Crystalline BaTiO3 Research Articles

A Low Temperature Preparation of BaTiO3 Thin Film by Sol-Gel-Hydrothermal Treatment below 210°C

BaTiO3 thin films with a perovskite structure have been prepared by the hydrohermal treatment of TiO2 gel films at temperatures below 210°C. The TiO2 gel films were produced at 200°C by the sol-gel method and then were transformed into crystalline BaTiO3 thin films with the hydrothermal treatment in Ba(OH)2 alkaline aqueous solutions below 210°C. The hydrothermal crystallization of BaTiO3 thin films depends remarkably on the prebaking temperature of the TiO2 gel film, and the morphology depends on the Ba(OH)2 concentration, but the crystalline structure is not changed according to the results of XRD θ-2θ and reciprocal space mapping measurements. The microscopic structure is columnar for BaTiO3 thin films treated in Ba(OH)2 solutions greater than 0.3 M and is granular for those treated in solutions less than 0.2 M. The morphology of the BaTiO3 thin film treated in 0.2 M Ba(OH)2 solution is an island structure near the surface and granular near the bottom. The BaTiO3 thin film treated at 210°C for 3 h in 0.2 M Ba(OH)2 solution has a hysteresis loop showing 5 µC/cm2 at zero electric field.

Formation of Ferroelectric Perovskite Nanostructure Patterns Using Latex Sphere Monolayers as Masks: An Ambient Gas Pressure Effect during Pulsed Laser Deposition

Nine-nanometer-thick ferro- and piezoelectric nanocrown patterns consisting of crystalline BaTiO3 have been prepared by pulsed laser deposition using latex sphere monolayer masks. The unusual crown-like shape of the nanopattern is achieved by selecting the appropriate high ambient pressure during deposition. The ferro- and piezoelectric properties were investigated by AFM in piezoresponse mode.

Continuous Production of BaTiO3 Nanoparticles by Hydrothermal Synthesis

Continuous production of BaTiO3 fine particles was performed by hydrothermal synthesis using a flow reaction system. The effect of reaction temperature on particle size and its distribution was investigated. Aqueous 0.1 M TiO2 sols and 0.12 M Ba(OH)2 solutions were used as starting materials. The reaction temperature was in the range 300−420 °C, and the reaction pressure was constant at 30 MPa. The reaction time was varied from 0.1 to 40 s with a flow rate of 15 or 75 g/min. Characterizations of products were performed by X-ray diffractometry, scanning electron microscopy equipped with energy dispersion X-ray spectrometry, and transmission electron microscopy. The conversion of TiO2 into BaTiO3 was also evaluated. At 300 °C, the Ti conversion increased with the reaction time and achieved a 95% yield at 38 s. With the increase in temperature, both the Ti conversion and the crystallinity of BaTiO3 became high. With an increase in temperature from 300 to 380 °C, the average particle size of BaTiO3 decreased ...

Direct Micropatterning by Laser-Induced Pyrolysis of Sol-Gel-Derived BaTiO3 Films Seeded with BaTiO3 Crystalline Nanoparticles

Direct Micropatterning by Laser-Induced Pyrolysis of Sol-Gel-Derived BaTiO3 Films Seeded with BaTiO3 Crystalline Nanoparticles

Low‐Temperature Synthesis of Fully Crystallized Spherical BaTiO3 Particles by the Gel–Sol Method

The synthesis of spherical BaTiO3 particles was attempted by a new technique, the “gel–sol method,” at 45°C. The (Ba–Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with a barium acetate aqueous solution ([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] = 4, [barium acetate]/[TIP] = 1) at 45°C for 48 h. Potassium hydroxide (KOH) was used as a catalyst for the formation of BaTiO3. Powder X‐ray diffractometry (XRD) results and Fourier‐transform infrared (FT‐IR) measurements for the (Ba–Ti) gel showed that the gel was amorphous, but the spatial arrangement of barium and titanium in the (Ba–Ti) gel is similar to that in crystalline BaTiO3 particles. Fully crystallized spherical BaTiO3 powder with a particle size of 40–250 nm formed at the very low reaction temperature of 45°C. Scanning electron microscopy images showed that the final particles formed via aggregation of the fine particles that seem to be the primary particles of bulk (Ba–Ti) gel. From the XRD, FT‐IR, and Raman spectroscopy analysis, it was found that the crystal structure of the as‐prepared particles continuously transformed from cubic to tetragonal as the calcination temperature increased, and high crystalline tetragonal BaTiO3 phase was obtained at 1000°C after 1 h of heat treatment.

