Ferroelectric Transition Temperature Research Articles

Efek Pendoping Nd3+ Pada Senyawa BaBi2-xNdxNb2O9 Terhadap Struktur, Sifat Dielektrik Dan Optik

The Aurivillius compound with formula BaBi2-xNdxNb2O9 (x = 0.05, 0.1, 0.2, and 0.4) has been successfully synthesized using the molten salt method, showing potential as a ferroelectric material. The impact of Nd3+ substitution on the structure, morphology, dielectric, and optical properties has been systematically analyzed. XRD data refinement confirms that BaBi2-xNdxNb2O9 (BBNN) exhibits an orthorhombic structure with an A21am space group. Anisotropic plate-like grains were observed across all samples, decreasing their size as Nd3+ content increases. The ferroelectric transition temperature (Tc) decreases due to structural distortion caused by the reduction of the lone pair 6s2 electron effect of Bi3+ when substituted with Nd3+. Moreover, this structural distortion also contributes to an increase in bandgap energy (Eg). The diffuse ferroelectric phase transition is characterized by a broadened Tc peak induced by Nd3+ substitution due to increased cationic disruption in the bismuth layers. The ferroelectric phase with a lower and broader Tc suggests that the x = 0.4 sample has the potential for electrocaloric applications.

Controlled Vapor-Liquid-Solid Growth of Long and Remarkably Thin Pb1-xSnxTe Nanowires with Strain-Tunable Ferroelectric Phase Transition.

The Pb1-xSnxTe family of compounds possess a wide range of intriguing and useful physical properties, including topologically protected surface states, robust ferroelectricity, remarkable thermoelectric properties, and potential topological superconductivity. Compared to bulk crystals, one-dimensional (1D) nanowires (NWs) offer a unique platform to enhance the functional properties and enable new capabilities, e.g., to realize 1D Majorana zero modes for quantum computations. However, it has been challenging to achieve controlled synthesis of ultrathin Pb1-xSnxTe (0 ≤ x ≤ 1) nanowires in the truly 1D region. In this work, we report on a Au-catalyzed vapor-liquid-solid (VLS) growth of remarkably thin (20-30 nm) and sufficiently long (several to tens of micrometers) Pb1-xSnxTe nanowires of high single-crystalline quality in a controlled fashion. This controlled growth was achieved by enhancing the incorporation of Te into the Au catalyst particle to facilitate the precipitation of the Sn/Pb species and suppress the enlargement of the particle, which we identified as a major challenge for the growth of ultrathin nanowires. Our growth strategy can be easily extended to other compound and alloy nanowires, where the constituent elements have different incorporation rates into the catalyst particle. Furthermore, the growth of thin Pb1-xSnxTe nanowires enabled strain-dependent electrical transport measurements, which shows an enhancement of electrical resistance and ferroelectric transition temperature induced by uniaxial tensile strain along the nanowire axial direction, consistent with density functional theory calculations of the structural phase stability.

Intrinsic Out-Of-Plane and In-Plane Ferroelectricity in 2D AgCrS2 with High Curie Temperature.

2D ferroelectric materials have attracted extensive research interest due to potential applications in nonvolatile memory, nanoelectronics and optoelectronics. However, the available 2D ferroelectric materials are scarce and most of them are limited by the uncontrollable preparation. Herein, a novel 2D ferroelectric material AgCrS2 is reported that are controllably synthesized in large-scale via salt-assist chemical vapor deposition growth. By tuning the growth temperature from 800 to 900°C, the thickness of AgCrS2 nanosheets can be precisely modulated from 2.1 to 40nm. Structural and nonlinear optical characterizations demonstrate that AgCrS2 nanosheet crystallizes in a non-centrosymmetric structure with high crystallinity and remarkable air stability. As a result, AgCrS2 of various thicknesses display robust ferroelectric polarization in both in-plane (IP) and out-of-plane (OOP)directions with strong intercorrelation and high ferroelectric phase transition temperature (682 K). Theoretical calculations suggest that the ferroelectricity in AgCrS2 originates from the displacement of Ag atoms in AgS4 tetrahedrons, which changes the dipole moment alignment. Moreover, ferroelectric switching is demonstrated in both lateral and vertical AgCrS2 devices, which exhibit exotic nonvolatile memory behavior with distinct high and low resistance states. This study expands the scope of 2D ferroelectric materials and facilitates the ferroelectric-based nonvolatile memory applications.

