Ferroelectric Curie Temperature Research Articles

Electrospun Ba(Ti0.80 Zr0.20)O3-0.5(Ba0.70Ca0.30)TiO3-CoFe2O4 multiferroic hybrid nanofiber for the localized piezocatalytic degradation of organic pollutants

Multiferroic Ba(Ti[Formula: see text]Zr[Formula: see text])O3-0.5(Ba[Formula: see text]Ca[Formula: see text])TiO3 (BCTZ)@CoFe2O4 (CFO) hybrid nanofibers (NFs) were fabricated by a sol–gel electrospinning. The perovskite structure of ferroelectric BCTZ and the spinel structure of ferromagnetic CFO coexist and are homogeneously distributed, and their interface along the perovskite [110] zone axis was directly observed. The indirect magnetoelectric (ME) coupling effect was observed from the magnetization versus temperature (M–T) curves, demonstrating a distinct singularity on the dM/dT curve near the ferroelectric Curie temperature ([Formula: see text][Formula: see text]) of 387 K. The piezocatalytic rate of BCTZ@CFO multiferroic hybrid NF (2.6 × 10[Formula: see text]min[Formula: see text]) is higher than NP (1.9 × 10[Formula: see text]min[Formula: see text]) because the piezoelectricity of the one-dimensional (1D) multiferroic NF is higher than that of NPs, beneficial for the mechanical vibration-induced localized built-in electric fields for piezocatalysis under ultrasound.

Investigation of the temperature-dependent functioning of BiFeO3 as a ferroelectric material through X-ray diffraction analysis

In recent years, Bismuth Ferrite (BiFeO3, BFO) has emerged as a promising multiferroic material due to its high antiferromagnetic Néel temperature (TN ~ 623–643 K) and ferroelectric Curie temperature (TC ~ 1083–1103 K). These properties make BFO a strong candidate for exhibiting a magnetoelectric effect even at room temperature. Understanding the temperature-dependent ferroelectric behavior of BFO is crucial for optimizing its performance in applications where stable ferroelectric behavior at operational temperatures is essential for enhancing device efficiency, stability, and functionality. This study investigates the impact of temperature on the crystallographic characteristics (unit cell type, bond lengths, and dimensions) and ferroelectric performance of BFO. X-ray diffraction and electrical hysteresis measurements confirm the presence of a ferroelectric phase with a rhombohedral R3c structure, along with two phase transitions: the first around 600 K from ferroelectric to paraelectric, and the second near 1050 K from paraelectric back to ferroelectric.

Structural, Magnetic, and Dielectric Properties of Laser-Ablated CoFe2O4/BaTiO3 Bilayers Deposited over Highly Doped Si(100).

Laser ablation was used to successfully fabricate multiferroic bilayer thin films, composed of BaTiO3 (BTO) and CoFe2O4 (CFO), on highly doped (100) Si substrates. This study investigates the influence of BaTiO3 layer thickness (50-220 nm) on the films' structural, magnetic, and dielectric properties. The dense, polycrystalline films exhibited a tetragonal BaTiO3 phase and a cubic spinel CoFe2O4 layer. Structural analysis revealed compression of the CoFe2O4 unit cell along the growth direction, while the BaTiO3 layer showed a tetragonal distortion, more pronounced in thinner BTO layers. These strain effects, attributed to the mechanical interaction between both layers, induced strain-dependent wasp-waisted behavior in the films' magnetic hysteresis cycles. The strain effects gradually relaxed with increasing BaTiO3 thickness. Raman spectroscopy and second harmonic generation studies confirmed BTO's non-centrosymmetric ferroelectric structure at room temperature. The displayed dielectric permittivity dispersion was modeled using the Havriliak-Negami function combined with a conductivity term. This analysis yielded relaxation times, DC conductivities, and activation energies. The observed BTO relaxation time behavior, indicative of small-polaron transport, changed significantly at the BTO ferroelectric Curie temperature (Tc), presenting activation energies Eτ in the 0.1-0.3 eV range for T < Tc and Eτ > 0.3 eV for T > Tc. The BTO thickness-dependent Tc behavior exhibited critical exponents ν ~ 0.82 consistent with the 3D random Ising universality class, suggesting local disorder and inhomogeneities in the films. This was attributed to the composite structure of BTO grains, comprising an inner bulk-like structure, a gradient strained layer, and a disordered surface layer. DC conductivity analysis indicated that CoFe2O4 conduction primarily occurred through hopping in octahedral sites. These findings provide crucial insights into the dynamic dielectric behavior of multiferroic bilayer thin films at the nanoscale, enhancing their potential for application in emerging Si electronics-compatible magneto-electric technologies.

