Double Hysteresis Loops Research Articles

Oxygen-vacancy-induced memory effect and large recoverable strain in a barium titanate single crystal

A phase field model is developed in this paper to study the influences of oxygen vacancies on domain evolutions under electric field in ${\text{BaTiO}}_{3}$ single crystal. The oxygen vacancies are modeled as defect dipoles, enabling the capture of domain memory effect. Three different domain structures are studied, and the distributions of defect density and the electromechanical responses under electric loading are simulated. The simulations reproduce well the reversible domain switching and large recoverable electric-field-induced strain observed in experiments on both engineered domain structure and single domain structure. It is also discovered that double hysteresis loop, stepwise hysteresis loop and shifted hysteresis loop can emerge due to vacancy induced depolarization field, which explains well the previous experimental observations. The results also indicate that domain memory effect and non-$180\ifmmode^\circ\else\textdegree\fi{}$ domain switching are the mechanisms for large recoverable electric-field-induced strain in ferroelectrics with oxygen vacancies.

Crystal Structure Analysis of High T<sub>C</sub> Barium Titanate – Bismuth Perovskite-Type Oxide System Ceramics and their Piezoelectric Property

Barium titanate (BaTiO3, BT) – bismuth titanate magnesium oxide (Bi(Mg0.5Ti0.5)O3, BMT) solid solution system ceramics were prepared by conventional sintering method in pursuit of the enhancement of the BT Curie temperature (TC, 132 °C). Normal ferroelectric polarization vs. electric-field (P-E) hysteresis loops were observed for BT-BMT ceramics with BMT contents below 20 and above 60 molar%. On the other hand, broad P-E double hysteresis loops were observed for BMT contents from 30 to 50 molar%. The origin was investigated using synchrotron XRD measurement and Rietveld analysis. The crystal structure was assigned to ferroelectric phase with domain-pinning by certain defect structures. A modified phase diagram was proposed on the basis of the temperature dependence of the crystal structure.

Dielectric properties of electron irradiated PbZrO3 thin films

The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO3 thin films grown by sol-gel technique. The films were (0.62 μm thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. T c was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of ɛ′(T) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase P s of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in T C, increase in dielectric constant, broader hysteresis loop, and increase in P r can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.

The characteristics of (Pb,La)(Zr,Sn,Ti)O3 ceramics synthesized by coprecipitation method compared to conventional mixed oxide method

The relaxor antiferroelectric (Pb,La)(Zr,Sn,Ti)O3 powders were synthesized by conventional mixed oxide method and coprecipitation method. The XRD patterns show that pure perovskite phase formation temperature was 700 °C for the coprecipitation method and that was 1,100 °C for the conventional mixed oxide method. Effect of the methods on sintering behavior and microstructures of the ceramics has been investigated by SEM. Both the samples exhibit typical antiferroelectric double hysteresis loops with maximum polarization of 18.2 μC/cm2, forward-switching field of 6.2 kV/mm by conventional mixed oxide method, and 33.1 μC/cm2, 4.3 kV/mm by coprecipitation method, respectively.

Universal Behavior and Electric‐Field‐Induced Structural Transition in Rare‐Earth‐Substituted BiFeO3

AbstractThe discovery of a universal behavior in rare‐earth (RE)‐substituted perovskite BiFeO3 is reported. The structural transition from the ferroelectric rhombohedral phase to an orthorhombic phase exhibiting a double‐polarization hysteresis loop and substantially enhanced electromechanical properties is found to occur independent of the RE dopant species. The structural transition can be universally achieved by controlling the average ionic radius of the A‐site cation. Using calculations based on first principles, the energy landscape of BiFeO3 is explored, and it is proposed that the origin of the double hysteresis loop and the concomitant enhancement in the piezoelectric coefficient is an electric‐field‐induced transformation from a paraelectric orthorhombic phase to the polar rhombohedral phase.

