Upside - down composites: Fabricating piezoceramics at room temperature

Piezoelectric materials have a multi-billion dollar impact on the electromechanical transducers market. Their conventional synthesis includes a sintering step (at over 1000 °C) that often hampers direct integration into monolithic devices and confines their applications to heterostructures made using tedious multi-step assembly or to composites with poor electromechanical behavior. Here, we demonstrate a new and easy to scale method for the integration of piezoelectric ceramics at ultra-low temperatures without compromising their functionality. We show that all-ceramic “upside-down” composites with exceptionally high fractions of piezoelectric filler (˜75 vol. %) and low porosity can be achieved using aqueous dispersion of lithium molybdate as a binder. The method is based only on coating, mixing, moulding and drying sequences. The measured piezoelectric charge coefficient, d₃₃ ˜84 pC·N⁻¹, outperforms any other known composite, whereas the voltage constant, g₃₃ ˜33 mV m·N⁻¹, competes with bulk materials, thus paving the way for versatile applications not previously considered.     

Enhanced piezoelectric and ferroelectric properties of BiFeO3-BaTiO3 lead-free ceramics by optimizing the sintering temperature and dwell time

0.7BiFeO₃-0.3BaTiO₃ (BFO-0.3BT) ceramics were prepared to uncover the impacts of sintering temperature (T_S) and dwell time (t_d) on the microstructure and electrical properties. With increasing the T_S or t_d, the grain sizes increase along with the porosity decreases, which is in favor of the alignment of dipole. However, excess T_S or t_d are inclined to cause the volatilization of Bi₂O₃, which deteriorates piezoelectric properties. Because of the R-T two-phase coexistence, low defect ions concentration and porosity, as well as appropriate grain size, the excellent d₃₃?=?208?pC/N and k_p?=?35.46% as well as P_r?=?28.52?μC/cm² were achieved in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. In addition,large unipolar strain 0.13% and d₃₃*?=?256.2?pm/V also were obtained in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. This research indicates that the porosity and defect ion concentration as well as grain size also play an important role in piezoelectric properties in BFO-BT ceramics.     

Field induced metastable ferroelectric phase in Pb0.97La0.03(Zr0.90Ti0.10)0.9925O3 ceramics

Pb_0.97La_0.03(Zr_0.9Ti_0.1)_0.9925O₃ (PLZT 3/90/10) ceramics prepared by solid-state reaction with the compositions near the antiferroelectric/ferroelectric (FE/AFE) phase boundary were studied. From the polarization–electric field P(E) dependence and ex situ X-ray study, an irreversible electric field induced AFE-to-FE phase transition is verified at room temperature. Dielectric and in situ temperature dependent X-ray analysis evidence that the phase transition sequence in PLZT 3/90/10-based ceramics can be readily altered by poling. A first order antiferroelectric-paraelectric (AFE-to-PE) transition occurred at?～190 °C in virgin sample and at?～180 °C in poled sample. In addition, a FE-to-AFE transition occurs in the poled ceramic at much lower temperatures (～120 °C) with respect to the Curie range (～190 °C). The temperature-induced FE-to-AFE transition is diffuse and takes place in a broad temperature range of 72–135 °C. The recovery of AFE is accompanied by an enhancement in the piezoelectric properties.     

改进压电传感器频率响应特性的措施

压电传感器的高频响应特性很好,但其低频响应特性较差,本文分析了压电传感器的高频响应特性,讨论了采用电压放大器和电荷放大器的低频响应特性,并提出了改进低频响应特性的方法。     

石墨对柔性压电导电制振材料性能的影响

以聚氨酯为压电聚合物,压电相和导电相分别采用经适量偶联剂改性过的压电陶瓷粉末和石墨粉末,制备了一种柔性压电导电制振材料。实验加入定量的优选配比的压电粉末,通过改变加入石墨粉体的量,研究石墨粉体的含量对复合材料压电导电制振性能的影响。     

Modelling of cross-ply piezoelectric composite laminates in cylindrical bending with interfacial shear slip

