Relaxor Ferroelectric Single Crystals Research Articles

Orientation dependence of dielectric and piezoelectric properties of tetragonal relaxor ferroelectric single crystals by alternate current poling

Piezoelectric and dielectric properties of [001] and [110]-oriented tetragonal Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 (PIN-PMN-PT) single crystals (SCs) after alternate current poling (ACP) were investigated. Compared with direct current poling (DCP), the piezoelectric and dielectric properties of [001]-oriented samples have no improvement, while the piezoelectric coefficient d33 and free dielectric constant ε33T/ε0 of [110]-oriented samples increase by 32% and 26%, respectively. The domain was observed on (001) and (11¯0) faces of [110]-oriented samples. The enhancement of the piezoelectric performance is attributed to the high density of domain wall, increase of distorted regions between 90° domains, and monoclinic phase. Compared with DCP, both intrinsic and extrinsic contributions enhance after ACP though the Rayleigh analysis. This work indicates that ACP is an effective way to enhance piezoelectric properties of non-polar axis oriented relaxor-PT ferroelectric SCs.

Multiple Softening of Low-Frequency Raman Modes of Tungsten-Bronze Lead Barium Niobate Relaxor Ferroelectric Single Crystals

The vibrational properties of tetragonal tungsten-bronze lead barium niobate, Pb(1−x)BaxNb2O6, with x = 0.5 were investigated by using Raman spectroscopy over a wide temperature range from room temperature to 550 °C. The Raman modes in the measured spectrum were divided into three spectral ranges, internal symmetric and antisymmetric vibrational modes of the oxygen octahedra and low-frequency external lattice modes. The temperature dependences of the Raman shifts showed anomalous changes at the ferroelectric phase transition temperature of ~350 °C. Especially, lowfrequency modes below ~300 cm−1 commonly exhibited multiple softening upon heating toward the transition temperature, indicating that the lattice becomes softer on approaching the ferroelectric phase transition temperature.

A method for determining the orientation of [011] poled relaxor ferroelectric single crystal disks

A new method for determining the crystal orientation of [011] poled relaxor ferroelectric single crystal (RFSC) disks has been developed. This Technical Note describes the measurement techniques and mathematical approaches associated with this new method, which is possible due to the anisotropic response of [011] poled single crystal disks. Experimentally, the disks are subject to a distributed edge load at a series of angular orientations, with the output voltage recorded at each orientation. Equations have been developed to govern a particle swarm to find an optimised fit to the experimental data yielding the crystal orientation of the disk which is required for practical applications. Approximate values for the piezoelectric charge constants d31, d32 are also determined. The method is demonstrated on a RFSC Mn-PMN-PZ-PT disk, comparing favourably with a synchrotron x-ray transmission diffraction study on the same disk.

Investigation of High-Power Properties of PIN-PMN-PT Relaxor-Based Ferroelectric Single Crystals and PZT-4 Piezoelectric Ceramics.

We developed a high-power piezoelectric characterization system that was used to study the high-field properties of (1-x-y)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3) O3-xPbTiO3 (PIN-PMN-PT) relaxor ferroelectric single crystals and PZT-4 piezoelectric ceramics. The impedance spectrum of 31 modes was measured under constant voltage by the high-power piezoelectric system. From measuring the resonance and antiresonance frequencies, the high-field behaviors of the electromechanical coupling coefficients, elastic compliances, and piezoelectric coefficients of the PIN-PMN-PT crystals were determined and compared with commercial PZT ceramics. By fitting the equivalent circuit parameters under large electric fields, the mechanical quality factors of the PIN-PMN-PT single crystals and PZT-4 ceramics were calculated as well. The results showed that the mechanical quality factor of the PZT-4 is higher than that of PIN-PMN-PT, and the mechanical quality factors of the PZT-4 and PIN-PMN-PT both decrease sharply first and then decrease slowly with increasing the electric field. The tensile strengths of PIN-PMN-PT crystals and PZT-4 ceramics were also determined by the impedance method, where we found that the tensile strengths of PIN-PMN-PT crystal and PZT-4 ceramic were 19.6 and 76.4 MPa, respectively. The 31-mode vibrators of PIN-PMN-PT crystals and PZT-4 ceramics can be driven by the largest electric field of 33 and 65 V/mm under resonance frequency, respectively.