In-plane distribution of huge local permittivity of KTa1-xNbxO3 estimated from local phase transition temperatures and spatially averaged permittivity.

Potassium tantalate niobate (KTa1-xNbxO3, KTN) single crystals have a very large relative permittivity εr (>104) just above the paraelectric to ferroelectric phase transition temperature (TC). The quadratic electro-optic coefficient and the electro-strictive coefficient are also very large because of their proportionality to εr2. However, the local relative permittivity can easily vary spatially due to the incongruently melting nature of KTN. In this study, we quantitatively estimated the in-plane distribution of the huge local relative permittivity of KTN. First, we measured the spatial distribution of TC using scanning nonlinear dielectric microscopy, then deposited the electrodes and measured the temperature dependence of the spatially averaged permittivity using an LCR meter. Following that, we evaluated the spatial distribution of the huge local permittivity from the combination of the spatial distribution of TC and the spatially averaged permittivity. Finally, we measured the deflection angle of light to confirm the validity of the εr estimation procedure. The maximum error for the estimated permittivity was estimated to be around 3.3%.

Phase transition and polar cluster behavior above Curie temperature in ferroelectric BaTi0.8Zr0.2O3

We study the phase transition behavior of the ferroelectric BaTi0.8Zr0.2O3 in the paraelectric region. The temperature dependencies of thermal, polar, elastic, and dielectric properties indicate the presence of local structures above the paraelectric–ferroelectric transition temperature Tc = 292 K. The non-zero remnant polarization is measured up to a characteristic temperature T* ∼ 350 K, which coincides with the temperature where the dielectric constant deviates from the Curie–Weiss law. Resonant piezoelectric spectroscopy shows that DC field cooling above Tc using fields smaller than the coercive field leads to an elastic response and remnant piezoelectricity below T*, which likely corresponds to the coherence temperature associated with polar nanostructures in ferroelectrics. The observed remnant effect is attributed to the reorientation of polar nanostructures above Tc.

Er2FeCrO6: Emerging efficient nanomaterials for multiferroics

The present work deals with the rare earth Erbium-based double perovskite. The chemical precipitation route was adopted followed by calcination at 700 °C for the synthesis of Er2FeCrO6 (EFCO). The phase identification was performed using Rietveld refinement. Morphological analysis shows the formation of nanoparticles of EFCO having an average size of ∼15 nm. The M − H curve recorded at 10 K shows the weak ferromagnetic nature of the sample. Temperature variation of magnetization illustrates that EFCO nanoparticles undergo ferromagnetic transition at Tc = 14 K. Temperature-dependent P-E studies display ferroelectric behaviour with a ferroelectric transition temperature (TCE = 453 K) which is beyond room temperature. The simultaneous existence of magnetic and electric orders may introduce EFCO as a new multiferroic oxide and a good alternative to the popular compound BiFeO3.

Electric, Dielectric, and Phonon Properties of Cu2OCl2

Investigating the multiferroic properties of , their temperature and magnetic‐field dependencies around the magnetic and ferroelectric phase transition temperatures and are analyzed using a microscopic model and Green's function technique. Near the Neel temperature , a kink in the specific heat and also in the phonon energy and damping due to strong anharmonic spin–phonon interaction is observed. The kink in disappears with increasing magnetic field h. The polarization shows also a small anomaly at and decreases with increasing magnetic field h. This behavior strongly suggests that exhibits multiferroic characteristics. A kink at can be seen in the real part of the dielectric constant , too. It should be noted that demonstrates a significant increase with increasing field strength h below , which is a pronounced magneto‐dielectric effect. These findings qualitatively agree with the experimental data.

Chemical Vapor Deposition Synthesis of Intrinsic High-Temperature Ferroelectric 2D CuCrSe2.

