relaxor-PbTiO3 Single Crystals Research Articles

Poling-free relaxor-PbTiO3 single crystals

Relaxor-PbTiO3 ferroelectric single crystals have drawn attention aiming at high-end piezoelectric applications thanks to their excellent piezoelectric properties. Like all the other ferroelectrics, relaxor-PbTiO3 single crystals can only be piezoelectrically active upon being electrically poled. However, this poled state is thermally unstable, limiting their uses because of their relatively low depolarization temperature. Here, we show that a non-destructible permanent poled state can be realized in relaxor-PbTiO3 single crystals by forming a 0–3 composite in the presence of charged mobile point defects. We demonstrate this on solid-state grown 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals doped with Mn (Mn-PMNT) as a donor with well-aligned and dispersed boron-rich MgO-based inclusions (MBIs). Mn-PMNTMBI sharing [001] axis with arrayed MBIs were spontaneously polarized during cooling across the Curie temperature without an external electric field. The piezoelectric coefficient and dielectric permittivity of self-poled Mn-PMNTMBI crystals were as large as 90 % of that achieved by a direct-current poling treatment at room temperature, and such poled state was reproducible against repeated thermal cycles. We expect that the poling-free high-performance piezoelectric relaxor-PbTiO3 single crystals offer an avenue for piezoelectric-based devices by removing the working temperature limit as one of the inherent fundamental limitations.

Comparison of field-cooling DC poling and AC poling for lead perovskite relaxor-PbTiO3 single crystals grown by a continuous feeding Bridgman process

We investigated the effectiveness of poling processes for Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals (SCs) produced using a continuous feeding Bridgman method, which is known to produce a high property uniformity. The four studied poling processes are: (I) standard direct current poling (STD-DCP); (II) low-voltage field-cooling DCP (LV-FCP); (III) high-voltage field-cooling DCP (HV-FCP); and (IV) mid-temperature alternating current poling (MT-ACP). The highest free dielectric constant (ε 33 T/ε 0) and piezoelectric constant (d 33) were obtained by MT-ACP (ε 33 T/ε 0 = 11 000, d 33 = 3000 pC/N), followed by LV-FCP (ε 33 T/ε 0 = 7500, d 33 = 2400 pC/N), HV-FCP (ε 33 T/ε 0 = 6250, d 33 = 1850 pC/N), and STD-DCP (ε 33 T/ε 0 = 6200, d 33 = 1800 pC/N). The LV-FCP SC showed a 21% and 33% increase in ε 33 T/ε 0 and d 33 compared to that of the STD-DCP SC; however, this was not as much as the 77% and 67% improvement of the MT-ACP SC. These results provide guidance for SC transducers.

Alternating current polarization to enhance piezoelectric performance of single crystal composites

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 (ε33T/ε0) and piezoelectric coefficient (d33) 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 d33 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.

Scaling effects in the alternating-current poling of thin PIN-PMN-PT single crystals

AC-poling of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals with a thickness of 0.06–0.16 mm was studied in this paper. Compared with DC-poled samples, enhancements in piezoelectric and dielectric properties can be obtained when the thickness is above 0.1 mm. However, inconsistency in poling effects was found in the crystals with thickness below 0.1 mm. To elucidate why such scaling effect arises, surface roughness was measured by an atomic force microscopy to correlate surface morphology and poling effects. It was found that non-uniform surface roughness led to inconsistent and decreased properties. Furthermore, temperature-dependent dielectric permittivity spectra were measured to explore how crystal thickness affects the thermal stability of ferroelectric phases. It is noted that complex changes in crystallographic symmetries emanate by decreasing thickness. Such phenomena can be attributed to more influential effects of surface morphology when thickness is reduced. We hope this work suggests a clue for solving the scaling effects of AC-poling on relaxor-PbTiO3 single crystals.

