Multilayer BaTiO3 Research Articles

Optical Properties and Upconversion Luminescence of BaTiO3 Xerogel Structures Doped with Erbium and Ytterbium

Erbium upconversion (UC) photoluminescence (PL) from sol-gel derived barium titanate (BaTiO3:Er) xerogel structures fabricated on silicon, glass or fused silica substrates has been studied. Under continuous-wave excitation at 980 nm and nanosecond pulsed excitation at 980 and 1540 nm, the fabricated structures demonstrate room temperature PL with several bands at 410, 523, 546, 658, 800 and 830 nm, corresponding to the 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2→ 4I15/2 and 4I9/2→ 4I15/2 transitions of Er3+ ions. The intensity of erbium UC PL increases when an additional macroporous layer of strontium titanate is used beneath the BaTiO3 xerogel layer. It is also enhanced in BaTiO3 xerogel films codoped with erbium and ytterbium (BaTiO3:(Er,Yb)). For the latter, a redistribution of the intensity of the PL bands is observed depending on the excitation conditions. A multilayer BaTiO3:(Er,Yb)/SiO2 microcavity structure was formed on a fused silica substrate with a cavity mode in the range of 650–680 nm corresponding to one of the UC PL bands of Er3+ ions. The obtained cavity structure annealed at 450 °C provides tuning of the cavity mode by 10 nm in the temperature range from 20 °C to 130 °C. Photonic application of BaTiO3 xerogel structures doped with lanthanides is discussed.

Multi-layered BTO/PVDF nanogenerator with highly enhanced performance induced by interlaminar electric field

The flexible piezoelectric nanogenerator (PNG) has been spotlighted as a promising candidate for sustainable power source in wireless portable device. Here, a multi-layered BaTiO3 (BTO) /poly(vinylidene fluoride) (PVDF) PNG has been designed by spin coating and layer by layer assembled method. Benefited from the composite strategy and interlaminar electric field effect, the typical four-layered BTO/PVDF nanogenerator contained with 20 wt% BTO nanoparticles represents excellent output performance with voltage of 14.22 V (about 6.49 times than that of 1 layered PNG), current of 2.42 μA, and maximum power of 11.55 μW. The dielectric constant and residual polarization of the PNG vary with the number of piezoelectric layers, which is suspected as the root cause for the enhancement of piezoelectric and output performance. In addition, 4000 pressing-releasing cycles test, finger tapping and foot striking measurements also demonstrated excellent stability of the synthesized BTO/PVDF PNG, showing their great potential in wireless sensing and wearable device applications.

Fermi Level Engineering for Large Permittivity in BaTiO3-Based Multilayers

Multilayered doped BaTiO3 thin films have been fabricated by physical vapor deposition (PVD) on low-cost polycrystalline substrates with the aim to improve dielectric properties by controlling point charge defects at the interfaces. We show that carefully designed interfaces lead to increasing the relative permittivity of the BaTiO3 thin films, in contradiction with the common belief that interfaces behave as dead layers. High relative permittivity up to 1030 and tanδ = 4% at 100 kHz and room temperature were obtained on BaTiO3 multilayered films deposited on Si/Pt substrates by PVD. The large permittivity is suspected to be an extrinsic contribution due to band bending at the interfaces, as inferred by in-situ X-ray photoelectron spectroscopy. A 20-nm depletion layer was found to be associated with an interdiffusion of dopants, as measured by depth profiling with time-of-flight secondary ion mass spectrometry. The films exhibit high permittivity and low dielectric losses stable between 200 and 400 K, which meet the requirement of electronic applications.

Fermi Level Engineering for Large Permittivity in BaTiO3-Based Multilayers

Multilayered doped BaTiO3 thin films have been fabricated by physical vapor deposition (PVD) on low-cost polycrystalline substrates with the aim to improve dielectric properties by controlling point charge defects at the interfaces. We show that carefully designed interfaces lead to increasing the relative permittivity of the BaTiO3 thin films, in contradiction with the common belief that interfaces behave as dead layers. High relative permittivity up to 1030 and tanδ = 4% at 100 kHz and room temperature were obtained on BaTiO3 multilayered films deposited on Si/Pt substrates by PVD. The large permittivity is suspected to be an extrinsic contribution due to band bending at the interfaces, as inferred by in-situ X-ray photoelectron spectroscopy. A 20-nm depletion layer was found to be associated with an interdiffusion of dopants, as measured by depth profiling with time-of-flight secondary ion mass spectrometry. The films exhibit high permittivity and low dielectric losses stable between 200 and 400 K, which meet the requirement of electronic applications.

