Tetragonal Phase Of BaTiO3 Research Articles

Properties of yttrium-doped barium titanate ceramics with positive temperature coefficient of resistivity and a novel method to evaluate the depletion layer width

Yttrium-doped barium titanate ceramics with positive temperature coefficient of resistivity (PTCR) are prepared by the sol-gel technique. The gel powder shows a size distribution around 0.18 µm with a tetragonal BaTiO3 phase identified. The Ba1-xYxTiO3 ceramics are sintered in a reducing atmosphere and oxidized in air. The grain size of the ceramics grows from 1.3 to 1.6 µm when Y-doping amount increases from 1.0% to 2.8%. The electrical properties of room temperature resistivity, PTCR jump and impedance spectroscopy are studied. A novel mathematical method is proposed to evaluate the depletion layer width of the BaTiO3 ceramics based on the dependence of room temperature resistivity on the donor density. The widths of depletion layer of 185 nm are evaluated for the Ba1-xYxTiO3 ceramics sintered at 1150 °C. The donor energy level and Fermi level are found to be essential factors that determine the width of depletion layer.

Preparation and study the structure of pure and impure barium titanate with Mg2+ ion

Pure and doped barium titanate with Mg2+ ion at two molar ratios x= (5%, 10%) mol. has been synthesized by solid state reaction technique. The powders sintered at two temperatures (1000 °C and 1400 °C). An XRD technique was used in order to study the crystal structure of pure and doped barium titanate, which confirmed the formation of the tetragonal phase of BaTiO3, and then calculate the lattice parameters of pure and doped barium titanate, the addition of magnesium ion Mg2+ can lead to decreases lattice parameters.

Preparation and study the structure of pure and impure barium titanate with Mg2+ ion

Pure and doped barium titanate with Mg2+ ion at two molar ratios x= (5%, 10%) mol. has been synthesized by solid state reaction technique. The powders sintered at two temperatures (1000 °C and 1400 °C). An XRD technique was used in order to study the crystal structure of pure and doped barium titanate, which confirmed the formation of the tetragonal phase of BaTiO3, and then calculate the lattice parameters of pure and doped barium titanate, the addition of magnesium ion Mg2+ can lead to decreases lattice parameters.

An Eco-Friendly Method of BaTiO3 Nanoparticle Synthesis Using Coconut Water

BaTiO3 nanoparticles were successfully synthesized by a new coconut water-based sol–gel method using Ba(CH3COO)2 and TiCl3 as the starting salts. The influence of the amount of coconut water and calcination conditions on the barium titanate crystallization was investigated. The resulting nanoparticles were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and Raman and Fourier transform infrared (FTIR) spectroscopies. The ferroelectric tetragonal single phase of BaTiO3 was obtained in samples prepared with a ratio of coconut water volume (mL)/BaTiO3 mass (g) of 25 : 2 and 30 : 2, calcined at 1100°C, which was confirmed by XRD measurements. Crystallites with an average size of about 31 nm for both samples were obtained, and microscopy images revealed the presence of particles in the range of 40 to 60 nm. Raman and FTIR spectra confirmed the dominant tetragonal phase of BaTiO3, meanwhile traces of BaCO3 were identified in FTIR spectra.

Synthesis of hierarchical barium titanate micro flowers with superior light-harvesting characteristics for dye sensitized solar cells

Hierarchical barium titanate (BaTiO3) micro flowers have been successfully grown on the conducting glass substrates by a two-step hydrothermal process. Morphological and crystal structure analyses revealed that the tetragonal phase BaTiO3 micro flowers have formed as clusters of highly crystalline, one dimensional parallelepiped nanorods of widths ranging from 50 to 500 nm. The as-grown BaTiO3 micro flowers tested as dye sensitized solar cell (DSSC) photoanode has showed maximum power conversion efficiency (PCE) of 5.13%, which is comparable to the PCE of TiO2 nanoparticles based DSSC photoanode (5.90%) measured under one sun illumination conditions. Besides, incident photon to current conversion efficiency (IPCE) and UV–visible absorption analyses have confirmed that the superior light-harvesting capability of BaTiO3 micro flowers over TiO2 nanoparticles is observed in DSSC due to their favorable morphological features and increased visible light absorption properties along with the superior charge transport characteristics of nanorods.

