Electric Hysteresis Loops Research Articles

Phase Transition, Large Strain and Energy Storage in Ferroelectric (Bi0.5Na0.5)TiO3-BaTiO3 Ceramics Tailored by (Mg1/3Nb2/3)4+ Complex Ions

Lead-free relaxor-ferroelectric (Mg1/3Nb2/3)4+ complex ions modified (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT-xMN) ceramics were fabricated by traditional solid-phase reaction sintering, and the effects of (Mg1/3Nb2/3)4+ complex ions on the structural, ferroelectric, dielectric, energy storage, and strain properties of these ceramics were studied. All of the samples illustrated a single perovskite phase with a pseudo-cubic structure. Electric field-induced polarization and strain hysteresis loops indicated the occurrence of reversible ferroelectric-to-relaxor phase transition, which gave rise to a large strain of 0.49%. (Mg1/3Nb2/3)4+ complex ions greatly influenced the coercive field and remanent polarization of the ceramics; these properties also affected energy storage density of the materials. The optimal energy storage density and efficiency of the ceramics were 0.54 J/cm3 and 38.4%, respectively, when x = 0.04. These results may stem from the electric field-induced transition between the ferroelectric and relaxor-ferroelectric phase of the proposed ceramics.

Ferroelectricity and magnetoelectric coupling in hexagonal Lu0.5In0.5FeO3 ceramics

Recently, hexagonal rare earth ferrites (h-RFeO3) have attracted much scientific attention due to their room-temperature multiferroicity. The primary issue for h-RFeO3 is how to manipulate from nonpolar orthorhombic (Pbnm) structure to polar hexagonal (P63cm) structure, and this could be realized by the wet-chemical method, epitaxial stain engineering, or introducing chemical pressure. Another key issue for h-RFeO3 is the experimental determination of its macroferroelectricity and magnetoelectric (ME) coupling because the semiconducting nature seriously obstructs the experimental characterization. In the present work, owing to the suppressed leakage current density with decreasing temperature, saturated electrical hysteresis loops were observed in A-site substituted h-Lu0.5In0.5FeO3 ceramics at 198 K, directly demonstrating the presence of the macroferroelectricity. Room-temperature switchable ferroelectric polarization was further confirmed by the piezoresponse force microscopy. Furthermore, noticeable ME coupling with a linear ME voltage coefficient of 0.67 mV/cm Oe was observed at room temperature.

Monte Carlo simulation of polarization plateaus and hysteresis behaviors of an antiferroelectric/ferroelectric BiFeO3/YMnO3 Ising bilayer

Abstract The mixed-spin Ising model with the crystal-field and the external electric field is used to describe an antiferroelectric/ferroelectric BiFeO3/YMnO3 bilayer structure. Using Monte Carlo simulation, we discuss the polarization plateaus and the hysteresis behaviors of the bilayer structure under the influence of different physical parameters. The results illustrate that the crystal-field, the exchange coupling and the external electric field have important roles in the low-temperature dielectric properties and multiple electric hysteresis loops of the antiferroelectric/ferroelectric BiFeO3/YMnO3 bilayer structure.

Intrinsic Magnetic and Ferroelectric Behaviour of Non-magnetic Al3+ Ion Substituted Dysprosium Iron Garnet Compounds

