNT–BZT with CuO dopant ceramics sintered at 1150–1180 °C for 2 h in air showed a pure perovskite structure. SEM images reveal that a small amount of CuO (<2 mol%) play a significant role on the microstructure to improve its sintering attributes, while it will degrade when the dopant is added beyond 2 mol%. The dielectric and piezoelectric properties of CuO-doped BNT–BZT ceramics were evaluated. At room temperature, the sample doped with 2 mol% CuO shows quite good properties such as a high piezoelectric constant (d ₃₃ ∼156.5 pC/N) and a high electromechanical coupling factor (k _t ∼52%). The depolarization temperature increased dramatically and the maximum permittivity temperature decreased slightly.     

Synthesis and characterization of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 fibers with Pt core

This paper reports the synthesis and electromechanical characterization of 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-35PT) ceramics and fibers. To prevent the lead loss during the sintering of the fibers, lead-atmosphere was used during the sintering process. As a consequence, it was possible to ensure a good densification of the fiber and a pure perovskite phase. The electromechanical coupling factor and piezoelectric coefficient of the piezoelectric fiber were found to be k₃₁ = 0.20 and d₃₁ = −130 pC/N, respectively. These results are lower than ceramic sample properties (k₃₁ = 0.32 and d₃₁ = −234 pC/N). In order to determine reasons for these lower results in fiber shape sample, density and poling studies were performed. It is shown that fiber shape samples cannot be poled correctly because of the ratio between core and ceramic diameters.     

Electrical properties of manganese modified sodium potassium lithium niobate lead-free piezoelectric ceramics

Effects of MnO₂ doping on the microstructure, densification, dielectric, ferroelectric and piezoelectric properties of (Na_0.5K_0.5)_0.935Li_0.065NbO₃ (NKLN) lead-free piezoelectric ceramics were investigated. On the one hand, the addition of a small amount of MnO₂ has little effect on the crystalline structure, however, slightly promotes sintering and grain growth, and improves the uniformity of microstructure to a certain degree. On the other hand, MnO₂ doped NKLN ceramics show hard properties in piezoelectric activities, possessing decreased room-temperature dielectric constant, loss tangent and piezoelectric constants d ₃₃, and increased mechanical quality factors Q _m. The 1.2 mol% MnO₂ doped NKLN ceramics have a loss tangent of approximately 1%, a Q _m of ∼170 and a d ₃₃ of 150 pC/N. These effects were considered to come from the formation of oxygen vacancies and the multi-valence states of Mn ions.     

Phase diagram and electric properties of the (Mn, K)-modified Bi0.5Na0.5TiO3–BaTiO3 lead-free ceramics

In this study, the phase diagram and electric properties were demonstrated for a (Mn, K)-modified Bi_0.5Na_0.5TiO₃ (BNT)-based solid solution. (0.935−x) Bi_0.5Na_0.5TiO₃−xBi_0.5K_0.5TiO₃−0.065BaTiO₃ with 0.5% mol Mn doping was prepared by a conventional solid-state reaction method. A morphotropic phase boundary (MPB) formed between the ferroelectric rhombohedral and tetragonal phases around x of 0.04 with the MPB tolerance factor t of 0.984–0.986. The temperature and composition dependence of the dielectric, piezoelectric, ferroelectric properties along with the strain characteristics were investigated in detail and a phase diagram was presented. Around the MPB region, the maximum values of piezoelectric constant d₃₃^* d_{33}^{*} of 290 pC/N, d ₃₃ of 155 pC/N, dielectric constant e₃₃^T /e₀ \varepsilon_{33}^{T} /\varepsilon_{0} of 1059 and low dielectric loss tangent tan δ of 0.017 were obtained. In addition, the authors also suggest that the solid solution with composition x of 0.24, exhibiting both high-depolarization temperature T _d of 182 °C, d₃₃^* d_{33}^{*} of 156 pC/N, d ₃₃ of 130 pC/N, will be favorable for high-temperature actuator and sensor applications.     

Transverse honeycomb composite transducers

Composites with 3-1 connectivity were fabricated by impregnating an extruded, sintered honeycomb configuration of PZT with epoxy. The composites had lower density (≈ 3000 Kg/m³) and lower dielectric constant (≈ 400) than that of solid PZT. The maximum piezoelectric d?₃₃ coefficient of the composites was 350 pC/N, and the maximum hydrostatic d?_h 220 pC/N. ?_h and d?_h?_h of the composites were an order of magnitude higher than that of solid PZT. Considering the symmetry and phase connectivity of the individual phases in the composite, an explanation is given for the improved piezoelectric properties of the composites.     

