Ferroelectric Properties Research Articles

Effect of DMSO and Triacetin Solvents on Polyvinylidene Fluoride Polymorphs: Molecular Dynamics Simulations

In this article, molecular dynamics simulations are performed to investigate the interaction between polyvinylidene fluoride (PVDF) polymorphs (β phase has more properties compared with α, such as polarity, higher mechanical strength, and piezoelectric, ferroelectric, and pyroelectric properties), and two solvents, dimethyl sulfoxide (DMSO) and glyceryl triacetate (GTA). Pure solvent boxes are built using two force fields (Compass and Dreiding) to study the stabilization of their density and solubility, which are used with the PVDF surfaces (for each solvent, computations are performed using two surfaces α and β). According to the radial distribution function results, DMSO shows a stronger interaction with two PVDF phases, allowing it to orient chains from the α phase to the β phase, while GTA exhibits a weaker interaction due to specific hydrogen bonds. These findings are confirmed by the experiment, where the fraction F(β) reaches 62% when using DMSO, while it is 36% when using GTA.

DFT + U accurate for strain effect and overall properties of perovskite oxide ferroelectrics and polaron

DFT + <i>U</i> accurate for strain effect and overall properties of perovskite oxide ferroelectrics and polaron

Influence of Biaxial Strain and Interfacial Layer Growth on Ferroelectric Wake-Up and Phase Transition Fields in ZrO2.

Investigations on fluorite-structured ferroelectric HfO2/ZrO2 thin films are aiming to achieve high-performance films required for memory and computing technologies. These films exhibit excellent scalability and compatibility with the complementary metal-oxide semiconductor process used by semiconductor foundries, but stabilizing ferroelectric properties with a low operation voltage in the as-fabricated state of these films is a critical component for technology advancement. After removing the influence of interfacial layers, a linear correlation is observed between the biaxial strain and the electric field for transforming the nonferroelectric tetragonal to the ferroelectric orthorhombic phase in ZrO2 thin films. This observation is supported by applying the principle of energy conservation in combination with ab initio and molecular dynamics simulations. According to the simulations, a rarely reported Pnm21 orthorhombic phase may be stabilized by tuning biaxial strain in the ZrO2 films. This study demonstrates the significant influence of interfacial layers and biaxial strain on the phase transition fields and shows how strain engineering can be used to improve ferroelectric wake-up in ZrO2.

High‐throughput combinatorial approach expedites the synthesis of a lead‐free relaxor ferroelectric system

AbstractDeveloping novel lead‐free ferroelectric materials is crucial for next‐generation microelectronic technologies that are energy efficient and environment friendly. However, materials discovery and property optimization are typically time‐consuming due to the limited throughput of traditional synthesis methods. In this work, we use a high‐throughput combinatorial synthesis approach to fabricate lead‐free ferroelectric superlattices and solid solutions of (Ba0.7Ca0.3)TiO3 (BCT) and Ba(Zr0.2Ti0.8)O3 (BZT) phases with continuous variation of composition and layer thickness. High‐resolution x‐ray diffraction (XRD) and analytical scanning transmission electron microscopy (STEM) demonstrate high film quality and well‐controlled compositional gradients. Ferroelectric and dielectric property measurements identify the “optimal property point” achieved at the composition of 48BZT–52BCT. Displacement vector maps reveal that ferroelectric domain sizes are tunable by varying {BCT–BZT}N superlattice geometry. This high‐throughput synthesis approach can be applied to many other material systems to expedite new materials discovery and properties optimization, allowing for the exploration of a large area of phase space within a single growth.image

Structural, Ferroelectric, and Ferromagnetic Properties of Yttrium-Doped Cobalt Ferrites to Produce Green Electricity by Hydroelectric Cells

Structural, Ferroelectric, and Ferromagnetic Properties of Yttrium-Doped Cobalt Ferrites to Produce Green Electricity by Hydroelectric Cells

Magnetism, ferroelectricity, and piezoelectricity in bulk α-CrOOH and its monolayer

Multifunctional materials with magnetic, piezoelectric, and ferroelectric properties have a wide range of applications. This study investigates the properties of bulk α-CrOOH and its monolayer using density functional theory. The findings reveal that bulk α-CrOOH exhibits a weak interlayer antiferromagnetism, but has a ferroelectric polarization of 28.45 µC/cm2 and piezoelectric strain constants d33 of 21.69 pm/V, which are comparable to those of the multiferroic material BiFeO3. The monolayer of α-CrOOH is a low-temperature ferromagnetic semiconductor that exhibits robust piezoelectricity. This is because of the intrinsic mirror symmetry breaking in the z-direction, resulting in large out-of-plane piezoelectric coefficients of e31 = 31.914 pC/m and d31 = 0.22 pm/V. These intriguing electric and magnetic properties make polarized bulk and monolayer α-CrOOH potential candidates for piezoelectric and ferroelectric device applications.

