Ferroelectric Hysteresis Loops Research Articles

Enhanced energy storage properties of epitaxial (Ba0.955Ca0.045)(Zr0.17Ti0.83)O3 ferroelectric thin films

Abstract(Ba0.955Ca0.045)(Zr0.17Ti0.83)O3 [BCZT] epitaxial were grown on La0.67Sr0.33MnO3 (LSMO)‐coated (100)‐oriented MgO single crystal substrates by the pulsed laser deposition (PLD) technique. Herein, we report crystal structure, ferroelectric, piezoresponse force microscopy (PFM), and energy storage properties near the morphotropic phase boundary (MPB) composition of [Ba0.850Ca0.15Zr0.1Ti0.90O3] solid solution. Epitaxial growth of the films was confirmed using X‐ray diffraction (XRD) spectra. Room‐temperature Raman spectroscopy confirms perovskite phase of BCZT films. Room‐temperature polarization‐electric field (P‐E) loops confirm the ferroelectric nature of BCZT films. Ferroelectric hysteresis loops demonstrate high saturation polarization (Pmax ~ 97.96 μC/cm2) and remanant polarization (Pr ~ 70.1 μC/cm2) at an applied maximum electric field ~2.77 MV/cm. The optimized BCZT epitaxial thin films have shown moderate dielectric properties at different measured frequencies (10‐100 kHz). Nanoscale piezoresponse force microscopy (PFM) images demonstrate switchable ferroelectric polarization of these thin films above ±9 V of dc voltage applied. Energy storage properties measured from ferroelectric loops revealed a high discharge curve energy density ~27.5 J/cm3 at a maximum electric field of 2.77 MV/cm. Epitaxial‐grown BCZT films are suitable candidate materials for capacitor applications.

Construction of a novel metal–organic framework adenine-UiO-66 piezocatalyst for efficient diclofenac removal

Piezoelectric materials, which could collect and convert mechanical energy into electrical energy, have recently emerged as promising catalysts for pollutants removal sustainably. Unfortunately, it remains a challenge to enhance the intrinsic piezoelectric property of piezoelectric materials. Herein, for the first time, the polar molecule adenine was introduced as a linking agent in the synthesis process of Zr-based UiO-66 (denoted as AD-U) to enhance the structure asymmetry and piezoelectric properties of UiO-66. The piezoresponse force microscopy (PFM) and ferroelectric hysteresis loop demonstrated that AD-U catalyst exhibited significantly enhanced piezoelectric potential than UiO-66. Furthermore, a series of electrochemical characterization evidenced that AD-U displayed higher charge separation efficiency than UiO-66. As expect, the optimized AD-U shown promoted diclofenac sodium (DCF) piezoelectric degradation efficiency by harvesting stirring energy compared with pure UiO-66. The electron paramagnetic resonance (EPR) spectra and trapping agent experiments convinced that h+ play the major role for destroying the DCF molecules. Moreover, three possible degradation pathways of DCF were put forward by DFT and liquid chromatography mass system (LC-MS). Our work offers a new pathway to enhance piezoelectric property of MOFs and extend the application of MOFs in the field of piezocatalysis.

Ferroelectricity in a semiconducting all-inorganic halide perovskite.

Ferroelectric semiconductors are rare materials with both spontaneous polarizations and visible light absorptions that are promising for designing functional photoferroelectrics, such as optical switches and ferroelectric photovoltaics. The emerging halide perovskites with remarkable semiconducting properties also have the potential of being ferroelectric, yet the evidence of robust ferroelectricity in the typical three-dimensional hybrid halide perovskites has been elusive. Here, we report on the investigation of ferroelectricity in all-inorganic halide perovskites, CsGeX3, with bandgaps of 1.6 to 3.3 eV. Their ferroelectricity originates from the lone pair stereochemical activity in Ge (II) that promotes the ion displacement. This gives rise to their spontaneous polarizations of ~10 to 20 μC/cm2, evidenced by both ab initio calculations and key experiments including atomic-level ionic displacement vector mapping and ferroelectric hysteresis loop measurement. Furthermore, characteristic ferroelectric domain patterns on the well-defined CsGeBr3 nanoplates are imaged with both piezo-response force microscopy and nonlinear optical microscopic method.