Effect of sample-preparation history on domain and crystal structure in a relaxor-ferroelectric single crystal

The effect of sample-preparation procedures on single crystals of the relaxor-based ferroelectric Pb(Mg1/3Nb2/3)O3–31%PbTiO3 (PMN–31%PT) has been investigated. PMN–31%PT single crystals were treated using the general sample-preparation methods of mechanical polishing and Ar-ion milling. Similar domain structures were artificially induced in both the mechanically polished and the Ar-ion milled PMN–31%PT; this domain structure was not observed in the original PMN–31%PT single crystal. Macroscopic structural investigation using X-ray diffraction showed that these general sample-preparation methods induce a structural change from a monoclinic-like to a tetragonal-like structure. A study of local symmetry also indicated that Ar-ion milling induces a structural change from the original monoclinic-like crystal symmetry to a tetragonal-like crystal symmetry. It is also demonstrated that the conventional sample-preparation methods induce a poling-like effect on PMN–31%PT.

Rotational intersite displacement of disordered lead atoms in a relaxor ferroelectric during piezoelectric lattice straining and ferroelectric domain switching

We report results of the time-resolved x-ray structure analysis of a relaxor ferroelectric single crystal under an alternating electric field. The time dependence of the lattice strain, atomic displacements, and ferroelectric domain volumes in a $0.955\mathrm{Pb}(\mathrm{Z}{\mathrm{n}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}0.045\mathrm{PbTi}{\mathrm{O}}_{3}$ (PZN-4.5PT) single crystal during piezoelectric lattice straining and ferroelectric domain switching is revealed. The lattice strain induced by an electric field is consistent with that expected from the piezoelectric constants. The crystal mosaicity is momentarily increased by a nucleation of nanosized ferroelectric domains when the polarization switching starts. The nucleated ferroelectric domains grow with the time constant of $\ensuremath{\tau}=14\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$. An intersite displacement of the disordered Pb atoms observed in those site occupancies suggests that a rotational intersite displacement of Pb atoms is easily induced by an electric field and causes continuous rotation of the spontaneous polarization. The rotational intersite displacement of Pb atoms is essential for the large piezoelectric lattice strain and fatigue-free ferroelectric domain switching.

Multi-step domain switching and polarization fatigue in [110]-oriented 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals

Domain switching in ferroelectrics is at the heart of many functionalities, and the visualization of switching pathway is the key to understand the fundamental properties and to promote the applications of high-performance ferroelectrics. Here, we directly documented the multi-step domain switching in [110]-oriented 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-0.33PT) single crystals under a cycling electric field with the help of in situ polarized light microscopy. Based on the characteristic domain configuration analysis, we demonstrated that the 180° switching process was consisted of multi-step 60° switching. Such a multi-step 60° switching pathway resulted in a large negative strain and an internal electric field, which contributes to a large polarization fatigue rate under the alternating electric field. Our works may provide a window to study the domain switching process and its effect on polarization fatigue in relaxor-ferroelectric single crystals.

Achieve single domain state in (111)-oriented rhombohedral phase PMN-PT relaxor ferroelectric single crystals for electro-optical application

An electro-optic (EO) modulator is one of the most important optical devices and has been widely used in the photonic industry. Performance of EO modulators mainly depends on the property of EO materials. Here, the EO property of the (111)-oriented single domain rhombohedra phase (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal is investigated. Due to the light scattering by domain walls, a single domain crystal is essential and has been well prepared here by a thermal annealing and high temperature poling process. It is found that domains become irregular with significantly decreased dimension after annealing, which indicates that the ferroelastic domain walls are eliminated. A crack-free single domain crystal shows excellent optical quality, with a high transmittance of approximately 70% in near-infrared regions. Finally, the effective EO coefficient of the (111)-oriented rhombohedral phase PMN-PT crystal is measured by a Senarmont compensator amplitude modulator. An effective EO coefficient of 112 pm/V is obtained in the (111)-oriented rhombohedral phase PMN-PT crystal, which is much higher than that of the commercial LiNbO3 crystal, indicating the potential for use in compact and low driving voltage EO devices.