Theoretical Study of the Multiferroic Properties of Pure and Ion-Doped Pb5M3F19, M = Fe, Cr, Al.

In a first theoretical investigation of the multiferroic properties of Pb5Fe3F19 (PFF) and Pb5Cr3F19 (PCF), we analyze their magnetic, ferroelectric, and dielectric characteristics as functions of temperature, magnetic field, and ion doping concentration using a microscopic model and Green's function theory. The temperature-dependent polarization in PFF and PCF shows a distinctive kink at the magnetic Neel temperature TN, which vanishes when an external magnetic field is applied, indicating the multiferroic behavior of these two compounds. Ion doping effectively tunes the properties of PFF and PCF. In PFF, Cr ion doping leads to a decrease in the Neel temperature TN, while Cr and Al ion doping lowers the ferroelectric Curie temperature TC. In the case of PCF, we observe the enhancement of TC by Fe ion doping and the reduction by Al ion doping. The last result coincides well quantitatively with the experimental data. Additionally, the magnetodielectric coefficient of PFF is enhanced with the increasing magnetic field.

Robust Ferrimagnetism and Ferroelectricity in 2D ɛ-Fe2O3 Semiconductor with Ultrahigh Ordering Temperature.

2D single-phase multiferroic materials with the coexistence of electric and spin polarization offer a tantalizing potential for high-density multilevel data storage. One of the current limitations for application is the scarcity of the materials, especially those combine ferromagnetism and ferroelectricity at high temperatures. Here, robust ferrimagnetism and ferroelectricity in 2D ɛ-Fe2O3 samples with both single-crystalline and polycrystalline form are demonstrated. Interestingly, the polycrystalline nanosheets also exhibit easily switchable ferroelectric polarizations comparable to that of single crystals. The existence of grain boundary does not hinder the switching and retention of ferroelectric polarization. Furthermore, the ɛ-Fe2O3 nanosheets show ferrimagnetic and ferroelectric Curie temperatures up to 800K, which reaches record highs in 2D single-phase multiferroic materials. This work provides important progress in the exploration of 2D high-temperature single-phase multiferroics for potentially compact high-temperature information nanodevices.

Electrocaloric effect with enhanced temperature stability in an interfacial polarization controlled ferroelectric laminated composite

Research on zero-emission lead-free ferroelectric materials is fascinating in the field of solid-state refrigeration due to the observed large electrocaloric phenomenon. However, one of the challenges involved is realizing a large adiabatic temperature change ( ΔT ) over a wide temperature span. Here, a laminated ferroelectric structure with layers, having successive phase transitions covering room temperature, is proposed to overcome this problem. BaTi1−x Sn x O3 with x = 0.08, 0.12, and 0.15 compositions exhibiting the required ferroelectric Curie temperatures was chosen for the component layers. The designed interfacial polarization engineered laminated structure with 0.15/0.08/0.12 compositional layers yielded a value of adiabatic temperature change ΔT max ⩾ 0.6 °C by an indirect method using Maxwell’s thermodynamic equations over a wide temperature span (30 °C–85 °C). The observed results are correlated to the interrelated cumulative effect of reduced interfacial polarization, homogeneous electric field distribution, field-induced phase transitions, and enhanced domain switching, which are the manifestation of the designed laminated geometry.