Ultrathin 2D ferroelectrics with high Curie temperature are critical for multifunctional ferroelectric devices. However, the ferroelectric spontaneous polarization is consistently broken by the strong thermal fluctuations at high temperature, resulting in the rare discovery of high-temperature ferroelectricity in 2D materials. Here, a chemical vapor deposition method is reported to synthesize 2D CuCrSe2 nanosheets. The crystal structure is confirmed by scanning transmission electron microscopy characterization. The measured ferroelectric phase transition temperature of ultrathin CuCrSe2 is about ≈800 K. Significantly, the switchable ferroelectric polarization is observed in ≈5.2nm nanosheet. Moreover, the in-plane and out-of-plane ferroelectric response are modulated by different maximum bias voltage. This work provides a new insight into the construction of 2D ferroelectrics with high Curie temperature.

Tuning ferroelectric phase transition temperature by enantiomer fraction

Tuning phase transition temperature is one of the central issues in phase transition materials. Herein, we report a case study of using enantiomer fraction engineering as a promising strategy to tune the Curie temperature (TC) and related properties of ferroelectrics. A series of metal-halide perovskite ferroelectrics (S−3AMP)x(R−3AMP)1−xPbBr4 was synthesized where 3AMP is the 3-(aminomethyl)piperidine divalent cation and enantiomer fraction x varies between 0 and 1 (0 and 1 = enantiomers; 0.5 = racemate). With the change of the enantiomer fraction, the TC, second-harmonic generation intensity, degree of circular polarization of photoluminescence, and photoluminescence intensity of the materials have been tuned. Particularly, when x = 0.70 − 1, a continuously linear tuning of the TC is achieved, showing a tunable temperature range of about 73 K. This strategy provides an effective means and insights for regulating the phase transition temperature and chiroptical properties of functional materials.

Near room temperature hexagonal multiferroic (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics

In this work, h-RFeO3 multiferroic high-entropy ceramics are designed by introducing high-entropy concept with four elements (Yb, Lu, In, Sc) for R site. (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics are prepared by the standard solid-state reaction methods. The samples prepared with precursors were identified to crystalize in the pure hexagonal structure with polar space group (P63cm) at room temperature. By the analysis of the variable XRD patterns, it is speculated that the ferroelectric transition temperature of the sample is above 773 K. Meanwhile, three magnetic anomalies are determined for high-entropy ceramics, which is the antiferromagnetic transition at Néel temperature TÑ280 K, the spin-reorientation temperature TSR∼145 K and the reasonable ferromagnetic-like clusters without long ordering in TN < T < TA (∼397 K). Besides, it is observed that the peak intensity of the pyroelectric current around TN can be tuned by magnetic field, which is indicated the magnetoelectric coupling effect in (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics. These results indicate the ferroelectric and antiferromagnetic orders are coexist in the h-RFeO3 high-entropy ceramics as promising near room temperature multiferroic materials, and it is an effective way to obtain a new type single-phase multiferroic materials.

The effect of cation size on structure and properties of Ba-based tetragonal tungsten bronzes Ba4M2Nb10O30 (M = Na, K or Rb) and Ba4M2Nb8Ti2O30 (M = Ca or Sr).

The second largest family of oxide ferroelectrics, after perovskites, are the tetragonal tungsten bronzes (TTB) with the general formula A24A12C4B12B28O30. Cation disorder in TTBs is known to occur if the size difference between cations is small, but the impact of cation disorder on structure and properties has not yet been extensively addressed. In this study we investigate the effect of the size of the M cation, including cation disorder, on the crystal structure and dielectric properties in the two series Ba4M2Nb10O30 (BMN, A = Na, K and Rb) and Ba4M2Nb8Ti2O30 (BMNT, M = Ca, Sr). Dense and phase pure ceramics in the two series were prepared by a two-step solid state synthesis route. The crystal structures of the materials were characterized by powder X-ray diffraction combined with Rietveld refinement. A close to linear relation between the in-plane lattice parameter (a) and the size of the M-cation were observed. Ba4M2Nb8Ti2O30 was shown to possess cation disorder on the A-sites in line with previous work on Ba4M2Nb10O30. Thermodynamic calculations from density functional theory also indicated a drive for cation disorder in the three BMN compositions. Non-ambient temperature X-ray diffraction revealed contraction of the in-plane (a) and expansion of the out-of-plane (c) lattice parameters at the ferroelectric phase transition for Ba4M2Nb10O30. The ferroelectric transition temperature acquired by dielectric spectroscopy showed a systematically increasing TC with decreasing size of the M-cation within both compositional series studied. The compositional dependence of TC is discussed with respect to the size of the M-cation, cation disorder and the tetragonality, as well as the Ti-content. The relaxor to ferroelectric properties observed by polarization-electric field hysteresis loops are discussed in relation to the relative size of cations on the on A1 and A2 sites and the Ti-content.