Ferroelectric properties and current mechanisms of BaTiO3/Nb:SrTiO3 thin films

[Formula: see text] thin film oxides have been deposited on [Formula: see text] substrates using a pulsed laser deposition system. Different annealing methods were thereafter used to assess the ferroelectricity of the grown films. The residual polarization value, 2Pr, of 4.205 [Formula: see text]C/cm2 and saturated residual polarization value, 2Pmax, of 15.484 [Formula: see text]C/cm2 were obtained using in-situ annealing. After performing rapid thermal annealing (RTA) annealing, the residual polarization value rose to 4.676 [Formula: see text]C/cm2 and the saturated residual polarization value rose to 18.723 [Formula: see text]C/cm2. Furthermore, a comparison of results showed that the saturation test frequency of the in-situ annealing was 10 times higher than the saturation test frequency of the RTA. This could be explained by the fact that the secondary high-temperature annealing led to a decrease in the conductivity of the doped oxide and, thereby, a decrease in the effective electric field that was applied to both ends of the BTO ([Formula: see text]) film. Thus, a lower frequency was required to ensure a flip of all ferroelectric domains within the BTO film. By testing the fatigue frequency at 100 kHz, [Formula: see text] stable cycles in both annealing methods and the results confirmed the good stability of the device performance. A linear fit analysis of the [Formula: see text] – [Formula: see text] curves showed under in-situ annealing the presence of both a bulk-limited current mechanism that was dominated by the space charge limited current (SCLC) and Pool–Frenkel (PF) mechanisms, and an interface-limited current that was dominated by the Fowler–Nordheim (FN) mechanism in the structure. After RTA annealing, the conducting mechanism is ohmic contact at low electric field and the SCLC mechanism at high field strength. The results show that after RTA annealing, the quality and ferroelectric properties of the films are significantly improved compared to those under in-situ annealing. These results showed that the BTO/NSTO/STO ([Formula: see text]) structure had a standard test frequency as well as reliable stability. The BTO/NSTO/STO structure showed, therefore, promising applications in future nonvolatile information memory devices.

Comprehensive investigation into the influence of oxygen vacancies on the ferroelectric properties of spin coated bismuth ferrite thin films

Bismuth ferrite (BFO) is a prime candidate for room-temperature magnetoelectric coupling and multiferroic applications. The rhombohedral R3c phase of BFO is the source of many properties, but the phase purity and oxygen vacancies are still the biggest obstacles to its real-world application. Considering these facts, the present work investigates the effects of oxygen vacancies on the functional properties through manipulation of drying temperatures of spin-cast films, especially at temperatures around 280 °C, where both the secondary phase and oxygen vacancies are prevalent. One of the biggest sources of oxygen vacancy is bismuth volatilisation, and our work deals with the situation head-on, uncovering the effect of bismuth volatilisation on functional properties. The structural properties were studied using x-ray diffraction (XRD), and deeper insights into the surface topography of the samples were obtained using AFM imaging. The electrical and dielectric characteristics help distinguish and analyse the samples in terms of the presence of resistive switching. PUND studies were performed to determine the ferroelectric properties of the samples. A fifty percent reduction in the oxygen vacancies in the presence of secondary phases was observed when compared with the phase-pure sample, as shown by the XPS analysis. Deeper insights were provided into the valence band spectra by first-principles studies. This work shows that phase purity may not be the singular condition for enhancing functional properties, and fine-tuning the presence of secondary phases and oxygen vacancies may be the way forward. The ferroelectric polarisation in one of the samples exhibits a notably higher value when using chemical solution deposition methods, making it a promising candidate for memory devices.

Large geometric polarization and magnetic behavior in the multiferroic quasi-2D SrNiF4 fluoride

In the last decades, multifunctional single-crystals that show multiferroic and magnetoelectric responses have attracted considerable attention due to the potential applications and physical phenomena involved in the entanglement of the ferroic orders. This paper explores the structural, ferroelectric, and magnetic properties of the unexplored layered SrNiF4 fluoride compound. We show that, in terms of the vibrational phonon modes, this fluoride compound shows a tangible ferroelectric behavior with an Ps = 14.8 μC cm−2 standing as the largest among its family. Besides, based on our findings such ferroelectric polarization presents a geometric origin that is strongly entangled with the octahedral rotations within the Γ2− phonon mode and enhanced by the structure’s Γ1+ mode. We also observed that the spontaneous polarization is coupled to the noncollinear antiferromagnetic ordering in the structure allowing a switching of the weak antiferromagnetic component when the polarization is reversed.