Investigation on microstructure transition and electrical behavior in (1-x)Bi4Ti3O12/xBi4.5K0.5Ti4O15 lead-free composites

The lead-free (1-x)Bi4Ti3O12/xBi4.5K0.5Ti4O15 composites (x = 0–0.4) have been synthesized by solid state reaction method. Evolution of microstructure and electric properties has been investigated with varying composition ratio. X-ray diffraction, Raman and IR absorption confirm the crystal transition tendency from orthorhombic to tetragonal phase. Evident texture along c-axis crystallographic orientation is observed in structure and morphology characteristics with x = 0.05 and 0.1. Through modulating the mole ratio of Bi4.5K0.5Ti4O15, coexistence of ferroelectric order and relaxor state is verified by the variation of ferroelectric hysteresis loops and polarization current density. This behavior can be attributed to the uncertain stability of discernable ferroelectric order induced by electric field among polar nanoregions during symmetry distoration. Temperature dependence of dielectric properties suggests an excellent thermal stability during a wide temperature range. Moreover, the detailed dielectric mechanism has been analyzed via various methods. Electrical conduction in grains and grain boundaries respectively plays the different role during the varying temperature process.

Comparative study on (Na0.47Bi0.47Ba0.06)0.95A0.05TiO3 (A = Sr2+/Ca2+) lead-free ceramics: Scaling behavior of ferroelectric hysteresis loop

Scaling behavior of dynamic hysteresis of (Na0.47Bi0.47Ba0.06)0.95A0.05TiO3 (A = Sr2+/Ca2+) (expressed as BNBT-Sr and BNBT-Ca, respectively) lead-free ceramics was comparatively studied. BNBT-Ca exhibits typical ferroelectric hysteresis (polarization vs electric field, P–E) loops, while BNBT-Sr shows pinched P–E loops. The two samples' electric field and frequency-dependent dynamic hysteresis behavior were systematically investigated. The dopants difference (Sr2+/Ca2+) produces different scaling behavior of dynamic hysteresis, which is related to the electric field-induced phase transition and domain size between BNBT-Sr and BNBT-Ca.

Molecular dynamics simulation of typical molecular ferroelectrics based on polarized crystal charge model

Molecular ferroelectrics are a promising class of ferro-electrics, with environmental friendliness, flexibility and low cost. In this work, a set of characteristic molecular ferroelectrics are simulated by molecular dynamics (MD) with polarized crystal charge (PCC). From the simulated results, their ferroelectric switching mechanisms are elucidated, with their ferroelectric hysteresis loops. The PCC charge model, recently developed by our group, containing the quantum electric polarization effect, is suitable in nature for studying molecular ferroelectrics. The simulated systems include the typical molecular ionic ferroelectrics, di-isopropyl-ammonium halide (DIPAX, X=C (Cl), B (Br), and I), as well as a pair of newly validated organic molecular ferroelectrics, salicylideneaniline and (-)-camphanic acid. In total, there are five systems under investigation. Results demonstrate that the PCC MD method is efficient and reliable. It not only elucidates the ferroelectric switching mechanism of the studied molecular ferroelectrics, but also extends the application range of the PCC MD. In conclusion, PCC MD provides an efficient protocol for extensive computer simulations of molecular ferroelectrics, with reliable ferroelectric properties and associated mechanisms, and would promote further exploration of novel molecular ferroelectrics.

Ferroelectric hysteresis and magnetoelectric effect in orthorhombic Dy-=SUB=-1-x-=/SUB=-Ho-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=- single crystals

In Dy1-xHoxMnO3 single crystals with the orthorhombic space group Pbnm, ferroelectric hysteresis loops were measured for compositions with x=0 and 0.3. As the content of Ho3+ ions increases, the hysteresis loop narrows and for x=0.3 it no longer manifests itself. An analysis of the signal corresponding to the hysteretic behavior of a ferroelectric showed that even harmonics can be obtained only if the hysteresis loop is not symmetric about the abscissa axis. In view of the latter, the hypothesis that the second harmonic of the magnetoelectric effect is a consequence of the complex dependence of the polarization on time due to its hysteresis becomes doubtful. Measurements of the dependence of the inverse magnetoelectric effect on the amplitude of the applied electric field Delta M(E) showed that the first harmonic remains linear with respect to the electric field even in the electric field strength region where the domain structure of the ferroelectric is rearranged. Keywords: multiferroics, ferroelectricity, hysteresis.

