Ferroelectric Single Crystals Research Articles

Mechanically induced rhombohedral to tetragonal phase transition in PMN–PT single crystals by nanoindentation

AbstractUnderstanding the phase transition behavior of the rhombohedral phase (R) and tetragonal phase (T) of the relaxor ferroelectric PMN–PT single crystals under mechanical load is essential for the potential voltage‐free controlled ferroelectric‐based nanodevices. Relaxor ferroelectric single crystals PMN–PT, under a local inhomogeneous mechanical load, were studied experimentally by the nanoindentation tests and Raman spectroscopy measurements. The observations show that the rhombohedral phase can be transformed successfully to the tetragonal phase under a mechanical stress, and the tetragonal phase in the PMN–PT single crystals presents a structural stability. The phase transition induced by the mechanical stress with different strain rates further indicates that the relaxor ferroelectric single crystals possess a potential mechanical controllability. The present study reveals the phase transition pathway of the relaxor ferroelectric single crystal under inhomogeneous stress and provides the exciting possibility of the control of mechanically induced phase transition for ferroelectrics.

A review of ferroelectric materials for high power devices

Compact autonomous ultrahigh power density energy storage and power generation devices that exploit the spontaneous polarization of ferroelectric materials are capable of producing hundreds of kilovolt voltages, multi-kiloampere currents, and megawatt power levels for brief interval of time. The storage life of these devices is four orders of magnitude longer than that for electrochemical batteries and electrochemical capacitors. Herein is an up to date survey of ferroelectric materials used for these high power devices. Several types of ferroelectric ceramics possess the ability to be depolarized under adiabatic compression and can be successfully used for high power applications. In addition to bulk ferroelectric ceramics, multilayer ferroelectric films are very efficient materials for high power systems. Of particular importance is the ability of relaxor ferroelectric single crystals to produce significantly higher electric charge density and energy density than ceramics, making them promising materials for high power applications. Also provided is a brief survey of recent developments of ferroelectric materials for high energy density and power density dielectric capacitors. Numerous ceramics have been developed, including antiferroelectric and relaxor antiferroelectric solid solutions, providing high energy density and efficiency simultaneously.

Influence of weak ac electric field on the temperature of dielectric maximum of (1-x)PbMg1/3Nb2/3O3-xPbTiO3 relaxor ferroelectric single crystals based on acoustic emission data studies

(1-x)PbMg1/3Nb2/3O3-xPbTiO3, [100]-oriented relaxor ferroelectric crystals were studied by means of dielectric and acoustic emission methods in dependence on temperature and under ac measuring electric field with several values and frequencies. The dependence of temperature of dielectric constant maximum on and without ac field value and frequency was plotted. Also a scatter of the temperature of dielectric constant maximum was calculated in dependence on ac field frequency. Such the phenomenon was discussed from a point of view of growth of the polar nanoregions on cooling.

Computer-aided characterization of ferroelectric phase transitions and domain structures using polarizing light microscopy

Optical microscopy is an essential characterization technique that is used as an initial step in the study of domain structures and phase transitions of ferroelectric materials. Image analysis aided by advanced computer algorithms is urgently required to enable an improved accuracy and higher efficiency of data processing. In this study, an automatic full-angle light intensity detection algorithm is developed to study polarizing light microscopy images of domain structures and the phase evolution process is decoded using the scale invariant feature transform method. This data processing algorithm is then used to characterize the phase transition process in relaxor ferroelectric PMN-0.29PT single crystals with complex domain structures. An emerging in-plane tetragonal phase is tracked during the rhombohedral (R) to tetragonal (T) phase transition, which is associated with peaks present in the temperature-dependent dielectric curve. Compared to the traditional polarizing light microscopy characterization method, this computer-aided algorithm enables a quicker and more informative analysis of domain evolutions in ferroelectric single crystals.