Effect of excess Bi2O3/PbO on the structural and electrical properties of ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 ceramics

The ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3:x(Bi2O3/PbO) [x = 0, 1, and 2 wt%] ceramics were synthesized via solid-state sintering technique. The impact of excess addition on structural and electrical properties was investigated. PXRD results confirmed the diffusion of excess addition in the 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 (BNPZT) lattice, exhibiting the perovskite structure with major rhombohedral (R3c) and minor tetragonal (P4mm) phases. The microstructure of the samples exhibits average grain size distribution (<8 μm). The temperature and frequency-dependent dielectric measurement revealed the relaxor-like ferroelectric behaviour and curie temperature (Tc∼290 °C) observed in BNPZT:1 Pb ceramics. The improved remnant polarization (Pr∼23.47 μC/cm2) and coercive field (Ec∼16.13 kV/cm) were obtained in BNPZT:2 Pb ceramics. The enhanced piezoelectric charge coefficient (d33∼ 496 pC/N) and maximum strain (Smax∼0.12 %) were obtained for BNPZT. The least asymmetric factor (γs) illustrates the lower concentration of inherent defects in BNPZT:1(Bi/Pb) ceramics. This study provides insight into microstructural and electrical properties tuning and paves the way for designing piezoelectric materials.

Room temperature ferroelectricity and ferromagnetism in Ni-substituted Bi5Ti3FeO15

Aurivillius-type bismuth layer-structured ferroelectric (BLSF) Bi5Ti3FeO15 (BTF) has recently attracted considerable attention as a typical multiferroic material because ferroelectric and magnetic orders coexist, but bulk BTF exhibits antiferromagnetic (AFM) orders and negligible intrinsic magnetoelectric (ME) coupling effects. In this study, nickel-substituted Bi5Ti3FeO15 (Bi5Ti3Fe0.5Ni0.5O15, abbreviated as BTF-Ni) was synthesized using a solid-state reaction method to explore and enhance both the magnetic and ferroelectric properties of BTF. Polarization-electric field P-E loops indicate that the BTF-Ni exhibits considerable maximum polarization P m of 11.9 μC/cm2 and remnant polarization P r of 5.8 μC/cm2, but still keeps a very high ferroelectric Curie temperature (FE T c) of 1029 K, which are much superior to those of pure BTF. Moreover, magnetization-magnetic field M-H loops indicate that BTF-Ni exhibits significant ferromagnetic properties with a large saturation magnetization M s of 60 memu/g, low coercive field H c of 31 Oe at room temperature, and a high ferromagnetic Curie temperature (FM T c) of 698 K, whereas pure BTF has an antiferromagnetic Néel temperature (T N) of 80 K. Our work suggests that nickel-substituted BTF is a potential room-temperature magnetoelectric multiferroic material.

High-precision and flexible magnetoelectric sensor operated at 25–330 °C

It is a big challenge to in situ monitor the health status of high-temperature magnetic equipment such as electric motors and generators since it is difficult to achieve a high-temperature magnetoelectric sensor. Here, the Pb(Zr0.52Ti0.48)O3 film with a ferroelectric Curie temperature of 400 °C and the Metglas alloy slice with a magnetic Curie temperature of 430 °C were combined by using a high-temperature inorganic glue to achieve a high-temperature magnetoelectric sensor. The magnetoelectric coefficient αE of the flexible sensor is as high as 104 V/(cm Oe) at 25 °C, 63.6 V/(cm Oe) at 200 °C, and 39.7 V/(cm Oe) at 330 °C. Besides, the magnetic sensor has a detection accuracy of ∼0.3 nT at 25–330 °C. Most importantly, the high-temperature sensor is flexible, high precision, low cost, light weight, and low power consumption simultaneously.