Quasi-static and dynamic piezoelectric <Emphasis Type="Italic">d</Emphasis><Subscript>33</Subscript> coefficients of irradiation cross-linked polypropylene ferroelectrets

Irradiation cross-linked polypropylene (IXPP) foams show high piezoelectric activity after proper hot-pressing treatment and corona charging. Quasi-static piezoelectric d ₃₃ coefficients around 400 pC/N were measured by means of the direct piezoelectric effect. Dynamic values of the inverse piezoelectric d ₃₃ coefficients, determined from the dielectric resonance spectra at 220 kHz, is about 68% of the quasi-static d ₃₃ values. The difference between the quasi-static and the dynamic values of d ₃₃ is probably due to the enhancement of Young’s modulus of IXPP with increasing frequency. The piezoelectric d ₃₃ coefficients are slightly dependent on the applied pressure in the range up to 50 kPa. The d ₃₃-values decrease by 70% when the samples are exposed to 90 °C for 1 day; and a pre-aging treatment improves the thermal stability of the d ₃₃ coefficients.     

A Rosen-type piezoelectric transformer employing lead-free K0.5Na0.5NbO3 ceramics

Lead-free K_0.5Na_0.5NbO₃–K_5.4Cu_1.3Ta₁₀O₂₉–MnO₂ (KNN–KCT–Mn) ceramics have been prepared by a conventional ceramic sintering technique. The ceramics show excellent piezoelectric properties for application in power devices, and the optimum properties measured are as follows: piezoelectric constant d ₃₃ = 90 pC/N, planar electromechanical coupling factor k _p = 0.40, mechanical quality factor Q _m = 1900, remanent polarization P _r = 11.8 μC/cm², coercive field E _c = 0.85 kV/mm. A Rosen-type piezoelectric transformer with a dimension of 21 mm × 6 mm × 1.2 mm was fabricated using the KNN–KCT–Mn ceramics. Properties of the piezoelectric transformer operating in the first and second modes have been characterized. For the first mode, the transformer has a maximum output power of 0.7 W with a temperature rise of 14 °C. For the second mode, the maximum output power of the transformer is 1.8 W with a temperature rise of 33 °C. KNN–KCT–Mn ceramics have shown to be a potential lead-free candidate to be used in high-voltage–low-current devices.     

Densification of (Na,K)NbO<Subscript>3</Subscript> piezoelectric ceramics by two-step mixing process

Lead-free Na_0.5K_0.5NbO₃ (NKN) piezoelectric ceramics were sintered with a new process, “two-step mixing process,” in which a part of alkali source powders was initially preserved and mixed with the rest matrix powders after the calcinations step. As a result, the sintering of NKN ceramics was improved, and the sample sintered at 1082 °C with the initial preservation ratio (R _A) of 5% demonstrated the highest density of ρ = 4.38 g/cm³ (97.1% of the theoretical density), compared with ρ = 4.36 g/cm³ (96.7% of the theoretical density) for the non-preservation specimen (R _A = 0%). The former sample showed the best piezoelectric constant of d ₃₃ = 125 pC/N and electromechanical coupling coefficient of k _p = 0.42, while the latter sample had d ₃₃ = 116 pC/N and k _p = 0.37. These results indicated that the two-step mixing process was effective for the sintering of lead-free NKN ceramics, despite no sintering additive and cold isostatic pressing were used.     

Large strain response in acceptor- and donor-doped Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi_0.5Na_0.5TiO₃–Bi_0.5Li_0.5TiO₃–BaTiO₃–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Q _m) ~ 160, coercive field (E _c) ~ 2.9 kV/mm, decreased dielectric constant ( e₃₃^T /e₀ ) ~ 80 3, \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d ₃₃) ~ 184 pC/N, e₃₃^T /e₀   ~ 983, \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, tanδ ~ 0.033, and decreased E _c ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature T _d, large strain value was obtained with the normalized d₃₃^* d_{33}^{*} up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.     

The effect of poling condition on the piezoelectric properties of 0.3PNN-0.7PZT ceramics in the vicinity of MPB

Piezoelectric ceramics 0.3Pb(Ni_1/3Nb_2/3)O₃–0.7Pb(Zr_xTi_(1−x))O₃ (x = 0.42−0.46) were successfully fabricated via the conventional solid-state reaction. XRD demonstrated that the morphotrophic phase boundary (MPB) lay at x = 0.44. The effect of poling condition on the piezoelectric properties of ceramics in the vicinity of MPB was studied by the reserval of domains. The piezoelectric properties at MPB under the optimum poling condition of 2 kV/mm for 10 min in a silicon oil bath at 60 °C were d ₃₃ of 538 pC/N and k _p of 0.636, respectively.     

