Sb doping effects on the piezoelectric and ferroelectric characteristics of lead-free Na0.5K0.5Nb1−x SbxO3 piezoelectric ceramics

The piezoelectric, phase structure and ferroelectric properties of lead-free Na_0.5K_0.5Nb_1−xSb_xO₃ piezoelectric ceramics were systematically investigated. (Na_0.5K_0.5)Nb_1−xSb_xO₃ ceramics were synthesized using the conventional solid-state reaction method. The effect of B-site Sb⁵⁺ substitution for Nb⁵⁺ on the structural characteristics and piezoelectric properties of samples was determined. According to XRD patterns, the phase gradually changes from tetragonal to orthorhombic with increasing Sb content. At x = 0.03, the tetragonal and orthorhombic phases coexist and relatively high piezoelectric properties were obtained. The relatively high Q_m value obtained after substitution with Sb⁵⁺ ions might be due to the increased electronegativity and decreased ionic radius at the morphotropic phase boundary (MPB) at x = 0.03. However, the Q_m value decreases with further Sb addition. Relatively high piezoelectric properties at x = 0.03 of k_p = 0.42, k_t = 0.48, ?_r = 446, Q_m = 143, tan δ = 2.3%, and density = 4.31 g/cm³, d₃₃ = 123 pC/N, were obtained.     

Anisotropic actuation of mechanically textured polypyrrole films

Free-standing polypyrrole films have been stretched or cold rolled to produce uniaxially and biaxially textured films. The oriented films show an increase in conductivity up to 3× when compared to unprocessed films, due to polymer chain alignment. Highly anisotropic active stress and strain are observed for the textured films, with up to 7× larger active strains transverse to the orientation direction. This anisotropy results in a 100% increase in active stress and 70% increase in active strain when compared to unprocessed films, and active strains over 10% (when cycled at 0.1 V/s) have been achieved with this method.     

Mechanism of significantly enhanced piezoelectric performance and stability in textured potassium-sodium niobate piezoelectric ceramics

In this study, the piezoelectric coefficient d₃₃ and planar electromechanical coupling coefficient k_p were enhanced 145% and 71%, respectively for the <001>-textured (K_0.5Na_0.5)_0.95Li_0.05Nb_0.93Sb_0.07O₃ piezoelectric ceramics compared with their randomly oriented counterpart. Significantly enhanced piezoelectric response in textured ceramics is originated from a combined effect of the intrinsic high piezoelectric activity of <001>-oriented grains in the tetragonal-orthorhombic phases, and easy polarization rotation of fine domains. Furthermore, a comparative analysis suggests that <001>-textured ceramics exhibit good thermal stability, benefiting from the weakened depolarization behavior via crystal orientation. The superior fatigue resistance in textured ceramics can be attributed to the reduced clamping effect as low defect density. These results show that high-performance textured ceramics reported in this work will be promising candidates in the field of lead-free piezoelectric materials.     

Piezoelectric thick films and their application in MEMS

Piezoelectric thick films (up to 10 μm thick) and piezoelectric micromachined ultrasonic transducer (pMUT) have been successfully demonstrated at low temperatures of 650 °C using a composite thick film processing route. Submicron-sized PZT powder was dispersed into sol–gel solution to form homogeneous slurry for spin-coating on silicon substrate. Issues associated with recipe of the slurry, deposition process and sintering of films have been summarized with a view to optimizing the properties of the films and pMUTs. Typical microstructure, ferroelectric and piezoelectric properties of the composite films are given. Thermal stability of bottom electrode, a key issue about device fabrication, has also been investigated. The ultrasound-radiating performance of the pMUT element in response to a continuous alternating current driving voltage has been reported. The generated sound pressure level is 116.8 dB at 76.3 kHz at a measuring distance of 12 mm. The pMUT is suitable for application of airborne object recognition.     

Enhanced piezoelectric properties of Sm3+-modified PMN-PT ceramics and their application in energy harvesting

Piezoelectric materials are widely used in electromechanical energy conversion, such as in sensors, transducers, and self-powered materials. In this paper, the influence of the Sm doping content on the microstructure and ferroelectric, piezoelectric, dielectric, and field-induced strain properties of 0.70Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (PMN-PT) ceramics was investigated. Sm-doped PMN-PT ceramics with both high piezoelectric properties (d₃₃～1406 pC/N) and a large electromechanical coupling coefficient (k_p～0.69) were synthesized. Based on their piezoelectric effect, a maximum output voltage of 31 V was achieved under external forces. The output voltages showed satisfactory stability, repeatability, and sensitivity under periodic external forces; hence, Sm-doped PMN-PT piezoelectric ceramics are potential candidates for energy conversion and signal monitoring.     

