Recent studies have shown that nitrogen doping of carbon nanotubes (CNTs) can lead to the formation of piezoelectric properties in them, not characteristic of pure CNTs. In this work, nitrogen-doped CNTs were grown by plasma-enhanced chemical vapor deposition and the effect of the aspect ratio of the nanotube length to its diameter on its piezoelectric coefficient d33 was shown. It was observed that as the aspect ratio of the nanotube increased from 7 to 21, the value of d33 increased linearly from 7.3 to 10.7 pm/V. This dependence is presumably due to an increase in curvature-induced polarization because of an increase in the curvature and the number of bamboo-like “bridges” in the nanotube cavity formed as a result of the incorporation of pyrrole-like nitrogen into the nanotube structure. The obtained results can be used in the development of promising elements of nanopiezotronics (nanogenerators, memory elements, and strain sensors).Recent studies have shown that nitrogen doping of carbon nanotubes (CNTs) can lead to the formation of piezoelectric properties in them, not characteristic of pure CNTs. In this work, nitrogen-doped CNTs were grown by plasma-enhanced chemical vapor deposition and the effect of the aspect ratio of the nanotube length to its diameter on its piezoelectric coefficient d33 was shown. It was observed that as the aspect ratio of the nanotube increased from 7 to 21, the value of d33 increased linearly from 7.3 to 10.7 pm/V. This dependence is presumably due to an increase in curvature-induced polarization because of an increase in the curvature and the number of bamboo-like “bridges” in the nanotube cavity formed as a result of the incorporation of pyrrole-like nitrogen into the nanotube structure. The obtained results can be used in the development of promising elements of nanopiezotronics (nanogenerators, memory elements, and strain sensors).

Relaxor-based ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals and ceramics are promising candidates for high-performance electromechanical conversion devices. It is known that the domain structure and dielectric diffusion–relaxation characteristics are crucial to the excellent performances of relaxor ferroelectrics. In this work, we prepared the PIN–PMN–PT ceramics with various PIN/PMN proportions and systematically investigated their domain structure and dielectric diffusion–relaxation properties. The effect of PIN/PMN proportion on the domain size and dielectric diffusion–relaxation characteristics was also studied. The investigations showed that PIN–PMN–PT ceramics presented multi-type domain patterns comprising irregular island domains and regular lamellar domains. Moreover, the dependent relations of PIN/PMN proportions on the dielectric diffusion and domain size indicated that the PIN composition has a stronger lattice distortion than PMN composition; increasing the PIN proportion can enhance the dielectric diffusion and decrease the domain size. Our results could deepen the understanding of structure–property relationships of multicomponent relaxor ferroelectrics and guide the design and exploration of new high-performance ferroelectric materials.Relaxor-based ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals and ceramics are promising candidates for high-performance electromechanical conversion devices. It is known that the domain structure and dielectric diffusion–relaxation characteristics are crucial to the excellent performances of relaxor ferroelectrics. In this work, we prepared the PIN–PMN–PT ceramics with various PIN/PMN proportions and systematically investigated their domain structure and dielectric diffusion–relaxation properties. The effect of PIN/PMN proportion on the domain size and dielectric diffusion–relaxation characteristics was also studied. The investigations showed that PIN–PMN–PT ceramics presented multi-type domain patterns comprising irregular island domains and regular lamellar domains. Moreover, the dependent relations of PIN/PMN proportions on the dielectric diffusion and domain size indicated that the PIN composition has a stronger lattice distortion than PMN composition; increasing the PIN proportion can enhance the dielectric diffusion and decrease the domain size. Our results could deepen the understanding of structure–property relationships of multicomponent relaxor ferroelectrics and guide the design and exploration of new high-performance ferroelectric materials.

In this work, Li2CO3 was added into 0.7BiFeO3?0.3BaZr0.02Ti0.98O3?0.01molMnO2 (70BFBTMn) piezoelectric ceramics to reduce their sintering temperatures. 70BFBTMn ceramics were sintered by a conventional solid reaction method, and their structural, dielectric, piezoelectric and ferroelectric properties were studied. These results indicate that 0.5% (mole) Li2CO3 is the optimized content and it can reduce the sintering temperature by 100°C, making the possibility of the piezoelectric ceramics cofiring with Ag electrodes at low temperatures to manufacture multilayer piezoelectric actuators.In this work, Li2CO3 was added into 0.7BiFeO3?0.3BaZr0.02Ti0.98O3?0.01molMnO2 (70BFBTMn) piezoelectric ceramics to reduce their sintering temperatures. 70BFBTMn ceramics were sintered by a conventional solid reaction method, and their structural, dielectric, piezoelectric and ferroelectric properties were studied. These results indicate that 0.5% (mole) Li2CO3 is the optimized content and it can reduce the sintering temperature by 100°C, making the possibility of the piezoelectric ceramics cofiring with Ag electrodes at low temperatures to manufacture multilayer piezoelectric actuators.