Less than mm2 macrosymmetry in polarized (011)-oriented relaxor-PbTiO3 single crystals reflected in the face shear properties

The macrosymmetry of (011)-oriented nominally rhombohedral relaxor-PbTiO3 single crystals poled along the [011] direction is investigated using the impedance spectroscopy method. Contrary to the common belief on the mm2 macrosymmetry, we find that the mm2 macrosymmetry significantly underestimates the electromechanical coupling of the ZXt 45°-cut transverse extension specimen by about 10%. We show that the underestimated electromechanical coupling can be corrected by assigning a lower symmetry of 2, i.e., an average monoclinic symmetry. The validity of the newly assigned macrosymmetry and the presence of non-regular phases presumably responsible for the apparent loss of mirror symmetry are confirmed by radial strain and thermally stimulated depolarization measurements, respectively.

Property enhancement in relaxor-PbTiO3 single crystals by alternating current poling: Evaluation of intrinsic and extrinsic contributions

Piezoelectric activity has always been the most concerned performance for PbTiO3-based relaxor ferroelectrics. Recently, the alternating current poling (ACP) method has been developed as a simple and economical technique to optimize piezoelectric performance. However, the mechanism of the ACP method is still debatable. In this work, we carried out the ACP on the 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal, a noticeable piezoelectric improvement of 20% has been achieved in comparison with the direct current poled sample, meanwhile, the dielectric loss is reduced by 26%. We found that the ACP sample demonstrates a uniform domain pattern with a large domain size dominated by 109° domain walls, in contrary to the complicated domain structures which contain both 109° and 71° domains in the DCP sample. With this uniform and simple domain structure, the crystal lattice is weakly constrained and very susceptive to external stimulation, resulting in enhanced piezoelectric response in ACP poled sample. Meanwhile, dielectric loss is reduced for the low domain wall density. The current work gives a comprehensive description of the ACP poled samples, including the microscopic domain structure, the quantitative estimation of contributions arise from lattice deformation and domain wall motions, and reveals the interactions between domain structure and the macro performance, which provide important guidelines for the design of high-performance ferroelectrics utilizing domain tailoring techniques.

A large and anisotropic enhancement of the mechanical quality factor in ternary relaxor-PbTiO3 single crystals

Enhancing the mechanical quality factor, Qm, in ferroelectrics is one of the most critical issues for high-power devices, such as therapeutic ultrasonic transducers, large-displacement actuators, and high-frequency transducers. Although previous results have indicated that Qm could be improved through acceptor doping, the mechanism behind this effect is still a mystery, and there have been few reports on the optimization of energy loss in ultrahigh piezoelectric materials such as relaxor-PbTiO3 (PT) single crystals. In this work, we investigate the energy loss associated with various vibration modes in Mn-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT:Mn) single crystals and compare with their undoped PIN–PMN–PT counterpart. We find that Q15, Q24, and Q33 in PIN–PMN–PT:Mn, respectively, undergo 160%, 100%, and 80% enhancements, thus demonstrating very large extrinsic contributions with unusual anisotropies in the Qm enhancement. Such a strong anisotropy is strongly interlinked with the orientation of the internal bias Ei and the charged domain walls. Our results provide some fundamental understanding of domain-engineered ferroelectric materials and materials-by-design for high-performance low-loss devices.

Ultrasonic pulse-echo technique for the characterization of elastic constants of single domain Pb(Zn1/3Nb2/3)O3–5.5%PbTiO3 single crystals with 3m symmetry