Gold nanoparticles decorated on BaTiO3 as photocatalyst: effect of SPR and ferroelectricity

BaTiO3(BTO) powders with cubic(C) and tetragonal(T) crystalline structures were prepared by sol-gel method followed by calcination at different temperatures, and they were decorated with gold nanoparticles(AuNPs) to form Au-T-BTO and Au-C-BTO respectively. All the samples (C-BTO, T-BTO, Au-C-BTO and Au-T-BTO) were used as photo-catalysts for the degradation of Rhodamine B (RhB). Au-T-BTO exhibits the highest photocatalytic activity due to thecombined effect of surface plasmon resonance (SPR) and the ferroelectricity of the tetragonalphase BTO. The light absorption peaks at 500 to 600 nm verify the presence of SPR effect from Au NPs. Based on density functional theory (DFC) within the generalized gradient approximation (GGA) approach, it was demonstrated that the tetragonal phase BaTiO3 shows a spontaneous polarization with the calculated value of 0.34 C m−2, which is absent in thecubic phase. The internal space charge layer in tetragonal phase BTO enhances the separation of photoexcited carriers due to the spontaneous ferroelectric polarization, which also benefits photocatalytic activities.

Ferroelectric spontaneous polarization steering charge carriers migration for promoting photocatalysis and molecular oxygen activation

Introducing a polarization electric field in photocatalyst system is regarded asa new concept for photocatalytic activity enhancement. In this work, we first unearth that the spontaneous polarization of ferroelectric BaTiO3 promotes the photocatalytic and molecular oxygen activation performance of the narrow-band-gap semiconductor BiOI. Ferroelectric tetragonal-phase BaTiO3 (T-BaTiO3) were prepared via calcination of nonferroelectric cubic-phase BaTiO3 (C-BaTiO3), and their polarization ability was verified via ultrasonication-assisted piezoelectric catalytic degradation. Then, the C-BaTiO3/BiOI and T-BaTiO3/BiOI heterostructures are fabricated by a soft-chemical method. To disclose the influence of ferroelectric spontaneous polarization on charge movement behavior, the photocatalytic and molecular oxygen activation properties are monitored by degradation of methyl orange (MO) and superoxide radical (O2−) evolution under visible light irradiation (λ>420nm), respectively. The results demonstrated that T-BaTiO3/BiOI far outperforms C-BaTiO3/BiOI and pristine BiOI. The ferroelectric spontaneous polarization of T-BaTiO3 can steer the migration of photogenerated charge carriers and induce efficient separation, accounting for the strengthened photodegradation and reactive oxygen species O2− production rate (11.02×10−7molL−1h−1). The study may furnish a new reference for developing efficient tactics to advance the photocatalytic and molecular oxygen activation ability for environmental chemistry and biochemistry applications.

Preparation of ferroelectric barium titanate through an energy effective solid state ultrasound assisted method

AbstractBarium titanate submicronic particles were prepared, for the first time, by a solid‐state reaction route, where the classical ball grinding/mixing and drying steps were replaced by ultrasonication and microwave assisted processes, respectively, resulting in significant reduction in both drying duration and temperature of the thermal treatment. The structure of the prepared samples was analyzed by Fourier transform infrared spectroscopy and X‐ray powder diffraction, while the morphology and particle size were followed by means of scanning electron microscopy and dynamic light scattering. Dielectric properties were evaluated in the frequency range of 106‐10−2 Hz. The obtained results showed that the employed synthesis process leads to well‐defined tetragonal phase BaTiO3 particles with relatively high tetragonality and average particle diameter of around 500 nm. The study on the dielectric behavior reveals that the obtained materials are appropriate for applications as passive electronic elements. The goal of the paper is to demonstrate the effectiveness of the ultrasonic treatment in the preparation of well‐defined perovskite‐like BaTiO3 particles by a solid‐state process.