Cu-modified Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 textured ceramics with enhanced electromechanical properties and improved thermal stability

Grain-oriented Pb(Mg_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ (PMN-PZ-PT) based ceramics were synthesized through templated grain growth via using BaTiO₃ (BT) templates. Although BT templates are partially destroyed by PMN-PZ-PT matrix, CuO addition remarkably promotes [001]_c-oriented grain growth behavior of the ceramics, resulting in an improvement of Lotgering factor F₀₀₁ from ~86% to 98%. Both crystallographic texture and CuO doping increase tetragonality and reduce average domain size of the ceramics dominated by rhombohedral phase. Consequently, 0.50 wt% CuO-doped ceramics (F₀₀₁~98%) exhibit optimum electromechanical properties: d₃₃~860 pC/N, d₃₃×g₃₃~48.6 × 10^?12 m²/N, k_p~0.80, E_c~7.2 kV/cm, tan δ~0.8% and T_c~222 °C. In addition to ~3.7 times and 6.6 times higher d₃₃ and d₃₃×g₃₃, those ceramics possess about 240% enhanced piezoelectric strain and much better thermal stability (S_max/E_max variation ≤2% between RT and 150 °C) relative to non-textured counterpart. This work offers a good paradigm for simultaneously exploring high piezoelectric response and good temperature stability in piezoceramics, benefiting the development of next-generation advanced electromechanical devices.     

Microstructure,ferroelectric and piezoelectric properties of Bi4Ti3O12 platelet incorporated 0.36BiScO3-0.64PbTiO3 thick films for high temperature piezoelectric device applications

Bi₄Ti₃O₁₂ (BiT) platelet incorporated 0.36BiScO₃-0.64PbTiO₃ (BS-PT) thick films were successfully developed for high temperature piezoelectric device applications. Their microstructure and ferroelectric and piezoelectric properties were systematically investigated to demonstrate the effect of the BiT template. It was found that the incorporation of BiT template was not responsible for textured grain growth of the BS-PT thick films; however, it could result in grain growth and densification of the BS-PT thick films by optimizing the sintering temperature and amount of BiT template. In particular, a 4 wt% BiT-incorporated BS-PT thick film sintered at 1000°C exhibited a pure perovskite structure and excellent piezoelectric properties of d₃₃ (440 pC/N) and k_p (53%), despite the presence of micro-pores caused by molten BiT. The BS-PT thick film, exhibiting good ferroelectric characteristics of P_r of 39.4 μC/cm² and E_c of 3.0 kV/mm at 1 kHz, also had an extremely high T_c of approximately 402°C. This implies that the BiT platelet incorporated BS-PT thick film is applicable for high temperature piezoelectric devices.     

Processing and electromechanical properties of lead zirconate titanate thick films by electrophoretic deposition

Electrophoretic deposition (EPD) was used for the fabrication of piezoelectric [lead zirconate titanate (PZT)] thick films on alumina substrates. The EPD was performed in constant current mode from an ethanol based suspension consisting of PZT and PbO particles. The influence of addition of ethyl cellulose (EC) and sintering temperature on the thickness, density, homogeneity and functional response of PZT thick films is studied. Results show that the highest electromechanical performance is obtained for the PZT thick films sintered at 900 or 950°C, with a thickness coupling factor k_t of 50%. The addition of EC influenced the thickness of the PZT thick films but had only minor effect on the porosity content for sintering temperatures over 900°C. Moreover, elastic constants of the thick films based on the suspension with EC were lower, which leads to lower acoustic impedance (15?MRa) while maintaining high (k_t) value. In this last case, a better acoustic matching can be expected with propagation media such as water or biological tissues for ultrasound medical imaging applications.     