Q-POP-Thermo: A general-purpose thermodynamics solver for ferroelectric materials

Q-POP-Thermo is a program designed to compute thermodynamic monodomain equilibrium states and their properties for ferroelectric single crystals and thin films based on the Landau-Ginzburg-Devonshire (LGD) Theory. Utilizing symbolic manipulation with the SymPy Library, the governing equations along with appropriate boundary conditions are solved for speedy minimization of the free energy of a crystal. Utilizing the popular Differential Evolution algorithm, with appropriate hybridization, multiple phase diagrams, such as the pressure-temperature phase diagram for bulk single crystals and the common strain-temperature phase diagram for monodomain thin-film systems can be readily generated. Furthermore, a variety of material properties of stable ferroelectric phases, including dielectric, piezoelectric, and electrocaloric properties, can simultaneously be calculated. Validation studies are presented for both thin-film and single crystal systems to test the effectiveness and capability of the open-source program. Program summaryProgram title: Q-POP-ThermoCPC Library link to program files:https://doi.org/10.17632/wd6228g9ww.1Code Ocean capsule:https://codeocean.com/capsule/1245708Licensing provisions: MITProgramming language: PythonExternal routines/libraries: numpy (Version 1.20.3), sympy (Version 1.8), numerical optimization (available with Q-POP-Thermo), pandas (Version 1.1.3), scipy (Version 1.6.3)Nature of program: Python-based program to perform energy minimization to determine the stable states and thermodynamic properties of ferroelectric systems.Solution method: Algebraic manipulation of boundary conditions and governing equations followed by a hybridized and improved a priori Differential Evolution solver to calculate equilibrium polar states and material properties.

Ferroelectric domain structure and atomic-scale phase distribution in a Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal

Lead-based relaxor ferroelectric crystals, such as Pb(Mg1/3Nb2/3)O3-PbTiO3, are promising for functional applications due to their outstanding ferroelectric properties. Revealing ferroelectric domain structure and phase distribution at the nanoscale are important to understand the basic theory of ferroelectricity and promote their practical applications. In this study, the ferroelectric domain structure and atomic-scale phase distribution in a Pb(Mg1/3Nb2/3)O3 - 35 at.% PbTiO3 single crystal in the region of morphotropic phase boundary are systematically investigated by a combination of optical microscopy, scanning electron microscopy, and aberration-corrected transmission electron microscopy. It is found that 90° and 180° coarse domains are formed simultaneously in the ferroelectric single crystal. Moreover, there are tweed-like nano-domains formed inside each coarse single domain. Through careful investigations of distribution of stress and tetragonality, it is revealed that the tweed-like nano-domains are composed of nano-sized rhombohedral (R), monoclinic (M), and tetragonal (T) phases. The nano-scale T, M, R phases have the best, moderate, and lowest ferroelectricity, respectively.

Optimization of Matching Layers to Extend the Usable Frequency Band for Underwater Single-Crystal Piezocomposite Transducers.

The ongoing robotic revolution in oceanic science puts new requirements on sonar technology. Small platforms require compact multi-purpose transducers, with strict requirements on power consumption and heat dissipation. Introducing single-crystal ferroelectrics as the active material of the transmitter can be one way of meeting the new requirements. The large electromechanical coupling coefficient of single crystals can enable an extension of the usable frequency band compared to conventional PZT. For the applications considered in this work, the usable frequency band is restricted by both the transmitted acoustic power and the reactive electrical power. Single crystals as the active materials can double the usable band, but the acoustic matching required for this can be difficult to obtain in practice. We investigated an air-backed, plane 1-3 composite transducer, matched to water by acoustic matching layers. For many applications, the diversity provided by a large usable frequency range is more important than a flat acoustic power response, and the transducer can be used far beyond the -3-dB limit. We defined the usable band by requiring maximum -12-dB ripple in transmitted acoustic power and maximum 50% reactive power. The matching layers were optimized to maximize the usable band according to this definition, in contrast to the conventional approach where matching layers are optimized for maximally flat response. Under the chosen definitions, our modeling showed that with a single crystal as the active material we could achieve 188% usable frequency band relative to the resonance frequency, compared to 121% for a PZT.