Double polarization hysteresis loop induced by the domain pinning by defect dipoles inHoMnO3epitaxial thin films

We report on antiferroelectriclike double polarization hysteresis loops in multiferroic ${\text{HoMnO}}_{3}$ thin films below the ferroelectric Curie temperature. This intriguing phenomenon is attributed to the domain pinning by defect dipoles which were introduced unintentionally during film growth process. Electron paramagnetic resonance suggests the existence of ${\text{Fe}}^{1+}$ defects in thin films and first-principles calculations reveal that the defect dipoles would be composed of oxygen vacancy and ${\text{Fe}}^{1+}$ defect. We discuss migration of charged point defects during film growth process and formation of defect dipoles along ferroelectric polarization direction, based on the site preference of point defects. Due to a high-temperature low-symmetry structure of ${\text{HoMnO}}_{3}$, aging is not required to form the defect dipoles in contrast to other ferroelectrics (e.g., ${\text{BaTiO}}_{3}$).

Electro-optical and dielectric properties of a high tilt antiferroelectric liquid crystal mixture (W-193B)

The electro-optical properties and dielectric relaxation have been investigated for an antiferroelectric liquid crystal mixture W-193B. The material exhibits smectic A*, smectic C* and a wide range of anticlinic smectic phases. The high tilt and broad room temperature smectic phase make it a good candidate for antiferroelectric display materials. Dielectric studies have been made in a planarly aligned cell in the frequency range 10 Hz–13 MHz. Dielectric spectroscopy reveals the existence of soft mode in the smectic A* phase and Goldstone mode in the smectic C* phase. In the smectic phase the dielectric spectrum of the material exhibits two absorption peaks related to the rotational fluctuation around the short axis of the molecules and antiphase azimuthal angle fluctuation, respectively, and are separated by about two orders of frequency. Electro-optical response using a low frequency triangular wave showed a very high quasi-static contrast ratio of 132 : 1, threshold voltage of around 7 V and saturation of 17 V. Surface-stabilized, low thickness cells of this mixture showed a perfect double hysteresis loop with a 1 Hz triangular signal, reaching different transmission levels for different voltage amplitudes. These levels can be stabilized with a single holding voltage, making it possible for the material to be passively multiplexed at video rate.

The Influence of the Electrode Type on the Electric–Ferroelectric Properties of Sandwich PbZr0.2Ti0.8O3-BiFeO3–PbZr0.2Ti0.8O3 Structure

PbZr 0.2 Ti 0.8 O 3 -BiFeO 3 -PbZr 0.2 Ti 0.8 O 3 (PZT-BFO-PZT) structure was prepared by sol-gel method on Pt/Si wafers. Three metals were tested as top electrod: Au, Cu, and Pt. A double hysteresis loop was observed in all cases, suggesting an antiferroelectric-like behavior. The values for remnant polarization and coercive field are about 3 μC/cm 2 and 115 kV/cm, respectively. The saturation polarization is about 22 μC/cm 2 . Capacitance and leakage current show significant dependence on the top metal electrode. The results were explained considering the presence of a Schottky-type contact at the PZT-metal interface.

Aging-induced double hysteresis loops in bismuth-doped (Ba,Ca)TiO3 ferroelectric ceramics

Bismuth-doped (Ba1−xCax)TiO3 ceramics (x = 0.10, Bi-BCT) were prepared by a conventional solid-state reaction technique. An abnormal double-like hysteresis polarization–electric (P–E) loop was observed at room temperature for aged Bi-BCT. Raman scattering gives critical evidence for the formation of O2− vacancies in Bi-BCT. The change from the single P–E loops in the fresh samples to the double loops in the aged samples excludes the existence of a ferroelectric–antiferroelectric transition in Bi-BCT. A reversible domain switching mechanism resulting from a symmetry-conforming short-range ordering of point defects gives a reasonable explanation for the naturally age-induced double-like P–E loops in Bi-BCT.