Structural and piezoelectric properties of <001> textured PZT‐PZNN piezoelectric ceramics

Rhombohedral 0.69Pb(Zr_0.47Ti_0.53)‐0.31Pb(Zn_0.6Ni_0.4)NbO₃ (PZT‐PZNN) ceramics were textured using 10.0 vol. % BaTiO₃ (BT) platelets along the <001> direction at 950°C with a high Lotgering factor of 95.3%. BT platelets did not react with the PZT‐PZNN ceramics, and the textured PZT‐PZNN ceramic had a tetragonal structure. The PZT‐PZNN ceramics exhibited a strain of 0.174% with a piezoelectric strain constant (d*₃₃) of 580 pC/N at 3.0 kV/mm. The textured PZT‐PZNN ceramic showed an increased strain of 0.276% and d*₃₃ of 920 pC/N at 3.0 kV/mm, which can be explained by the domain rotation. However, the d₃₃ values of the textured specimens are smaller than those of the untextured specimens because of the small remanent polarization and relative dielectric constant of BT platelets. The textured PZT‐PZNN ceramic synthesized in this work can be used for piezoelectric multilayer actuators because of its large strain and low sintering temperature.     

CNT loaded PVDF-KNN nanocomposite films with enhanced piezoelectric properties

The emerging smart PVDF-based composites can compensate for the intrinsic property deficiencies in either of their components. The properties of the composite are determined by the properties of the constituents and its fabrication method. In this research, a lead-free piezoelectric ceramic, potassium sodium niobate (KNN), was used as the primary reinforcement, and MWCNTs were added to improve the electrical properties. Solution casting was used to prepare PVDF-KNN-CNT composite films. After phase and structure identification of composites using SEM, XRD, FTIR, and TGA methods, the dielectric, piezoelectric and ferroelectric properties of the products were investigated. The obtained results indicated a strong dependency of dielectric, piezoelectric, and ferroelectric properties of composites on KNN content. Samples with the highest KNN content rendered ε_r, d₃₃ and g₃₃ values of 156, 28 pC/N, and 20.32 mV m/N, respectively. Introducing a small amount of conductive CNT to primary PVDF-KNN composites can drastically affect the electrical properties by severely interfering in the charge distribution within the sample. While the dielectric constant was enhanced by increasing CNT content, both piezoelectric and ferroelectric properties showed their best behavior at a critical CNT loading. Beyond this limit, a percolation path formed, which is responsible for power consumption. At the optimum CNT amount, d₃₃ and g₃₃ reached 50 pC/N and 31.93 mV m/N, respectively. The presence of conducting CNTs gave rise to the formation of more round polarization curves with higher remnant polarization. The present findings give a prospective understanding of smart piezoelectric polymer-based composites that can be used as sensors and energy harvesters.     

Structural and mechanical properties of Sr-doped barium niobate thick films

Polycrystalline strontium barium niobates Sr _x Ba_{1 ? x} Nb₂O₆ (SBN, 0.40 ≤ x ≤ 0.75) were prepared by standard solid state ceramic method at relatively at low temperatures. Thick SBN films prepared by simple, low-cost, screen printing route were characterized by XRD. Preliminary structural analysis exhibits the formation of tetragonal tungsten bronze crystal structure at room temperature. Texture coefficient [TC(hkl)], dislocation density (ρ_D), density of crystallites per unit surface area (Ψ), mechanical properties, and microwave behavior of synthesized materials are reported.     

Electrophoretic deposition and characterization of helical piezoelectric actuator

The helical actuator was successfully fabricated using the versatile technique of electrophoretic deposition (EPD), which was achieved by depositing two electrode-separated layers of PZT powders on the helical shaped substrate and co-sintering. The actuator is able to generate a rotational displacement Δl in the circumferential direction and also a radial displacement ΔR in the radial direction, as a result of field-induced rotation of the cross section. Theoretical analysis and experimental results show that the displacements are linearly proportional to the number of the turns n and applied electric field. And also, rotational motion shows larger displacement than the radial motion due to the circular configuration. For the fabricated actuator (45.76 mm in length, 4.09 mm in outer diameter, 0.55 mm in the wall thickness and 4 turns), approximately 43 and 9 μm displacements have been achieved for the rotational and radial motions, respectively.     

An easy approach to obtain textured microstructure and transparent seed crystal prepared by simple molten salt synthesis in modified potassium sodium Niobate

Microstructural engineering in conjunction with compositional design has been used for tailoring the properties of piezoelectric materials. In piezoelectric ceramics, the plate-like particles are used for the seed materials in order to realize the textured microstructures. In this study, the seed crystals are synthesized by simple molten salt synthesis (SMSS), using a generalized rule for driving the abnormal grain growth in (K,Na)NbO₃ (KNN)-based ceramics. Furthermore, the textured ceramics are successfully produced in Ba-doped KNN materials, using the seed crystals which are grown by SMSS. Consequently, the textured ceramic shows the Lotgering factor of 92% and the piezoelectric constant (d₃₃) which is similar to that of a single crystal. It is suggested that the excess donor ratio must be considered to obtain the seed crystals (synthesized by SMSS) and textured microstructures in KNN-based ceramics.     

