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Transparent piezoelectrics are highly desirable for numerous hybrid ultrasound-optical devices ranging from photoacoustic imaging transducers to transparent actuators for haptic applications.sup.1-7. However, it is challenging to achieve high piezoelectricity and perfect transparency simultaneously because most high-performance piezoelectrics are ferroelectrics that contain high-density light-scattering domain walls. Here, through a combination of phase-field simulations and experiments, we demonstrate a relatively simple method of using an alternating-current electric field to engineer the domain structures of originally opaque rhombohedral Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3-PbTiO.sub.3 (PMN-PT) crystals to simultaneously generate near-perfect transparency, an ultrahigh piezoelectric coefficient d.sub.33 (greater than 2,100 picocoulombs per newton), an excellent electromechanical coupling factor k.sub.33 (about 94 per cent) and a large electro-optical coefficient [gamma].sub.33 (approximately 220 picometres per volt), which is far beyond the performance of the commonly used transparent ferroelectric crystal LiNbO.sub.3. We find that increasing the domain size leads to a higher d.sub.33 value for the [001]-oriented rhombohedral PMN-PT crystals, challenging the conventional wisdom that decreasing the domain size always results in higher piezoelectricity.sup.8-10. This work presents a paradigm for achieving high transparency and piezoelectricity by ferroelectric domain engineering, and we expect the transparent ferroelectric crystals reported here to provide a route to a wide range of hybrid device applications, such as medical imaging, self-energy-harvesting touch screens and invisible robotic devices. The use of alternating-current electric fields to control domain size in ferroelectric crystals affords excellent transparency, piezoelectricity and birefringence., Author(s): Chaorui Qiu [sup.1] , Bo Wang [sup.2] , Nan Zhang [sup.1] , Shujun Zhang [sup.2] [sup.3] , Jinfeng Liu [sup.1] , David Walker [sup.4] , Yu Wang [sup.5] , [...]

The piezoelectric and dielectric properties of PMN-PT single crystals were significantly enhanced by alternating current electric field poling (ACP). In this work, to investigate the mechanisms of piezoelectric performance enhancement in relaxor ferroelectric single crystals by ACP, a [001]-oriented PIN-PMN-PT single crystal with a diameter of 3 in was grown by the modified Bridgman method, and a series of single crystal samples within 100 mm of the height of the crystal boule were prepared. Compared with their direct current electric field poling (DCP) counterparts, the electrical properties of single crystal samples at different heights by ACP were regularly enhanced. The piezoelectric coefficient d33 and the dielectric constant ɛ33 of the rhombohedral samples both increased by nearly 20%. Based on the results of polarized light microscopy, the domain wall in [001]-poled ACP samples could not be observed along the [001] direction. The brightness of polarized light propagating along the [010] orientation was enhanced after ACP. The domain images of {100} in the DCP and ACP samples were observed by piezoelectric force microscopy. The results showed that the domain size of ACP samples increased. The existence of layered domains can be clearly found in the scanning electron microscopy results of the stress fracture surface of the ACP sample. According to the analysis, the improvement of the piezoelectric performance in ACP samples comes from the elimination of the 71° domain walls. This work demonstrates that certain ACPs can regulate the domain structure and steadily improve the piezoelectric properties of R-phase PIN-PMN-PT single crystals. [ABSTRACT FROM AUTHOR]

Compared with the state-of-the-art Pb(Zr,Ti)O3 ceramics, relaxor-PbTiO3 (PT) based ferroelectric single crystals possess much higher piezoelectricity, thus receiving considerable attention from the ferroelectric community. Recently, it was found that the alternating current electric field poling (AC-poling) could further improve the piezoelectricity of [001]-poled rhombohedral (R) relaxor-PT single crystals. In this work, we investigated the domain structures and electromechanical properties of alternating current electric field poled (AC-poled) relaxor ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) crystals with different orientations and phase structures, including [001]-oriented R PIN–PMN–PT (23/47/30), [011]-oriented R PIN–PMN–PT (23/47/30), and [001]-oriented monoclinic (MC) PIN–PMN–PT (22/44/34) single crystals. We found that the piezoelectric coefficient (d33), free dielectric permittivity (ɛ33T/ɛ0), and clamped dielectric permittivity (ɛ33S/ɛ0) for AC-poled [001]-oriented R PIN–PMN–PT (23/47/30) crystals were improved by 24.4%, 22.6%, and 8.5%, respectively, when compared with the direct current electric field poled (DC-poled) counterparts. This phenomenon is attributed to the increase of domain size according to the observations from polarized light microscopy. Nevertheless, for [011]-poled R PIN–PMN–PT and [001]-poled MC PIN–PMN–PT crystals, the dielectric permittivities and piezoelectric coefficients were decreased a bit by AC-poling, being attributed to the depolarization phenomenon caused by the AC electric field. This work demonstrates that impacts of AC-poling on the properties of ferroelectrics are highly related to the orientation and phase of ferroelectric crystals. [ABSTRACT FROM AUTHOR]

Pb-based relaxor piezoelectric single crystal composites (PSCCs) have attracted widespread attention for improving the bandwidth and sensitivity performance of acoustic transducers due to their excellent electromechanical and piezoelectric properties. Alternating current polarization (ACP) has been proven as an effective method for enhancing the dielectric and piezoelectric properties of relaxor-PbTiO3 single crystals. Herein, we investigated the effects of the amplitude, frequency, and cycle number of the poling electric field on the piezoelectric and dielectric performances of PSCCs and obtained the optimum poling condition of ACP. Compared with the traditional direct current poling method, both the dielectric permittivity ( ε 33 T / ε 0 ) and piezoelectric coefficient ( d 33 ) of the AC-poled PSCCs were both increased by up to 20%. Notably, the ACP PSCC with a volume fraction of 60% exhibited a high d 33 of 1610 pC/N, which is superior to values previously reported for PSCCs. This work provides an alternative strategy for enhancing the properties of PSCCs and may contribute to the further development of piezoelectric applications. [ABSTRACT FROM AUTHOR]

Relaxor-PbTiO3 crystals possess ultrahigh piezoelectricity when compared with state-of-the-art Pb(Zr,Ti)O3 ceramics. Recently, even higher piezoelectricity is observed in alternating current electric-field-poled (AC-poled) crystals. This poling technique may benefit many piezoelectric materials and corresponding applications. The scaling effect is quite important for piezoelectric applications, since the operational frequency of devices is associated with the dimension of piezoelectric elements. Here, we investigated the thickness dependence of dielectric and piezoelectric properties for AC-poled relaxor-PbTiO3 crystals. Compared with the traditional poling method, the piezoelectric coefficient (d33) and dielectric permittivity (ɛT33/ɛ0) were found to be increased by 20%-30% via alternating current electric field poling (AC-poling). A weak scaling effect was observed for the samples with thickness above 200 μm. While, for 100-μm samples, the dielectric permittivity was only enhanced by 6%, and a clear degradation of properties was observed when the cycle of alternating current electric field is beyond three. These features are thought to be associated with the impacts of surface damages for thin samples. Of particular interest is that the coercive field was found to decrease during AC-poling, which should be considered for the design of piezoelectric devices. This work provides important information for AC-poled relaxor-PbTiO3 crystals and will benefit the piezoelectric applications using these crystals. [ABSTRACT FROM AUTHOR]