BaTiO3 Layer Research Articles

Optically Induced Picosecond Lattice Compression in the Dielectric Component of a Strongly Coupled Ferroelectric/Dielectric Superlattice

AbstractAbove‐bandgap femtosecond optical excitation of a ferroelectric/dielectric BaTiO3/CaTiO3 superlattice leads to structural responses that are a consequence of the screening of the strong electrostatic coupling between the component layers. Time‐resolved X‐ray free‐electron laser diffraction shows that the structural response to optical excitation includes a net lattice expansion of the superlattice consistent with depolarization‐field screening driven by the photoexcited charge carriers. The depolarization‐field‐screening‐driven expansion is separate from a photoacoustic pulse launched from the bottom electrode on which the superlattice is epitaxially grown. The distribution of diffracted intensity of superlattice X‐ray reflections indicates that the depolarization‐field‐screening‐induced strain includes a photoinduced expansion in the ferroelectric BaTiO3 and a contraction in CaTiO3. The magnitude of expansion in BaTiO3 layers is larger than the contraction in CaTiO3. The difference in the magnitude of depolarization‐field‐screening‐driven strain in the BaTiO3 and CaTiO3 components can arise from the contribution of the oxygen octahedral rotation patterns at the BaTiO3/CaTiO3 interfaces to the polarization of CaTiO3. The depolarization‐field‐screening‐driven polarization reduction in the CaTiO3 layers points to a new direction for the manipulation of polarization in the component layers of a strongly coupled ferroelectric/dielectric superlattice.

Red ZnGa2O4:Cr3+ powder electroluminescence co-generating sounds with a longer lifetime and no thermal quenching behaviors

The ZnGa2O4:Cr3+ powder electroluminescence (PEL) device has been demonstrated through a conventional screen printing method. The phosphor powder was prepared by a solid-state reaction in an air ambient and dispersed in an ethyl cellulose binder before screen printing in ITO glass. The PEL device consists of 20 μm-thick BaTiO3 as an insulating layer and 30 μm-thick ZnGa2O4:Cr3+ as an active layer. It has a comparatively lower threshold voltage (40 V) than the previous PEL device. It generates the red light peaking at 696 nm and 708 nm attributed to the forbidden transition of Cr3+ ions and the sound depending on the applied frequency due to the BaTiO3 layer. Its EL intensity was exponentially increased with voltage and linearly increased with the frequency before saturating at a frequency of 3 kHz, which is consistent with the 1/10 decay time. It has the best luminous efficiency of 0.74 lm/W and the maximum EL luminance of 1.64 cd/m2. In particular, it was not thermally quenched even at a higher temperature due to the anti-thermal quenching effect. Moreover, it shows high reliability under ultrasonic frequency (>20 kHz) and is long-lived in an accelerated aging environment (>740 min, temperature of 60 °C and humidity of 50%).

Enhanced thermal conductivity and retained electrical insulation of epoxy composites filled with Cu@BaTiO3 core–shell particles

The application of polymer for thermal interface materials is limited by its low thermal conductivity. In this work, barium titanate coated Cu core–shell particles were prepared and then employed as thermal conductive fillers to reinforce epoxy matrix. The results indicate that thermal conductivity of the Cu@BaTiO3/epoxy composites reaches 1.09 W m-1K−1 at 10 vol% loading, achieving 580% elevation on neat epoxy matrix. Meanwhile, the composites retain high electrical insulation (7.90 × 1013 Ω·cm) due to the existence of insulative BaTiO3 layer on Cu surface. This study will provide a novel insight of the design of functionalized core–shell thermal conductive fillers and construction of high-performance thermal interface materials.

Effect of low temperature structural phase transitions in BaTiO3 on electrical transport through a metal–ferroelectric–metal multilayer of AuCr/BaTiO3/Nb:SrTiO3