Fabrication and properties of nonreducible lead-free piezoelectric Mn-doped (Ba,Ca)TiO 3 ceramics

Abstract Nonreducible lead-free (Ba,Ca)TiO3 piezoceramics were fabricated by controlling the level of Mn doping. Similar to Mn-doped (Ba0.85Ca0.15)TiO3 ceramics sintered in air, stable dielectric properties with temperature change were achieved for the nonreducible sample by stabilizing the tetragonal phase of BaTiO3 over a wide temperature range. In addition, optimization of the level of Mn doping was very effective in improving the sintered density and electrical resistivity for (Ba0.85Ca0.15)TiO3 ceramics sintered under a low oxygen partial pressure. The valence state of doped Mn in nonreducible (Ba,Ca)TiO3 after sintering was confirmed to be Mn2+ or Mn3+ by electron spin resonance analysis. Sintered bodies of 1 mol% Ba excess and 1 mol% Mn-doped (Ba0.85Ca0.15)TiO3, which were sintered at 1350 °C in a H2(0.3%)/Ar atmosphere, exhibited sufficient sintered density and resistivity to allow the characterization of several electrical properties. The ferroelectric, field-induced strain, and piezoelectric properties of the nonreducible (Ba0.85Ca0.15)TiO3 ceramics sintered in the reducing atmosphere were comparable with those of (Ba0.85Ca0.15)TiO3 samples sintered in air.

Fabrication of submicron BaTiO3@YFeO3 particles and fine-grained composite magnetodielectric ceramics with a core–shell structure by means of a co-precipitation method

The submicron BaTiO3@YFeO3 particles (diameter about 240 nm) with core–shell structure using a co-precipitation method were prepared. We obtained fine-grained BaTiO3@YFeO3 composite magnetodielectric ceramics (grain size ≤250 nm) with a tetragonal-phase BaTiO3 core and an orthorhombic-phase YFeO3 shell by means of sintering at a low temperature (1180 °C) in air. The temperature coefficient of capacitance characteristic (TCC) of the BaTiO3@YFeO3 ceramics satisfied the X8R specification. As the YFeO3 content increased from 2.0 to 8.0 mol%, the room-temperature permittivity of the samples first increased and then decreased, and the maximum room-temperature permittivity was 2319 at 6.0 mol% YFeO3, and a low dielectric loss at room temperature (<0.020). The saturation magnetization (Ms) and remnant magnetization (Mr) increased as the YFeO3 content increased, reaching values of 2.74 and 1.75 emu/g, respectively, at 8.0 mol% YFeO3. The improved microstructure and properties of BaTiO3@YFeO3 materials indicated that the co-precipitation approach represents a good way to prepare such materials for use in multifunctional devices.

Hydrothermal synthesis of tetragonal phase BaTiO3 on carbon fiber with enhanced electromechanical coupling

Core–shell fibers utilizing carbon fiber as the load-bearing element and a functional shell are in the early stages of research and development, but are already showing promising results in multifunctional composite fabrication. This study builds on prior multifunctional fiber research that applied hydrothermal synthesis to grow BaTiO3 on carbon fibers. In this work, the hydrothermal reaction conditions are thoroughly explored and illustrate the typical trade-off between the tensile strength of the core fiber and the d 33 piezoelectric strain coefficient. This trade-off exemplifies the difficulty in synthesizing multifunctional fibers that maintain mechanical integrity while offering enhanced electromechanical functionality. By studying the hydrothermal synthesis conditions, parameters are established that result in the first demonstration of tetragonal phase BaTiO3 on carbon fiber. Synthesis parameters are developed that maintain the tensile strength of the core carbon fiber while increasing the d 33 piezoelectric strain coefficient of the BaTiO3 film. The optimal fiber has a tensile strength of 4.96 GPa and a d 33 of 39.2 pm/V, which equate to 16.2 and 49.6% increases over the prior synthesis of BaTiO3 coated carbon fibers, respectively. Therefore, this work establishes hydrothermal reaction conditions that create higher-performance multifunctional fibers through the development of tetragonal phase BaTiO3 on carbon fiber.

Identification of Novel Short BaTiO3-Binding/Nucleating Peptides for Phage-Templated in Situ Synthesis of BaTiO3 Polycrystalline Nanowires at Room Temperature.