Сегнетоэлектрический гистерезис и магнитоэлектрический эффект в орторомбических монокристаллах Dy-=SUB=-1-x-=/SUB=-Ho-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=-

In Dy1-xHoxMnO3 single crystals with the orthorhombic space group Pbnm, ferroelectric hysteresis loops were measured for compositions with x=0 and 0.3. As the content of Ho3+ ions increases, the hysteresis loop narrows and for x=0.3 it no longer manifests itself. An analysis of the signal corresponding to the hysteretic behavior of a ferroelectric showed that even harmonics can be obtained only if the hysteresis loop is not symmetric about the abscissa axis. In view of the latter, the hypothesis that the second harmonic of the magnetoelectric effect is a consequence of the complex dependence of the polarization on time due to its hysteresis becomes doubtful. Measurements of the dependence of the inverse magnetoelectric effect on the amplitude of the applied electric field ΔM(E) showed that the first harmonic remains linear with respect to the electric field even in the electric field strength region where the domain structure of the ferroelectric is rearranged.

Frequency dependence on polarization switching measurement in ferroelectric capacitors

Ferroelectric hysteresis loop measurement under high driving frequency generally faces great challenges. Parasitic factors in testing circuits such as leakage current and RC delay could result in abnormal hysteresis loops with erroneous remnant polarization (P r) and coercive field (E c). In this study, positive-up-negative-down (PUND) measurement under a wide frequency range was performed on a 10-nm thick Hf0.5Zr0.5O2 ferroelectric film. Detailed analysis on the leakage current and RC delay was conducted as the polarization switching occurs in the FE capacitor. After considering the time lag caused by RC delay, reasonable calibration of current response over the voltage pulse stimulus was employed in the integral of polarization current over time. In such a method, rational P–V loops measured at high frequencies (>1 MHz) was successfully achieved. This work provides a comprehensive understanding on the effect of parasitic factors on the polarization switching behavior of FE films.

High energy-storage performance of lead-free Ba0.4Sr0.6TiO3–Sr0.7Bi0.2TiO3 relaxor-ferroelectric ceramics with ultrafine grain size

Relaxor-ferroelectric (RFE) ceramics possess slender ferroelectric hysteresis loop and low remnant polarization ( P r ). They have great potential to provide excellent energy-storage performance as dielectric energy-storage materials. Herein, a lead-free 0.8Ba 0.4 Sr 0.6 TiO 3 –0.2Sr 0.7 Bi 0.2 TiO 3 (0.8BST–0.2SBT) RFE ceramic with high energy-storage performance has been realized successfully. The addition of Bi 3+ and increase in Sr 2+ content at the A site of the BST can effectively inhibit the growth of grains for high breakdown strength ( E b ). As a result, an ultrafine average grain size of 0.7 μm was obtained in 0.8BST–0.2SBT RFE ceramic, affording a high E b of 300 kV/cm. Further investigation revealed that the mutual conversion of short-range polar nanoregions and long-range-ordered ferroelectric domains upon application and withdrawal of a 300 kV/cm applied electric field resulted in a high maximum polarization ( P max ) of 31 μC/cm 2 and a low P r of 2.5 μC/cm 2 . Hence, the 0.8BST–0.2SBT RFE ceramic simultaneously exhibited a high recoverable energy-storage density of 3.3 J/cm 3 and a high energy-storage efficiency of 85% at 300 kV/cm. Additionally, a good energy-storage performance was reported over a temperature range of 50°C-120 °C and frequency from 10 to 1000 Hz, making the 0.8BST-0.2SBT RFE ceramic a potential lead-free dielectric energy-storage material.