Mechanical-Induced Polarization Switching in Relaxor Ferroelectric Single Crystals.

Control of coupling between electric and elastic orders in ferroelectric bulks is vital to understand their nature and enrich the multifunctionality of polarization manipulation applied in domain-based electronic devices such as ferroelectric memories and data storage ones. Herein, taking (1 - x%)Pb(Mg1/3Nb2/3)O3-x%PbTiO3 (PMN-x%PT, x = 32, 40) as the prototype, we demonstrate the less-explored mechanical switching in relaxor ferroelectric single crystals using scanning probe microscopy. Low mechanical forces can induce metastable and electrically erasable polarization reversal clearly from electrical-created bipolar domains around the 180° domain wall in monoclinic PMN-32%PT and inside the c+ domain in tetragonal PMN-40%PT. The mechanical switching evolutions show force/time dependence and time-force equivalence. The time-dependent mechanical switching behavior stems from the participation and contribution of polar nanoregions. Flexoelectricity and bulk Vegard strain effect can account for the mechanical switching but notably, the former in the two has very different origins. These investigations exhibit the possibility of mechanical switching as a tool to manipulate polarization states in ferroelectric bulks, and provide the potential of these crystals as substrates in mechanical polarization control of future thin-film devices.

Investigations on the electrical properties, domain structure, and local piezoelectric response in 0.3Pb(In1/2Nb1/2)–0.4Pb(Mg1/3Nb2/3)–0.3PbTiO3 single crystal

High-Curie temperature relaxor ferroelectric single crystals attracted attention recently due to the excellent global electrical properties for electromechanical devices. In this work, the electrical properties, domain structure, and local piezoelectric response of ternary 0.3Pb(In1/2Nb1/2)–0.4Pb(Mg1/3Nb2/3)–0.3PbTiO3 (0.3PIN-0.4PMN-0.3PT) single crystal was investigated. Large electric field-induced strain with little hysteresis was obtained in -oriented high-quality crystal. Nanosized fingerprint pattern domain of ~ 100–300 nm with obvious local piezoelectric response was observed. The temperature-dependent dielectric spectrum revealed a ferroelectric rhombohedral to tetragonal phase transition at 106 °C, obviously higher than that of binary 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single-crystal (~80 °C). The evolution of the ferroelectric property and strain response was also studied at elevated temperature. The temperature dependence of the PFM results demonstrated that the surface domain structure of the 0.3PIN–0.4PMN–0.3PT single crystals could still be detected above the Curie temperature. The local piezoelectric hysteresis loop exhibited strong dependence on the DC bias field and obvious local butterfly shape displacement curve could be induced at 180 °C under larger local DC field.

Phase structure and quasi-single-domain mechanism in Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals near morphotropic phase boundary

Based on the domain configuration analysis, we demonstrate that orthorhombic (O) phase is a structural bridge between the rhombohedral (R) and tetragonal (T) phase in Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) crystals near the morphotropic phase boundary (MPB), as illustrated in the composition-temperature phase diagram. After poling along the polar direction, domain patterns in PMN-0.30PT, PMN-0.33PT, and PMN-0.37PT single crystals are found to accord with quasisingle-domain configurations (1R*, 1O*, and 1T*) after removal of the electric field. Furthermore, by the thermodynamic theory analysis, the quasisingle-domain states present one dominant domain and other adjacent domains owing to partial depolarization. Our results provide a reliable and nondestructive method to identify the phase structures near the MPB region in the PMN-xPT and other similar relaxor-ferroelectric single crystals.