An Emergent Quadruple Phase Ensemble in Doped Bismuth Ferrite Thin Films Through Site and Strain Engineering

AbstractIn ferroic materials, giant susceptibilities can be realized at artificially constructed phase boundaries through deterministic manipulation of the order parameter. Here, emergent ferroelectric structural phase evolution behavior is demonstrated through a synergistic combination of A‐site doping and strain engineering. Using chemical solution deposition derived (001)‐oriented Sm‐substituted bismuth ferrite (Bi1‐xSmxFeO3) films as a prototypical system, a morphotropic phase boundary comprising a coexistence of four distinct crystallographic phases is uncovered. These ferroelectric, polar, and nonpolar phases form a nanoscale mixture without the presence of crystallographically hard boundaries. The system thus possesses the ability to show both polarization rotation and extension, effectively releasing the polarization from its crystallographic constraint. Consequently, both robust ferroelectric properties and giant electromechanical responses are obtained. For instance, the optimized composition with x = 0.14 has a remnant polarization of 2Pr = 103 µC cm−2 and electromechanical response 175% that of undoped BFO. These findings showcase the tremendous potential of synthetic phase boundaries, particularly in the context of lead‐free functional multiferroics.

Multiferroic kinks and spin-flop transition in Ni2InSbO6 from first principles

Magnetoelectric multiferroics are key materials for next-generation spintronic devices due to their entangled magnetic and ferroelectric properties. Spiral multiferroics possess ferroelectric polarization and are particularly promising for electric control of magnetism and magnetic control of ferroelectricity. In this work, we uncover long-period incommensurate states characterized by unique multiferroic kinks in corundum nickelate Ni2InSbO6, a member of a promising family of polar magnets. Utilizing a 2-orbital S = 1 model, we derive formulas for Heisenberg and anisotropic magnetic exchanges and magnetically-induced polarization, enabling their calculations from first principles. We use these parameters in Monte Carlo and Landau theory-based calculations to reproduce experimentally observed magnetic structures and polarization dependence on the magnetic field. We predict magnetic phase transitions between flat spiral, conical spiral, canted antiferromagnetic and ferromagnetic states under increasing magnetic fields. Kinks in the spiral phases repel each other through a Yukawa-like potential arising from exchange of massive magnons. We also find that suitably directed electric fields can be used to stabilize the ferromagnetic and spiral states. The findings open a new pathway to predictive first-principles modelling of multiferroics and will inspire experiments and technological applications based on multiferroic kinks.

Ferroelectric Order in the Chiral Coordination Polymers [Ln2(L*)2(ox)2(H2O)2] with Ln=Gd3+ or Dy3+, L*=((S, S)‐1,3‐bis(1‐Carboxylethyl)imidazolium and Ox=Oxalate.

AbstractWe evidence the ferroelectricity of two isostructural magnetic coordination networks obtained from a chiral imidazolium dicarboxylate salt ((S, S)‐1,3‐bis(1‐carboxylethyl)imidazolium or [HL*]) and Gd3+ or Dy3+ ions in presence of oxalic acid (H2ox). The two compounds exhibit a chiral structure P1 and ferroelectric properties. The crystallographic study shows that the Dy based‐compound is isostructural to the Gd analog. The non‐centrosymmetry of the two samples was further checked by means of nonlinear optical spectroscopy. The room temperature ferroelectric character of the compounds has been investigated through by an original method, derived from that used for thin films, made possible by preparing the sample as thin slices of resin containing inclusions of the coordination compounds.

Wide working temperature range and large electrocaloric effect in BaTiO3 based ceramics achieved by regulating phase boundaries through a compensatory ion co-doping strategy

Electrocaloric refrigeration shows the merits of environmental safeguarding, large efficiency, easy combination, and miniaturization as a novel solid-state refrigeration technique. In this paper, Sn4+ is doped into the B site of BLNT ceramics. By adjusting the doping content, the T-C phase transition peak was successfully shifted to room temperature and promoted the formation of relaxor ferroelectrics, resulting in a wider operating temperature range (Tspan) and improved adiabatic temperature change (ΔT). A comprehensive study was conducted on the crystal structure, surface morphology, dielectric properties, ferroelectricity, and electrical properties of BLNTS ceramics with varying levels of Sn4+ doping. Wherein, when the doping amount is 5Sn, a maximum adiabatic temperature change value (ΔTmax) of 1.14 K was obtained, and the temperature span (Tspan) reached 45 °C (Tspan is defined as ΔT ≥ 80 % ΔTmax). This work proposes a high-performance environmentally friendly electrocaloric effect (ECE) material suitable for solid-state cooling applications.