Epitaxial integration of a perpendicularly magnetized ferrimagnetic metal on a ferroelectric oxide for electric-field control

Ferrimagnets, which contain the advantages of both ferromagnets (detectable moments) and antiferromagnets (ultrafast spin dynamics), have recently attracted great attention. Here we report the optimization of epitaxial growth of a tetragonal perpendicularly magnetized ferrimagnet Mn2Ga on MgO. Electrical transport, magnetic properties and the anomalous Hall effect (AHE) were systematically studied. Furthermore, we successfully integrated high-quality epitaxial ferrimagnetic Mn2Ga thin films onto ferroelectric PMN-PT single crystals with a MgO buffer layer. It was found that the AHE of such a ferrimagnet can be effectively modulated by a small electric field over a large temperature range in a nonvolatile manner. This work thus demonstrates the great potential of ferrimagnets for developing high-density and low-power spintronic devices.

Temperature-dependent structure and electromechanical properties of Er doped PMN-PT single crystal grown by modified Bridgman technique

In this work, the Er-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal with a large size was successfully grown by the modified Bridgman technique. The temperature dependent phase structure, domain configuration and electromechanical properties of the single crystal with the composition of 2 wt%Er-0.66PMN-0.34PT (Er-0.66PMN-0.34PT) were investigated in detail. For [001]C oriented Er-0.66PMN-0.34PT single crystal, it is found that the room temperature phase structure is the coexistence of rhombohedral (R) and monoclinic (M) phases and M phase is dominated. The piezoelectric constant d33 through the converse piezoelectric effect is about 2410 pC/N. The phase transition from R+M to tetragonal (T) phase begins at 80 ℃ and finishes at 120 ℃. Between 80 ℃ and 120 ℃, the single crystal belongs to the coexistence of R, M and T phases. At 135 ℃, the T phase and polar nanoregions (PNRs) transform into cubic phase and PNRs. The compliance constantss33Dand s33E, longitudinal coupling factor k33 and piezoelectric constant d33 increase by 32%, 77%, 34% and 133%, respectively, with temperature increasing from 22 ℃ to 80 ℃. The ultrahigh increase of d33 is derived from the increase of dielectric constant due to easier polarization rotation and domain wall movement at elevated temperature. Our results will helpful for the study of rare-earth doped relaxor ferroelectric single crystals.

Position and electric field dependent local lattice strain detected by nanobeam x-ray diffraction on a relaxor ferroelectric single crystal

Under a static electric field, we present the scanning nanobeam x-ray diffraction of a relaxor ferroelectric single crystal. The x-ray intensity distributions of a Bragg peak in reciprocal space diffracted from local volumes on the surface of a $0.7\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}0.3\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-30PT) single crystal show position and electric field dependence. While the spatially averaged intensity distribution has a single peak corresponding to the average crystal structure, intensity distributions from each local volume have several strong sharp peaks and a weak broad peak, and show strong position dependence as the translation symmetry is broken in nano- to microscale. A static local lattice strain with spatially valuable lattice constants and nanodomains is responsible for peak splitting and heterogeneous crystal structure. The locally strained lattice exhibits a significant tensile lattice strain caused by an electric field, which is compatible with its large piezoelectric constant of approximately $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{0.16em}{0ex}}\mathrm{pC}/\mathrm{N}$. When the electric field surpasses the coercive field of 3 kV/cm, polarization switching causes a substantial shear lattice strain with intensity redistribution. Position dependence can also be seen in the piezoelectric constants and coercive fields calculated from x-ray diffraction data for each local location. The standard deviation of the local lattice strain distribution is $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ regardless of the electric field, which is greater than the piezoelectric lattice strain of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ caused by an electric field of 8 kV/cm. The enormous electric field induced lattice strain and fatigue-free polarization switching are enabled and facilitated by the nano- to microscale heterogeneous crystal structure with widely and continuously distributed local lattice strain.