Real-time observation of stress-induced domain evolution in a [011] PIN-PMN-PT relaxor ferroelectric single crystal

This paper reports on the real-time observation of mechanical stress-induced micro and nano domain evolution in a single crystal relaxor ferroelectric [011] poled 24PIN-PMN-PT “3-2 mode” nano-sized lamella. Mechanical loading in the [100] direction was applied to lamella in situ within a transmission electron microscope, with a [01¯1] viewing direction selected for the recording of real-time videos of the domain evolution within the lamella. The observed dominant behaviour under loading is a reversible response composed of the movement of microdomains and the disappearance of nanodomains. Changes in the selected area diffraction pattern down the [01¯1] zone axis are reported, and provide evidence of a significant increase in crystal symmetry under compression. A qualitative insight into the behaviour of the lamella's mechanical response is obtained via predictions of the non-uniform stress distribution within the lamella found using simple finite element analysis. The correlation between the observed morphology changes, diffraction pattern changes, and the known mechanical stress induced polydomain-rhombohedral to monodomain-orthorhombic phase transition of bulk [011] poled 24PIN-PMN-PT “3-2 mode” single crystal is discussed.

Investigation of thermal properties and energy harvesting of the Pb(Mg1/3Nb2/3)1-xTixO3 perovskite single crystals

Thermal energy harvesting has great potential for environment-friendly self-powered devices. Materials based on relaxor-ferroelectric single crystals such as PMN-PT (lead titanium-lead magnesium niobate) have gained significant interest for their outstanding properties. In this context, single crystals from (1-x)PbMg1/3Nb2/3O3-xPbTiO3 solid solution were grown using the modified Bridgman method in the composition range of x = 0.25, 0.35, and 0.40. This paper presents a systematic comparison between (1-x)PMN-xPT single crystals and ceramics involving the effect of composition and the crystal orientation on thermal properties assuming a one-dimensional heat-flow process. Results demonstrate that thermal and pyroelectrical properties are intimately coupled to the chemical composition, where the studied single crystals have a good performances compared to their corresponding ceramics, which make them very promising for efficient cooling systems, and IR devices applications.

Aging Behavior and Electric Field Induced Instabilities in Lead Magnesium Niobate - Titanate Relaxor Ferroelectric Single Crystal

The aging characteristics and influence of electric field poling on the phase transitions in (1-x)Pb (Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) [110]-oriented single crystal were examined through temperature dependent complex capacitance study. In addition to two phase transition anomalies exhibited by the crystal in the virgin state, other phase transition instabilities were observed in the complex capacitance of the crystal under the external applied electric field. The aging behavior deviated from the linear logarithmic law and followed the stretched exponential expression typical for relaxor ferroelectrics. Moreover, aging decreased with frequency while it became faster with increase in temperature towards the paraelectric – ferroelectric structural phase transition temperature.

Identification of elastic-plastic and phase transition characteristics for relaxor ferroelectric PMN-PT anisotropic single crystals using nanoindentation technique

ABSTRACTAs one kind of important ferroelectric ceramics, relaxor ferroelectric PMN-PT single crystals have triggered a revolution in electromechanical devices owing to their giant piezoelectric properties and ultra-high electromechanical coupling factors. The present study focused on the mechanical responses of [100]- and [110]-oriented poled PMN-PT ferroelectric single crystals under an indenter loading. The hardness and Young’s modulus with different crystallographic orientations of the crystals were measured by using the continuous stiffness measurement (CSM) with nanoindentation technique. Using a spherical indenter pressured at different indentation depths, the typical quasi-static nanoindentation tests with displacement-controlled mode were performed on the PMN-PT single crystal samples. Load–displacement curves of indentations were recorded to reveal the yielding or inelasticity behaviour in [100]- and [110]-oriented PMN-PT through a pop-in event. It was further verified by the stress–strain curves evaluated from the corresponding load–displacement curves, to show the similar characteristic on the elastic–inelastic transition. When a Berkovich indenter was employed for mechanical response testing, another pop-in event was observed at a smaller indentation depth compared to the one for elastic–inelastic transition, which may indicate a pressure-induced phase transition from rhombohedral (R) to tetragonal (T) of the PMN-PT single crystals.