Influence of composition and pressure on the electric field-induced antiferroelectric to ferroelectric phase transformation in lanthanum modified lead zirconate titanate ceramics

The electric field-induced phase transformation behavior in lanthanum-doped lead zirconate titanate ceramics was examined by polarization versus electrical field (P-E) measurements carried out from room temperature to 130 degrees C and under hydrostatic pressures from 20 to 300 MPa. The samples with composition (Pb(1-x)La(x))(Zr(0.90)Ti(0.10))(1-x/4)O(3) [PLZT x/90/10; x = 2,3,4 at%] were prepared by the standard solid-state reaction method. The analysis at room temperature under atmospheric pressure showed that the increase in the lanthanum content induces a transformation from the typical ferroelectric hysteresis, observed for PLZT 2,3/90/10, to double-hysteresis loops, typical of antiferroelectric phases, for PLZT 4/90/10 under a strong electric field. Hydrostatic pressure- induced and temperature-induced ferroelectric (FE) to antiferroelectric (AFE) phase transformations were examined. The measured hysteresis loops indicated that the FE-AFE phase transformation depends on both temperature and hydrostatic pressure for PLZT 3/90/10. This composition, which is in a ferroelectric state at room temperature under atmospheric pressure, can be transformed into the antiferroelectric phase by the application of a hydrostatic pressure of 100 MPa or by increasing the temperature to around 90 degrees C. The PLZT 2/90/10 and 4/90/10 compositions displayed predominantly ferroelectric and antiferroelectric behavior, respectively, over the ranges of temperature and hydrostatic pressure examined in the present study.

Three-dimensional spin structure in exchange-biased antiferromagnetic/ferromagnetic thin films

A coexistence of lateral and in-depth domain walls in antiferromagnet/ferromagnet (AF/FM) thin films exhibiting double hysteresis loops (DHLs) is demonstrated. Comparison of single and DHLs together with local and global measurements confirms the formation of two oppositely oriented domains in the AF that imprint a lateral domain structure into the FM layer. Most significantly, the magnetization reversal mechanism within each opposite domain takes place by incoherent rotation of spring-like domain walls extending through the Ni thickness. Therefore, complex three-dimensional domain walls are created perpendicular and parallel to the AF/FM interface in exchange biased systems.

Bias dependent relaxation in different phases of an orthoconic antiferroelectric liquid crystal mixture (W-182)

The electro-optical behavior of the orthoconic antiferroelectric liquid crystal mixture W-182 has been studied. Surface-stabilized, low thickness cells of this mixture give a perfect double hysteresis loop with 1 Hz triangular signal, reaching different transmission levels for different voltages amplitudes. These levels can be stabilized with a single holding voltage, making it possible for the material to be passively multiplexed at video rate. With the application of bias field at three different temperatures, we have observed the field-induced Fréedericksz transition from SmI A ∗ – SmC A ∗ , antiferroelectric to ferroelectric, and ferroelectric to paraelectric transition. Such Fréedericksz transition point is decreased with the increase of temperature.

Double hysteresis loops induced by Mn doping in Pb 0.99Nb 0.02(Zr 0.95Ti 0.05) 0.98O 3 ferroelectric ceramics

Pb 0.99Nb 0.02(Zr 0.95Ti 0.05) 0.98O 3 (PNZT95/5) ceramics with 1 mol% and without Mn doping were prepared via conventional solid state reaction process. X-ray diffraction patterns show that the PNZT95/5 and Mn-doped PNZT95/5 (PNZTM95/5) ceramics, with composition near the boundary of the ferroelectric phase (FE)/antiferroelectric phase (AFE), have a rhombohedral perovskite structure. The ferroelectric behavior of PNZT95/5 ceramics is strongly affected by Mn doping. Without any aging process the PNZTM95/5 ceramics possess double hysteresis loops ( P–E loops), whereas the PNZT95/5 ceramics possess normal single hysteresis loops. Due to the defect dipoles formed by effectively negatively charged Mn 3+ dopants and positively charged O 2− vacancies, the PNZTM95/5 ceramics exhibit the double P–E loops. The defect dipole effect has been proved by investigating the P–E loops under different external fields. As a result, the PNZTM95/5 ceramics become “hardened”, exhibiting a high mechanical quality factor (1300).