The ultrasonic pulse-echo (UPE) technique is a classical method to characterize the elastic constants of solid materials. However, no detailed analysis exists in the literature regarding the application of this technique on the characterization of relaxor–PbTiO3 single crystals with 3m symmetry. This study systematically investigated the UPE technique for the characterization of elastic constants of [111]c poled Pb(Zn1/3Nb2/3)O3–5.5%PbTiO3 single domain single crystals with 3m symmetry. Longitudinal and transversal wave echoes in a rectangular parallelepiped sample were identified based on the theory of wave propagation in piezoelectric materials. Experimental results showed that $$c_{11}^{\text{E}}$$ and $$c_{33}^{\text{D}}$$ can be directly and precisely determined by UPE, but $$c_{44}^{\text{E}}$$ cannot be determined by UPE neither directly nor indirectly. The elastic constants $$c_{14}^{\text{D}}$$ , $$c_{44}^{\text{D}}$$ , and $$c_{66}^{\text{D}}$$ cannot be directly determined by UPE but they can be calculated from directly measured ci (i = 1, 2, 3, 4). Experimental results also showed that c4 cannot be precisely determined by UPE. Based on error analysis, the uncertainty of c4 will strongly influence the precision of measured $$c_{44}^{\text{D}}$$ and $$c_{66}^{\text{D}}$$ but only weakly influence the accuracy of $$c_{14}^{\text{D}}$$ .

Domain wall contributions to piezoelectricity in relaxor-lead titanate single crystals

It is demonstrated that the dielectric permittivity and piezoelectric coefficients in relaxor-PbTiO3 single crystals close to the morphotropic phase boundary (MPB) can be augmented by contributions from domain walls. Landau-Ginzburg-Devonshire models, incorporating both polarization and strain gradients through the domain walls, show that wall contributions in domain engineered single crystals originate from enhanced, field-induced polarization rotation in static domain walls, unlike ceramics, in which piezoelectricity is enhanced by domain wall translation. For 71° domain walls in 0.7 Pb(Mg1/3Nb2/3)O3 – 0.3PbTiO3 the piezoelectric charge coefficient d33 at the center of the wall ranges from 5000 to >30,000 pC N−1 depending on the wall width. Thus, a sufficiently high domain wall density can account for the experimentally observed augmentation in the measured properties compared to single domain models. The symmetry of the domain walls explains both the variety of average symmetries observed close to the MPB and the experimentally observed switching of the [001]-oriented crystals into the tetragonal phase via a symmetry-improbable MC phase. For a crystal of rhombohedral ground state, the presence of domain walls will impart monoclinic symmetry, the predominance of which increases with increasing domain wall density.

Symmetry-bridging phase as the mechanism for the large strains in relaxor-PbTiO3 single crystals

Relaxor-PbTiO3 piezoelectric single crystals have been of a great interest, since the discovery of ultrahigh piezoresponse demonstrated in <001> -oriented crystals of the composition at the rhombohedral side of morphotropic phase boundary. It has been proposed that the exceptionally large piezoelectric properties should originate from an electric-field-induced polarization rotation that involves a reversible phase transformation between rhombohedral and tetragonal via monoclinic symmetry. However, this commonly accepted polarization rotation mechanism has its limit in explaining still the excellent piezoelectricity even at a small excitation field far below the coercive field. Here, we show by a comparative study using single crystals from two distinct processing techniques, the polarization rotation has, if ever, little influence on the strain properties of <001 > -oriented rhombohedral relaxor-PbTiO3 single crystals. Instead, they may come from a reversible shear-mode piezoelectric contribution from electric-field-susceptible ‘symmetry-bridging’ unit-cell-level phases, the polarization direction of which spans monoclinic symmetry.

Accurate characterization of complete set constants of single domain 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 single crystal by resonant ultrasound spectroscopy using only one sample

In order to find out the origin of the giant piezoelectric effects of relaxor-PbTiO3 single crystals when poled along nonpolar directions, it is necessary to obtain the complete physical property data of a single domain state. Conventional characterization methods using multiple samples of different geometries often produce inconsistent data set because the domain patterns produced during poling are strongly dependent on the sample geometry. Here, we used the resonant ultrasound spectroscopy (RUS) technique to determine the material constants of a single domain 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 single crystal, which has a high mechanical quality factor (QM). Errors caused by sample-to-sample variation are avoided because all constants were measured from the same sample. The data set obtained is highly self-consistent, which provides a base for theoretical analysis as well as the input for simulation designs of piezoelectric devices. Comparison with data measured by other methods shows the advantage and higher accuracy of this characterization strategy.