Establishment of magneto-electric response in GdFeO3 doped PbTiO3 solid solutions

This work promotes a thorough examination of the magnetic impact on the multiferroicity of the sample. The usual solid-state reaction method was used to synthesis Pb1-xGdxTi1-xFexO3 with x = 0.21, 0.22, and 0.23. XRD analysis showed a pure homogeneous single-phase compound with a tetragonal structure, indicating perfect diffusivity of Gd atoms into the PbTiO3 lattice. All of the samples show clear grain growth between 7.8 and 10.5 μm in the SEM images, proving that they were sintered at the correct temperature. Furthermore, ferroelectric transition temperature reduces from 388 K to below the ambient temperature range as the doping value of Gd grows. The room temperature P-E hysteresis loops indicated that the remnant polarization of the sample drops from 8.66 μC/cm2 to 2.065 μC/cm2 for x = 0.21 to 0.23 sample. Three distinct phenomena supported the ME coupling of all samples. The sample x = 0.21 exhibits the maximum magneto-dielectric response of 2.2 % at 1.2T having highest MDR coupling coefficient value of −1.41g2/emu2. Moreover, the sample x = 0.21 shows the highest shift in magnetization before and after electric poling of about 0.105 emu/g. As a result, the sample x = 0.21 emerges as a viable choice for application in a variety of multifunctional devices.

Molecular Shape, Electronic Factors, and the Ferroelectric Nematic Phase: Investigating the Impact of Structural Modifications.

The synthesis and characterisation of two series of low molar mass mesogens, the (4-nitrophenyl) 2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3.m) and the (3-fluoro-4-nitrophenyl) 2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3F.m), are reported in order to investigate the effect of changing the position of a lateral alkoxy chain from the methoxy-substituted terminal ring to the central phenyl ring in these two series of materials based on RM734. All members of the NT3.m series exhibited a conventional nematic phase, N, which preceded the ferroelectric nematic phase, NF , whereas all the members of the NT3F.m series exhibited direct NF -I transitions except for NT3F.1 which also exhibited an N phase. These materials cannot be described as wedge-shaped, yet their values of the ferroelectric nematic-nematic transition temperature, T , exceed those of the corresponding materials with the lateral alkoxy chain located on the methoxy-substituted terminal ring. In part, this may be attributed to the effect that changing the position of the lateral alkoxy chain has on the electronic properties of these materials, specifically on the electron density associated with the methoxy-substituted terminal aromatic ring. The value of TNI decreased with the addition of a fluorine atom ortho to the nitro group in NT3F.1, however, the opposite behaviour was found when the transition temperatures of the NF phase were compared which are higher for the NT3F.m series. This may reflect a change in the polarity and polarizability of the NT3F.m series compared to the NT3.m series. Therefore, it is suggested that, rather than simply promoting a tapered shape, the role of the lateral chain in inhibiting anti-parallel associations and its effect on the electronic properties of the molecules are the key factors in driving the formation of the NF phase.

A snapshot of domain evolution between topological vortex and stripe in ferroelectric hexagonal ErMnO3

Hexagonal manganites exhibit three distinct domain patterns: stripe, loop, and vortex. Due to the high ferroelectric phase transition temperature and the lack of reliable visualization methods, it is still a mystery about the evolution and the formation of vortex networks. In this study, we managed to capture the coexistence of vortices, loops, and stripes by accurately controlling the annealing temperature right at Tc. We proposed a merging process between the V–AV pair and the stripe, which result in two different forms of vortex networks, namely, the normal vortex and the zigzag vortex. In addition, the connection between the density of stripes and the orientation of V–AV pairs is analyzed, which are both influenced by self-straining of the crystal. The mystery of evolution of the vortex network is unveiled by capturing the snapshot, and the experimental database provided calls for more analysis to understand the evolution of different domain topologies.