Large in-plane piezo-strain enhanced voltage control of magnetic anisotropy in Si-compatible multiferroic thin films.

Voltage control of magnetic anisotropy (VCMA) in Si-compatible ferroelectric/ferromagnetic multiferroic thin films is promising to enable power-efficient and integrated magnetic memories. However, their VCMA effect is weak and is always smaller than that of the bulk counterparts. Here, we achieve a more substantial VCMA effect in thin films than in the bulk, benefiting from the large in-plane piezo-strain mediated magnetoelectric coupling under strong fields. Si-compatible ferroelectric Pb(Zr,Ti)O3 (PZT) thin films with large breakdown strength of up to 3.2 MV cm-1 are fabricated to further construct multiferroic thin films. Since conventional methods fail to measure the VCMA effect under strong fields, we establish a micro-ferromagnetic resonance method based on micro-fabrication. An enhanced VCMA effect is demonstrated in PZT/CoFeB thin films, whose voltage-induced effective magnetic field (Heff) could experimentally reach 26.1 Oe, which is much stronger than that in bulk control samples "PZT ceramic/CoFeB" (2.6 Oe) and "PMN-PT single crystal/CoFeB" (18.5 Oe) as well as previous reports. Theoretically, the Heff in thin films could be > 60 Oe near the breakdown strength, resulting from a giant in-plane piezo-strain S31 < -0.3%, which is comparable to that of the best ferroelectric single crystals. Si-compatible multiferroic thin films with enhanced VCMA will be a useful platform for developing integrated magnetic and spintronic devices.

High Curie temperature bismuth-based piezo-/ferroelectric single crystals of complex perovskite structure: recent progress and perspectives

The recent progress in high TC bismuth-based piezo-/ferroelectric single crystals is reviewed in terms of materials design, crystal growth, physical properties, crystal chemistry, and complex domain structures, and the future perspectives are discussed.

Coupled straintronic-optoelectronic effect in Mott oxide films.

Controlling the electronic properties of complex oxides by an external stimulus is of significant importance for exploring exotic quantum states and developing modern electronic devices with low-level energy consumption. Here, we demonstrate the electro-photo double control of electronic transport for Mott insulating LaVO3 thin films deposited onto ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 substrates. An electrically driven linear electroresistance effect is acquired at room temperature through the converse piezoelectric response, which can be optically regulated by 79%. Furthermore, the visible light-activated photoresistance response can be efficiently tuned by piezo strain. These results demonstrate that the strain-excited effect and photo-generated effect strongly correlated with each other, mediated by lattice-charge-orbital coupling. Our work points to an effective strategy for realizing the coupled straintronic-optoelectronic effect in hybrid correlated oxide/ferroelectric systems and delivering multi-field tunable low-dissipation versatile electronic and photonic devices.

Broadband coherent anti-Stokes Raman scattering for crystalline materials

Broadband coherent anti-Stokes Raman scattering (B-CARS) has emerged in recent years as a promising chemosensitive high-speed imaging technique. B-CARS allows for the detection of vibrational sample properties in analogy to spontaneous Raman spectroscopy, but also makes electronic sample environments accessible due to its resonant excitation mechanism. Nevertheless, this technique has only gained interest in the biomedical field so far, whereas CARS investigations on solid-state materials are rare and concentrate on layered, two-dimensional materials such as graphene and hexagonal boron nitride . In this work, we discuss the specific properties of this technique when applied to single-crystalline samples, with respect to signal generation, phase matching, and selection rules in the model systems lithium niobate and lithium tantalate. Via polarized B-CARS measurements and subsequent phase retrieval, we validate the predicted selection rules, unequivocally assign the phonons of the ${\mathrm{A}}_{1}$(TO), E(TO) and ${\mathrm{A}}_{1}$(LO) branches to the detected CARS peaks, and address differences in spontaneous Raman spectroscopy concerning peak frequencies and scattering efficiencies. We thus establish this technique for future investigations of solid-state materials, specifically in the field of ferroelectric single crystals.