Phase-field simulation of domain walls in rhombohedral ferroelectric single crystals

Domain engineered ferroelectric relaxor-PbTiO3 single crystals exhibit ultrahigh piezoelectric coefficients. A 10th order Landau-Devonshire energy function for rhombohedral PIN-PMN-PT ferroelectric single crystals was implemented in a phase-field model to study the behavior of domain walls under external electric field. The domain formation and domain wall evolution were simulated. A new way to apply periodic boundary conditions was implemented to accommodate nonzero strain during the domain formation and evolution. It was found that 71 and 109 domain walls reacted differently to external electric field along the [110] direction. A domain wall broadening effect was observed in the 71 domain walls when the electric field was below the coercive field. When the electric field exceeded the coercive field, homogeneous polarization switching occurred with no motion of the 71 domain walls. Heterogeneous polarization switching occurred by the sweeping of the 109 domain walls. The evolution mechanism of the two types of domain walls helps explain the behavior of engineered domain structures subjected to external electric field.

Minimization of pyroelectric effects in relaxor-PbTiO3 crystals for piezoelectric sensors

To minimize pyroelectric effects while keeping high piezoelectric effects in relaxor-PbTiO3 single crystals, the crystallographic orientation dependence of the pyroelectric and piezoelectric coefficients were investigated for binary (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT), ternary (1 − x − y)Pb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–xPbTiO3 (PIN–PMN–PT) and Mn-doped PIN–PMN–PT single crystals with the “4R” multidomain state. The secondary pyroelectric coefficients were calculated from the thermodynamic inter-relationship between the piezoelectric, elastic, and thermal expansion coefficients, being on the order of (1.16–1.23) × 10−4 C m−2 K−1 for binary crystals and (0.97–2.03) × 10−4 C m−2 K−1 for ternary ones. The primary pyroelectric coefficients were –(6.73–6.84) × 10−4 C m−2 K−1 and −(5.44–6.43) × 10−4 C m−2 K−1 for binary and ternary crystals, respectively. The pyroelectric coefficients could be reduced by matrix rotation, but at the cost of decreasing longitudinal piezoelectric coefficients d33. Of particular interest is that the maximum piezoelectric coefficients d24∗ at θ = ±55o and d34∗ at θ = ±35o by a counterclockwise rotation of θ about the X axis (θ is the rotation angle about the coordinate axes), or d15∗ at θ = ±55o, and d35∗ at θ = ±35o by a counterclockwise rotation the Y axis, were found on the order of 3000 pC N−1. The corresponding pyroelectric coefficients could be reduced by ∼20%. The reduced pyroelectric coefficients that can contribute to decrease undesirable output signals, together with the high piezoelectric coefficients, enable relaxor-PT crystals as favorable candidates for high-sensitivity piezoelectric sensors.

Anisotropy of the piezoelectric properties of the domain-engineered pseudotetragonal ferroelectric relaxor-PbTiO3 single crystals

In the frame of thermodynamic approach the areas of the admissible values of longitudinal (d33) and transverse (d31) piezoelectric moduli have been determined for 12 domain-engineered pseudotetragonal ferroelectric relaxor-PbTiO3 single crystals’ compositions belonging to so-called first, second and third generations. The parameters characterizing the piezoelectric anisotropy are shown to be practically the same for all the crystals considered, independently of their composition. Such behavior is explained in the frame of a simple averaging model.