Sintering,microwave properties,and circulator applications of textured Sc-substituted M-type ferrite thick films

Sc³⁺ substituted M-type ferrites are effective microwave magnetic materials with a ferromagnetic resonance frequency in the range of 20 GHz–50 GHz. We report on the fabrication of oriented ferrite thick films as microwave components for application in the K_a-band at 30 GHz. Films of BaFe_11.5.Sc_0.5O₁₉ were prepared by screen-printing on alumina substrates, drying in an external magnetic field, and sintering at 900 °C. Low-temperature sintering is achieved through use of a mixed BBSZ/CuO sintering aid. A strong anisotropy of the sintered ferrite films is revealed by XRD analysis. Microwave properties of the films were determined in a coplanar waveguide setup. The ferromagnetic resonance frequency of the films is at 30 GHz and the textured films possess good nonreciprocal properties which scale with film thickness. The films were tested in a Y-junction circulator, and represent promising materials for self-biased microwave components fabricated in thick film technology.     

EPD of thick films for their application in lithium batteries

Electrophoretic deposition (EPD) is an appropriate tool to prepare thick film electrodes of lithium batteries, once optimized the different factors that affect to this coating method. Compared with other deposition methods, EPD has the ability to allow the simultaneous deposition of the active material, an additive conductor such as carbon black (CB) and a binder to improve the plastic properties of the deposit. However, for obtaining an appropriate electrochemical response they need so far to be compressed. With this simple process, the electrode performance is excellent in terms of the delivered capacity by the cell and the capacity retention on cycling.     

Microstructure,dielectric, piezoelectric,and ferroelectric properties of fine-grained 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

For preparing fine-grained 0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃ lead-free ferroelectric ceramics, the precursor powders were synthesized via sol-gel method and calcined at various temperatures. The precursor powders calcined at 520 °C, 550 °C, and 600 °C exhibit mean grain sizes of 30 ± 4 nm, 54 ± 3 nm, and 78 ± 5 nm, respectively. By optimizing the synthesis parameters, the fine-grained ceramics with high relative densities (>97%) and mean grain size around 100 nm were prepared. The ferroelectric, dielectric, and piezoelectric behavior were investigated. The ceramics prepared using the different precursor powders show different piezoelectric, ferroelectric, and dielectric behavior. The ceramic calcined at 550 °C and sintered at 900 °C exhibits the breakdown strength higher than 85 kV/cm, which exhibits the maximum polarization of 38.4 ± 0.3 μC/cm², remanent polarization of 20.6 ± 0.4 μC/cm².     

Effect of sintering aid and repeated sol infiltrations on the dielectric and piezoelectric properties of a PZT composite thick film

Thick PZT films have been produced using a combination of spin coating of a composite slurry and subsequent infiltration of PZT producing sol. The effect of adding a Cu₂O–PbO sintering aid and repeated sol infiltrations have been studied with the aim of producing dense PZT films. Relative permittivity has been shown to increase with the addition of sintering aid and increased levels of sol infiltration. Measurements of piezoelectric properties indicate that sol infiltrations have no effect on d₃₃ once a critical density has been exceeded. A sample with approximately 10% closed porosity was obtained following the incorporation of sintering aid and four infiltration steps per layer. This resulted in a mean relative permittivity of approximately 700 and a d₃₃ of 62 pC/N (poling conditions: 8 V/μm for 5 min at 200 °C).     

Microstructural,structural, dielectric and piezoelectric properties of potassium sodium niobate thick films

In the framework of a systematic study, we present the influence of processing parameters – in particular the presence of a packing powder during sintering and the sintering temperature – on the microstructural and structural properties of potassium sodium niobate (K_0.5Na_0.5NbO₃ or KNN) thick films. These KNN thick films were prepared with a 1 mass% addition of potassium sodium germanate (KNG), which serves as a liquid-phase sintering aid. The sintered films exhibited preferential crystallographic orientations along [100]_pc and [10−1]_pc, the origin of which lies in the compressive stresses developed during cooling as a result of the thermal expansion mismatch between the film and the substrate. In addition, the dielectric permittivity, dielectric losses and the piezoelectric d₃₃ coefficient of the obtained films were compared with those of KNN bulk ceramics.