Ferroelectric materials, such as tetragonal barium titanate (BaTiO3), have been widely used in a variety of areas including bioimaging, biosensing, and high power switching devices. However, conventional methods for the synthesis of tetragonal phase BaTiO3 usually require toxic organic reagents and high temperature treatments, and are thus not environment-friendly and energy-efficient. Here, we took advantage of the phage display technique to develop a novel strategy for the synthesis of BaTiO3 nanowires. We identified a short BaTiO3-binding/nucleating peptide, CRGATPMSC (named RS), from a phage-displayed random peptide library by biopanning technique and then genetically fused the peptide to the major coat protein (pVIII) of filamentous M13 phages to form the pVIII-RS phages. We found that the resultant phages could not only bind with the presynthesized BaTiO3 crystals but also induce the nucleation of uniform tetragonal BaTiO3 nanocrystals at room temperature and without the use of toxic reagents to form one-dimensional polycrystalline BaTiO3 nanowires. This approach enables the green synthesis of BaTiO3 polycrystalline nanowires with potential applications in bioimaging and biosensing fields.

The achievement of the super short channel control in the magnetic Ge n-FinFETs with the negative capacitance effect

Super short channel control (sub-threshold swing = 95 mV/dec) in Ge n-type Fin Field-Effect Transistors (n-FinFETs) is achieved through the promising gate stack characteristics of gate leakage (Jg)-equivalent-oxide-thickness (EOT) and ultra-high k-value (∼312) with the implement of the magnetic gate stack scheme. On the other hand, the negative capacitance effect is also observed in the magnetic Ge n-FinFETs by the extraction of the body factor (m = 0.47) at low temperature measurement. The proposed magnetic gate stack scheme (tetragonal-phase BaTiO3 as the dielectric layer and magnetic FePt film as the metal gate) in the Ge n-FinFETs has super Jg-EOT characteristics, negative capacitance phenomenon, and promising transistor performance. It provides the useful solution for the future low power mobile devices designed on the high mobility (Ge) material.

Tetragonal BaTiO3 nanoparticles: An efficient photocatalyst for the degradation of organic pollutants

Photocatalytically active cubic and tetragonal phase BaTiO3 nanoparticles have been prepared by polymeric complex method. The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Photoluminescence spectroscopy (PL), Ultraviolet-visible (UV–vis) diffuse reflectance spectrophotometry (UV-DRS). In addition, the morphology of BaTiO3 was investigated using Transmission electron microscopy (TEM). The cubic and tetragonal phases of the prepared BaTiO3 were confirmed by XRD and Raman spectra. Methylene blue dye was used as a probe to evaluate the photocatalytic activities of cubic and tetragonal BaTiO3. This investigation revealed that BaTiO3 with tetragonal phase showed higher photocatalytic activity than that of the cubic BaTiO3. The photoluminescence result also supported the improved photocatalytic activity of tetragonal BaTiO3. However, a noticeable change in photocatalytic property could be observed on varying the amount of BaTiO3. The enhanced photocatalytic activity of tetragonal BaTiO3 makes it an excellent photocatalyst candidate for the degradation of pollutants.

Modification of the ferromagnetic properties of Fe-doped BaTiO3 polycrystalline ceramics by using Bi3+ doping

We study the crystal structure and the magnetic properties of Ba1−xBixTi0.9Fe0.1O3 (0 ≤ x ≤ 0.12) ceramics prepared by using a conventional solid-state reaction. X-ray diffraction and Raman scattering spectroscopy measurements show that Bi3+ substitution suppresses the formation of the hexagonal BaTiO3 phase and stabilizes the tetragonal BaTiO3 phase. The samples with x ≥ 0.08 demonstrate a single tetragonal BaTiO3 phase. Samples with x ≤ 0.1 show obvious magnetic orders at room temperature. The saturated magnetization, paramagnetic contribution and magnetic transition temperature are found to depend on the Bi doping concentration. Samples with 0.08 ≤ x ≤ 0.1 show a single tetragonal phase structure with a ferromagnetic order. These results indicate that the crystal structure and the ferromagnetic properties of Ba1−xBixTi0.9Fe0.1O3 (0 ≤ x ≤ 0.12) ceramics are intrinsic.

The demonstration of promising Ge n-type multi-gate-field-effect transistors with the magnetic FePt metal gate scheme

In this work, the tetragonal-phase BaTiO3 high dielectric (HK) layer and the magnetic FePt metal gate (MG) film are proposed to be the gate stack scheme on the Ge three dimensional (3D) n-type multi-gate-field-effect transistors (FETs). The ∼75% dielectric constant (κ-value) improvement, ∼100× gate leakage (Jg) reduction, and ∼70% on-state current (Ion) enhancement are achieved due to the colossal magneto-capacitance effect. The magnetic field from the magnetic FePt MG film couples and triggers more dipoles in the BaTiO3 HK layer and then results in the super gate stack characteristics. The promising transistor's performance (∼200 μA/μm on the device with the gate length Lch = 60 nm) on the high mobility (Ge) material in the 3D n-type multi-gate-FETs device structure demonstrated in this work provides the useful solution for the future advanced logic device design.

