Ferroelectric Single Crystals Research Articles

Charge redistribution of a spatially differentiated ferroelectric Bi4Ti3O12 single crystal for photocatalytic overall water splitting

Artificial photosynthesis is a promising approach to produce clean fuels via renewable solar energy. However, it is practically constrained by two issues of slow photogenerated carrier migration and rapid electron/hole recombination. It is also a challenge to achieve a 2:1 ratio of H2 and O2 for overall water splitting. Here we report a rational design of spatially differentiated two-dimensional Bi4Ti3O12 nanosheets to enhance overall water splitting. Such a spatially differentiated structure overcomes the limitation of charge transfer across different crystal planes in a single crystal semiconductor. The experimental results show a redistribution of charge within a crystal plane. The resulting photocatalyst produces 40.3 μmol h–1 of hydrogen and 20.1 μmol h–1 of oxygen at a near stoichiometric ratio of 2:1 and a solar-to-hydrogen efficiency of 0.1% under simulated solar light.

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.

Thermal cycle stability and microstructure of Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

The Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) ferroelectric single crystals have been commercially available as important components in medical ultrasound transducers due to their excellent piezoelectric and electromechanical coupling performance. The variation in piezoelectric and dielectric properties of PMN-PT single crystals with ambient temperature is an important application indicator. In this work, the PMN-PT single crystals after direct current poling (DCP) and alternating current poling (ACP) were subjected to the cyclic thermal treatment process. The thermal cycling stability and microstructural changes in PMN-PT single crystals were investigated. The ACP single crystals exhibit a higher dielectric constant ε33T/ε0 (6500–7600) and piezoelectric coefficient d33 (2100–2500 pC N−1) compared to the DCP single crystals (ε33T/ε0 of 4100–5000, d33 of 1200–1300 pC N−1). Under thermal cycling at 60 °C, the DCP and ACP single crystals exhibit good thermal cycling stability after 150 cycles. Microstructural observations show that the domain structure of the DCP single crystals exhibits “staggered domain walls, inhomogeneous domain size, variety of domain structure,” while the relatively homogeneous stripe-like domains were observed in the ACP single crystals. After thermal cycling, new fine striped domains appear in both the DCP and ACP single crystals due to the instability of rotated polarization, but the piezoelectric and dielectric properties are not greatly affected. This work provides an intensive understanding of the effects of thermal cycling on the domain structure, which is useful for applications.

Electric‐Field‐Induced in‐Plane Anisotropy of Superconducting Transition Temperature for FeSe0.5Te0.5 Thin Films

AbstractSuperconductor/ferroelectric heterostructures are very important for fundamental research and applications since superconductivity can be controlled by electric fields via ferroelectric polarization/piezostrain. Superconductivity is a macroscopic quantum phenomenon and it is commonly believed that the in‐plane superconducting transition temperature (Tc) should be isotropic for superconductors with crystal structures of stacking layers (quasi 2D). Here, the observation of piezostrain‐induced in‐plane anisotropy of Tc in FeSe0.5Te0.5 (FST) thin films grown on ferroelectric single crystals is reported. The as‐prepared FST shows a tetragonal phase with equal in‐plane lattice parameters and an absence of in‐plane anisotropy of Tc. Upon applying electric fields, piezostrain induces a difference in the in‐plane lattice parameters (a‐b) and in‐plane anisotropy of Tc. The in‐plane anisotropy of Tc correlates with a‐b and becomes more remarkable for larger values of a‐b. Some possible extrinsic effects are ruled out by experiments and analysis. A possible mechanism is proposed involving electronic nematicity and inhomogeneous superconductivity in FST to account for this unusual phenomenon. This work is significant for uncovering the exotic nature of unconventional superconductors, as well as applications.

Reversible nanocracks-induced resistive switching manipulated by ferroelectric polarizing in Te/PMN-PT heterostructures

Ferroelectricity-based storage technology is anticipated to achieve nonvolatile, low-power, and high-density storage in integrated field circuits. Here, the phenomena of electrically reversible switching of nanocracks in the tellurium film/ferroelectric PMN-PT heterojunctions are discussed. Upon the application of external electric fields (±2 kV/cm), the nonvolatile resistance on-off ratio reached over 106 at room temperature. This was achieved through the opening and closing of cracks in the Te film caused by the electric-field-driven flipping of 109° ferroelectric domains in a ferroelectric single crystal. In addition, the ON/OFF resistance states remain stable even after more than 103 cycles and the retention time exceeds 6 h, demonstrating excellent fatigue resistance performance of the device. This work renders a window to design nonvolatile memory by constructing electric-field tunable nanocracks in a semiconductor film/ferroelectrics heterojunction system.