Anisotropic field induced phase transitions and negative electrocaloric effect in rhombohedral Mn doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

The electrocaloric effect (ECE) of Mn doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT:Mn) single crystals with particular emphasis on the impact of crystallographic orientations and phase transitions were investigated systematically. Orientation-dependent phase transitions have been demonstrated by the dielectric and strain behaviors. Intriguingly, the negative ECE of –0.02 °C and –0.002 °C were obtained firstly in [001]-oriented PIN-PMN-PT:Mn crystals near the rhombohedral→tetragonal phase transformation and in [011]-oriented crystals near the rhombohedral→orthorhombic phase transformation, respectively. However, only the positive ECE was found in [111]-oriented crystals near the tetragonal→rhombohedral phase transition. Additionally, the maximum ECE temperature changes calculated in [001]-, [011]- and [111]-oriented crystals were 0.33 °C, 0.46 °C and 0.38 °C, respectively. Our results suggest that the negative ECE is attributed to electric field-induced phase transitions, whose critical field decreases with the increase of temperature. The phase transition-mediated coexistence of positive and negative effects in the relaxor-ferroelectric single crystals is beneficial to enhance the efficiency of the solid-state cooling devices.

Effect of segregation on Mn-doped relaxor-PT single crystal

The effect of compositional segregation on the properties of relaxor ferroelectric single crystal are attracting increasing attention for its serious limitation on the application field. In this paper, the composition, phase structure, optical properties and electric properties of Mn-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal were investigated. The real composition of the single crystal fluctuated around the original ratio, except for MnO2. The single crystal contained less Mn element after removing inclusions compared with the starting ratio. The single crystal samples exhibited rhombohedral phase (R phase), orthorhombic phase (O phase) and tetragonal phase (T phase) structures with different composition due to the segregation. The rhombohedral to tetragonal phase transition temperature (TR-T) shifted to a lower value along the growth direction, while the Curie Temperature (TC) shifted to a higher value instead. The relaxation level of the single crystal went down to a lower level when the crystal structure changed from R phase to T and O phase. The coercive field (EC) with [001] poling in R phase remained stable before a rise in O phase and T phase. However, the composition segregation didn't obviously affected the internal bias field and kept around 0.2 kV/cm. The piezoelectric coefficient d33 and unipolar strain with poling direction along [001] had the same trend along growth direction. The curves of them both took a rapid fall at the top of the single crystal boule, which related to the T phase.

A phenomenological thermodynamic energy function for PIN-PMN-PT relaxor ferroelectric single crystals

Domain engineered rhombohedral relaxor ferroelectric single crystals of PIN-PMN-PT near the morphotropic phase boundary (MPB) have stable domain structures that increase piezoelectric constants and reduce dielectric loss. They also undergo domain switching and phase transformation with temperature and applied field that make modeling the energetics of the domain formation and evolution challenging. In this work a 10th order Landau-Devonshire energy function is developed to describe the dielectric, piezoelectric and ferroelectric properties of PIN-PMN-PT with a composition near the MPB. Coefficients of the energy function were determined based on the results of many experimental measurements. The resulting energy function reproduces temperature induced phase transformations as well as polarization and strain hysteresis loops of domain engineered rhombohedral crystals at multiple temperatures. This energy function is suitable for implementation in a phase field model to further investigate the evolution of engineered rhombohedral domain structures and the energetics associated with other characteristics of rhombohedral PIN-PMN-PT ferroelectric single crystals.

Ultrahigh energy density harvested from domain-engineered relaxor ferroelectric single crystals under high strain rate loading

Relaxor ferroelectric single crystals have triggered revolution in electromechanical systems due to their superior piezoelectric properties. Here the results are reported on experimental studies of energy harvested from (1-y-x)Pb(In1/2Nb1/2)O3–(y)Pb(Mg1/3Nb2/3)O3–(x)PbTiO3 (PIN-PMN-PT) crystals under high strain rate loading. Precise control of ferroelectric properties through composition, size and crystallographic orientation of domains made it possible to identify single crystals that release up to three times more electric charge density than that produced by PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5) ferroelectric ceramics under identical loading conditions. The obtained results indicate that PIN-PMN-PT crystals became completely depolarized under 3.9 GPa compression. It was found that the energy density generated in the crystals during depolarization in the high voltage mode is four times higher than that for PZT 52/48 and 95/5. The obtained results promise new single crystal applications in ultrahigh-power transducers that are capable of producing hundreds kilovolt pulses and gigawatt-peak power microwave radiation.

The origin of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution crystals.

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric properties is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.