Polarization Of Single Crystals Research Articles

Ferroelectricity driven by soft phonon and spin order in multiferroic BiMn3Cr4O12

AbstractBiMn3Cr4O12 shows an unusual joint multiferroicity, which facilitates the coexistence of considerable ferroelectric polarization and remarkable magnetoelectric coupling in a single‐phase multiferroic material. Based on first‐principles calculations, we investigate the two different types of ferroelectric phase transitions in the BiMn3Cr4O12 material. Our results show that the first ferroelectric phase transition is driven by soft mode and leads BiMn3Cr4O12 into the Cm space group. The predicted ferroelectric polarization in single crystal is about ~9.8 μC/cm2. With the emergence of spin order on both Mn and Cr sublattices, it is the polar Cm structure that triggers the exchange striction mechanism and therefore results in a large type‐II multiferroicity (~1.1 μC/cm2). In addition, the intrinsic direction of the spin‐driven ferroelectric polarization is always opposite to that of the existing Cm phase structure. Our results imply a feasible strategy in searching/designing novel type‐II multiferroics with large ferroelectric polarization.

Temperature and electric-field induced phase transition behavior and electrical properties of [001]-oriented 0.23Pb(In1/2Nb1/2)O3-0.47Pb(Mg1/3Nb2/3)O3-0.3PbTiO3-Mn single crystals

The temperature and electric-field induced phase transition behavior and dielectric, piezoelectric, and ferroelectric properties of [001]-oriented 0.23Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.3PbTiO3-Mn (PIMNT-Mn) single crystals were investigated. Dielectric performance analysis and temperature-dependent Raman spectra show three apparent ferroelectric phase transition temperatures around 120 °C(TR-M),145 °C(TM-T), and 170 °C(TT-C), respectively. In addition, the temperature dependence of the relative Raman intensities of Lorentzian peaks indicates the poled PIMNT-Mn single crystals exhibit rhombohedral(R) → monoclinic(M) → tetragonal(T) → cubic(C) phase transition path. The electrical properties of the PIMNT-Mn single crystals such as the longitudinal electrostrictive coefficient (Q), the converse piezoelectric constant (d33), and the maximum strain value (Smax%) have changed abnormally around the phase transition temperatures (TR-M and TM-T).

Electric polarization observed in single crystals of multiferroicLu2MnCoO6

We report electric polarization and magnetization measurements in single crystals of double perovskite Lu2MnCoO6 using pulsed magnetic fields and optical second harmonic generation (SHG) in DC magnetic fields. we observe well-resolved magnetic field-induced changes in the electric polarization in single crystals and thereby resolve the question about whether multiferroic behavior is intrinsic to these materials or an extrinsic feature of polycrystals. We find electric polarization along the crystalline b-axis, that is suppressed by applying a magnetic fields along c-axis and advance a model for the origin of magnetoelectric coupling. We furthermore map the phase diagram using both capacitance and electric polarization to identify regions of ordering and regions of magnetoelectric hysteresis. This compound is a rare example of coupled hysteretic behavior in the magnetic and electric properties. The ferromagnetic-like magnetic hysteresis loop that couples to hysteretic polarization can be attributed not to ordinary ferromagnetic domains, but to the rich physics of magnetic frustration of Ising-like spins in the axial next-nearest neighbor interaction model.

Study of temperature-dependent Raman spectroscopy and electrical properties in [001]-oriented 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3-Mn single crystals