Sol–Gel Fabrication and Luminescence Properties of Multilayer Eu-Doped BaTiO3–SiO2 Xerogel Nanostructures

With the use of sol–gel method BaTiO3–SiO2 multilayer structures were fabricated on glass or fused silica substrates employing dipping or spinning procedure. The photonic stop band was observed in the reflection and transmission spectra of the multilayer structure annealed at [Formula: see text]C. It is redshifted with an increase of the thicknesses of BaTiO3 and SiO2 layers. For structures comprising Eu-doped BaTiO3 layers of different thicknesses photoluminescence with the main band at 614[Formula: see text]nm was detected. It is characterized with the double-exponential decay with the lifetimes of about 0.5[Formula: see text]ms and 1.1[Formula: see text]ms which do not depend significantly on the photonic stop band position.

Paper‐Derived Ferroelectric Ceramics: A Feasibility Study

Preceramic paper may serve as a preform to manufacture single sheet as well as multilayer porous ferroelectric ceramic products. In this article, the authors discuss the formation, microstructure, and properties of preceramic papers highly loaded with BaTiO3 filler ranging from 70 to 80 vol% and their conversion into ceramic materials. In order to increase the density of the single sheets, post calendering is applied. These sheets are used for the fabrication of multilayer ceramics using warm lamination technique. After binder burnout and sintering up to 1300 °C for 2 h in air, porous paper‐derived multilayer BaTiO3 is obtained. The effect of ceramic filler content and calendering on the residual porosity in sintered samples is studied. Furthermore, the influence of porosity on the microstructure, mechanical, dielectric, and piezoelectric properties of the sintered BaTiO3 ceramics is investigated.

Influence of Reoxidation Time on Electrical Properties of Y2O3-doped BaTiO3 Ceramics Sintered in a Reducing Atmosphere

The influence of the reoxidation time on electrical properties and the positive temperature coefficient of resistance (PTCR) effect in multilayer Y2O3-doped BaTiO3 (BTO) ceramics were investigated. The BTO ceramics were sintered at 1160 °C−1270 °C for 2 h in a reducing atmosphere and then reoxidized at 500 °C–900 °C for 0 h−4 h. Results indicated that the room-temperature resistance of BTO ceramics reoxidized at 750 °C for 2 h after sintering at 1160 °C−1270 °C for 2 h decreased with the increasing of the sintering temperature. As the reoxidation time increased, the room-temperature resistance of the BTO samples slightly increased. In addition, the effect of the reoxidation time on the PTCR effect of the ceramics was also studied. The BTO ceramics had a low room-temperature resistance of 0.3 Ω and a resistance jump greater than 3.0 orders of magnitude.

Thin-film perovskite electroluminescence with BaTiO3 films as insulating layers

ABSTRACTWe have prepared perovskite thin-film electroluminescence with multilayered BaTiO3/((Ca0.6Sr0.4)0.997Pr0.002)TiO3/BaTiO3, obtaining low-electric-field driving. Complete epitaxial growth of all layers and very flat interfaces with monoatomic steps have been obtained. With increasing driving voltage, the intensity of the electroluminescence dramatically increases. The sharp electroluminescence peak at around 610 nm at 11 V becomes much stronger with increasing ac voltage. As a result, more than 95% of the source voltage could be effectively applied to phosphor layers. To effectively apply a source voltage to a phosphor layer, insulating layers with large dielectric constants are recommended.

Piezoelectric and Dielectric Properties of Multilayered BaTiO3/(Ba,Ca)TiO3/CaTiO3 Thin Films.

Highly oriented multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films were fabricated on Nb-doped (001) SrTiO3 (Nb:STO) substrates by pulsed laser deposition. The configurations of multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films are designed with the thickness ratio of 1:1:1 and 2:1:1 and total thickness ∼300 nm. Microstructural characterization by X-ray diffraction indicates that the as-deposited thin films are highly c-axis oriented and large in-plane strain is determined in BaTiO3 and CaTiO3 layers. Piezoresponse force microscopy (PFM) studies reveal an intense in-plane polarization component, whereas the out-of-plane shows inferior phase contrast. The optimized combination is found to be the BaTiO3-(Ba0.85Ca0.15)TiO3-CaTiO3 structure with combination ratio 2:1:1, which displays the largest domain switching amplitude under DC electric field, the largest room-temperature dielectric constant ∼646, a small dielectric loss of 0.03, and the largest dielectric tunability of ∼50% at 400 kV/cm. These results suggest that the enhanced dielectric and tunability performance are greatly associated with the large in-plane polarization component and domain switching.