An approximate theory for cross-ply piezoelectric composite laminates in cylindrical bending with interfacial shear slip is developed. This theory uses only 4 displacement and potential variables, the number of which is independent of the number of layers involved. The displacement and electric potential fields are depicted by the displacement and electric potential distribution functions through thickness, respectively. The two functions are formulated according to particular solutions to the three-dimensional elasticity equilibrium equations and electrostatics charge equation. In this shear slip modelling interfacial opening is neglected. The interfacial bonding conditions are characterised by a linear slip law and an electrically permeable assumption. A corresponding finite element is also developed to deal with piezoelectric laminates with local shear slip. The accuracy and effectiveness of the present theory are demonstrated in numerical examples.     

Axisymmetric response of circular plates with piezoelectric layers: an exact solution

Electromechanical responses of symmetric circular laminates consisting of piezoelectric layers are studied, and the influence of surface and interlayer electrodes are involved. The laminates are traction-free on the top and bottom surfaces, but may be subjected to external forces at the lateral edge and to voltages applied across certain layers. Under axisymmetric deformation conditions, an approximate model which employs Kirchhoff hypothesis and incorporates the charge equation of electrostatic is established. Then, a closed-form three-dimensional solution of the laminates is generated in a very straightforward manner by the solution of the approximate model. The three-dimensional solution fulfills all field equations and interface or surface conditions as well as the specified electric edge boundary conditions; the only restriction is that the mechanical edge boundary conditions are satisfied in an average manner, rather than point by point. Thus, according to Saint-Venant's principle the proposed solution is exact in the interior region of the laminates.     

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     

Piezo and photoelectric coupled nanogenerator using CdSe quantum dots incorporated ZnO nanowires in ITO/ZnO NW/Si structure

We report the fabrication of ITO/n-ZnO NW/p-Si sandwiched structure and its photoelectric and piezoelectric conversion properties. This hybrid cell was designed to harvest simultaneously both solar and mechanical energies. ZnO nanowires used in the work were grown on p-type Si substrates employing seed mediated low-temperature aqueous solution method. The synthesized ZnO nanowires were characterized by XRD, SEM and EDX characterization for their structural and morphological evaluation. The as-grown ZnO nanowires showed good crystallinity with c-axis preferable orientation. Free ZnO nanowires and CdSe quantum dots were also incorporated with the vertically grown nanowires and their response in harvesting optical and mechanical energies were investigated. The piezoelectric and photoelectric coupled effects of a ZnO nanowire device in the simultaneous conversion of both optical and mechanical energies have been studied for the first time with the goal of designing piezoelectric and photoelectric hybrid nanogenerator. This presented ITO/n-ZnO NW/p-Si heterojunction architecture is envisaged as a potentially valuable candidate for the next generation energy harvesting devices. Graphene-coated ITO was also used and its response was studied.     

Enhanced magnetoelectrical coupling in cobalt ferrite/lead lanthanum zirconate titanate 0-3 composites through phase boundary modification

We have developed a processing technique for producing cobalt ferrite (CFO)/lead lanthanum zirconate titanate (PLZT) 0-3 composites with enhanced piezoelectric, ferroelectric and magnetoelectrical (ME) coupling properties. It includes modifying the phase boundary with zirconia barrier layer and decreasing the sintering temperature with Li₂O + 0.5Bi₂O₃ additives. The CFO/PLZT 0-3 composites were successfully fabricated via conventional co-firing procedures. The obtained 0-3 composite ceramics can withstand a DC electric field of 6 kV mm⁻¹. The effects of CFO/PLZT ratio on the crystalline structure, piezoelectric, ferroelectric, dielectric and M–E properties were investigated. The M–E coefficients of the composites with CFO:PLZT volume ratio of 14.4:85.6, 27.4:72.6 and 39.3:60.7 were found to be 31, 52 and 143 mV (Oe cm)⁻¹ at 100 kHz under a bias field of ∼1 kOe.