High piezoelectricity after field cooling AC poling in temperature stable ternary single crystals manufactured by continuous-feeding Bridgman method

After field cooling (FC) alternating current poling (ACP), we investigated the dielectric and piezoelectric properties of [001]pc-oriented 0.24Pb(In1/2Nb1/2)O3 (PIN)-0.46Pb(Mg1/3Nb2/3)O3 (PMN)-0.30PbTiO3 (PT) (PIMN-0.30PT) single crystals (SCs), which were manufactured by continuous-feeding Bridgman (CF BM) within morphotropic phase boundary (MPB) region. By ACP with 4 kVrms/cm from 100 to 70 °C, the PIMN-0.30PT SC attained high dielectric permittivity (ε33T/ε0) of 8330, piezoelectric coefficient (d33) of 2750 pC/N, bar mode electromechanical coupling factor k33 of 0.96 with higher phase change temperature (Tpc) of 103 °C, and high Curie temperature (TC) of 180 °C. These values are the highest ever reported as PIMN-xPT SC system with Tpc > 100 °C. The enhancement of these properties is attributed to the induced low symmetry multi-phase supported by phase analysis. This work indicates that FC ACP is a smart and promising method to enhance piezoelectric properties of relaxor-PT ferroelectric SCs including PIMN-xPT, and provides a route to a wide range of piezoelectric device applications.

Temperature dependent Raman spectroscopic study of Fano resonance in perovskite ferroelectric KTa1-xNbxO3 single crystal

Fano resonance arises from the interference of a localized discrete state coupled to the continuum states, which has become an indispensable probe in physical and chemical sciences. Compared with plenty of studies in the artificial meta-structures, Fano resonances in single crystals were rarely reported. Herein, we performed a comprehensive study on Fano resonances of KTa1-xNbxO3 (KTN) ferroelectric single crystals using temperature dependent Raman spectroscopy. The Fano asymmetric q factors were fitted for KTN crystals with various Nb concentrations. We found that the q factors were strongly correlated to Curie temperature Tc and ferroelectric polarization arrangement in different phase regions. In addition, the regulation of dopant transition metals on the Fano effect was also investigated in Cu:KTN and Fe:KTN crystals.

Voltage Control of Perpendicular Magnetic Anisotropy in Multiferroic Composite Thin Films under Strong Electric Fields.

"Ferroelectric/ferromagnetic" multiferroic composites with perpendicular magnetic anisotropy (PMA) are useful for developing power-efficient magnetic memories. Voltage control of PMA has been demonstrated in bulk multiferroic composites based on ferroelectric single crystals, but they are not compatible for integration. Multiferroic composite thin films are useful for developing integrated devices; however, voltage control of PMA in them has not been achieved yet at room temperature due to their low magnetoelectric (ME) coupling coefficient. Here, we demonstrate such functionality and propose to enhance their ME coupling effect under a strong electric field by taking full advantage of the large dielectric strength of ferroelectric thin films. First, the thickness-dependent breakdown of Pb(Zr0.384Ti0.576Nb0.04)O3 (PNZT) thin films was studied, and the two-layer (∼200 nm) samples exhibited the highest breakdown strength (3.68 MV/cm) and small surface roughness (<1 nm). Second, we fabricated "PNZT/(Co/Pt)5" thin films with strong PMA whose breakdown strength is nearly independent of the top electrode materials. Finally, voltage-induced effective magnetic field (Heff) in "PNZT/(Co/Pt)5" was studied. It is comparable to that achieved in bulk composites and will induce magnetization switching under strong electric fields. Multiferroic composite thin films with large breakdown strength will provide a useful platform for enabling integrated multiferroic devices.