In this paper we report an investigation of electronic transport through the metal–ferroelectric–metal (MFM) multilayer consisting of AuCr/BaTiO3/Nb:SrTiO3 over a temperature range of 100 K–300 K where BaTiO3 (BTO) shows a series of structural phase transitions leading to change of magnitude as well as the orientation of the polarization . We observed that the bias dependent barrier heights associated with the interfaces carry strong signature of the phase transitions in the BTO layer which lead to a strong temperature dependent asymmetric transport, when cooled down below room temperature. Specifically, it is observed that the temperature dependence is closely correlated to low temperature transitions in the BTO layer as revealed through the temperature dependent x-ray diffraction (XRD), capacitance as well as resistivity behavior of the BTO layer. There is substantial enhancement of the asymmetry in the device current that occurs at or close to temperatures T 2 ∼ 190 K where BTO shows a crystallographic phase change to the low temperature rhombohedral phase. The temperature dependent changes occur due to barrier modulation at the interfaces of AuCr/BaTiO3 as well as BaTiO3/Nb:SrTiO3 that softens on cooling due to inhomogenities present there. The change in barrier on change of the bias direction has been observed below T 2 which arises from alignment of the polarization in-plane or out-of-plane as determined by tensile or compressive character of the in-plane strain in the BTO film. We also discuss the effect of space charge determined by the oxygen vacancies in the interface region, regulated by the applied bias.

Polarization and Dielectric Properties of BiFeO3-BaTiO3 Superlattice-Structured Ferroelectric Films.

Superlattice-structured epitaxial thin films composed of Mn(5%)-doped BiFeO3 and BaTiO3 with a total thickness of 600 perovskite (ABO3) unit cells were grown on single-crystal SrTiO3 substrates by pulsed laser deposition, and their polarization and dielectric properties were investigated. When the layers of Mn-BiFeO3 and BaTiO3 have over 25 ABO3 unit cells (N), the superlattice can be regarded as a simple series connection of their individual capacitors. The superlattices with an N of 5 or less behave as a unified ferroelectric, where the BaTiO3 and Mn-BiFeO3 layers are structurally and electronically coupled. Density functional theory calculations can explain the behavior of spontaneous polarization for the superlattices in this thin regime. We propose that a superlattice formation comprising two types of perovskite layers with different crystal symmetries opens a path to novel ferroelectrics that cannot be obtained in a solid solution system.

Magnetoelectric coupling in micropatterned BaTiO3/CoFe2O4 epitaxial thin film structures: Augmentation and site-dependency

The prominent magnetoelectric (ME) effect in ME composites usually originates from an interfacial strain-mediated coupling between ferroelectric and ferromagnetic components. While ME composite bilayer thin films have been proposed for microdevice applications, the ME coupling is usually diminished because of the substrate clamping effect. Here, we apply simple CMOS/MEMS compatible top-down fabrication techniques to ferroelectric BaTiO3 (BTO) and ferromagnetic CoFe2O4 (CFO) bilayer epitaxial thin films to control the substrate clamping. We found augmented ME coupling in micro-patterned bilayer thin films compared to the as-deposited films due to the reduced substrate clamping. In addition, a site-dependent ME coupling within the microstructure was observed. Larger ME coupling was obtained near the edge of the microstructure, and site-dependent ferroelectric imprints were observed on the micropattern. This can be attributed to the non-uniform substrate clamping across the film, and the strain gradient developed in the BTO layer due to the magnetostriction of CFO. Our findings provide additional insights to the design of micro- and nanoscale devices based on 2–2 ME composite thin films.

Numerical Analysis of a Highly Sensitive Surface Plasmon Resonance Sensor for SARS-CoV-2 Detection.

In this paper, we propose a surface plasmon resonance (SPR) structure based on Kretschmann configuration incorporating layers of silicon and BaTiO3 on top of Ag for real-time detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using thiol-tethered DNA as a ligand. Extensive numerical analysis based on transfer matrix theory as well as finite-difference time-domain (FDTD) technique has been performed to characterize the sensor response considering sensitivity, full width at half maxima, and minimum reflection. About 7.6 times enhanced sensitivity has been obtained using the proposed architecture for SARS-CoV-2 detection, compared to the basic Kretschmann configuration. Notably, the structure provides consistent enhancement over other competitive SPR structures for both angular and wavelength interrogations with a figure-of-merit of 692.28. Additionally, we repeated simulations for various ligate–ligand pairs to assess the range of applicability and robust performance improvement has been observed. As a result, the proposed sensor design provides a suitable configuration for highly sensitive, rapid, noninvasive biosensing which can be useful if adopted in experimental sensing protocols.