Prominent Size Effects without a Depolarization Field Observed in Ultrathin Ferroelectric Oxide Membranes.

The increasing miniaturization of electronics requires a better understanding of material properties at the nanoscale. Many studies have shown that there is a ferroelectric size limit in oxides, below which the ferroelectricity will be strongly suppressed due to the depolarization field, and whether such a limit still exists in the absence of the depolarization field remains unclear. Here, by applying uniaxial strain, we obtain pure in-plane polarized ferroelectricity in ultrathin SrTiO_{3} membranes, providing a clean system with high tunability to explore ferroelectric size effects especially the thickness-dependent ferroelectric instability with no depolarization field. Surprisingly, the domain size, ferroelectric transition temperature, and critical strain for room-temperature ferroelectricity all exhibit significant thickness dependence. These results indicate that the stability of ferroelectricity is suppressed (enhanced) by increasing the surface or bulk ratio (strain), which can be explained by considering the thickness-dependent dipole-dipole interactions within the transverse Ising model. Our study provides new insights into ferroelectric size effects and sheds light on the applications of ferroelectric thin films in nanoelectronics.

Ferroelastic and 90∘ ferroelectric domains in Bi2WO6 single crystals

High-quality single crystals of [Formula: see text] are grown using a flux method. With different flux growth recipes, we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition temperature, resulting in mono-domain and multi-domain [Formula: see text] crystals, respectively. Abundant ferroelastic orthorhombic twin domains are observed in the multi-domain crystals under an optical microscope. PFM studies unveil the 90[Formula: see text] polarization change across those ferroelastic domain walls, as well as the absence of 180[Formula: see text] ferroelectric domains in the as-grown multi-domain crystals, indicating a high energy cost of 180[Formula: see text] ferroelectric domains. Moreover, a 45[Formula: see text] tilt of the 90[Formula: see text] ferroelectric domain walls is discovered, and this tilt creates a new type of charged 90[Formula: see text] ferroelectric walls, which have not been observed in other bulk ferroelectrics.

Catalytic Activity of BaTiO3 Nanoparticles for Wastewater Treatment: Piezo- or Sono-Driven?

Piezocatalytic reactions are generally excited by ultrasonication and, as such, should occur simultaneously with other catalytic reactions caused by different mechanisms such as sonocatalysis or tribocatalysis. One of the main challenges is how to discriminate between these effects in a catalysis experiment and quantify each contribution. In order to distinguish these effects, we use nano- and micro-particles of piezoelectric barium titanate (BaTiO3) and then compare their catalytic properties below and close to the piezoelectric to non-piezoelectric phase transition temperature at which the crystalline structure changes from the low-temperature tetragonal, piezoelectric phase to the higher-temperature cubic, non-piezoelectric phase. All other parameters, such as particle size, surface termination, etc., remain unaltered. The phase transition in bulk occurs at about 120 °C, but the transition temperature decreases as a function of particle size and reaches room temperature for particle sizes of about 20 nm. Transmission electron microscopy and X-ray diffraction were used to characterize the morphology and crystalline phase of the nanoparticles, respectively. Since the piezoelectric properties and the lattice dynamics are closely related, temperature-dependent Raman spectroscopy provides an even better insight into the nano- and micro-structural properties, allowing the ferroelectric phase transition temperature to be estimated. The catalytic activities of the BaTiO3 nanoparticles were determined by monitoring the optical absorption of a solution containing the model pollutant methyl orange, after ultrasonication of the solution to which were added the dispersed piezoelectric BaTiO3 particles as catalysts. An exponential-like correlation has been found between the catalytic reaction rates and the tetragonal distortion of the crystal structure of the BaTiO3 particles. Our study has also established that while 10% of the catalytic reaction of BaTiO3 is related to either sonocatalysis or tribocatalysis, the remaining 90% of the overall catalytic activity is ascribed to the piezocatalytic contribution.