Synthetic garnets are a group of oxide materials that play a vital role in the development of solid state lasers, magnetic and optic-electronic devices. The analysis on the solubility of rare-earth elements in the well-crystallized system has led to the discovery of peculiar oxide materials with multifunctional properties. By following the above importance, Aluminium ion (Al3+) substituted Dysprosium Iron Garnet compounds with the chemical formula of Dy3Fe5−xAlxO12 (x = 0–0.5) have been synthesized by the solid state reaction method and the effect of substitution of non-magnetic ions into the magnetic sub-lattices have been analyzed. The Rietveld refinement of powder x-ray diffraction patterns confirms that the pure Dy3Fe5O12 compound crystallizes with cubic (Space group: Ia3d) superstructure whereas all the Al3+ substituted samples exhibit the coexistence of cubic (Ia3d) and trigonal Fe2O3 (R3c) phases. The energy gap values of the prepared compounds is found to be around 1.6 eV which reveals the semiconducting nature and the decreasing trend of band gap values may be due to the growth factor of crystallites, structural disorder and distortion introduced into the crystal lattice. From the Micro-Raman analysis, it is found that the substituted Al3+ ions starts filling into both tetrahedral and octahedral positions and the assignments of vibrational modes observed from Raman spectra confirm the incorporation of Al3+ ions into the Dy3Fe5O12 garnet structure. From the magnetization analysis, it is found that the response of super-exchange interaction between Fe3+ ions in the a and d sites of Dy3Fe5O12 compound leads to net magnetic moment and the substitution of Al3+ ions preferably replaces Fe3+ ions in d sites and suggests the decrease in net magnetization values. From the photoluminescence studies, it is noticed that the luminescence behavior of Al3+ ions substituted Dy3Fe5−xAlxO12 compounds are due to the superposition of a broad emission band and reveals the variation in concentration of Al3+ ions in the prepared compounds. An interesting point to note is that, a well saturated “soft” ferroelectric hysteresis loop is obtained in both pure and Al3+ substituted Dy3Fe5−xAlxO12 compounds, and the observed electric hysteresis loops are found to be influenced by the factors such as capacitance nature, resistivity effects and leakage current of the compounds. Hence, the study on effect of trivalent non-magnetic ion substitution in a hard magnetic Dy3Fe5O12 system leads to interesting intrinsic magnetic and ferroelectric properties and found suitability for the fabrication of energy storage and optoelectronic devices.

Room-temperature anisotropic magnetoresistance of magnetic carbon films with vertically-grown graphene nanocrystallites

In this study, graphene nanocrystallited carbon films were deposited with electron irradiation induced deposition in electron cyclotron resonance plasma. The orientation of nanocrstallites was revealed with transmission electron microscope (TEM) images. The TEM results showed that the graphene nanocrystallites aligned perpendicular to substrate surface. The anisotropic-magneto-resistive performances of the films were investigated under diowed that from 400 to 2 K, the film resistance varied periodically as the film rotated along its surface axial, exhibiting a sinusoidal feature. In room temperature, the average angular resolution of the film was better than 0.5%/degree, and the largest relative changing rate of the film MR ratio reached over 400% as magnetic field increased from 3 to 9 T. The mechanism of this performance was investigated through electrical transport measurement and magnetic hysteresis loops, which revealed the spin-enhanced magnetism of the nanocrystallites were the main origin of this anisotropic magnetic response behaviors.

Significance of isostructural distortion and strong magnetoelastic coupling in the weak ferromagnet YFe0.9Cr0.1O3

We report the appearance of weak ferromagnetism above the long-range canted antiferromagnetic order TN = 553 K at which the Fe-Cr interactions become dominant in YFe0.9Cr0.1O3. The weak ferromagnetic order above TN appears due to the increasing magnetic interactions in Fe-sublattices resulting in a canted antiferromagnetic transition at TFe-Fe = 620 K. Electrical hysteresis loop studies and Positive-Up Negative-Down protocol measurements reveal spontaneous but weak ferroelectricity in the system. Dielectric measurements as a function of temperature and frequency reveal a relaxorlike dielectric anomaly within a temperature interval of 400–500 K and anomalous signatures at and temperatures above TN. Synchrotron x-ray diffraction studies over a broad temperature range, 298–873 K, illustrate a significant magnetoelastic coupling at TN and around TFe-Fe. Isostructural distortions are further revealed over the temperature range of 400–500 K from the x-ray diffraction studies. Analyses of the diffraction patterns reveal the delicate interplay between the in-plane and out-of-plane exchange interactions over TN and in isostructural distortion regions. We strongly argue that the ferroelectricity in YFe0.9Cr0.1O3 results from the magnetostriction and Dzyaloshinskii-Moriya interaction manifested through a significant magnetoelastic coupling at TN and TFe-Fe.