Interfacial structure of multi-layered thin-films produced by pulsed laser deposition for use in small-scale ceramic capacitors

The aim of this study was to develop thin film capacitors with superior properties that could provide an alternative to materials currently used in conventional multi-layer ceramic capacitors fabricated by sintering. To this end, an artificial dielectric super lattice technique, incorporating pulsed laser deposition, was applied to improving the dielectric properties of thin film capacitors. This method permits the A-site atoms of a perovskite ABO3 structure to be selected layer by layer at a nanoscopic scale; consequently, multi-layer BaTiO3- SrTiO3 thin films were produced on Pt(111)/Ti/SiO2/Si(100) and SrTiO3(111) substrates. Hetero-epitaxial grain growth was observed between BaTiO3 and SrTiO3, with the lattice mismatch between them introducing a compressive residual strain at the interface. The dielectric properties of these multi-layer thin-film capacitors were found to be superior to those of conventional solid-solution thin films once the thickness of the layers and the ratio of the two oxides were optimized.

Synthesis and characterization of multilayered BaTiO3/NiFe2O4 thin films

Presented research was focused on the fabrication of multiferroic thin film structures, composed of ferrielectric barium titanate perovskite phase and magnetostrictive nickel ferrite spinel phase. The applicability of different, solution based, deposition techniques (film growth from solution, dip coating and spin coating) for the fabrication of multilayered BaTiO3 /NiFe2O4 thin films was investigated. It was shown that only spin coating produces films of desired nanostructure, thickness and smooth and crackfree surfaces.

Multiferroic properties of multilayered BaTiO3–CoFe2O4 composites via tape casting method

Multiferroic magnetoelectric (ME) BaTiO3–CoFe2O4 (BTO–CFO) ceramic composites with different thicknesses were fabricated via tape casting technique. The interfacial morphology of the composite demonstrates the presence of plate-like grains with a thickness of ~400 nm. This could be associated with the residual stresses originated from lattice mismatch and different thermal expansion coefficients between BTO and CFO layers. The dielectric constant, piezoelectric constant, and ferroelectric properties of the multilayered composite are degraded in the presence of CFO layers in comparison with those of BTO bulk. Furthermore, the dielectric constant and polarization of the composite decrease with increasing frequency. The leakage current density and magnetic remanence ratio of the composite reach up to the order of 10−6 A/cm2 and 40 %, respectively. The direct and converse ME coefficients were measured to be 8.1 μV/cm Oe and 1.1 × 10−3 G/V, respectively. Based on the converse ME effect, an electrically controlled ME inductor was designed using the composite as its core. The inductance and tunability of the inductor increase with increase of applied dc electric field.

Stability of a ferroelectric phase with electrical domains in multilayers

Multilayer BaTiO3–SrTiO3 and PbTiO3–SrTiO3 structures with different electrical domain states are studied using a Landau–Ginzburg–Devonshire free energy. Polarizations in the layers are computed for multidomain and single-domain states where the paraelectric-to-ferroelectric volumetric layer ratio is varied. It is shown that the ferroelectric layers with electrical domains are thermodynamically more stable than the single-domain ferroelectric state. High domain wall energies result in the stabilization of the paraelectric state in the ferroelectric layers for large depolarizing fields. It is concluded that the stability of single-domain state ferroelectric layers correspond to a very small paraelectric-to-ferroelectric ratio after which multidomain ferroelectric state is favored.

Preparation of Multilayer Semiconducting BaTiO3 Ceramics Co-Fired with Ni Inner Electrodes

A multilayer semiconducting BaTiO3 ceramics having positive temperature coefficient of resistivity (PTCR) characteristics is investigated with the aim of lowering its resistance. The multilayer BaTiO3 ceramics was fired in reducing atmosphere and reoxidized at 700 °C in air. The result reveals that the multilayer semiconducting BaTiO3 ceramics with Ni inner electrodes shows high resistance even when the thickness is lowered; however, excessive donor doping markedly decreases the resistance of BaTiO3 ceramics to a very low value. The donor in excessive amounts is considered to cancel the Ni acceptors occupying the Ti sites; these acceptors diffuse from the Ni inner electrode and increase resistivity. As a result, a multilayer BaTiO3 ceramics element (3.2×2.5 mm2) with a low resistance of 0.05 Ω is realized by using excess donor doping (Sm=0.35 mol %).

Studies of Functionally-Gradient Multilayer BaTiO3 Ceramics

Physical properties of a bimorph and two trimorph multilayer BaTiO3 ceramic compositions with a gradient in Sn content were studied. The measurements made included polarization and strain hysteresis, dielectric permittivity, thermal diffusivity and polarization distributions by means of the Laser Intensity Modulation Method (LIMM).