Growth, Structure, and characterization of new High-TC Piezo-/Ferroelectric Bi(Zn2/3Ta1/3)O3-PbTiO3 single crystals

In this work, new bismuth-based complex perovskite piezo-/ferroelectric single crystals of the (1-x)PbTiO3-xBi(Zn2/3Ta1/3)O3 solid solution have been successfully grown by the high temperature solution method (HTSG). The crystal structure was found to be tetragonal at room temperature by means of structural analysis by X-ray diffraction and domain examination by polarized light microscopy (PLM). High Curie temperature (TC = 470 °C) was determined by dielectric measurements and PLM observations. Band-like domain structures were observed in the (001)-oriented single crystal with a width of 100–200 µm. Good piezoelectric performance (d33 = 251 pC/N) and high coercive field (EC = 30 kV/cm) were found by the piezoelectric and ferroelectric characterizations. Detailed crystal structural refinement was performed to establish the structure–property relationship in this system. Comparative studies of current bismuth-based complex perovskite solid solution single crystals point to the advantages of the Bi(Zn2/3Ta1/3)O3-PbTiO3 single crystals in terms of high TC, good piezoelectric performance, and high coercive field. These advantages make this piezo-crystal system a favourable candidate for potential high-temperature and high-power electromechanical applications.

A critical field study of ferroelectric domain in Al-doped KNbO3 single crystal

-Ferroelectric domain engineering is important for studying the dipolar structure of these materials. This dipolar structure is formed because of defects and imperfections produced using various doping. The KNbO3 ferroelectric single crystal was prepared using flux methods. Al2O3 aluminum trioxide (Al) was used as a dopant in a KNbO3 crystal. The domain structure of the crystal was studied by applying electric fields of 50 V/cm, 60 V/cm, 70 V/cm, 80V/cm, and 100 V/cm in an Al-doped KNbO3 single crystal. Furthermore, the critical field on which domains were nucleated after applying the electric field, was also studied. This work confirmed that the critical field of nucleation of the new domain in an Al-doped KNbO3 single crystal was 70 V/cm, which is slightly less than that of pure KNbO3 single crystal.

Scaling relations of domain reversal dynamics in rhombohedral and tetragonal PIN–PMN–PT ferroelectric single crystals

The domain reversal dynamics of rhombohedral and tetragonal PIN–PMN–PT ferroelectric single crystals has been investigated by analyzing the variation of hysteresis loops under various electric fields and frequencies. As the electric field amplitude E0 continuously increases, the hysteresis area ⟨A⟩ clearly reflects three stages of polarization reversal. The complete scaling relations of domain reversal dynamics were determined. For rhombohedral PIN–47PMN–29PT crystals, the dynamic hysteresis area follows the law of ⟨A⟩ ∝ f −0.38816E05.21244 in the first E0-stage and ⟨A⟩ ∝ f 0.03553E00.37126 in the third E0-stage. For tetragonal PIN–37PMN–39PT crystals, the dynamic hysteresis area follows the law of ⟨A⟩ ∝ f −0.09054E02.74854 in the first E0-stage and ⟨A⟩ ∝ f −0.15504E02.06936 in the third E0-stage. The negative α indicates that with the alternating velocity of the increasing periodic electric field, more and more domain reversals fail to follow with the alternating electric field. However, rhombohedral PIN–47PMN–29PT crystals possess a positive α in the third E0-stage, indicating that 71° and 109° domains can keep pace with varying E0 more easily. The positive β indicates that when the electric field frequency is fixed, more and more domains begin to reverse with the intensity of the increasing electric field. In addition, the function of ⟨A⟩ ∝ f αE0β cannot be applied to the second E0-stage, where the non-180° domain rotation starts occurring but 180° domain rotation has not finished yet.