Energy storage properties in SrTiO3–Bi3.25La0.75Ti3O12 thin films

Ferroelectric thin films with slim electric field dependent polarization hysteresis loops, showing small remnant polarization and large polarization, are desired to obtain high recoverable energy density and efficiency for ferroelectric capacitors in energy storage performance. Here, SrTiO3 alloying effects on Bi3.25La0.75Ti3O12 thin films are prepared by sol-gel method and the energy storage performance have been investigated. With increasing the Bi3.25La0.75Ti3O12 content, the crystalline quality and grain size are increased as well as the improvement in polarization. Slim electric field dependent hysteresis loops can be obtained when the Bi3.25La0.75Ti3O12 content is higher than 0.6. The optimized composition is 0.4SrTiO3-0.6Bi3.25La0.75Ti3O12 thin film with the recoverable energy density and high efficiency of 44.7 J/cm3 and 87.4%, respectively. Moreover, the 0.4SrTiO3-0.6Bi3.25La0.75Ti3O12 thin film shows excellent energy storage performance in wide frequency range, fatigue endurance and thermal stability. The results suggest that energy storage performance in Bi3.25La0.75Ti3O12 thin films can be effectively improved through SrTiO3 alloying, and can be considered as candidates for dielectric energy storage capacitors.

Superior energy storage performance in Pb0.97La0.02(Zr0.50 Sn0.43Ti0.07)O3 antiferroelectric ceramics

To develop antiferroelectric based dielectric capacitors with superior energy storage capacity, antiferroelectric materials must possess simultaneously large recoverable energy density and high energy efficiency. With this motivation, in this work, we design and prepare Pb0.97La0.02(Zr0.50Sn0.43Ti0.07)O3 antiferroelectric ceramics with high Sn content considering that Sn element can narrow the electric hysteresis loops and thus improve the energy density and efficiency. The experiment results indicate that a large room-temperature recoverable energy density of 3.47J/cm3 and a high energy efficiency of 78% are realized simultaneously in this kind of ceramic. Besides, in the wide temperature range of 20–120°C, the recoverable energy density and the energy efficiency both show superior temperature stability. The large recoverable energy density and high energy efficiency in a wide temperature range demonstrate that the Pb0.97La0.02(Zr0.50Sn0.43Ti0.07)O3 antiferroelectric ceramic is a good candidate for preparing pulse power capacitors usable in various conditions.

Three dimensional phase-field simulations on the frequency dependence of polarization vectors and hysteresis loops in ferroelectric crystals

The phase field approach has been widely used to study the domain structure of ferroelectric crystals in both two and three dimensions (2D and 3D), but in the 3D case, little has been done to address the frequency dependence of ferroelectric characteristics. In this work, we adopt the 3D time-dependent Ginzburg–Landau kinetic equation to calculate the evolution of local polarization vectors and the overall hysteresis loops of ferroelectric crystals under the frequencies from 0.4 kHz to 120 kHz, and then use the fast Fourier transform to analyze the frequency characteristics of the polarizations. It shows the phenomenon of multiple frequencies at low field frequency but not at high one. The distribution and evolution of polarization vectors in x, y, and z directions are obtained, and various forms of electrical hysteresis loops are found from the average of local polarization vectors. The results indicate that, as the frequency increases, the hysteresis loops of Pz versus Ez change from the standard shape to the oval shape, but the loops for Px and Py change from the dumbbell shape to an oblique ellipse, and then to figure-eight curve and eventually to the superparaelectric one. The detailed distribution and evolution of the polarization vectors in the crystal are also vividly displayed. Finally, the effects of lattice size, amplitude of the applied field, depolarization energy, and the initial state of polarizations in the crystal are investigated. It shows that the nature of polarization evolution in a 3D crystal is highly complex and that each of these factors can have a significant effect.