Primary and secondary pyroelectric coefficients of rhombohedral and tetragonal single-domain relaxor-PbTiO3 single crystals

The primary and secondary pyroelectric coefficients were determined for binary (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN-PT) and ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PIN-PMN-PT) relaxor-PT single crystals. The secondary pyroelectric coefficients were calculated from the thermodynamic inter-relationship between the piezoelectric, elastic, and thermal expansion coefficients. Poling along [111] and [001] directions resulted in single-domain state of “1R” and “1T” and a macroscopic symmetry of 3m and 4mm for rhombohedral (x = 0.28) and tetragonal (x = 0.42) crystals, respectively, enabling relatively large values of pyroelectric coefficients p ≥ 5.7 × 10−4 C/m2 K. The calculated results show that the secondary pyroelectric coefficients are in the range of (−0.62 ∼ −1.06) × 10−4 C/m2 K for rhombohedral crystals and (0.70 ∼ 1.14) × 10−4 C/m2 K for tetragonal crystals, significantly lower than that of primary pyroelectric coefficients, which is important for thermal directional and imaging applications. In contrast, high d15 piezoelectric coefficients (&amp;gt;2000 pC/N), together with zero pyroelectric coefficients in thickness shear crystals, also makes them promising candidates for piezoelectric sensors where thermal noise is undesirable.

Relaxor-PbTiO3 single crystals for various applications.

Piezoelectric materials lie at the heart of electromechanical devices. Applications include actuators, ultrasonic imaging, high intensity focused ultrasound, underwater ultrasound, nondestructive evaluation transducer, pressure sensors, and accelerometers, to name a few. In this work, the advantages and disadvantages of relaxor-PbTiO(3)-based single crystals are discussed, based on the requirements (figure of merit) of various applications, with emphasis on recent developments of the shear properties of single crystals as a function of temperature and applied fields.

Pure low-frequency flexural mode of [011]c poled relaxor-PbTiO3 single crystals excited by k32 mode

Rhombohedral phase relaxor-PbTiO(3) solid solution single crystals poled along [011](c) exhibits superior lateral extensional piezoelectric response, which enables the excitation of a pure low frequency flexural mode with a bridge-type electrode configuration. For the ternary 0.24Pb(In(1/2)Nb(1/2)) O(3)-0.46Pb(Mg(1/3)Nb(2/3))O(3)-0.30PbTiO(3) single crystal poled along [011](c), the electromechanical coupling factor of the flexural mode reached as high as 0.66, and the resonance frequency of this mode can be easily made in kHz range, making it possible to fabricate very small size low frequency sensors and actuators. We have delineated theoretically the coupling between flexural mode and other modes and realized a strong pure flexure mode.

High performance ferroelectric relaxor-PbTiO3 single crystals: Status and perspective

Ferroelectrics are essential components in a wide range of applications, including ultrasonic transducers, sensors, and actuators. In the single crystal form, relaxor-PbTiO3 (PT) piezoelectric materials have been extensively studied due to their ultrahigh piezoelectric and electromechanical properties. In this article, a perspective and future development of relaxor-PT crystals are given. Initially, various techniques for the growth of relaxor-PT crystals are reviewed, with crystals up to 100 mm in diameter and 200 mm in length being readily achievable using the Bridgman technique. Second, the characterizations of dielectric and electromechanical properties are surveyed. Boundary conditions, including temperature, electric field, and stress, are discussed in relation to device limitations. Third, the physical origins of the high piezoelectric properties and unique loss characteristics in relaxor-PT crystals are discussed with respect to their crystal structure, phase, engineered domain configuration, macrosymmetry, and domain size. Finally, relaxor-PT single crystals are reviewed with respect to specific applications and contrasted to conventional piezoelectric ceramics.

Measurements of face shear properties in relaxor-PbTiO3 single crystals

The face (contour) shear piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) single crystals were experimentally determined by the impedance method. Zt ± 45° cut samples with various aspect ratios were investigated based on Bechmann’s zero-order approximate solution. Square plates were found to exhibit a clean face shear vibration mode and the experimental data were in good agreement with the rotated matrix calculations and finite element method simulations. The piezoelectric coefficients d36 were determined to be in the range of 1600-2800 pC/N, depending on the compositional variations, with an ultralow frequency constant N36, in the range of 490–630 Hz.m. In contrast to conventional thickness shear modes, the mechanical quality factors of face shear vibrations are relatively high, with Q values being on the order of ∼100-450, demonstrate promising for low frequency transducer applications.