Modified microstructure, magnetic and ferroelectric properties in narrow bandgap Bi0.5Na0.5Ti1-xCoxO3 ceramics

The multiferroic (Bi0.5Na0.5)Ti1-xCoxO3 (xBNTCO) ceramics, where x = 0, 0.02, 0.04, 0.06 and 0.08, have been fabricated by using conventional solid-state sintering method. The effects of doped metal concentrations on microstructure, visible-light response, ferromagnetic and ferroelectric orders have been investigated in detail. X-ray diffraction patterns show that all samples are single rhombohedral phase, but also demonstrate the lattice dilatation phenomenon based on the Williamson-hall analysis theory. The band gaps of samples significantly decrease from 3.0 eV to 1.43 eV with increasing Co concentrations up to 0.08, which results from the appearance of Co 3d electronic orbits between the valence band and the conduction band of BNTO. According to ferroelectric hysteresis loop, the improvement of ferroelectric properties can be attributed to the accurately dominating element content in perovskite compounds. When × = 0.04, the sample with maximum remnant polarization Pr (11.47 μC/cm2) is obtained. Besides, the ferromagnetic order is observed at room temperature (RT), which is explained using an F center exchange theory. These results are significant in perovskite oxides for the further research on optical, ferroelectric and magnetic properties and exhibit significant values in solar energy cells and multiferroic applications.

Synthesis and characterization of niobium doped bismuth titanate

Pure and niobium doped bismuth titanate ceramics Bi4Ti3−xNbxO12(Nb−BiT) with x ranging from 0% to 2% are prepared by sol–gel method. Pellets are sintered by pressureless sintering (PLS) and spark plasma sintering (SPS). Raman spectroscopy indicates distortion in the structure due to the substitution of titanium by niobium. X-ray photoelectron spectroscopy (XPS) displays the Nb integration to the bismuth titanate ceramic structure. X-ray diffraction shows no secondary phases and offers clues about crystallographic texturing due to the SPS technique. The shape and size of the grains are strongly influenced by the niobium added to the system as reported by scanning electron microscopy. Ferroelectric hysteresis loops exhibit the effect of the niobium and the texturing on the ferroelectric behavior. Higher values of remanent polarization are reported for PLS samples. In comparison with PLS, higher values of the relative permittivity are reported for SPS samples due to the non-homogeneous incorporation of Nb.

Hf1–xZrxO2/ZrO2 Nanolaminate Thin Films as a High-κ Dielectric

Engineering of HfO2–ZrO2 ferroelectric thin films can substantially increase their dielectric constant. Here, we investigate dielectric and structural properties of ∼10 nm thin films consisting of stacked 1 nm thin ferroelectric (FE) Hf1–xZrxO2 (HZO(x)) and antiferroelectric (AFE) ZrO2 layers. At x < 0.5, the measurements of polarization vs electric field revealed pure FE hysteresis loops, whereas at x > 0.5, pinched hysteresis loops with some remnant polarization were observed, which indicate a coexistence of FE and AFE orderings. Finally, a pure ZrO2 thin film (x = 1) exhibits only an AFE double hysteresis loop. In this way, we demonstrate that the coexistence of FE and AFE orderings can be controlled by adjusting the composition of HZO(x) layers in the HZO(x)/ZrO2 nanolaminate films. At x = 0.5, the dielectric constant is ∼60 in nanolaminate films, which is much higher than that of the conventional HZO(x) solid solution thin films. Structural investigations confirm a coexistence of polar orthorhombic and nonpolar tetragonal structures, which is consistent with the observed polarization hysteresis loops. We also show that the strain generated in the nanolaminate structure significantly facilitates a field-induced transition from the AFE to the FE phase. The design does not considerably affect the leakage current in HZO(x)/ZrO2 nanolaminate films, which makes this system highly promising for complementary metal oxide semiconductor-compatible capacitors.

Investigation of structural and enhanced piezoelectric properties in low lead content Na0.5Bi0.5TiO3-BaTiO3-PbTiO3 system