On the emergence of out-of-plane ferroelectricity in ultrathin films

The presence of a spontaneous and switchable polarization is the defining property of a ferroelectric material. Such materials are indispensable in a countless number of industrial and scientific applications. Furthermore, the enhancement of ferroelectric property at reduced dimensions is crucial for continuous advancement in nanoelectronic applications. In this work, we investigate the onset of out-of-plane ferroelectricity in open-circuited stress-free BaTiO $$_3$$ ultrathin films by performing molecular dynamics simulations using the core–shell model potential. In doing so, we try to obtain electric polarization hysteresis loops using an appropriate range of external electric loading. It is found that out-of-plane ferroelectricity is suppressed in ultrathin films with thickness 10 or less than 10 unit cells, indicating that there exists a critical thickness for the emergence of out-of-plane ferroelectricity in ultrathin films. It is also found that the ultrathin films exhibit asymmetrical hysteresis loops slightly above the critical thickness.

Crystal structures, dielectric properties, and phase transition in hybrid improper ferroelectric Sr3Sn2O7-based ceramics

Hybrid improper ferroelectricity is induced by the coupling of oxygen octahedral rotation and tilt, and it may provide a promising way to develop new room-temperature single-phase multiferroic materials with a strong magnetoelectric effect. Though ferroelectric polarizations are confirmed by the electric hysteresis loops at room temperature, the ferroelectric-paraelectric phase transition has not been well understood. In the present work, the crystal structures, dielectric properties, and phase transition behaviors of Ruddlesden-Popper Sr3–xCaxSn2O7 ceramics are thoroughly determined. Ferroelectricity is confirmed through the polarization-electric field hysteresis loops at room temperature, and the Curie temperature is identified by the variable-temperature differential scanning calorimetric analysis and dielectric characterization. The polarizations and Curie temperatures of the present ceramics increase with increasing the calcium content. An improper ferroelectric transition is experimentally evidenced by a small dielectric constant and a step variation of dielectric constant around the Curie temperature, and the thermal hysteresis of dielectric constant confirms the first order transition nature. Moreover, the fitting result of Landau phase transition theory also suggests the first-order improper ferroelectric transition nature. The variable-temperature Raman result implies a tetragonal paraelectric phase above TC. The present work confidently confirms the first-order hybrid improper ferroelectric transitions in the present ceramics, and ferroelectric properties can be readily tuned by substituting the cations at the A-site.

The ferroelectric properties of 4-aminopyridinium perchlorate

Molecule-based ferroelectrics are a class of highly desirable intelligent materials for their highly variable physical properties, easy and environmentally friendly processing, especial light weight and mechanical flexibility. 4-Aminopyridinium Perchlorate (APP), used to be known as a pyroelectric below 243 K, is first discovered to be a new molecular ferroelectric in this work, which has a perfect electric hysteresis loops with a large spontaneous polarization of 1.0 μC/cm2 and a small coercive field of 0.67 kV/cm below 246 K. Owing to the dramatic changes of the protonated cations and order–disorder of anions, the crystal symmetry of APP transforms from P21/c to P21 in this first-order phase transition, which is revealed by other measurements, such as differential scanning calorimetry, heat capacity, dielectric anomalies and Raman spectrum.

Piezoelectric and ferroelectric characteristics of P(VDF-TrFE) thin films on Pt and ITO substrates

Organic P(VDF-TrFE) 70/30 copolymer thin films were fabricated on Pt/Ti/SiO2/Si(1 1 1) and ITO/glass substrates at 140 °C using a spin coater. Both P(VDF-TrFE) thin films exhibited ferroelectric β-phase crystallinity, as confirmed by X-ray diffraction analysis. The polarization–electric hysteresis loops of the P(VDF-TrFE) thin films on the Pt and indium-tin-oxide substrates showed high remnant polarizations of 15.5 and 11.8 μC/cm2, respectively. Atomic force microscopy characterization showed rod-like features of the P(VDF-TrFE) thin films on both substrates, where larger rod diameters were observed on the Pt substrate compared to those fabricated on the ITO substrate. Piezoelectric force microscopy measurements further confirmed the superior piezoelectric and ferroelectric properties of the P(VDF-TrFE) thin films on the Pt substrate compared to those on the ITO substrate, which arose from the increased diameter of the rod-like features.