Aging-Induced Double Ferroelectric Hysteresis Loops and Asymmetric Coercivity in As-Deposited BiFe0.95Zn0.05O3Thin Film

The BiFe0.95Zn0.05O3 (BFZO) thin film was fabricated on indium tin oxide/glass substrate using a metal organic decomposition method combined with sequential layer annealing. Double ferroelectric hysteresis loops were observed in the as-deposited film, indicating that the film is partially aged. This aging phenomenon can be attributed to the formation of defect complexes between oxygen vacancies and acceptors of in the film. The nonreversible transition from double ferroelectric hysteresis loop to the single one can occur during the course of increasing the applied electric field. More importantly, an asymmetry of the coercive field can be found to be strongly dependent on the magnitude and frequency of the electric field. This phenomenon was discussed based on the asymmetric driving force for domain backswitching in BFZO film with a preferential polarization.

Double Hysteresis Loop and Aging Effect in K0.5Na0.5NbO3-K5.4Cu1.3Ta10O9Lead-Free Ceramics

In this work, the double-loop-like characteristics of K0.5Na0.5NbO3+x mol% K5.4Cu1.3Ta10O9 ceramic and its relationships with the transition temperature, aging, and switching have been investigated. Our results reveal that the phase transition temperature is an important parameter determining the aging requirement for the ceramics to exhibit the double-loop-like characteristics. For a ceramic with a high transition temperature, e.g. the ceramic with x=0.75 (tetragonal–orthorhombic phase temperature ∼206°C), the vacancies can migrate during the crystal transformation and settle in a distribution with the same symmetry as the crystal after the transformation. As a result, defect dipoles along the polarization direction are formed and provide restoring forces to reverse the switched polarizations, and thus producing a double polarization hysteresis (P–E) loop. On the other hand, aging is required for a ceramic with a low transition temperature, e.g. aging at 80°C for 30 days is required for the ceramic with x=1.5 (transition temperature ∼175°C). Our results also reveal that the defect dipoles can be switched under a slow-switching electric field (<1 Hz) or at high temperatures (>100°C), thus leading to an opening of the double P–E loop.

Single-domain-wall states in millimeter-scale samples ofErFeO3

Hysteresis loops in a $3.9\ifmmode\times\else\texttimes\fi{}3.9\ifmmode\times\else\texttimes\fi{}3.1\text{ }{\text{mm}}^{3}$ single-crystal ${\text{ErFeO}}_{3}$ sample were studied in the $4&lt;T&lt;70\text{ }\text{K}$ temperature interval. Above and near the compensation point ${T}_{\text{comp}}=46\text{ }\text{K}$ the hysteresis loops are rectangular, with the coercive force diverging at ${T}_{\text{comp}}$. As the temperature is lowered toward the erbium ordering transition at ${T}_{N2}=4.1\text{ }\text{K}$, the shape of the loops experiences a dramatic change. First, the loops develop triangular ``tails.'' Then the triangles become prominent while the central rectangular part collapses. A double-loop hysteresis pattern with two triangular loops emerges. This behavior is explained by a reversible motion of a single magnetic domain wall in the sample. The simplicity of the magnetic state is related to the small magnetization and correspondingly large domain sizes in orthoferrites. Our model reproduces the correlation of the loops' shape with the temperature dependence of the total magnetic moment of ${\text{ErFeO}}_{3}$.