Through this work the authors report the structural, ferroelectric, and piezoelectric properties of PbTiO3 modified ceramics: (1–2x)Na0.5Bi0.5TiO3-xBaTiO3-xPbTiO3: (1–2x)NBT-xBT-xPT with x = 0.01, 0.03, 0.05, 0.07 and 0.09. The X-ray diffraction analysis of (1–2x)NBT-xBT-xPT revealed the existence of monoclinic (M) phase for x = 0.01 and 0.03 with the presence of ½(311) superlattice reflection, which acts as a structural bridge between the Rhombohedral (R) and Tetragonal (T) phases. Phase transition from M to T phase was observed at x = 0.03 which is supported by the presence of (002)/(200) splitting in the diffraction pattern. The measured mean grain size and density for x = 0.03 was 5.7 µm and 5.834 g/cm3 respectively, which was the maximum compared to other compositions. The chemical state of elements in the ternary system is found out using the X-ray photoelectron spectroscopy. A diffuse phase transition is perceived from the temperature dependent dielectric studies for x ≤ 0.03, while this diffusiveness decreases for x > 0.03 with the increase in concentration of substituents. Besides, the ferroelectric (FE) to relaxor (RE) transition, TFR is also diminished in higher concentration of BT and PT. A well saturated ferroelectric hysteresis loop with saturation polarization (Ps) and remnant polarisation (Pr) values of 35 and 32 µC/cm2 respectively is achieved for x = 0.03. Under an applied field of 48 kV/cm, a unipolar strain value of 0.26% is achieved for the same composition with a piezoelectric charge co-efficient (d33*) of 541 pm/V. The superior piezoelectric performance shown by (1–2x)NBT-xBT-xPT with a very low lead content of 3 mol%, which is at the proximity of M-T phase transition is explained using the polarisation rotation mechanism, that occurs in conjunction between polar-polar phases. The flat free energy profile that exists at the phase boundaries, eases the rotation of the polarisation vector and hence the piezoelectric constant. Also, a larger grain size will also relieve the polarisation rotation.

Dielectric and electrical properties of hexagonal BaTi0.5Co0.5O3 ceramic with NTC effect

Barium Titanate doped with Cobalt is known for both its electric and magnetic properties. The synthesis and characterization of Cobalt doped barium titanate; BaTi1-xCoxO3(BTCO) x = 0.5was investigated with a view to understand its structural, magnetic and electrical properties. A finest possible sample of Co doped micro particles of BaTiO3 (BTO) with possible tetragonal structure via a solid-state route was prepared. Prepared samples of BaTi1-xCoxO3 (BTCO) were structural characterized by X-ray diffraction (XRD). The dielectric constant measurements of the samples were carried out at 1Hz to1 MHz Vibrating Sample Magnetometer (VSM) measurements revealed the magnetic nature of Cobalt doped BaTiO3. Ferroelectric hysteresis loop traced at the electric field in-between -15 to +15 (KV/cm). The relaxation phenomena that take place cane be attributable to the damping of dipole oscillator due to the application of external field. The impedance measurements were done up to 473 K in order to separate grain (bulk) and grain boundary contributions. The FESEM micrographs show proper grain growth and EDAX confirmed the presence of all the elements in samples. In the present study, various electrical properties of barium titanate based ceramics were explained and examples of the relevant applications were given. Copyright © 2017 VBRI Press.

Imprinted hysteresis loops and size-reduced ferroelectric polarization nanodots in epitaxial PbTiO3 thin film after heat treatment

We investigated the imprinted ferroelectric hysteresis loops and size-reduced ferroelectric polarization nanodots in epitaxial PbTiO3 thin films by heat treatment. The epitaxial c-oriented PbTiO3 thin films deposited on the Nb-doped SrTiO3 thin films exhibited imprinted ferroelectric hysteresis loops by heat treatment. The imprinted ferroelectric hysteresis loops of the PbTiO3 thin films had distinct differences between positive and negative coercive fields as well as between positive and negative remanent polarizations. By applying external biases to a piezoresponse force microscope (PFM) tip, ferroelectric polarization nanodots were formed in the PbTiO3 thin films. The switching voltages for forming ferroelectric polarization nanodots significantly decreased as the asymmetry of the coercive fields of the imprinted ferroelectric hysteresis loops increased. In particular, the reduced ferroelectric polarization switching voltages made it possible to form size-reduced ferroelectric polarization nanodots.