Impact of compressive and tensile epitaxial strain on transport and nonlinear optical properties of magnetoelectric BaTiO3-(LaCa)MnO3 tunnel junction

This work is devoted to disclosing the effect of epitaxial strain on crystallographic, transport, and nonlinear optical properties of a bilayer structure consisting of one ferroelectric (FE) (BaTiO3 with a thickness of 4 nm) and one ferromagnetic (La0.7Ca0.3MnO3 with the thickness of 12 nm) layers. Both tensile (of about ∼6% caused by the MgO substrate) and compressive (of about ∼1% caused by the SrTiO3 substrate) strains reduce the bulk metal-to-insulator phase transition temperature of the La0.7Ca0.3MnO3 layer from 240 K towards 195 K and 160 K, respectively. The appearance of the effect of colossal electroresistance, linear and nonlinear current–voltage behaviours and contribution of FE polarization switching in the BaTiO3 layer to the conductivity are associated with the influence of epitaxial strain. The predominance of the compressive over the tensile strain leads to the hysteresis behaviour of electroresistance, maximum conductivity caused by the resonant-tunnelling mechanism, and strong nonlinear optical dependence on the applied electric field.

Sensitivity enhancement of surface plasmon resonance sensor using Al–Au–BaTiO3–Graphene layers

The performance of prism-based surface plasmon resonance sensor utilizing new sensing configuration composed of thin metallic (Al–Au) film coated with a thin layer of BaTiO3is investigated theoretically based on angular interrogation method. It is observed that optimizing the thickness of bimetallic (Al–Au) and BaTiO3 layers, the sensitivity of the sensor improved greatly and still can maintain its minimum reflectivity and linewidth of the SPR reflectivity curve. We also observed addition of dual layer of graphene on BaTiO3 further enhanced the sensitivity. The sensitivity of the proposed sensor is found to be 227 deg/RIU, and the FWHM of resonance curve is observed to be 4.47 deg for the thickness of 28 nm of Al, 8 nm of Au and 10 nm of BaTiO3added with double layer of graphene.

Regulating Zn Deposition via an Artificial Solid–Electrolyte Interface with Aligned Dipoles for Long Life Zn Anode

HighlightsAn artificial solid–electrolyte interface composed of a perovskite type material, BaTiO3, is introduced to Zn anode surface in aqueous zinc ion batteries.The BaTiO3 layer endowing inherent character of the switched polarization can regulate the interfacial electric field at anode/electrolyte interface.Zn dendrite can be restrained, and Zn metal batteries based on BaTiO3 layer show stable cycling.Aqueous zinc ion batteries show prospects for next-generation renewable energy storage devices. However, the practical applications have been limited by the issues derived from Zn anode. As one of serious problems, Zn dendrite growth caused from the uncontrollable Zn deposition is unfavorable. Herein, with the aim to regulate Zn deposition, an artificial solid–electrolyte interface is subtly engineered with a perovskite type material, BaTiO3, which can be polarized, and its polarization could be switched under the external electric field. Resulting from the aligned dipole in BaTiO3 layer, zinc ions could move in order during cycling process. Regulated Zn migration at the anode/electrolyte interface contributes to the even Zn stripping/plating and confined Zn dendrite growth. As a result, the reversible Zn plating/stripping processes for over 2000 h have been achieved at 1 mA cm−2 with capacity of 1 mAh cm−2. Furthermore, this anode endowing the electric dipoles shows enhanced cycling stability for aqueous Zn-MnO2 batteries. The battery can deliver nearly 100% Coulombic efficiency at 2 A g−1 after 300 cycles.

A theoretical analysis on sensitivity improvement of an SPR refractive index sensor with graphene and barium titanate nanosheets

The sensitivity of the surface plasmons resonance (SPR) refractive index sensor is investigated using angle interrogation. The modified configuration is presented to enhance the performance of the sensor. A multilayer SPR Sensor is proposed with the BK7 prism, silver (Ag), barium titanate, and graphene sheets. The thickness of both the Ag layer is 50 nm and 10 nm, respectively. A layer of BaTiO3 is sandwiched between two thin layers of Ag. The sensitivity is high as 280°/RIU has been achieved with four thin layers of BaTiO3 and mono layer of graphene, which is 108 % higher than the conventional sensor. The graphene layer is used as a bio-compatible reagent, which improves the sensitivity of the sensor. The investigated sensor is susceptible to a 1.358 refractive index. This sensor has the potential for biomedical and biochemical sensing applications.