Hexagonal RFeO3 (R = Dy, Er, and Lu) Films Grown on Glass Substrates with Both Magnetic and Ferroelectric Orders

Hexagonal rare-earth ferrites (h-RFeO3) are promising multiferroic materials owing to the spontaneous magnetization, high ferroelectric transition temperature, and fascinating features provided by strong magnetoelectric coupling. However, h-RFeO3 is metastable, and its synthetic methods are limited, particularly when ionic size of R is large. One of useful synthesis methods is epitaxial thin-film growth on single-crystal substrates, because the metastable phase is stabilized by the lattice match between h-RFeO3 and the substrate. Compared to single-crystal substrates, glass substrates are more cost-effective. However, films on glass tend to consist of a thermodynamically stable phase owing to the amorphous nature of glass substrates. Herein, we report that a h-RFeO3 pure phase can be obtained as thin film even on glass substrates. The metastable phase was formed owing to the nonequilibrium synthesis process of pulsed laser deposition. The obtained h-RFeO3 thin films on glass with R = Dy, Er, and Lu exhibited weak ferromagnetism with Néel temperatures of 120–140 K. Furthermore, a clear magnetic phase transition from weak ferromagnetic to antiferromagnetic phase was observed in the h-ErFeO3 films. Additionally, piezoelectric force microscopy measurements exhibited the ferroelectricity of the film at room temperature. These results provide a convenient synthesis method of a pure phase multiferroic h-RFeO3 system.

Effect of Gd3+/Ti4+ heterovalent substitution on the crystal structure, morphology, optical properties, and phase transition behavior of bismuth layer-structured SrBi2Nb2O9

The double-layer Aurivillius compounds Sr1-xGdxBi2Nb2-xTixO9 (x ​= ​0, 0.2, 0.4, 0.6, 0.8, and 1), which have the potential to be developed as a ferroelectric material, have been synthesized using the molten salt method. This study aims to investigate the effect of the simultaneous substitution of Gd3+ and Ti4+ ions in SrBi2Nb2O9 on the phase formation, crystal structure, morphology, and ferroelectric properties. The single-phase product with A21am orthorhombic structure was obtained for all samples by X-ray diffraction analysis. The unit cell becomes more orthorhombic with increasing x as the degree of tetragonality increases. SEM micrographs demonstrate the plate-like grain morphology with an anisotropic growth direction, and the grain is smaller in size with increasing x. FTIR spectra indicate that cation substitution was successful, especially Ti4+ ions at the B-site. With increasing x, the ferroelectric transition temperature (Tc) increases, which has been explained in terms of a reduction in the tetragonality. The open hysteresis loops provide evidence of ferroelectric properties which is consistent with the trend of room-temperature dielectric constant. The optical bandgap value is proportional to the trend of the dielectric characteristics of the samples.

Insights into the structural symmetry of YCrO3 from synchrotron X-ray diffraction

A high-resolution synchrotron X-ray diffraction study of a single-crystal YCrO3 compound was employed to obtain its crystallographic information, such as lattice parameters, atomic positions, bond lengths and angles, and local crystalline distortion size and mode. The measurements were taken at 120 K (below the antiferromagnetic transition temperature T N ≃ 141.5 K), 300 K (between T N and the ferroelectric transition temperature T C ≃ 473 K) and 500 K (above T C). Using the high intensity of synchrotron X-rays, it was possible to refine collected patterns with the previously proposed noncentrosymmetric monoclinic structural model (P1211, No. 4) and determine detailed structural parameters. Meanwhile, for a controlled study, the data were refined with the centrosymmetric orthorhombic space group (Pmnb, No. 62). The lattice constants a, b and c and the unit-cell volume increased nearly linearly upon heating. With the P1211 space group, the distributions of bond lengths and angles, as well as local distortion strengths, were observed to be more dispersed. This implies that (i) the local distortion mode of Cr2O6 at 120 K correlates with the formation of canted antiferromagnetic order by Cr1–Cr2 spin interactions, primarily via intermediate O3 and O4 ions; and (ii) the previously reported dielectric anomaly may have a microscopic origin in the strain-balanced Cr1—O3(O4) and Cr2—O5(O6) bonds as well as the local distortion modes of Cr1O6 and Cr2O6 octahedra at 300 K. Local crystalline distortion is shown to be an important factor in the formation of ferroelectric order. The comprehensive set of crystallographic information reported here allows for a complete understanding of the unique magnetic and ferroelectric properties of YCrO3.