Electronic properties of ferroelectric BaTiO3∕MgO capacitors on GaAs

Thin films of MgO and BaTiO3 were deposited on (001) GaAs substrates using molecular beam epitaxy and pulsed laser deposition, respectively. X-ray diffraction scans indicate crystalline MgO and BaTiO3 thin films with preferential c-axis orientation. Capacitors fabricated from the BaTiO3∕MgO∕GaAs structures demonstrate ferroelectric hysteresis behavior with a remenant polarization of 0.4μC∕cm2. Small-signal capacitance measurements indicate an effective dielectric constant for the BaTiO3∕MgO structure of 45.5ε0. A hysteresis behavior indicative of ferroelectric switching is observed in the capacitance–voltage characteristics with a memory window of approximately 2 V. The observation of ferroelectric behavior in these materials are promising for future multifunctional devices on GaAs.

Nonaqueous and Halide‐Free Route to Crystalline BaTiO3, SrTiO3, and (Ba,Sr)TiO3 Nanoparticles via a Mechanism Involving C—C Bond Formation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

One-step Preparation of BaTiO3 Nanoparticles by Liquid Source Chemical Vapor Deposition

Barium titanate (BaTiO3) nanoparticles were prepared by means of a liquid source chemical vapor deposition method under atmospheric pressure. The effects of precursor composition, concentration, operating temperature, and residence time in the hot zone on the surface morphology, composition, and crystallinity of the resulting particles were investigated. By increasing the Ba/Ti ratio in the precursor, the amount of TiO2 particles tended to decrease, while the amount of barium carbonate (BaCO3) particles increased. By decreasing the precursor concentration or the residence time in the hot zone, both particle size and degree of aggregation of the particles produced decreased, but the amount of barium carbonate increased. At a Ba/Ti ratio of 2.3, spherical and highly crystalline cubic BaTiO3 particles 27 nm in size with a narrow size distribution (σg = 1.33) were produced at 900°C.

Annealing of BaTiO 3 thin films after heavy ion implantation

Single crystalline BaTiO 3 films have been grown by pulsed laser deposition on SrTiO 3. Radioactive 111In ions were implanted with energies of 60 and 400 keV, respectively. The lattice site of 111In has been determined by emission channeling of conversion electrons emitted after the nuclear decay to 111Cd. Besides a large random fraction, 11(3)% of the events show that In substitutes Ti-sites directly after the implantation. The recovery of the lattice after the implantation has been monitored in the direct vicinity of the probes by perturbed angular correlation (PAC) spectroscopy in a wide temperature range. After annealing in air at a temperature of 1420 K for 10 min, PAC spectroscopy yields a unique electric field gradient at the site of the 111In( 111Cd)-probe with a quadrupole coupling constant of 28.7(5) MHz and a frequency distribution with a width of 4.2(2) MHz. The film starts to degrade at a temperature of 1520 K. Scanning electron microscopy and energy dispersive X-ray spectroscopy investigations have been used to monitor the degradation.

Effects of KOH/BaTi and Ba/Ti ratios on synthesis of BaTiO 3 powder by coprecipitation/hydrothermal reaction

BaTiO 3 powders were synthesized by coprecipitation and by the hydrothermal reaction using barium acetate and acylated titanium isopropoxide as starting materials (KOH/BaTi molar ratios: 6:20, Ba/Ti molar ratios: 1.0:1.8). An increase in the Ba/Ti ratio of starting materials was found to give a lower degree of agglomeration in synthesized powders, presumably due to the enhanced adsorption of compounds like barium acetate into titanium-based complexes. A high Ba/Ti ratio of starting materials was found to be more favorable for the formation of stoichiometric BaTiO 3. The higher the ratio of KOH to Ba and Ti precursor, the smaller the sizes of crystalline BaTiO 3 powders synthesized. When the KOH/BaTi ratio was higher than 13, crystalline BaTiO 3 powders were synthesized without subsequent hydrothermal reaction.

Comments on the Defect Chemistry of Undoped and Acceptor-Doped BaTiO3

In a recent study of the defect chemistry of undoped polycrystalline and acceptor-doped single crystalline BaTiO3 an attempt was made to obtain defect and thermodynamic parameters without any a priori assumptions, e.g. about the magnitude and temperature dependence of the carrier mobilities. The parameters found for the undoped sample differ significantly from those obtained from the acceptor-doped sample, and even more substantially from those reported from several earlier studies. It is suggested that these discrepancies result from the lack of sufficient data in certain critical regions of temperature and oxygen activity. As a result, the attempt to extract parameters from the equilibrium conductivity by multiparameter curve-fitting has considerable uncertainty. However, the electron and hole mobility products and ratios, μ n μ p and μ n /μp, were determined by linear extrapolation of the well-established log-log slopes of +1/4 and −1/4 for the equilibrium conductivities and oxygen diffusivities to their intersection. Both the products and the ratios were found to be independent of temperature, indicating that both mobilities are also independent of temperature. This important conclusion validates the thermodynamic parameters obtained in earlier studies in which it was assumed that the mobilities are temperature independent or nearly so, and that the carrier concentrations are proportional to the conductivities.