Perspectives on MXene-PZT based ferroelectric memristor in computation in memory applications

Lead zirconate titanate (PZT) is the promising candidate in advanced ferroelectric memory application due to its excellent piezoelectricity, ferroelectricity, pyroelectricity, non-linear dielectric behavior, multiferroic properties, high ferroelectric Curie temperature, and extremely strong stability. It has gained attention in the field beyond von-Neumann computing, which inspires the development of computation in memory applications. Various structures of the ferroelectric memristive device, including ferroelectric field effect transistor, tunnel junctions, nonvolatile memory, and capacitor, based on PZT have been proposed for the realization of computation in memory application. On the other hand, unique designs realize the performance enhancement of PZT ferroelectric memristive devices, i.e., the insertion of 2D material MXene. This perspective further points out some of the challenges that MXene-PZT based ferroelectric memristive devices encounter in reality and finally give our viewpoint on possible developments toward computation in memory in a neuromorphic platform.

Solid solutions of lithium niobate and lithium tantalate: crystal growth and the ferroelectric transition

Specific heat capacity measurements by differential scanning calorimetry (DSC) of single crystals of solid solutions of LiNbO3 and LiTaO3 are reported and compared with corresponding ab initio calculations, with the aim to investigate the variation of the ferroelectric Curie temperature as a function of composition. For this purpose, single crystals of these solid solutions were grown with Czochralski pulling along the c-axis. Elemental composition of Nb and Ta was investigated using XRF analysis, and small samples with homogeneous and well known composition were used for the DSC measurements. We observed that the ferroelectric Curie temperature decreases linearly with increasing Ta concentration in the LiNb 1 − x Ta x O3 solid solution crystals. Furthermore, the ferroelectric transition width of a mixed crystal appears to be smaller, as compared to pure LiTaO3.

On phase transitions in the NaH3(SeO3)2 crystal

Experimental studies of elastic, anelastic, dielectric, polarization and thermal properties of sodium trihydrogen selenite NaN3(SeO3)2 crystal in the temperature range of 5–210 K. Above the ferroelectric Curie temperature, an intermediate ferroelastic β′-phase was detected between the paraelectric α-phase and the ferroelectric β-phase. The phase transition from α- to β′–phase at 195 K is classified as a first-order transition, accompanied by the occurrence of spontaneous deformation x 6s. When the temperature decreases, in addition to the previously known transition from the β-phase to the γ-phase, a new phase transition from the γ-phase to the nonpolar η-phase at a temperature of 112.4 K was detected.

Observation of relaxor ferroelectric behavior and energy storage performances in Sr1.25Bi2.75Nb1.25Ti1.75O12 aurivillius ceramic synthesized by molten salt method

In this work, a novel three-layer Aurivillius phase Sr1.25Bi2.75Nb1.25Ti1.75O12 was synthesized using the molten salt method, and the crystal structure, morphology, electrical, optical, and energy storage properties were systematically investigated. XRD data supported by the Le Bail refinement technique shows that the product adopts a B2cb orthorhombic crystal structure. FTIR analysis indicates that the Nb5+/Ti4+ ions occupy the perovskite B-site and suggests that the two local environments on the B-site as Ti–O–Ti and Nb–O–Nb linkages. Ferroelectric ordering takes place below the ferroelectric Curie temperature, Tc of 100 °C, which is also revealed by the open ferroelectric hysteresis loops. The characteristic of relaxor-ferroelectric behavior is characterized by the broadened phase transition peaks and the frequency-dispersive behavior. The energy storage density of 12.69 mJ/cm3 with an energy efficiency (η) of 42.1% was obtained in the ceramic sample at applied electric field of 75 kV/cm and room temperature. These findings will provide an important contribution to further research to explore new Aurivillius compounds as potential energy storage materials.