Mesophase induced by alternating-current poling in relaxor ferroelectric single crystals

Alternating-current poling (AC-Poling) has attracted wide interests in enhancing piezoelectric performance of ferroelectric single crystals. However, the mechanism of phase transformations and domain morphology underlying AC-Poling has not been thoroughly investigated. In this work, we have systematically studied the AC-poling effect on domain structures and piezoelectric properties in the relaxor ferroelectric single crystals of 0.24Pb(In1/2Nb1/2)O3–0.44Pb(Mg1/3Nb2/3)O3–0.32PbTiO3. It is shown that the piezoelectric constant (d33) and permittivity (ε33) are greatly enhanced via [001]-AC-poling compared to DC-poling, related to the presence of modified domain configurations as indicated previously. For [110]-oriented specimens, the piezoelectricity through AC-poling is only half as that for the DC-poled single crystals. We attribute this to the transition from the monoclinic-B phase to an orthorhombic phase under AC-poling, confirmed by synchrotron radiation X-ray diffraction and piezo-response force microscopy. The transition to the orthorhombic phase is likely a consequence of lower Gibbs energy. This study on orientation-dependent characteristics of AC-poling for PIN-PMN-PT single crystals will guide the development of AC-poling technology in applications.

Acoustic shock wave-induced ordered to disordered switchable phase transitions: A case study of ferroelectric triglycine sulphate single crystal for the application of molecular switches

Highly efficient switchable materials for external stimuli have impressive applications in the development of precious sensor devices. However, most of the materials do not possess effective switchable structural features such that finding potential switchable materials is one of the critical research tasks for materials science researchers. In the present research perspective, we demonstrate successive switchable phase transitions occurring between the order to disorder states in the ferroelectric triglycine sulphate (TGS) single crystal along the (011) plane with respect to the number of shock pulses (0,1 and 2 counts) and the observed results are evaluated by the diffraction, spectroscopic, microscopic and thermal approaches. The observed switchable phase transitions occur due to the shock wave-induced inter-conversion of planar configuration to the non-planar configuration of Glycine molecules, particularly GII and GIII. The ratio of the normalized Raman bands Sym-CH2/Asym-CH2 is found to be 2.0 and 2.5 for the respective order to disorder states such that these values are identified to be well-matched with the literature reports. In addition to that, the SEM images authenticate that, during the amorphous to crystalline phase transitions, the appearance of well-defined (011) plane on the surface is ensured due to the dynamic recrystallization. To the best of our knowledge, to date, it is probably the first report for the phase switching of order to disorder states of TGS sample by the impact of acoustical shock waves and because of its efficient switchability, it can be strongly suggested for the application of molecular switches.

Growth and characterization of novel piezo-/ferroelectric single crystals from the PSN-BS-PT ternary system

Bismuth-based single crystals with the nominal composition of 0.1Pb(Sc1/2Nb1/2)O3-0.315BiScO3-0.585PbTiO3 (0.1PSN-0.315BS-0.585PT) ternary complex perovskite system were successfully grown using a high-temperature solution growth (HTSG) method. A mixture of PbO and Bi2O3 in a molar ratio of 73:27 was used as flux, and the flux to charge ratio was optimized to be 70:30 (wt%). The grown crystals, with dimensions up to 3 mm, exhibit a pseudo-cubic morphology. The XRD patterns of the ground powder and naturally formed pseudo-cubic facets confirm that the grown single crystals crystallize in the perovskite structure with the rhombohedral symmetry as the major phase, and the naturally grown pseudo-cubic facets are parallel to {100}C. The domain structures in the (001)-oriented single crystals examined by polarized light microscopy (PLM) and optical crystallography reveal the coexistence of rhombohedral and monoclinic phases in majority, with the presence of a minor tetragonal phase likely grown at the late stage of the growth, demonstrating the morphotropic phase boundary (MPB) characteristics for the grown crystals. Upon heating, phase transition from the major rhombohedral and monoclinic to the cubic phase take place at TC = 370 °C. The ferroelectric properties are displayed by polarization-electric field (P-E) hysteresis loops with a remanent polarization of 17 µC/cm2 and a high coercive field of 68 kV/cm. The piezoelectric coefficient (d33) is found to be 478 pC/N. The high Curie temperature and decent piezo- and ferroelectric performance of the PSN-BS-PT crystals make this ternary complex perovskite system a promising candidate for potential applications in high-temperature and high-power electromechanical transduction.