Lateral electric-field control of giant magnetoresistance in Co/Cu/Fe/BaTiO3 multiferroic heterostructure

We report lateral electric-field-driven sizable changes in the magnetoresistance of Co/Cu/Fe tri-layered wires on BaTiO3 single crystal. While the observed change is marginal in the tetragonal phase of BaTiO3, it reaches over 40% in the orthorhombic and rhombohedral phases with an electric field of 66 kV/cm. We attribute it to possible electric-field-induced variations of the spin-dependent electronic structures, i.e., spin polarization, of the Fe via interfacial strain transfer from BaTiO3. The contrasting results for the different phases of BaTiO3 are discussed, associated with the distinct aspects of the ferroelectric polarization switching processes in each phase.

Controlled synthesis and novel photoluminescence properties of BaTiO3:Eu3+/Eu2+ nanocrystals

Tetragonal phase BaTiO3:Eu nanocrystals were successfully synthesized using a hydrothermal method and a subsequent calcination treatment. The structures and morphologies of nanocrystals were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy. The photoluminescence properties of BaTiO3:Eu were investigated in detail. Under 398nm excitation, the emissions from Eu2+ and Eu3+ ions were observed, indicating that Eu2+ and Eu3+ ions coexisted in BaTiO3:Eu nanocrystals. Especially, the emission band of Eu2+ from BaTiO3:Eu was observed to broaden with increasing Eu concentration. When the Eu concentration was 0.5mol%, the 5D0→7F0 and 5D1→7F0 emissions were observed. In addition, under 537nm excitation, the emission intensity increased with increasing Eu concentration.

Study of nanoscale local structures of ferroelectric barium titanate using CBED

It is well known that BaTiO3 undergoes successive phase transformations from the cubic paraelectric phase to three ferroelectric phases: tetragonal, orthorhombic and rhombohedral ones. Coexistence of the displacive and order-disorder characters in the phase transformations of BaTiO3 was pointed out from many experiments and theories. However, local structures related to the order-disorder character were discovered neither in crystal structure analyses using neutron and X-ray diffraction nor by TEM observations. In the present study, the convergent-beam electron diffraction (CBED) method was applied to examine nanometer-scale local structures of BaTiO3. Rhombohedral nanostructures were observed in the orthorhombic and tetragonal phases of BaTiO3 using CBED [1]. It was found that the symmetry of the orthorhombic phase is formed as the average of two rhombohedral variants with different polarizations, and that of the tetragonal phase is formed as the average of four rhombohedral variants. These results indicate an order-disorder character in their phase transformations. Similar results were obtained in the ferroelectric orthorhombic phase of KNbO3 [2], while it was found that the ferroelectric tetragonal phase of PbTiO3 does not have such rhombohedral nanostructures. We also proposed a combined use of STEM and CBED methods (STEM-CBED method) to observe the nanostructures of polarizations [3]. Using the method, two-dimensional distribution of the rhombohedral nanostructures, or nanoscale fluctuations of the polarization clusters, were successfully visualized in the tetragonal phase of BaTiO3.

The demonstration of colossal magneto-capacitance effect with the promising gate stack characteristics on Ge (100) by the magnetic gate stack design

The tetragonal-phase BaTiO3 as the high dielectric (HK) layer and the magnetic FePt film as the metal gate (MG) are proposed to be the gate stack scheme on the Ge (100) substrate. The ∼75% dielectric constant (κ-value) improvement, ∼100X gate leakage (Jg) reduction, and the promising Jg-equivalent-oxide-thickness (EOT) gate stack characteristics are achieved in this work with the colossal magneto-capacitance effect. The perpendicular magnetic field from the magnetic FePt MG film couples and triggers the more dipoles in the BaTiO3 HK layer and then results in the super gate capacitance (Cgate) and κ-value. Super Jg-EOT gate stack characteristics with the magnetic gate stack design on the high mobility (Ge) substrate demonstrated in this work provides the useful solution for the future low power mobile device design.