In-plane quasi-single-domain BaTiO3 via interfacial symmetry engineering

The control of the in-plane domain evolution in ferroelectric thin films is not only critical to understanding ferroelectric phenomena but also to enabling functional device fabrication. However, in-plane polarized ferroelectric thin films typically exhibit complicated multi-domain states, not desirable for optoelectronic device performance. Here we report a strategy combining interfacial symmetry engineering and anisotropic strain to design single-domain, in-plane polarized ferroelectric BaTiO3 thin films. Theoretical calculations predict the key role of the BaTiO3/PrScO3{({{{{{boldsymbol{110}}}}}})}_{{{{{{bf{O}}}}}}} substrate interfacial environment, where anisotropic strain, monoclinic distortions, and interfacial electrostatic potential stabilize a single-variant spontaneous polarization. A combination of scanning transmission electron microscopy, piezoresponse force microscopy, ferroelectric hysteresis loop measurements, and second harmonic generation measurements directly reveals the stabilization of the in-plane quasi-single-domain polarization state. This work offers design principles for engineering in-plane domains of ferroelectric oxide thin films, which is a prerequisite for high performance optoelectronic devices.

Low temperature synthesis of multicomponent perovskite by mechanochemical route

The synthesis of a novel multicomponent perovskite was carried out by substituting 5 cations in the A-site of BaTiO3 lattice. The mechanochemical synthesis involved 5 h of ball milling followed by annealing at 800 °C for 2 h and the compound was sintered at 1200 °C for 2 h to form the cubic perovskite phase adopting the Pm3‾m space group. The lattice parameter was found to be 0.391 nm. The reduction in the tetragonality and the local distortion in the compound were observed in the 2D charge distribution maps. The band gap of the compound was found to be 2.94 eV with a dielectric constant value of 270. Ferroelectric hysteresis loops were recorded and the leakage current density was found to be in the order of 10-5 A/cm2.

Solution processing of morphotropic phase boundary BiFeO3‐PbTiO3 thin films with reduced conductivity for high room temperature switchable polarization

AbstractThe (1 – x)BiFeO3‐xPbTiO3 (BFO‐PTO) perovskite solid solution has great potential for being used in practical devices, as it exhibits significant ferroelectric response at its morphotropic phase boundary (MPB). However, the significant conduction, particularly high electrical leakage currents that BFO‐PTO films show at room temperature, deteriorates their functionality. This is mainly associated with the presence of multivalent iron along with A‐site and oxygen vacancies. Here, solution‐derived BFO‐PTO thin films have been crystallized at low temperature on Pt/TiO2/SiO2/Si substrates, by a rapid thermal annealing process to minimize Bi and Pb volatilization. X‐ray analyses have revealed that textured films are obtained with a pseudocubic perovskite structure and without the formation of detectable second phases. Microstructural studies indicated a columnar growth of the films with grain size well above the nanometric range, which, therefore, should not produce an appreciable reduction of the ferroelectric response due to size effects. Because of the relatively low content of charged defects produced in these BFO‐PTO films during processing, ferroelectric hysteresis loops can be measured at room temperature. The highest value of remnant polarizations (2PR = 58 μC/cm2) was obtained for the 0.65BiFeO3‐0.35PbTiO3 (65BFO‐35PTO) films, which suggests that this film composition lies in the proximity of the MPB where the coexistence of a highly textured &lt;100&gt; tetragonal phase and a rhombohedral one seems to occur.

Achieving Large Switchable Polarization and Enhanced Piezoelectric Response in BiFeO3‐PbTiO3 Solid Solution Ceramics

AbstractPerovskite materials based on BiFeO3‐PbTiO3 (BFPT) solid solutions are promising for various applications thanks to the extremely large spontaneous polarization (Ps) and existence of multiferroic morphotropic phase boundary. For applications in piezoelectric and memory devices, complete switching of Ps is needed, which is hard to achieve practically. In this work, a simple modified mixed‐oxide reaction method is developed allowing to prepare Dy‐ and Sm‐modified BFPT ceramics with significantly improved properties. The MPB compositions demonstrate well‐saturated ferroelectric hysteresis loops with large switchable remanent polarization of 60 µC cm−2 and enhanced piezoelectric properties with a large‐signal piezoelectric coefficient d33* = 214 pm V−1 and a direct piezoelectric coefficient d33 = 128 pC N−1, which is one and a half times larger than the best d33 value reported for the BFPT ceramics so far. The Curie temperature reaches 539 °C, suggesting a potential for high‐temperature applications. The domain structure is studied by piezoresponse force microscopy. It is found that the enhanced dielectric/piezoelectric properties are mainly due to polarization rotation/extension (intrinsic) mechanism, while the extrinsic contributions of the interphase and domain walls are virtually absent. The strategies for improvement of properties of BFPT and related materials are proposed.