Crystalline structure and the unusual dielectric behavior of nylon 93

Large dielectric constants (390 for a slowly cooled sample, and 2400 for a quenched sample at 0.3 kHz) were measured for nylon 93. A displacement–electric hysteresis loop was obtained for a slowly cooled sample of nylon 93, and the remanent polarization was calculated to be 0.543 C m−2 for the slowly cooled sample at 75 °C. The structure of nylon 93 was investigated in detail to clarify the origin of these unusual electric properties. The infrared peaks assigned to the amide groups of nylon 93 were changed by a corona poling treatment, which suggests that the hydrogen bonds formed by the amide groups of nylon 93 were weak enough to allow the amide groups to be aligned by an external electric field. The results obtained by X-ray diffraction, polarizing optical micrography, and differential scanning calorimetry indicated that α- and γ-crystals were formed in the slowly cooled and quenched samples, respectively, and the γ-crystals in the quenched samples were gradually changed into α-crystals by annealing. Large dielectric constants were measured for nylon 93. A displacement–electric hysteresis loop was obtained for a slowly cooled sample of nylon 93. The structure of nylon 93 was investigated in detail to clarify the origin of these unusual electric properties. The results obtained by X-ray diffraction, polarizing optical micrography, and differential scanning calorimetry indicated that α- and γ-crystals were formed in the slowly cooled and quenched samples, respectively, and the γ-crystals in the quenched samples were gradually changed into α-crystals by annealing.

Ferroelectric Property, Switchable Dielectric, and Excellent Second Harmonic Generation Response in a Homochiral Organic Salt: l-Prolinammonium 1-Adamantane Carboxylate

Molecular ferroelectrics have attracted increasing interest recently; however, the research on homochiral molecular ferroelectrics based on organic salts is relatively spare. Here we present a novel homochiral molecular ferroelectric [Hpla]·[ac] (Hpla = protonated l-prolinammonium, ac = deprotonated 1-adamantane carboxylate), 1, which goes through a reversible phase transition in the vicinity of 140 K. The distinct dielectric and heat anomalies further confirm the reversible phase transition. Single crystal X-ray diffraction analysis before and after the phase transition temperature indicates that 1 belongs to the P21 chiral space group, and the synergetic motions from the hydrogen bond and disorder–order of adamantane grids triggered the phase transition. The polarization–electric hysteresis loop shows that 1 has spontaneous polarization of 0.15 muC/cm2. Notably, compound 1 displays ultralarge second harmonic generation signals (9.1 a.u.), approximately equal to three times that of potassium dihydrogen p...

Chiral to Chiral Phase Transition in a Novel Hydrogen Bond Type Molecular Ferroelectric

AbstractAlthough great progress has been made for H‐bonds type molecular ferroelectrics, the systems accompanying with chiral to chiral phase transitions are still very spare. Here we display a new hydrogen bond type molecular ferroelectric, the salt of 1‐(1‐naphthyl) ethylammonium‐nopinate, 1, which undergoes a paraelectric–ferroelectric phase transition around 202 K from one chiral point group (P212121) to another chiral point group (P21). The electric hysteresis loop under 100 K directly indicates it is a potential ferroelectric material with maximum spontaneous polarization (Ps) 2.3 uC/cm2. X‐ray single crystal diffraction analysis shows that the significant hydrogen bond change along the b‐axis direction results net dipole moment and leads to the spontaneous polarization. The exceptional dielectric response in the vicinity of 202 K exhibits remarkable dielectric anomalies along the b‐axis direction than the other two directions. The strong SHG (second harmonic generation) signal (‐1.31) without obvious changes dependence on temperature further confirm the chiral to chiral structural phase transition.