Microstructure,electrical properties of CeO<Subscript>2</Subscript>-doped (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

CeO₂-doped K_0.5Na_0.5NbO₃ lead-free piezoelectric ceramics have been fabricated by a conventional ceramic fabrication technique. The ceramics retain the orthorhombic perovskite structure at low doping levels (<1 mol.%). Our results also demonstrate that the Ce-doping can suppress the grain growth, promote the densification, decrease the ferroelectric–paraelectric phase transition temperature (T _C), and improve the dielectric and piezoelectric properties. For the ceramic doped with 0.75 mol.% CeO₂, the dielectric and piezoelectric properties become optimum: piezoelectric coefficient d ₃₃ = 130 pC/N, planar electromechanical coupling coefficient k _p = 0.38, relative permittivity ε_r = 820, and loss tangent tanδ = 3%.     

Poling field versus piezoelectric property for [001]<Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> oriented 91%Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–9%PbTiO<Subscript>3</Subscript> single crystals

Electromechanical property measurements and microstructure observations using optical microscopy were performed on a [001] _c oriented k ₃₃ resonator made of 91%Pb(Zn_1/3Nb_2/3)O₃–9%PbTiO₃ single crystal, which was polarized under different electric fields. At room temperature, when the poling field is 1100 V/mm, the electromechanical coupling factor k ₃₃ is 0.90 and piezoelectric coefficient d ₃₃ is 1665 pC/N. Such superior electromechanical properties could be attributed to the formation of monoclinic multi-domain structure, which transforms to tetragonal phase at 46 °C. While at a higher poling field of 1200 V/mm, the crystal becomes single-domain tetragonal state and its k ₃₃ and d ₃₃ are only about 0.69 and 850 pC/N, respectively. The critical poling field to transform the monoclinic phase to the tetragonal phase is found to be ~1120 V/mm.     

Piezoelectric properties of [Bi<Subscript>0.5</Subscript>(Na<Subscript>0.7</Subscript>K<Subscript>0.25</Subscript>Li<Subscript>0.05</Subscript>)<Subscript>0.5</Subscript>]TiO<Subscript>3</Subscript>−Ba(Ti,Zr)O<Subscript>3</Subscript> binary system ceramics

Dense lead-free binary system piezoelectric ceramics (1 − x)[Bi_0.5(Na_0.7K_0.25Li_0.05)_0.5]TiO₃−xBa(Ti_0.95Zr_0.05)O₃ (BNKLT–BZT) were prepared by a two-step sintering process. A phase transition from rhombohedral to tetragonal was observed with increasing BZT fraction in the range x = 0.06–0.1 and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal appears in this range. Ceramics containing 10 mol% BZT with tetragonal phase near the MPB region has the maximum piezoelectric constant d ₃₃(151pC/N).     

Effect of ZnO on the microstructure and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

K_0.5Na_0.5NbO₃–x ZnO (KNN–xZn) lead-free ceramics have been prepared using the conventional sintering technique and the effects of ZnO addition on the phase structure and piezoelectric properties of the ceramics have been studied. Our results reveal that a small amount of ZnO can improve the density of the ceramics effectively. Because of the high density and ZnO doping effects, the piezoelectric and dielectric properties of the ceramics are improved considerably. The good piezoelectric and dielectric properties of d ₃₃ = 114 pC/N, k _p = 0.36, ε _r = 395, and Q _m = 68 were obtained for the KNN ceramics doped with 1 mol% ZnO. Therefore, the KNN-1.0 mol%Zn ceramics is a good candidate for lead-free piezoelectric application.     

Microconfigured piezoelectric artificial materials for hydrophones

Piezoelectric PZT–air composites with a complex design optimized for hydrophones were fabricated as arrays of hundreds of 60 μ units using a microfabrication technique involving coextrusion of mixtures of thermoplastic with PZT powder or carbon powder. The measured piezoelectric coefficient was 300 pC/N with a figure of merit of 18 pm²/N, in excellent agreement with the predicted properties.     

Fabrication and properties of an anisotropic PZT/polymer 0–3 composite

Anisotropic 0–3 PZT platelet/polymer composites were prepared by a route involving the tape casting and sintering of PZT sheets and the subsequent alignment of platelets in a polymer matrix by either calendering or tape casting; both techniques induced a strong alignment of the platelets. At 60 vol 1/2 loading, measured d ₃₃- and d _h-values of ~ 30 pC N^–1 and ~ 100 pC N^–1, respectively, were obtained; the calculated g _h-value was 83 mV mN^–1. A strong relaxation effect observed is considered most likely to be dependent on the characteristics of the polymer phase.     

Relaxor based ferroelectric single crystals for electro-mechanical actuators

 The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn_1/3Nb_2/3)O3−PbTiO₃ (PZN-PT) and Pb(Mg_1/3Nb_2/3)O₃−PbTiO₃ (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O₃ (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d₃₃’s ) >2200 pC/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, possibly being related to an E-field induced phase transformation. High electromechanical coupling (k₃₃) >90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators. Received: 2 January 1997 / Accepted: 27 March 1997