To improve the acoustic radiation performance of the spherical transducer, a prestressed layer is formed in the transducer through fiber winding. The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress (Tr) and acoustic impedance, respectively. First, a theoretical estimation of Tr is established with a thin shell approximation of the prestressed layer. Then, the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer. Further, the ideal effects of Tr on the sound radiation performances of the transducer are analyzed through finite element analysis (FEA). Finally, four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer. The results show that with the growth of Tr, the acoustic impedance of the prestressed layer grows, mitigating the enormous impedance mismatch between the piezoelectric ceramic and water, while increasing attenuation of the acoustic energy, resulting in a peak value of the maximum transmitting voltage response (TVRmax) at 1.18 MPa. The maximum drive voltage increases with Tr, leading to a steady growth of the maximum transmitting sound level (SLmax), with a noticeable ascend of 3.9 dB at a 3.44 MPa Tr. This is a strong credibility that the prestressed layer could improve the sound radiation performance of the spherical transducer.To improve the acoustic radiation performance of the spherical transducer, a prestressed layer is formed in the transducer through fiber winding. The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress (Tr) and acoustic impedance, respectively. First, a theoretical estimation of Tr is established with a thin shell approximation of the prestressed layer. Then, the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer. Further, the ideal effects of Tr on the sound radiation performances of the transducer are analyzed through finite element analysis (FEA). Finally, four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer. The results show that with the growth of Tr, the acoustic impedance of the prestressed layer grows, mitigating the enormous impedance mismatch between the piezoelectric ceramic and water, while increasing attenuation of the acoustic energy, resulting in a peak value of the maximum transmitting voltage response (TVRmax) at 1.18 MPa. The maximum drive voltage increases with Tr, leading to a steady growth of the maximum transmitting sound level (SLmax), with a noticeable ascend of 3.9 dB at a 3.44 MPa Tr. This is a strong credibility that the prestressed layer could improve the sound radiation performance of the spherical transducer.

The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 μm-thick Bi(Fe0.93Mn0.05Ti0.02)O3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 μC/cm2, and a remanent polarization of 70 μC/cm2. Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field (P?E) loops with a positive shift along the x-axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of P?E loops on frequency (1–50 kHz) and temperature (25–125°C) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems.The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 μm-thick Bi(Fe0.93Mn0.05Ti0.02)O3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 μC/cm2, and a remanent polarization of 70 μC/cm2. Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field (P?E) loops with a positive shift along the x-axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of P?E loops on frequency (1–50 kHz) and temperature (25–125°C) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems.

BiScO3–PbTiO3 binary ceramics own both high Curie temperature and prominent piezoelectric properties, while the high dielectric loss needs to be reduced substantially for practical application especially at high temperatures. In this work, a ternary perovskite system of (1–x–y)BiScO3–yPbTiO3–xBi(Mn2/3Sb1/3)O3 (BS–yPT–xBMS) with x = 0.005, y = 0.630–0.645 and x = 0.015, y = 0.625–0.640 was prepared by the traditional solid-state reaction method. The phase structure, microstructure, dielectric/piezoelectric/ferroelectric properties were studied. Among BS–yPT–xBMS ceramic series, the BS–0.630PT–0.015BMS at morphotropic phase boundary possesses the reduced dielectric loss factor (tanδ = 1.20%) and increased mechanical quality factor (Qm = 84), and maintains a high Curie temperature ( TC = 410°C) and excellent piezoelectric properties (d33 = 330 pC/N) simultaneously. Of particular importance, at elevated temperature of 200°C, the value of tanδ is only increased to 1.59%. All these properties indicate that the BS–0.630PT–0.015BMS ceramic has great potential for application in high-temperature piezoelectric devices.BiScO3–PbTiO3 binary ceramics own both high Curie temperature and prominent piezoelectric properties, while the high dielectric loss needs to be reduced substantially for practical application especially at high temperatures. In this work, a ternary perovskite system of (1–x–y)BiScO3–yPbTiO3–xBi(Mn2/3Sb1/3)O3 (BS–yPT–xBMS) with x = 0.005, y = 0.630–0.645 and x = 0.015, y = 0.625–0.640 was prepared by the traditional solid-state reaction method. The phase structure, microstructure, dielectric/piezoelectric/ferroelectric properties were studied. Among BS–yPT–xBMS ceramic series, the BS–0.630PT–0.015BMS at morphotropic phase boundary possesses the reduced dielectric loss factor (tanδ = 1.20%) and increased mechanical quality factor (Qm = 84), and maintains a high Curie temperature ( TC = 410°C) and excellent piezoelectric properties (d33 = 330 pC/N) simultaneously. Of particular importance, at elevated temperature of 200°C, the value of tanδ is only increased to 1.59%. All these properties indicate that the BS–0.630PT–0.015BMS ceramic has great potential for application in high-temperature piezoelectric devices.

In this work, we show that a d33～150 pC/N can be obtained in nonpoled poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) copolymer films with an arch structure. The copolymer films, which are often thought to be homogeneous, are in fact inhomogeneous in microstructure and physical properties after film fabrication. Although a large proportion of the copolymer film is nonpolar, as expected in a nonpoled ferroelectric film, the surface regions of the film are spontaneously polarized. We propose that inhomogeneous stress in the surface regions, which is either from the constraint of the substrate or skin layer effect formed during the film fabrication, generates a flexoelectric response and orients the spontaneous polarization of the ferroelectric film. As a result of the polar surface regions, the nonpoled films exhibit a piezoelectric response. The piezoelectric response is further amplified by the special arch structure of the films, leading to the observed large effective piezoelectric response. This study not only discovers the polar surface effect in ferroelectric polymer films, but also proposes an approach to design polymer materials with a strong piezoelectric response.In this work, we show that a d33～150 pC/N can be obtained in nonpoled poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) copolymer films with an arch structure. The copolymer films, which are often thought to be homogeneous, are in fact inhomogeneous in microstructure and physical properties after film fabrication. Although a large proportion of the copolymer film is nonpolar, as expected in a nonpoled ferroelectric film, the surface regions of the film are spontaneously polarized. We propose that inhomogeneous stress in the surface regions, which is either from the constraint of the substrate or skin layer effect formed during the film fabrication, generates a flexoelectric response and orients the spontaneous polarization of the ferroelectric film. As a result of the polar surface regions, the nonpoled films exhibit a piezoelectric response. The piezoelectric response is further amplified by the special arch structure of the films, leading to the observed large effective piezoelectric response. This study not only discovers the polar surface effect in ferroelectric polymer films, but also proposes an approach to design polymer materials with a strong piezoelectric response.