Crystallization investigation of BaTiO 3 coating layer on Ni nanoparticles

The crystallization of oxide coating layer on base metal electrode (BME) has facing challenges for a long time. In this paper, a sol-gel method was used to coat nickel (Ni) nanoparticles with polycrystalline BaTiO3 (BT). By adjusting the reaction condition, continuous and homogeneous BT coating layer was obtained based on the transmission electron microscopy (TEM) observation. Powder X-ray diffraction (XRD) of the coated sample indicated that deionized water content, which can change the pH value of the reaction solvent, is the key factor to influence the crystallization of the BT layer. With the increase of the deionized water, the crystallinity of the BT layer increased, which greatly enhanced the anti-oxidation properties of the Ni nanoparticles. When the amount of deionized water increased to 20 wt%, Ni3C impurity appeared and the properties of the Ni nanoparticles deteriorated. As a result, an optimized deionized water content of 16 wt% is adopted for the best performance of the BT coated Ni (Ni@BT) nanoparticles.

Ultraflexible and Malleable Fe/BaTiO3 Multiferroic Heterostructures for Functional Devices

AbstractThe high demand for flexible spintronics based on multiferroic heterostructures makes growing high‐quality flexible, functional oxides urgently, in which needs to be deposited on lattice‐matched substrates. In this paper, ultraflexible and malleable iron (Fe)/BaTiO3 (BTO) multiferroic heterostructures are demonstrated, showing a perfect crystallinity and hetero‐epitaxial growth. In terms of performance, they indicate good multiferroic properties and excellent bending tunability, as well as obvious magnetoelectric (ME) coupling effect. During the phase transformation from the rhombohedral phase to the orthorhombic phase of BTO layers in the heating process, a large ME coupling coefficient of 120 Oe °C−1 along the out‐of‐plane direction is obtained. This value keeps consistent in the phase‐field simulation of magnetic domain evolution, in which the biaxial compressive strain induced‐magnetoelastic anisotropy facilitates the magnetic easy axis of Fe layers to the [110] or [–1–10] direction. Besides, ultraflexible Fe/BTO heterostructures are found to have a 690 Oe ferromagnetic resonance (FMR) field shift along the out‐of‐plane direction under the flexible tuning (R = 5 mm). This work should pave a way toward flexible spintronic and functional devices with fast speed, portability, and low energy consumption.

Improved Dielectric Properties of Polypropylene Nanocomposites with BaTiO3 Nanoparticles

Polymer nanocomposites with improved dielectric permittivity are extremely desirable for the power capacitors. With the existing capacitor polypropylene (PP) film as the substrate, the surface of PP film is coated with a layer of BaTiO3 (BT) with high dielectric constant of nanoparticles. Through the BT layer with high dielectric constant, the dielectric constant of the whole composite dielectric film is improved, and the dielectric loss is controlled at a relatively low level. The organic solvent system of BT paste coating and water system of BT paste coating research were prepared. Two kind of composite dielectric films which are PP/PVDF/BT and PP/BT were prepared by coating. The permittivity of PP/ BT nano-composites with 50 wt% fillers at 1000 Hz was up to 4.49, which was nearly 2 times higher than that of pure PP film. According to the method, a pilot experiment was carried out. The strategy could be extended to a variety of inorganic fillers to improve the dielectric properties of polymer nano- composites for power capacitors.

A wide-frequency range dielectric tuning of BaTiO3 by embedding metal nanocrystals.

Fe nanocrystals (NCs) were embedded into the epitaxial BaTiO3 (BTO) matrix. According to optimized growth processes, a novel nanocomposite system was constructed, which consisted a well epitaxial BTO layer and three-dimensional Fe NCs. Based on this, the different dielectric response in the regions of low temperature-high frequency and low frequency-high temperature were revealed by the contribution of hopping and interfacial polarizations, respectively. With the increased amount of Fe NCs, the obvious enhancement in the low-frequency conductivity, middle frequency capacitance, and high-frequency inductive effect was found. The embedded metal NCs play an important role in tuning the dielectric behaviors and AC conductivity of oxide dielectrics. This significant rectification effect in wide-frequency ranges opens up a new direction for designing embedded nano-capacitors.

Epitaxy and controlled oxidation of chromium ultrathin films on ferroelectric BaTiO3 templates

Interfaces play a crucial role in the study of novel phenomena emerging at heterostructures comprising metals and functional oxides. In this work, we consider Cr/BaTiO3 heterostructures grown on Nb:SrTiO3 (001) substrates. Chromium thin films with 2 nm nominal thickness are deposited by molecular beam epitaxy on the BaTiO3 layer, and subsequently annealed in vacuum at temperatures ranging from 800 K to 970 K, and finally exposed to 10−7 torr of molecular oxygen for 300 s. Highly ordered films are obtained for each of this condition, ranging from metallic Cr to insulating Cr2O3 with tetragonal structure. Quite unexpectedly, an intermediate – fully ordered – case exists, with the co-presence of Cr and Cr2O3 compounds, each one with its proper crystal orientation. These results show the opportunity of controlling the metal/oxide state of crystalline Cr films grown onto the ferroelectric template BaTiO3/Nb:SrTiO3.