Improper ferroelectricity in ultrathin hexagonal ferrites films

Suppression of ferroelectricity in ultrathin films of improper ferroelectric hexagonal ferrites or manganites has been attributed to the effect of interfacial clamping; however, the quantitative understanding and related phenomenological model are still lacking. In this work, we report on the paraelectric-to-ferroelectric phase transition of epitaxial h-ScFeO3 films with different thicknesses through in situ reflection high-energy electron diffraction. Based on the interfacial clamping model and the Landau theory, we show that the thickness-dependence of the ferroelectric Curie temperature can be understood in terms of the characteristic length of an interfacial clamping layer and the bulk Curie temperature. Furthermore, we found that the critical thickness of improper ferroelectricity is proportional to the characteristic length of the interfacial clamping layer. These results reveal the essential role of mechanical clamping from interface on the improper ferroelectricity of hexagonal ferrites or manganites and could serve as the guidance to achieve robust improper ferroelectricity in ultrathin films.

Proton transfer in layered hydrogen-bonded system γ-MOOH (M = Al, Sc): Robust bi-mode ferroelectricity and 1D superionic conductivity

Layered γ-MOOH, such as synthetic boehmite γ-AlOOH and γ-ScOOH, has been explored for various applications since 1950s. In this paper, based on first-principles calculations, we show the evidence of two proton transfer modes in their hydrogen-bonded network that give rise to extraordinary properties: (1) they, respectively, result in two distinct types of ferroelectricity with different switching mechanisms and polarizations, while the exhibiting mode under an electric field depends on various factors, including the field intensity and direction, the existence of vacancies, and temperature; and (2) the combination of two modes can lead to ultra-high proton conductivity along 1D channels. Their proton migration barriers ensure high ferroelectric Curie temperature, while still much lower compared with current proton conductors, giving rise to 1D superionicity with unprecedented protonic conductivity over 24 mS/cm. Those light weight nontoxic layered materials with high polarizations, Curie temperature, and ultra-high protonic conductivity should provide vast opportunities for various applications.

Phase evolution and enhanced room temperature piezoelectric properties response of lead-free Ru-doped BaTiO3 ceramic

Abstract Recent years have witnessed considerable work on the development of lead-free piezoelectric ceramic materials and their structure–property correlations. The development of piezo response is a strong function of phase evolution in these materials. In this work, we report the effect of Ru doping and consequent phase evolution on the maximization of piezoelectric response of polycrystalline lead-free barium titanate, depicted as Ba(RuxTi1-x)O3 (BRT). The samples were prepared in a narrow compositional range of 0 ≤ x ≤ 0.03 using the conventional solid-state reaction method. Ru doping increases the leakage current of BaTiO3 samples attributed to increased oxygen vacancy concentration due to substitution of Ti4+ by Ru3+. Detailed structural analysis reveals that samples exhibiting coexistence of tetragonal (space group: P4mm) and orthorhombic (space group: Amm2) structured phases near room temperature reveal relatively enhanced piezoelectric properties. The BRT sample with Ru content of 2 mol% yields a maximum longitudinal piezoelectric coefficient, d33 of ∼269 pC/N, a high strain value of 0.16% with a large remnant polarization of ∼19 µC/cm2 and a coercive field of 5.8 kV/cm. We propose that the ‘4d’ orbital of Ruthenium plays a crucial role in improving the functional properties and in decreasing the ferroelectric Curie temperature. Our work provides clues into tailoring the phase evolution for designing lead-free piezoelectric materials with enhanced piezoelectric properties.

Coexistence of ferroelectricity and ferromagnetism in hex-GeS nanowires.