In this work, the temperature-dependent Raman spectra and electrical properties of the [001]-oriented 0.5 mol. % Mn-doped 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3-Mn (PIMNT-Mn) single crystals were investigated. All the unpoled and poled PIMNT-Mn single crystals experience a ferroelectric tetragonal phase to paraelectric cubic phase transition (FET-PC) around 183 °C (TC), which exhibits a second-order transition behavior. Whereas, the poled PIMNT-Mn single crystals exhibit another two dielectric anomalies around 130 °C (TRM) and 148 °C (TMT), in which the ferroelectric rhombohedral phase to ferroelectric monoclinic phase (FER-FEM) and the ferroelectric monoclinic phase to ferroelectric tetragonal phase (FEM-FET) transitions take place, respectively. Both the two ferroelectric phase transitions exhibit a first-order transition behavior. The discontinuous change of the phase degree (θ) and frequencies (fr and fa) around TRM suggest the occurrence of the FER-FEM phase transition in the poled PIMNT-Mn single crystals. The narrowing of the 510 cm−1 and 582 cm−1 Raman modes around the TRM, TMT, and TC temperatures shown in the temperature-dependent Raman spectra suggests their increased ordering of the local structure. The intensity ratio of I272 cm−1/I801 cm−1 increases obviously around the phase transition temperatures (TRM, TMT, and TC), indicating the reduction of the long-range order. The anomalous broadening of the 272 cm−1 Raman mode around the TRM, TMT, and TC temperatures indicates the occurrence of the successive ferroelectric phase transitions (FER-FEM, FEM-FET, and FET-PC) with increasing temperature in the poled PIMNT-Mn single crystals.

Residual stress and interface effect on dielectric mechanisms in poled ultrathin relaxor ferroelectric single crystals

We have investigated the dielectric performances and mechanism of super-thin Mn-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals, exhibiting significantly different dielectric behaviors compared with thick wafer. Dramatic decrease by 5 times and large frequency dispersion of permittivity, changed diffuse degree of phase transition, dielectric loss anomaly with frequency and dielectric performances with direct-current electric field for thin wafers are observed, proving the existence of large surface residual stress and interface effects. Additionally, a theoretical model of low-permittivity and low-ferroelectric surface damage layers is concurrently proposed. These observations have important implications for actual performances of thin wafers applied in practical devices.

Phase Transition Behaviors in [011]-Oriented Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals Studied by Dielectric and Micro-Brillouin Spectroscopies

Phase transition behaviors of unpoled and [011]-poled relaxor ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals were investigated over a wide temperature range by dielectric and Brillouin scattering spectroscopies. The [011]-poled crystal exhibited two discontinuous dielectric and acoustic anomalies at ∼119 and ∼126 °C, which were attributed to two poling-induced structural phase transitions from rhombohedral to orthorhombic, and then to tetragonal symmetry. However, this poled crystal maintained the diffused phase transition behaviors of the unpoled one at higher temperatures above ∼126 °C. The disappearance of the poling effect upon the diffuse phase transition near the TC suggests that the macroscopic ferroelectric domains formed by poling are decomposed into mesoscopic and nano size polar regions at ∼126 °C. These polarization fluctuations and the coupling of these dynamic polar regions to the acoustic waves play the dominant role in the dielectric and acoustic anomalies, respectively. Therefore, a diffusive nature was commonly observed in both unpoled and poled single crystals near TC.

Manipulation of domain wall mobility by oxygen vacancy ordering in multiferroic YMnO3

The mobility of the ferroelectric domain phases and the local conductivity of ferroelectric domain walls in multiferroic YMnO3 crystals grown in air and reduced atmosphere were studied by piezoresponse force microscopy (PFM), tip-enhanced Raman spectroscopy (TERS) and conductive atomic force microscopy (CAFM). Oxygen vacancies were found to reduce the strength of 4d-2p (Y(3+)-O(2-)) hybridization and structural trimerization distortion, leading to the disappearance of the six wedge-shaped ferroelectric domain phases in oxygen deficient YMnO3-δ crystals. We observed anisotropic domain wall motion such that the wedge-shaped domain configuration joined at one point could be changed to the stripe domain configuration by applying high electric fields in oxygen deficient YMnO3-δ single crystals. The local conductivity of the domain walls increased significantly in poled YMnO3-δ single crystals. The straight conductive domain walls in YMnO3-δ, instead of the twisted insulating ones in the stoichiometric crystal, are induced by the ordered oxygen vacancies which are verified by TERS measurements.