Thermal behavior and characteristic of submicron sized barium titanate ceramic synthesized by acetylacetonate precursor

This article reports the synthesis of tetragonal and submicron sized BaTiO3 (BTO) ceramic prepared by Ba(acac)2 and TiO(acac)2 precursors. The thermal behavior and characteristic of BaTiO3 ceramic were investigated by TG/DTA analyzer, XRD, SEM, Raman spectrum and ferroelectric property analyses. The results show that the thermal decomposition process of TiO(acac)2 finished earlier than that of Ba(acac)2. The thermal reaction of the mixed precursors completed approximately at 800 °C. The results of the XRD and Raman spectrum analysis reveal that the product is tetragonal BTO ceramic. The SEM micrograph shows that the grain size of the BTO ceramic is 200–420 nm and the average size is 330 nm. The electric hysteresis loop of the submicron BTO ceramic shows a remanence and saturation polarization of 4.7 and 5.3 μC/cm2, respectively. The BTO ceramic prepared in this study display favorable ferroelectric properties at the submicron level, which make it suitable for applications in microelectronic devices.

Dependence of dielectric and photovoltaic properties of Pt/PLZT/LNO on the temperature and La doping content

In this study, Pb1−xLax(Zr0.52Ti0.48)O3/LaNiO3 (PLZT/LNO) heterostructures with different doping contents of La (x = 0.02–0.15) were prepared on a Si substrate by sol–gel process. First, the effects of the La doping content on the crystal structure, electric hysteresis loop, and dielectric performance of the PLZT thin film were investigated. With the increase in the La doping content, the results revealed that the XRD diffraction peaks of the PLZT thin film shifted to large angles, indicative of the decrease in the film grain size; meanwhile, the residual polarization intensity and coercive field strength of the thin film decreased. The dielectric-temperature spectrum revealed that with the increase in the La doping content, the Curie temperature of the PLZT thin film gradually decreased, while the relative dielectric constant tended to first decrease and then increase. When x (La) was 0.08, the constant reached the minimum. Furthermore, the dependences of the photovoltaic characteristics of the PLZT thin films on the temperature and La doping content were investigated. Under the same test temperature, the open-circuit voltage of the PLZT film tended to first increase and then decreased with the increase in the La doping content. When x (La) = 0.08, the open-circuit voltage reached the maximum. For PLZT with the same doping content of La, the open-circuit voltage also increased first and then decreased with increasing temperature. When T = 223 K and x (La) = 0.08, the open-circuit voltage reached the maximum of around 693 mV.

Exceptional second harmonic generation responses, switchable dielectric behaviours, and ferroelectric property in an adduct of hexamethylene-tetramine·bisnopinic acid

Most reversible phase transitions undergo transformations from high symmetry with non-active second harmonic generation (SHG) above Tc to low symmetry with active SHG below Tc (Tc refers the phase transition temperature). Here we display a new adduct of hexamethylenetetramine·bisnopinic acid, 1, which exhibits an abnormal phase transition from a low symmetrical structure with strong SHG responses above 235 K to a same symmetrical structure with weak SHG below Tc. X-ray single crystal diffraction research indicates the hydrogen-bond displacements trigger the structural phase transition. A pseudo symmetrical element C/2 exists in the low temperature structure (1-LTP) and vanishes in the room temperature (1-RTP). This abnormal change may be proved that its SHG responses from strong signal 1.04 (above Tc, about one-third of KDP) to weak signal 0.78 a.u. (below Tc). The ferroelectric measurement displays a typical electric hysteresis loop at room temperature with spontaneous polarization (Ps) 0.51 uC/cm2.

Effects of electric field induced polarization on dielectric tunability and pyroelectric coefficient

ABSTRACTBased on the Devonshire theory, a ratio of two thermodynamic parameters, a polarization – temperature coefficient, is found as the crucial for pyroelectric and dielectric tunability effects. Smaller ratio corresponds to larger degree of shift of dielectric peak and larger E-induced polarization. The materials will have higher temperature-stable dielectric tunability suitable for microwave devices. Larger ratio corresponds to larger change of electric hysteresis loop in shape and size with decreasing temperature from the Curie point. The materials will have larger pyroelectric coefficient. An experimental law that pyroelectric coefficient over square root of dielectric constant is a constant is derived.