The PLD of BaTiO 3 target produced by SPS and its electrical properties for MLCC application

The pulsed laser deposition (PLD) of barium titanate (BaTiO 3) target produced by spark plasma sintering (SPS) has been carried out by using excimer laser. The effects of sintering conditions of SPS on the BaTiO 3 target, the influence of PLD conditions and oxygen pressure on thin film were investigated. Furthermore, the effects of the post-deposition annealing and the oxygen pressure on the dielectric properties were also studied. At a mixing ratio of 2:5 with diameter powder of 0.1 and 0.5 μm and at sintering temperature of 1423 K, the relative density of a sintered compact was 99.6%. At an oxygen pressure of 5 Pa, the ratio of Ba/Ti of thin film was approximately 1, making it ideal as dielectric materials. However, the crystalline of film as deposited was still not obtained. The crystalline BaTiO 3 film with a tetragonal and cubic structure was obtained by annealing at 873 K in the atmosphere for 10 min. At the oxygen pressure below 10 Pa, the relative permittivity increased with the increase of oxygen pressure. The highest relative permittivity was obtained at 5 Pa; the relative permittivity reached 300 at the BaTiO 3 ratio of about 1.0. The surface form of thin film as deposited and after crystallization did not change; it was flat and smooth.

Semiconducting barium titanate ceramics prepared by using yttrium hexaboride as sintering aid

Nb-doped BaTiO 3 semiconducting ceramics have been prepared at 1150 °C by employing YB 6 as the sintering aid. The low-temperature sintered samples exhibit a positive temperature coefficient of resistivity (PTCR) effect. The room-temperature resistivity and the magnitude of PTCR effect depend on the amount of YB 6 added, the Nb 2O 5 content and the sintering conditions. At 1 mol% of YB 6, the sample has a low room-temperature resistivity and a resistivity jump of about 10 4. Transmission electron microscope studies revealed that the intergranular region between the crystalline BaTiO 3 grains has an amorphous structure. Y, Ba and Ti are present in the intergranular region but no Y is detectable in the crystalline grains. A liquid phase is believed to be present during sintering and it helps to facilitate the densification process and to enhance the PTCR effect.

Simultaneous measurements of heat flux and thermal expansion on hyperfine multistage transitions of single crystalline BaTiO 3

The heat flux and the thermal expansion of BaTiO 3 were simultaneously measured with a temperature resolution of milli-Kelvin to observe the multistage transitions. Heat flux was detected by the thermomodule and thermal expansion was detected by observing the change of capacitance due to the change of the sample length. At least six thermal anomalies were observed between 402 and 405 K in BaTiO 3 simultaneously in heat flux and thermal expansion in the cooling process. The correspondence of the anomalies observed in the two physical properties was excellent. The thermal expansion curves along 〈0 0 1〉 direction obtained at the cooling rates less than 20 μK s −1 consisted of several steps with different number and magnitude depending on the cooling rate. The hysteresis behaviors for the phase transition of BaTiO 3 are discussed in terms of domains.

Hetero-Epitaxy of Crystalline Perovskite Oxides on GaAs(001)

ABSTRACTHetero-epitaxy of crystalline perovskite SrTiO3 and BaTiO3 on GaAs(001) was achieved using molecular beam epitaxy. A number of surface and interface techniques were used to characterize the growth, structural, and chemical properties of epitaxial oxide films on GaAs. Reflection-high-energy-electron diffraction of SrTiO3 and BaTiO3 showed streaky diffraction features and low diffraction background through out growth, indicating that the epitaxial SrTiO3 and BaTiO3 films had good crystallinity. X-ray diffraction showed an epitaxial relationship between these perovskite oxides and GaAs(001) substrates. Transmission electron microscopy and scanning probe microscopy revealed an abrupt oxide/GaAs interface and smooth SrTiO3 and BaTiO3 surfaces. The success of growth of epitaxial perovskite oxides on GaAs enabled us to integrate a number of functional oxides such as piezoelectric and magnetic oxides epitaxially on GaAs substrates.