Quantitative Raman and x-ray photoelectron spectroscopy of mixed-phase indium selenide films

Indium selenide is a polymorphous material system that has attracted considerable attention due to the outstanding electronic, optical, ferroelectric, and antiferroelectric properties of its various crystalline phases; however, this polymorphism adds a layer of complexity to the analysis of Raman and x-ray photoelectron (XPS) data of these materials. In this report, a method of quantitative analysis of combined Raman and XPS data is developed to determine the stoichiometry of indium selenide thin films, as well as the phase fraction of β-In2Se3, γ-In2Se3, and κ-In2Se3 within the films. A 13:1 ratio of the indium to selenium sensitivity factors (σIn/σSe = 13) was found to yield the most accurate stoichiometry results. Further structural characterization of the κ-In2Se3 film was performed and points to its existence in these films as a distinct phase, rather than strained γ-In2Se3.

Exploring tungsten-oxygen vacancy synergy: Impact on leakage characteristics in Hf0.5Zr0.5O2 ferroelectric thin films

The recent discovery of ferroelectric properties in HfO2 has sparked significant interest in the fields of nonvolatile memory and neuromorphic computing. Yet, as device scaling approaches sub-nanometer dimensions, leakage currents present a formidable challenge. While tungsten (W) electrodes are favored over traditional TiN electrodes for their superior strain and interface engineering capabilities, they are significantly hampered by leakage issues. In this study, we elucidate a positive feedback mechanism attributable to W electrodes that exacerbates oxygen vacancy defects, as evidenced by density functional theory computations. Specifically, intrinsic oxygen vacancies facilitate the diffusion of W, which, in turn, lowers the formation energy of additional oxygen vacancies. This cascade effect introduces extra defect energy levels, thereby compromising the leakage characteristics of the device. We introduce a pre-annealing method to impede W diffusion, diminishing oxygen vacancy concentration by 5%. This reduction significantly curtails leakage currents by an order of magnitude. Our findings provide a foundational understanding for developing effective leakage suppression strategies in ferroelectric devices.

Electrical and Ferroelectric Properties of Strontium Doped Lead-Free BCZT Ceramics

Herein, we synthesized Ba0.9-xCa0.1SrxTi0.8Zr0.2O3 (x = 0.05, 0.1, 0.15, 0.2) ceramic samples by employing a solid-state reaction technique. The variation of dielectric constant is studied concerning temperature in the range 1 kHz to 1 MHz frequency. Variation of dielectric constant ( εr ) with temperature reveals that charge carrier dispersion pushes the transition temperature towards higher frequency. Impedance analysis reveals that the maximum value of the imaginary part of impedance i.e., Z″ maxima, increases in all samples except for x = 0.05, which shows the opposite behaviour. This behaviour is due to the calcium (Ca2+) substitution at the titanium (Ti4+)-site at low doping concentration of Sr2+ ions. Nyquist plots show the presence of a single semi-circular arc, indicating the contribution of resistance and capacitance through grain boundary. PE hysteresis loops reveal that the values of saturation polarization ( Ps ) decrease with increasing Sr-doping, from 10.989 μC cm−2 to 6.586 μC cm−2, whereas the remnant polarization ( Pr ) shows variable values with increasing Sr-doping.

Tunable ferroelectricity of group Ⅳ–Ⅵ nanowires under composition modulation

Low dimensional ferroelectrics are anticipated to play a dominant role in micro/nano-electromechanical field. However, as their intrinsic size decreasing to one-dimension (1D), their ferroelectric polarization will weaken or even disappear, which severely limiting the further development of these promising materials. Therefore, it is of great significance to design one-dimensional ferroelectric materials with high-performance. In this work, first-principles calculations are employed to investigate the ferroelectricity and atomic configuration of MX (MX, M = Ge, Sn; X = S, Se) nanowires with composition tuning. Their ferroelectric characteristics, including spontaneous polarization Ps, transition barrier TL and TQ, Curie temperature Tc, as well as their stabilities, electronic structures, and transformation modes were systematically investigated. The findings indicate that their stability and forming tendency are strongly correlated with the bonding type. Moreover, all nine nanowires retained nanowires exhibit intrinsic 1D ferroelectrics with the maximal Ps of 6.40×10−10C/m for GeS nanowire and the minimum Ps of 3.95×10−10C/m for SnSe nanowire. The obtained calculation results indicate that the ferroelectric properties can be tuned by alteration of composition, which holds significant implications for the design and performance enhancement of 1D ferroelectric materials.