Piezoelectricity and up-conversion photoluminescence of Er3+-doped Pb(Zn1/3Nb2/3)O3- PbTiO3 single crystals

Pure Pb(Zn1/3Nb2/3)O3-11mol%PbTiO3 (PZN-11PT) and Er3+-doped Pb(Zn1/3Nb2/3)O3-11 mol%PbTiO3 (PZN-11PT-Er) relaxor ferroelectric single crystals were grown by large gradient high-temperature flux method. The phase structure, electrical properties, and up-conversion photoluminescence (UC PL) of the single crystal were studied systematically. The results show that PZN-11PT-Er has a pure perovskite structure with the coexistence of rhombohedral and tetragonal phases. The piezoelectric coefficient (d33) with the Er3+ dope increases to 1550 pC/N from 854 pC/N than without dopant. However, the coercive electric field (EC) is maintained constant in spite that the remnant polarization (Pr) is increased from 25 μC/cm2 to 51 μC/cm2. The dielectric relaxation behavior of PZN-11PT was absolutely enhanced by rare Er3+-doped. In addition, UC PL was successfully achieved for PZN-11PT-Er. Optical temperature sensing property of PZN-11PT-Er was studied based on the fluorescence intensity ratio technique, showing its potential for use in a wide temperature region. These results indicate that the PZN-11PT-Er relaxor ferroelectric single crystals are suitable for applications in electromechanical coupling devices and optical temperature sensing, simultaneously.

Huge piezoelectricity and electro-optic effects in rhombohedral relaxor ferroelectric single crystals by Sm3+ doping

In recent years, relaxor ferroelectric single crystals have attracted people's attention and research because of their excellent piezoelectric properties at morphotropic phase boundary(MPB). The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) crystals have higher Curie temperature and coercive field, which have the opportunity to be applied in high-temperature devices. The crystals of the rhombohedral phase have better stability, but their performance is not as good as that of the MPB component crystals. In this paper, the piezoelectric properties of rhombohedral PIN-PMN-28PT single crystals are improved by Sm3+ doping. The piezoelectric coefficient d33 after AC polarization along [001] direction can reach 3125pC/N, which is 60% higher than that of undoped crystals. Meanwhile, the crystal exhibits excellent optical performance after DC polarization along [110] direction. The crystal has an effective electro-optic coefficient of 386 pm/V at room temperature and a stable frequency-dependent characteristic, which is expected to be an ideal material for electro-optic devices.

Single Crystal (K,Na)Nb)3/CuO Heterostructures for Synergistic Photo-Piezocatalytic Activity

In this study, we designed a heterostructure piezo-photocatalyst composed of Ba, Li doped- (K,Na)NbO3 (KNN) single-crystal microcuboids and CuO nanodots. KNN was selected because of its high piezoelectric coefficient (d33 ), good chemical stability, and environmental friendliness. As a cocatalyst, CuO was considered owing to its advantages such as narrow bandgap, low cost, and nontoxicity. The n-type semiconducting Pb-free KNN single-crystal ferroelectric microcuboids (~30 μm) were synthesized by molten-salt reaction. Then, p-type semiconducting CuO nanodots (less than 5 nm) were uniformly decorated onto KNN microcuboids via deposition of Cu(OH)2, followed by conversion to CuO through calcination. From our heterostructure, it is expected that excellent piezoelectric properties could be obtained from KNN single-crystal microcuboids and a high surface area for catalytic reactions is guaranteed by CuO nanodots that are evenly deposited on the surface of KNN without aggregation. The novel KNN/CuO micro/nano heterostructures exhibited increased current density, and enhanced removal organic dye (RhB) efficiencies under the ultrasonic vibration when compared with bare KNN single-crystal catalysts. Specifically, the reaction rate constant (k) for the photo-piezocatalytic RhB dye degradation of the KNN/CuO micro/nano heterostructure exhibited ~ 0.093 min-1, which is higher when compared with other KNN-based piezo, photo, and photo-piezocatalysts. Additionally, the coupled photo-piezocatalyst for KNN/CuO realized an enhanced RhB dye degradation efficiency of 1.6 times and 48.6 times higher when compared with individual piezocatalytic and photocatalytic dye degradation capabilities, respectively. Our approach could provide insights into the design of heterostructure photo-piezocatalysts containing single-crystal ferroelectrics, which requires the enhancement of the photo-piezocatalytic activities.