The influence of concentration on the formation of BaTiO3 by direct reaction of TiCl4 with Ba(OH)2 in aqueous solution

Abstract The formation of fine BaTiO 3 particles by reaction between liquid TiCl 4 and Ba(OH) 2 in aqueous solution at 85 °C and pH⩾13 has been studied for 0.062⩽[Ba 2+ ]⩽0.51 mol l −1 . The concentration of Ba 2+ ions has a strong influence on reaction kinetics, particle size and crystallite size. When [Ba 2+ ]>≈0.12 mol l −1 , the precipitate consists of nanosized (≈30 nm) to submicron (100–300 nm) particles of crystalline BaTiO 3 . At lower concentrations, the final product is a mixture of crystalline BaTiO 3 and a Ti-rich amorphous phase even for very long reaction times. A two-steps precipitation mechanism is proposed. Initially, a Ti-rich amorphous precipitate is rapidly produced. Reaction between the amorphous phase and the Ba 2+ ions left in solution then leads to crystallisation of BaTiO 3 . In addition to nucleation and growth of nanocrystals, the final size and morphology of BaTiO 3 particles obtained at low concentration can be determined by aggregation of nanocrystals and heterogeneous nucleation on existing crystal surfaces.

Effect of molar ratio of KOH to Ti-isopropoxide on the formation of BaTiO3 powders by hydrothermal method

Nano-crystalline BaTiO3 powders were prepared using acylated titanium and barium acetate with hydrothermal method. The solution pH given by the molar ratio of KOH to Ti-isopropoxide was found to have an important effect on the size, morphology, and crystallinity of BaTiO3 powders. FT-IR and Raman analyses showed that there were still some Ba–OAc bonds in the structure of as-prepared powders formed from the low pH alkaline solution. As hydrothermal aging time increased, the crystal structure of as-prepared powders was continuously transformed from amorphous to crystalline BaTiO3 powders with breakage of Ba–OAc bonds and elimination of acetyl groups in the powders. When the solution pH was high, most of the acetyl groups bonded to Ba or Ti atoms were eliminated rapidly by hydrolysis in the solution. As a consequence, crystalline BaTiO3 directly precipitated from homogeneous solution via condensation reaction between –Ba–OH and –Ti–OH bonds without subsequent hydrothermal reaction.

Laser crystallisation during pulsed laser deposition of barium titanate thin films at low temperatures

Using a high dielectric material as substitute for SiO x N y in dielectric film capacitors of dynamic memories (DRAM) allows a significantly higher integration density and a reduction of the die size, even with planar capacitors. BaTiO 3 is such a material. A dielectric constant of ε r>1000 has been achieved in thin films, made by pulsed laser deposition (PLD). For applications in microelectronic memories it is necessary to produce crystalline, defect-free and oriented BaTiO 3 thin films at substrate temperatures, T S<450 °C. Sintered targets of BaTiO 3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O 2 at pressures of 0.1–50 Pa. The substrate is resitively heated to 360–440 °C and annealed after or during PLD on Pt/Ti/Si multilayer substrates using KrF excimer laser radiation with fluences up to 120 mJ/cm 2. The temperature distribution in the BaTiO 3/Pt/Ti/Si multilayers during laser annealing is dynamically modelled and related to the resulting crystal quality and the dielectric properties of the films. With PLD a minimum substrate temperature of 500 °C is necessary to deposit crystalline BaTiO 3 films. Using in situ laser crystallisation crystalline BaTiO 3 films can be deposited at substrate temperatures of T S=360–440 °C showing a dielectric constant of up to ε r=1200. The ferroelectric and dielectric properties of the films are determined by C– V and P– V impedance measurements and correlated to the chemical and structural properties, as determined by X-ray photoemission spectroscopy, X-ray diffraction, micro Raman spectroscopy and scanning electron microscopy.

Growth and Morphology of Pentacene Films on Oxide Surfaces

ABSTRACTPentacene thin films were grown in ultra high vacuum on amorphous SiO2 and on a high dielectric constant material, crystalline BaTiO3. During pentacene deposition, substrates were held at three different temperatures (-650, 250 and 750 C). In general, three different morphologies were identified: a first closed interfacial layer, a thin film mode composed of faceted grains with single molecule step height, and a volume mode with features substantially higher than those of the thin film mode. Analysis was carried out by atomic force microscopy and in some cases by synchrotron X-ray diffraction.

Segregation phenomena in thin films of BaTiO3

The near-surface region in perovskite bulk crystals is known to be subject to segregation processes at elevated temperatures which can lead to the formation of non-perovskite phases. We have addressed the question whether analogue phenomena may occur in thin films. Thin films of BaTiO3 prepared by different methods (PLD, CSD) and heat-treated in the temperature range of 700°C-1000°C are characterised by surface analytical methods and microanalysis (AFM, SIMS, XPS). Our studies reveals dramatic changes in the surface morphology and in-depth elemental distribution suggesting a chemical restructuring comparable to the effects known for single crystalline BaTiO3. Possible driving forces for the observed segregation phenomena are discussed taking into account specific properties of the thin films.