A solution flow system for hydrothermal–electrochemical growth of multilayered thin films

A solution flow system equipment for hydrothermal–electrochemical synthesis of advanced thin films has been designed, constructed, and successfully tested. The synthesis using recyclable (aqueous) solutions as precursors can be carried out up to temperature of 200 °C and pressure of 50 kg cm−2 utilizing electrochemical activation of the nucleation and growth processes. Any clear solution can be used as a precursor; there are almost no limitations of the substrates used. The equipment is easy to use, versatile, and inexpensive. Applicability of the solution flow system for synthesis of advanced materials has been demonstrated using single-layer and multilayer BaTiO3–SrTiO3 thin films. Our equipment allows control of the microstructure of the films in a nanometric scale by changing the preparation conditions, for example the growth rate can be increased by increasing the flow rate. In addition, the multilayered films can be prepared in only one experiment just by changing the kind of flowing solution. The technique using the solution flow under the hydrothermal–electrochemical conditions is an important step in integration of the solution processing with the advanced device technology.

Impact of surface properties on the dielectric breakdown for polycrystalline and multilayered BaTiO3 thin films

The dielectric reliability for polycrystalline and multilayered BaTiO3 thin films has been evaluated using time-zero and time-dependent dielectric breakdown techniques. The histogram of dielectric breakdown for multilayered BaTiO3 thin films showed a typical Weibull distribution in contrast to a random distribution when compared with polycrystalline BaTiO3 thin films. The measurement resulted in that the 400 nm-thick multilayered BaTiO3 thin film sustained about 105 hour-long operation at 1 MV/cm, showing superior properties when compared with polycrystalline. The smaller leakage current level was obtained for a multilayered BaTiO3 film having a relatively thick underlayer of polycrystalline BaTiO3 film. The value of the breakdown field was smaller at the thicker multilayered BaTiO3 while the distribution of the breakdown widened for thicker film. Analysis of the roughness for the films confirmed that the field breakdown mechanism (e.g., lowering and spreading) is related to the surface roughness of the topmost layer which varies with the thickness of underlying polycrystalline BaTiO3. The reduced leakage current at the thick multilayered BaTiO3 was due to the presence of a wide transition layer between polycrystalline and amorphous BaTiO3.

Effects of a new stacking method on characteristics of multilayered BaTiO3 thin film

A new deposition method used to prepare BaTiO3 thin films resulted in multilayered structure with higher dielectric constant, capacitance per unit area, and breakdown strength than those prepared by a conventional stacking method; the new method continuously decreased the substrate temperature after initial deposition of a polycrystalline BaTiO3 layer. The observed high dielectric constant could be explained only by a multilayered amorphous/microcrystalline/polycrystalline structure, the nature of which was confirmed by scanning electron microscopy and index of refraction measurement. Well-defined ferroelectric hysteresis loops were observed as well with insignificant leakage current effects.

Sol-gel processed barium titanate waveguides

Monolayer monomode and multilayer multimode BaTiO3 waveguides have been prepared on amorphous silica substrates by using the dip-coating technique and the sol-gel process. After heat treatment, these waveguides were hard and of good optical quality (losses as low as 2.6 dB/cm were measured) but, their structure was found to depend strongly on the number of layers. Monolayer waveguides were totally amorphous even when heated at 1000°C, while multilayer ones exhibited the tetragonal BaTiO3 structure at an annealing temperature of 600°C.

PTCR Characteristics of Semiconducting (Ba, Ca)TiO<sub>3</sub> Ceramics Fired in Reducing-Reoxidizing Atmospheres

Three electrode materials, nickel, palladium and platinum were tested about the ohmic contact to semiconducting BaTiO3 ceramics for the application in multilayer BaTiO3 semiconductors with a positive temperature coefficient (PTC) of resistivity. Semiconducting BaTiO3 ceramics with nickel electrodes showed a good ohmic contact, while palladium and platinum electrodes showed rectifying contacts at the junctions. Semiconducting BaTiO3 ceramics with a PTC characteristic of resistivity were fired at 1350°C in a reducing atmosphere and then annealed at various temperatures in the cooling process and in various oxidizing atmospheres, with a view to fabricate multilayer PTC ceramics having Ni metal or Pd-Ni alloy as internal electrodes. The resistivity anomaly of PTC characteristics increased with increasing oxygen concentration in the annealing atmosphere and with increasing annealing temperature below 1200°C. The resistivities at room temperature were almost independent of the annealing conditions. The reoxidation in annealing occurs probably only at grain boundaries.