Research on low-frequency bender disk transducer driven by multiple relaxor ferroelectric single crystal disks

In this paper, we investigate the low-frequency bender disk transducer designed by the relaxor ferroelectric single crystal. First, we introduce the principle of the bender disk transducer, and use multiple single crystal disks as driving materials to excite the bending vibration mode of the metal plate, which reduces the operating frequency of the transducer. Then we establish the three-dimensional finite element model of the bender disk transducer driven by multiple single crystal disks, analyze the influence of the number and position distribution of single crystal disks on the transducer performance, and compare with that of the piezoelectric ceramic transducer with the same structure. Finally, we manufacture the proposed relaxor ferroelectric single crystal, piezoelectric ceramic transducers and the conventional piezoelectric ceramic bender disk transducer respectively, and carry out the experimental measurement in an anechoic water tank. The experimental results show that for the proposed single crystal transducer, its measured maximum transmitting voltage response (TVR) is 126.2 dB at 1.1 kHz, which is 13.4 dB higher than that of the proposed piezoelectric ceramic transducer, and its frequency corresponding to the maximum TVR is reduced by 700 Hz compared with the conventional piezoelectric ceramic bender disk transducer.

Thermal expansion properties of three-dimensional relaxor ferroelectric single crystals

Large-size Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals have been successfully produced. Nevertheless, the susceptibility of these crystals to cracking substantially hampers their application. This study investigates the thermal expansion characteristics of PMN-PT and PIN-PMN-PT crystals oriented along the 〈100〉, 〈110〉, and 〈111〉 directions, revealing no significant anisotropy. The average thermal expansion coefficients for the PMN-PT and PIN-PMN-PT crystals range from 7.77 to 8.21 × 10−6 K−1 and from 6.59 to 6.79 × 10−6 K−1, respectively, within the temperature range of 20 to 600 °C. Interestingly, the PMN-PT and PIN-PMN-PT crystals demonstrate unusual thermal expansion behavior around the phase transition temperature. The magnitudes of their thermal expansion coefficients are comparable to those of certain commercial crystals but are lower than that of platinum. The main causes inferred for crystal cracking include the pressure exerted by the platinum crucible and the abnormal thermal expansion behavior around the phase transition temperature.

Growth of large-sized relaxor ferroelectric PZN-PT single crystals by modified flux growth method

A novel bottom-cooling high-temperature solution growth technique is developed for growing large-sized relaxor ferroelectric 0.91Pb(Zn1/3Nb2/3O3)-0.09PbTiO3 (PZN-PT) single crystals. During the growth, an inverse temperature gradient is maintained in the crucible base by flowing air at a controlled rate. This method restricts the number of spontaneously nucleated crystals at crucible bottom, reduces loss of volatile PbO component and favours the growth of large-sized PZN-PT single crystals. Large-sized PZN-PT single crystals of dimensions ∼ 22 × 20 × 14 mm3 are reproducibly grown by the proposed method. The electrical characteristics of the PZN-PT wafers oriented along the 〈100〉, 〈010〉 and 〈001〉 directions are investigated. PZN-PT wafers oriented along the 〈001〉 direction exhibited superior piezoelectric coefficient (d33) of ∼ 2221 pm/V. The homogeneity of the physical parameters is analysed by preparing 10 elements with dimensions of ∼ 5 × 2.5 × 2.5 mm3 which were cut from single wafer oriented along the 〈001〉 direction. The ferro-, piezo- and dielectric characteristics of these wafers were found to be highly uniform with small standard deviation. The observation of d33 value with less than 2 % deviation from mean value confirms the growth of highly quality PZN-PT single crystals.

Mechanically induced reversible/irreversible phase transition in PMN–0.3PT single crystal: A phase-field simulation

Relaxor ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) have outstanding electromechanical properties in the linear regime. When operated across a phase transition, these properties are significantly enhanced. Understanding the phase transition mechanism under electromechanical external fields is crucial for the new application of PMN–PT that takes advantage of this phase transition. In the present study, the phase transition of PMN–0.3PT single crystals subjected to a mechanical loading/unloading process and the effects of electric field on the phase transition and electromechanical responses of PMN–0.3PT single crystal under coupled mechanical-electrical loading were systematically investigated using a thermodynamics-based phase-field model. The roles the different energy terms play in the evolution of domain and phase structures were assessed. These findings have important implications for both understanding of the phase transition of relaxor ferroelectric single crystal PMN–0.3PT and applications that take advantage of phase transitions in these materials. The model results for the reversible/irreversible phase transition of PMN–0.3PT during the mechanical loading/unloading process are qualitatively consistent with experimental results.