Fabrication of homogeneous nanosized nickel powders using a planetary ball mill: Applications to multilayer ceramic capacitors (MLCCs)

Given the increasing demand for multilayer ceramic capacitors (MLCCs) for miniaturization of electronic parts, a narrow nanoparticle size distribution is crucial to optimize MLCC performance and stability. We explored the sintering behavior of nickel powder with the goal of controlling particle size. A micro-sized nickel oxide powder was milled to uniform size (183.2 ± 53.8 nm) using a planetary ball mill; the size distribution was more uniform than that of a commercial powder (400.2 ± 183.4 nm). The sintering characteristics and capacitive features of the powders were analyzed after reduction in hydrogen. We found that the milled powder, with a narrow particle size distribution, exhibited delayed sintering rate, which paralleled the shrinkage of the of BaTiO3 layer. Discrete layers were thus obtained. Moreover, use of the milled powder reduced capacitance noise by 25% compared to that when other powders were employed; our milled powder contributed to the formation of stable electrodes.

Strain control of layer-resolved negative capacitance in superlattices

Negative capacitance in BaTiO3/SrTiO3 superlattices is investigated by Monte Carlo simulations in an atomistic effective Hamiltonian model, using fluctuation formulas for responses to the local macroscopic field that incorporates depolarizing fields. We show that epitaxial strain can tune the negative capacitance of the BaTiO3 ferroelectric layer and the overall capacitance of the system. In addition, we predict and explain an original switching of the negative capacitance from the BaTiO3 layer to the SrTiO3 layer at low temperatures for intermediate strains.

Enhanced compressive strengths and induced cell growth of 1-3-type BaTiO3/PMMA bio-piezoelectric composites

Barium titanate (BaTiO3) has been used as a bone implant material because of its piezoelectric properties and the ability to promote cell growth when combined with hydroxyapatite. However, the brittleness of BaTiO3 inhibits its use as a bone replacement material at load-bearing sites, and the reduction of BaTiO3 content in the composite reduces its piezoelectric effect on bone growth. In this study, we explored a preparation method, which included directional freeze casting and self-solidification of bone cement, to obtain 1-3-type BaTiO3/PMMA bio-piezoelectric composites with a lamellar structure. The lamellar BaTiO3 layer through the composite from the bottom to the top significantly improved the piezoelectric properties of the composite. In addition, the dendritic ceramic bridges on the BaTiO3 pore walls can improve the compressive strength and elastic modulus of BaTiO3/PMMA bio-piezoelectric composites with a lamellar structure. More importantly, it was found that polarized lamellar BaTiO3 could induce osteoblasts to grow in the direction of the BaTiO3 layers. When the width of the BaTiO3 layer was in the range of 8–21 μm, osteoblasts along the BaTiO3 layer showed well growth, which can be of great value for the production of biomimetic bone units.

Periodic Wrinkle-Patterned Single-Crystalline Ferroelectric Oxide Membranes with Enhanced Piezoelectricity.

Self-assembled membranes with periodic wrinkled patterns are the critical building blocks of various flexible electronics, where the wrinkles are usually designed and fabricated to provide distinct functionalities. These membranes are typically metallic and organic materials with good ductility that are tolerant of complex deformation. However, the preparation of oxide membranes, especially those with intricate wrinkle patterns, is challenging due to their inherently strong covalent or ionic bonding, which usually leads to material crazing and brittle fracture. Here, wrinkle-patterned BaTiO3 (BTO)/poly(dimethylsiloxane) membranes with finely controlled parallel, zigzag, and mosaic patterns are prepared. The BTO layers show excellent flexibility and can form well-ordered and periodic wrinkles under compressive in-plane stress. Enhanced piezoelectricity is observed at the sites of peaks and valleys of the wrinkles where the largest strain gradient is generated. Atomistic simulations further reveal that the excellent elasticity and the correlated coupling between polarization and strain/strain gradient are strongly associated with ferroelectric domain switching and continuous dipole rotation. The out-of-plane polarization is primarily generated at compressive regions, while the in-plane polarization dominates at the tensile regions. The wrinkled ferroelectric oxides with differently strained regions and correlated polarization distributions would pave a way toward novel flexible electronics.