The evolution of 2D vdW ferroelectric materials: Theoretical prediction, experiment confirmation, applications

Since J. Valasek first discovered ferroelectric materials in 1920, researchers have been exploring continuously in various fields through theory and experiments. With the rapid development of the computing technology, energy efficiency and size requirements of semiconductor devices are becoming increasingly demanding. However, the conventional ferroelectric materials, which have been limited by physical size restrictions, can no longer satisfy the above requirements. Two-dimensional (2D) ferroelectric materials can effectively overcome the size limitation of traditional ferroelectrics due to the weak van der Waals force between layers, which is easy to thin while retaining their own unique properties. Currently, a small number of 2D materials have been proved to be ferroelectric properties by experiments and have shown great application potential in nanoscale electrical and optoelectronic devices, expected to become the leaders of next-generation computing. In this review, the current 2D ferroelectric materials are summarized and discussed in detail from seven aspects: theoretical prediction, fabrication methods, ferroelectric characterization methods, principles of typical 2D ferroelectrics, optimization methods of ferroelectric performance, application, and challenges. Finally, the development of 2D ferroelectric materials looks into the future.

Recent progresses in transmission electron microscopy studies of two-dimensional ferroelectrics

The rich potential of two-dimensional materials endows them with superior properties suitable for a wide range of applications, thereby attracting substantial interest across various fields. The ongoing trend towards device miniaturization aligns with the development of materials at progressively smaller scales, aiming to achieve higher integration density in electronics. In the realm of nano-scaling ferroelectric phenomena, numerous new two-dimensional ferroelectric materials have been predicted theoretically and subsequently validated through experimental confirmation. However, the capabilities of conventional tools, such as electrical measurements, are limited in providing a comprehensive investigation into the intrinsic origins of ferroelectricity and its interactions with structural factors. These factors include stacking, doping, functionalization, and defects. Consequently, the progress of potential applications, such as high-density memory devices, energy conversion systems, sensing technologies, catalysis, and more, is impeded. In this paper, we present a review of recent research that employs advanced transmission electron microscopy (TEM) techniques for the direct visualization and analysis of ferroelectric domains, domain walls, and other crucial features at the atomic level within two-dimensional materials. We discuss the essential interplay between structural characteristics and ferroelectric properties on the nanoscale, which facilitates understanding of the complex relationships governing their behavior. By doing so, we aim to pave the way for future innovative applications in this field.

A comprehensive study of ferroelectric, dielectric and optical properties of europium-doped SBD metal- organic framework

The synthesis of Europium-doped Strontium based benzene dicarboxylate dimethylformamide metal–organic framework- Eu([Sr(μ-BDC)(DMF)])- with short form as Eu:SBD@MOF was carried out using the solvothermal method. The investigation involved characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), CHN analysis, and energy-dispersive X-ray (EDX) elemental analysis. The results confirmed the formation of metal–organic crystals in the framework. The XRD characterization shows good alignment with the simulated pattern of SBD. The experimental absorption spectrum displays distinct transitions of the Eu (III) ion alongside transitions of the ligands. Calculations of line strengths for all observed transitions have been conducted. The Judd-Ofelt theory has been employed to determine intensity parameters, transition probabilities, branching ratios, and radiative lifetimes for the Eu: SBD@MOF. These JO parameters further aid in calculating various excited state properties. When excited by ultraviolet and visible photons, the complex exhibits emission in the red region respectively. The crystal’s dielectric loss and dielectric constant were investigated for their frequency dependence. It was observed that by virtue of DMF, a molecule linked to the crystal, a synthesized MOF exhibits a good dielectric characteristic and when the temperature is raised to 558 K, the dielectric constant drops sharply as DMF molecule could not stand after this temperature. Further ferroelectric studies reveal that the Eu: SBD@MOF has maximum polarization of 0.27 C/cm2 which is greater than Rochelle salt and other MOF’s. Exploring the broadband dielectric response of metal–organic frameworks (MOFs) open up new avenues in research, potentially leading to innovative applications in smart optoelectronics, terahertz sensors, high-speed telecommunications, and microelectronics.