Piezoelectric response of single-crystal PbZr1−xTixO3 near morphotropic phase boundary predicted by phase-field simulation

The piezoelectric property of hypothetic single-crystal PbZr1−xTixO3 (PZT) is studied using phase-field simulations. The dependence of piezoelectric coefficient (d33) on PbTiO3 compositions (x) near the morphotropic phase boundary of PZT was obtained. Using the existing thermodynamic description of PZT, it is shown that d33 reaches a peak value of 720 pC/N at x=0.47 which is more than three times of that for the ceramic counterpart. The relation between the domain structure of the poled PZT single crystals and the enhancement of d33 near the MPB composition is discussed.

Probing the Nanodomain Origin and Phase Transition Mechanisms in (Un)Poled PMN-PT Single Crystals and Textured Ceramics.

Outstanding electrical properties of solids are often due to the composition heterogeneity and/or the competition between two or more sublattices. This is true for superionic and superprotonic conductors and supraconductors, as well as for many ferroelectric materials. As in PLZT ferroelectric materials, the exceptional ferro- and piezoelectric properties of the PMN-PT ((1−x)PbMg1/3Nb2/3O3−xPbTiO3) solid solutions arise from the coexistence of different symmetries with long and short scales in the morphotropic phase boundary (MPB) region. This complex physical behavior requires the use of experimental techniques able to probe the local structure at the nanoregion scale. Since both Raman signature and thermal expansion behavior depend on the chemical bond anharmonicity, these techniques are very efficient to detect and then to analyze the subtitle structural modifications with an efficiency comparable to neutron scattering. Using the example of poled (field cooling or room temperature) and unpoled PMN-PT single crystal and textured ceramic, we show how the competition between the different sublattices with competing degrees of freedom, namely the Pb-Pb dominated by the Coulombian interactions and those built of covalent bonded entities (NbO6 and TiO6), determine the short range arrangement and the outstanding ferro- and piezoelectric properties.

Spherical nanoindentation and Vickers microhardness study of the deformation of poled BaTiO3 single crystals

In this work, Vickers microhardness and spherical nanoindentation (NI) experiments—with hemispherical radii, R, of 13.5, 5, and 1.4μm—were used to explore the room temperature deformation behavior of poled barium titanate (BaTiO3) single crystals with two orientations: (001) and (110). At 209±11 and 193±11GPa, Young’s moduli of the (001) and (110) surfaces, respectively, were comparable. The (001) surface deforms elastically, before a pop-in event, followed by a strain-hardening regime. The pop-in stresses are stochastic in nature and can be described by Weibull statistics. The (110) surface deforms elastically, then plastically at lower stresses, before cracks are initiated, beyond which the strain-hardening regime is almost identical to that of the (001) surface. This three-regime behavior of the (110) surface was confirmed by postindentation scanning electron microscope micrographs. This work confirms that the room temperature deformation of single crystal BaTiO3 occurs by glide on the {110} slip planes that are also the cleavage planes. Furthermore fully reversible reproducible stress/strain loops were observed and attributed to the formation and annihilation of fully reversible dislocation loops, whose threshold stresses were a function of the domain size that forms under the various indenters. The domain sizes appear to scale with R and are believed to be responsible for the NI size effect observed.

Strain-Gradient-Induced Polarization inSrTiO3Single Crystals

Piezoelectricity is inherent only in noncentrosymmetric materials, but a piezoelectric response can also be obtained in centrosymmetric crystals if subjected to inhomogeneous deformation. This phenomenon, known as flexoelectricity, can significantly affect the functional properties of insulators, particularly thin films of high permittivity materials. We have measured strain-gradient-induced polarization in single crystals of paraelectric SrTiO3 as a function of temperature and orientation down to and below the 105 K phase transition. Estimates were obtained for all the components of the flexoelectric tensor, and calculations based on these indicate that local polarization around defects in SrTiO3 may exceed the largest ferroelectric polarizations. A sign reversal of the flexoelectric response detected below the phase transition suggests that the ferroelastic domain walls of SrTiO3 may be polar.