Compensation-dependent in-plane magnetization reversal processes inGa1−xMnxP1−ySy

We report the effect of dilute alloying of the anion sublattice with S on the in-plane uniaxial magnetic anisotropy and magnetization reversal process in ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{P}$ as measured by both ferromagnetic resonance (FMR) spectroscopy and superconducting quantum interference device (SQUID) magnetometry. At $T=5\text{ }\text{K}$, raising the S concentration increases the uniaxial magnetic anisotropy between in-plane $⟨011⟩$ directions while decreasing the magnitude of the (negative) cubic anisotropy field. Simulation of the SQUID magnetometry indicates that the energy required for the nucleation and growth of domain walls decreases with increasing $y$. These combined effects have a marked influence on the shape of the field-dependent magnetization curves; while the $[0\overline{1}1]$ direction remains the easy axis in the plane of the film, the field dependence of the magnetization develops double hysteresis loops in the [011] direction as the S concentration increases, similar to those observed for perpendicular magnetization reversal in lightly doped ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$. The incidence of double hysteresis loops is explained with a simple model whereby magnetization reversal occurs by a combination of coherent spin rotation and noncoherent spin switching, which is consistent with both FMR and magnetometry experiments. The evolution of magnetic properties with S concentration is attributed to compensation of Mn acceptors by S donors, which results in a lowering of the concentration of holes that mediate ferromagnetism.

Ferroelectric and Dielectric Aging Effects of Fe&lt;sup&gt;3+&lt;/sup&gt;/Nb&lt;sup&gt;5+&lt;/sup&gt; Hybrid-Doped Barium Titanate Ceramics

It is well known that acceptor and donor doping results in opposite ferroelectric aging effects; however, the aging effects in hybrid-doped (acceptor+donor) has remained unclear. Thus, the aging effect of dielectric and ferroelectric properties in Fe3+/Nb5+ hybrid-doped BaTiO3 ceramics was investigated in this research. The concentration of acceptor dopant (Fe3+) was fixed at 1 mol% while that of donor dopant (Nb5+) was varied from 0.5-2.0 mol%. XRD technique was used to study the phase morphology. Before measuring dielectric and ferroelectric aging effect, all samples were deaged at 250 °C for 1 hour. The results showed that the dielectric properties of all deaged samples have decreased exponentially with time. The deaged samples with 0.5 and 1.0 mol% of Nb5+ obviously showed double hysteresis loop while that with higher concentration of Nb5+ (1.5-2.0 mol%) showed the rectangular (normal) hysteresis loop. The explanations based on the effect of defect dipole were discussed.

Striking similarity of ferroelectric aging effect in tetragonal, orthorhombic and rhombohedral crystal structures

A series of Mn-doped alkaline niobate-based and lead zirconic titanate ferroelectrics that possess tetragonal, orthorhombic, and rhombohedral perovskite structures was fabricated, and the aging behavior of their hysteresis loop and electrostrain was studied. We found that after aging, all the samples showed a similar double hysteresis loop and large recoverable electrostrain behavior, regardless of their crystal structure and of their ionic species. The striking similarity of the aging effect in different ferroelectric phases suggests that there exists a common physical origin of aging in ferroelectric perovskites. Based on a symmetry-conforming short-range ordering mechanism of point defects, we provided a unified microscopic explanation for the aging effect in the tetragonal, orthorhombic, and rhombohedral ferroelectrics.

Aging-induced giant recoverable electrostrain in Fe-doped 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 single crystals

The aging effect of a 0.2mol% Fe-doped 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 single crystal was investigated. The authors found that aging induced a double ferroelectric hysteresis loop and a giant recoverable electrostrain of 0.8% at an electric field of 1.2kV∕mm in the ⟨001⟩-oriented tetragonal crystal. This result is much higher than the strains obtained in crystals near the morphotropic phase boundary under the same field. Such aging effect is attributed to a point-defect-mediated reversible domain-switching mechanism. Large electrostrains (&amp;gt;0.55%) at 1.2kV∕mm for a broad temperature from room temperature to 160°C suggest that the aged single crystal is a promising electromechanical material.