A single crystal Lamb wave sensing array

This paper reports on a multi-element relaxor ferroelectric single crystal (RFSC) based acoustic emission (AE) sensor called LAMDA (linear array for modal decomposition and analysis). This sensor is being developed foracoustic-signature detection applications, including for AE-based damage detection on space-based and undersea platforms. RFSC [011] Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (or PIN-PMN-PT) was machined into 200 μm thick × 1 mm long × 4 mm wide elements, with 16 of these elements arranged on a flexible-polyimide-carrier to form a LAMDA. This sensor was bonded to a 1.6 mm thick aluminium plate with dimensions 600 mm x 600 mm. Acoustic emissions consisting of Lamb waves (e.g., A0, S0) were generated in the plate using both piezoceramic (Pz26) disk-actuators and pencil lead breaks (PLBs). LAMDA measurements and one-dimensional laser-vibrometry were undertaken on the plate and compared with two-dimensional multi-physics model predictions. The plane-strain model geometry comprised a rectangular-section 1.6 mm thick and 600 mm long with a LAMDA located centrally. An AE, being a 5.5-cycle Hann-windowed function with centre-frequencies 300–1000 kHz, was introduced 150 mm from the LAMDA via point loading perpendicular to the surface. The Lamb wave dispersion-curves generated from the model showed good agreement with the experimental curves determined from LAMDA and laser-vibrometry.

Enhanced piezoelectric and optical properties of tetragonal Sm‐doped Pb(In1/2Nb1/2)–Pb(Mg1/3Nb2/3)–PbTiO3 crystals

AbstractRelaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) has received extensive research and attention due to its excellent piezoelectric, electromechanical, and other properties. In particular, tetragonal relaxor ferroelectric single crystals have shown greater application potential in high‐temperature devices due to their higher Curie temperature and better stability. However, the low piezoelectric performance of tetragonal crystals also greatly limits its application, and research on its optical properties is not sufficient. In this paper, the tetragonal phase Sm–PIN–PMN–PT single crystal was obtained by the Bridgman method, and its piezoelectric and electro‐optical properties are studied. At the same time, we gave a complete set of piezoelectric, dielectric, and elastic coefficient matrices. The results show that the crystal has excellent piezoelectric and electromechanical properties. The piezoelectric coefficient can reach 905pC/N, the electromechanical coupling coefficient k33 is 85%, and the kt is 72%. The transmittance of the sample polarized along [001] direction can reach 66%. The effective electro‐optical coefficient γc is 60 pm/V at room temperature and can reach 86 pm/V at 70°C. It has a wide operating temperature range and stable performance with frequency variation, which has certain reference significance for application in new electro‐optical devices.

Stress and electric field induced phase transitions for ultra high energy conversion in ferroelectrics

This work focuses on energy harvesting of ferroelectric relaxors PMN-25PT and PZN-8PT single crystals with high uniaxial stress and electric field. Ericsson cycle, which consists of applying and releasing electric field and stress at different steps of the cycle, has been used. A large energy density for PZN-8PT high as 410 mJ/cm3 was obtained. Different working temperatures were tested by experiment and modeled via Landau–Devonshire theory. Optimal working temperatures were identified for high level energy conversion and were successfully predicted by simulation. It appeared that the optimum working temperature was different from that optimizing the d33. Polarization mechanisms induced by these extreme conditions for energy harvesting are explained in the frame of experimental and modeling results. The results obtained at high stress levels tend to indicate that operating along the polarization direction yields the best results, which contradicts conclusions drawn in the case of domain engineered crystals.

Time-resolved nanobeam X-ray diffraction of a relaxor ferroelectric single crystal under an alternating electric field

Time-resolved nanobeam X-ray diffraction of a relaxor ferroelectric single crystal under an alternating electric field

Fabrication of titanium in-diffusion waveguide in the PIN-PMN-PT single crystal

Fabrication of the optical waveguide is essential for the application of high-performance relaxor ferroelectric single crystals in broadband integrated electro-optic devices. Here, a multimode titanium in-diffusion planar waveguide is demonstrated in a rhombohedral phase Pb(In1/2Nb2/3)O3–Pb(In1/2Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystal. Influences of titanium in-diffusion on the crystalline phase and composition were carefully studied. Guided modes in the planar waveguide were characterized by prism couple measurements. Using the inverse Wentzel-Krames-Brillouin method, the refractive index profile in the waveguide was constructed. The results show that the PIN-PMN-PT crystal retains its single crystal structure and excellent electro-optic response after titanium in-diffusion. The mode refractive index change between the diffused layer and substrate crystal is approximately 3%, which is sufficient to constrain the energy of transmitted light. Moreover, the titanium-diffused PIN-PMN-PT waveguide is confirmed to be a graded optical waveguide with a Gaussian index profile. Our work indicates that the titanium in-diffusion is a feasible way to fabricate waveguides in PIN-PMN-PT crystals, which is of great significance for their application in integrated photonic devices.