Thermal Expansion Characteristics In [001]-Oriented PMN-0.32PT Single Crystals

The thermal strain on cooling and heating process during −60°C to 200°C have been measured using DIL402C dilatometer for unpoled and poled [001]-oriented PMN-0.32PT single crystal. The thermal expansion anomalies were found within a wide temperature range around 0°C. Effects of poling electric field on thermal strain for single crystals were investigated. The obvious expansion and contraction were presented at rhombohedral → tetragonal and tetragonal → cubic phase transition for poled single crystal. However, thermal expansion responses at phase transition were weak for unpoled single crystal. The thermal expansion characteristics in [001]-oriented PMN-0.32PT single crystals are discussed together with data on dielectric properties.

Composition and orientation dependence of dielectric and piezoelectric properties in poled Pb(Mg1∕3Nb2∕3)O3–PbTiO3 crystals

Temperature and orientation dependence of dielectric constant and discharging current was investigated in the poled single crystals of (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 with x varying from 0.24 to 0.38, furthermore, composition and orientation dependence of the room temperature piezoelectric constant d33 was also summarized. Temperature, frequency, orientation, and composition dependence of the dielectric constant in the poled crystals shows that domain configurations and phase transitions in the poled crystals strongly depend on both composition and orientation. Compared to the monodomain crystals, the poled polydomain crystals, especially near the morphotropic phase boundary, presented large piezoelectric and dielectric susceptibilities. High piezoelectric response of these ⟨001⟩ poled crystals with x between 0.28 and 0.30 in a broad temperature scope makes them the most promising candidate for potential practical applications.

Heterophase states and dual structures in(1−x)PbZn1∕3Nb2∕3O3−xPbTiO3single crystals

Important structural distinctions between the inside part and the outer layer of relaxor-ferroelectric $(1\ensuremath{-}x){\mathrm{PbZn}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}\text{\ensuremath{-}}x\phantom{\rule{0.3em}{0ex}}{\mathrm{PbTiO}}_{3}$ single crystals have been revealed in recent $\mathrm{x}$-ray diffraction studies. Based on the structural data from papers by Xu et al. [Phys. Rev. B 67, 104102 (2003); Appl. Phys. Lett. 84, 3975 (2004)], different dual structures are considered in the present paper in terms of orientation states and their distortions. An elastic matching of inside and outer phases coexisting at molar concentrations $0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.08$ is analyzed for unpoled and poled single crystals, and this analysis results in a series of diagrams of orientation states and interfaces. An idea on transition regions in the crystal samples with the dual structures is put forward, and factors are studied that play the key role in relieving the internal stress. Two possible models of the transition regions in the $(1\ensuremath{-}x){\mathrm{PbZn}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}\text{\ensuremath{-}}x\phantom{\rule{0.3em}{0ex}}{\mathrm{PbTiO}}_{3}$ single crystals are proposed and discussed as well as different unit-cell parameter variations are determined within the framework of these models.

Composition and orientation dependence of phase configuration and dielectric constant tunability inpoled Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

The composition and orientation dependence of the room temperature piezoelectric constantd33 and the dielectric constant tunability was investigated in poled single crystals of(1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT)with x varying from 0.24 to 0.38. The temperature, frequency, orientation and compositiondependence of the dielectric constant in the poled crystals shows that domainconfigurations and phase transitions in the poled crystals strongly depend on bothcomposition and orientation. Poled polydomain crystals near the morphotropic phaseboundary, especially for -poled 0.70PMN–0.30PT crystals with a critical composition for the relaxor state, possess a large piezoelectricconstant d33 = 2210 pC N−1 and a high dielectric constant tunability of 40.6% (at a dc bias of1 kV mm−1). The largetunability of εr in PMN–PT crystals is expected to be the most promising candidate for potentialapplications in continuously adjustable capacitors and dielectric amplifiers.