The existence of one-dimensional (1D) ferroelectricity and ferromagnetism provides an opportunity to expand the field of research in low-dimensional magnetoelectric and multiferroics and explore the future development of high-performance nanometer devices. Here, we predict a novel 1D ferroelectric hex-GeS nanowire with coexisting ferromagnetism. The electric polarization comes from the atomic displacements between Ge and S atoms, and it exhibits a far-higher than room temperature ferroelectric Curie temperature TEc = 830 K. The ferromagnetism, stemming from the Stoner instability, can be tuned by hole doping and maintained over a wide range of hole concentrations. Additionally, an indirect-direct-indirect band gap transition can be achieved via strain engineering and the bonding nature of the near-band-edge electronic orbitals revealed this transition mechanism. These results offer a platform to investigate 1D ferroelectric and ferromagnetic systems, and the presented hex-GeS nanowire demonstrates the potential for high-performance electronic and spintronic applications.

Evaluation of dielectric, energy storage and multiferroic properties of PrFeO3-PbTiO3 solid solutions

This work promotes the room temperature energy storage properties of the multiferroics. In this approach, impacts of PrFeO3 doping on PT-based solid solutions (Pb[Formula: see text][Formula: see text]Pr[Formula: see text]Ti[Formula: see text][Formula: see text]Fe[Formula: see text]O3, [Formula: see text] = 0.21, 0.22, 0.23, 0.24, 0.25 and 0.26) have been explored. X-ray diffraction (XRD) patterns were used to estimate the crystallographic parameters, confirming the single phase tetragonal structure. The ferroelectric Curie temperature ([Formula: see text][Formula: see text]) is observed to drop from 410 K to below room temperature as the Pr concentration increases. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The sample [Formula: see text] = 0.24 achieved the maximum value of energy storage density of 362.25 mJ/cm3 with the efficiency of 40.5%. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The validity of magnetoelectric coupling in all samples was confirmed by magneto-dielectric studies and found that the sample [Formula: see text] = 0.24 shows the maximum response with the coupling coefficient ([Formula: see text]) = 15.54 g2/emu2.

Low-temperature preparation and electrical properties of CaBi2Nb2O9 piezoelectric ceramic by addition of B2O3

CaBi2Nb2O9 ceramics were fabricated via the solid-state reaction method by the addition of B2O3 as a sintering aid at lower sintering temperatures than that prepared without B2O3. Ferroelectricity, piezoelectricity, and resistivity can be still greatly enhanced when the sintering temperature is decreased from 1075 °C for CaBi2Nb2O9 to 975 °C for CaBi2Nb2O9–0.25 wt. % B2O3. The high resistivity and weak c-axis texture ensure that the ceramics can be fully polarized in a high enough electric field. The increased spontaneous ferroelectric and remanent polarization result in a significant enhancement in the piezoelectric properties of CaBi2Nb2O9–0.25 wt. % B2O3. The sample sintered at 975 °C possesses a high piezoelectric coefficient d33 of ∼15.0 pC/N and resistivity of 1.4 × 106 Ω cm (at 600 °C) along with a high ferroelectric Curie temperature TC of ∼954 °C. This work is beneficial for the preparation of high-temperature piezoelectric ceramics with excellent electrical properties at a low sintering temperature.

Evidence of a glassy magnetic transition driven by structural disorder in BiFeO3 nanoparticles

Important effects appear in low and high temperature magnetometry of multiferroic BiFeO3 (BFO) nanoparticles as sizes are reduced from 105 nm to 18 nm. In these particles, a magnetic transition appears close to 200 K probably associated with a spin reorientation which is absent in bigger particles. At higher temperatures and up to the bulk ferroelectric Curie temperature (1000 K), two additional magnetic transitions can be identified. Around TN 600 K, a size-dependent magnetic transition appears, associated with an antiferromagnetic transition. A model based on atomic vibration instability can describe the variation of TN with nanoparticle size. Furthermore, for certain sizes, the properties are dominated by the glassy state arising from the disorder produced by the formation of a core-shell structure. This implies that the magnetic behavior of nanoparticles is strongly affected by their crystal structure close to the transition temperature. The structural disorder which couples to the magnetic properties add control to the magnetic and ferroelectric properties of BFO nanoparticles.