Ground state of the relaxor ferroelectricPb(Zn1/3Nb2/3)O3

High energy x-ray diffraction measurements on $\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$ (PZN) single crystals show that the system does not have a rhombohedral symmetry at room temperature as previously believed. The phase (X) in the bulk of the crystal gives Bragg peaks similar to that of a nearly cubic lattice with a slight tetragonal distortion. The Bragg profile remains sharp with no evidence of size broadening due to the polar microcrystals. However, in our preliminary studies of the skin, we have found the expected rhombohedral (R) phase as a surface state. On the other hand, studies on an electric-field poled PZN single crystal clearly indicate a rhombohedral phase at room temperature.

Local crystal analysis using near-field optical second harmonic microscopy: Application to thin ferroelectric films

Application of near-field optical second harmonic microscopy to nanometer scale crystal and strain analysis of thin polycrystalline ferroelectric films is described. The near-field signal is shown to be sensitive to local crystal orientation by experimental and theoretical studies of polarization properties of second harmonic generation from a poled single crystal of BaTiO3. Spatial resolution of the order of 80 nm has been demonstrated by recovery of the local poling direction of individual ferroelectric domains in polycrystalline thin Pb(ZrxTi1−x)O3 films. Near-field strain induced second harmonic generation from thin BaxSr1−xTiO3 films has also been studied, and an agreement between theory and experiment has been established. Thus, the technique described provides a tool for nanometer scale crystal and strain analysis of polycrystalline samples.

Dielectric and pyroelectric properties of crystal ion sliced (CIS) LiNbO3 thin film

10 μm thick LiNbO3 crystal films have been fabricated from a poled bulk single crystal by the technique of Crystal Ion Slicing (CIS). The CIS technique is a promising approach to fabricate the free standing ferroelectric films for various integration applications and thin film structures. In this paper, the dielectric and pyroelectric properties of CIS LiNbO3 films as well as their temperature dependence were investigated in order to evaluate the ferroelectric properties of the films compared to the parent bulk single crystals. The investigation of the dielectric and pyroelectric responses were carried out in the temperature range of 30-100°C. The results suggest that the film retains the ferroelectric properties of the bulk crystal with magnitudes close to those of single crystal values at room temperature. However, the virgin CIS film showed an additional distinct phase transition in the temperature range around 75°C, as determined from the dielectric and pyroelectric responses. This phase transition does not exist in the original poled bulk crystal. The origin and the effect of thermal annealing on this phase transition are discussed in this paper.

Photochemical Reduction and Oxidation Reactions on Barium Titanate Surfaces

AbstractThe influence of the ferroelectric domain structure of BaTiO3 on the photochemical reactions that occur on its surface has been examined using atomic force microscopy. Both the photochemical reduction of aqueous silver cations and the oxidation of steric acid thin films were studied. During reduction, silver selectively deposits on the surface in patterns determined by the ferroelectric domain structure. Based on the analysis of domain polarization in single crystals, we find that the photochemical reduction reaction occurs preferentially on the positive ends of the dipoles. The most likely explanation for this phenomenon is that when the static dipolar field is oriented with the positive end of the dipole on the surface, photogenerated electrons are driven to the solid-liquid interface where they reduce metal cations. The oxidation of steric acid films, on the other hand, is not spatially selective. During oxidation, the films dissipate uniformly as they are converted to CO2 and H2O. In this case, we conclude that the oxidation occurs indirectly. Photogenerated holes create hydroxyl radicals which can migrate on the surface before reacting with the steric acid molecules.

Kinetic study of PZN single crystal polarization under a static electric field

A kinetic effect is evidenced in lead zinc niobate (PZN). We measured the time dependencies of the polarisation P(t) of a single crystal. At a given temperature and electric field, P(t) is described by the expression P(t) = P ∞(T) f(t/τ(E, T)) where τ(E, T) is the incubation time above which the sample is completely polarised. The τ(E, T) was fitted using the exponential law exp[(W+kδ T /E)/kT] where the activation energy W is equal to 0.91±0.36 eV and δ T is equal to 2.2x108 K V/m in the 300—360 K temperature range. Taking into account this kinetic effect the electric-field-temperature diagram and the existence of an electric field threshold were discussed.