Crystallization Of BaTiO3 Research Articles

Twinning microstructure in the solid-phase epitaxial crystallization of BaTiO3

Amorphous BaTiO3 layers deposited on SrTiO3 (001) substrates at room temperature were subsequently crystallized using solid phase epitaxy (SPE). Heating an initially amorphous BaTiO3 layer in air at 650 °C for 3 h resulted in crystallization with components in two distinct crystallographic orientation relationships with respect to the substrate. Part of the volume of the BaTiO3 layer crystallized in a cube-on-cube relationship with the substrate. Other volumes crystallized in four variants of a 70.5° rotation about ⟨110⟩, resulting in a ⟨221⟩ surface normal in each case. Each of these four variants forms a Σ = 3 coincident site lattice with respect to the SrTiO3 substrate and the cube-on-cube oriented BaTiO3. Heating for the same duration and temperature in a reducing gas atmosphere resulted in the formation of polycrystalline BaTiO3 with no preferred crystallographic orientation. The dependence on the gas atmosphere indicates that it may be possible to tune the annealing time, temperature, and atmosphere to produce a single crystalline BTO on STO by SPE or produce a desired distribution of orientations.

Improved dielectric constant and leakage current characteristics of BaTiO3 thin film on SrRuO3 seed layer

The fabrication of high-k BaTiO3 (BTO) films for applications such as multilayer ceramic capacitors or dynamic random access memory has been achieved via the ex-situ crystallization of amorphous BTO into perovskite structure through post-deposition annealing (PDA). However, high-temperature PDA at temperatures exceeding 700 °C results in the severe degradation of BTO properties. In other words, ex-situ crystallization via PDA results in an increased dielectric constant but is accompanied by inferior leakage current characteristics caused by rough surface morphologies and defects such as voids and cracks. In this study, we demonstrate the in-situ crystallization of BTO films by introducing a high-quality SrRuO3 (SRO) film as a seed layer. The SRO film is deposited using rf magnetron sputtering at 270–350 °C, and stoichiometric SRO films are obtained on SiO2, Al2O3, and TiN substrates by controlling the growth temperature; subsequently, rapid thermal annealing at 700 °C is conducted to crystallize the SRO film. The polycrystalline SRO film on the TiN substrate exhibits excellent morphology with uniform grains as well as a continuous and smooth surface, whereas the SRO films on the SiO2 and Al2O3 substrates exhibit rough and discontinuous surfaces. The SRO seed layer on TiN permits the in-situ growth of crystalline BTO films at a relatively low temperature of 500 °C featuring a high dielectric constant of 160 and a low leakage current density of 9.5 × 10−7 A/cm2 at 0.8 V, which are 2.2 and 3.4 × 107 times improved compared with those of the ex-situ crystallized BTO film on bare TiN, respectively.

Experimental setup for high-temperature in situ studies of crystallization of thin films with atmosphere control.

Understanding the crystallization process for chemical solution deposition (CSD) processed thin films is key in designing the fabrication strategy for obtaining high-quality devices. Here, an in situ sample environment is presented for studying the crystallization of CSD processed thin films under typical processing parameters using near-grazing-incidence synchrotron X-ray diffraction. Typically, the pyrolysis is performed in a rapid thermal processing (RTP) unit, where high heating rates, high temperatures and atmosphere control are the main control parameters. The presented in situ setup can reach heating rates of 20°C s-1 and sample surface temperatures of 1000°C, comparable with commercial RTP units. Three examples for lead-free ferroelectric thin films are presented to show the potential of the new experimental set-up: high temperature, for crystallization of highly textured Sr0.4Ba0.6Nb2O6 on a SrTiO3 (001) substrate, high heating rate, revealing polycrystalline BaTiO3, and atmosphere control with 25% CO2, for crystallization of BaTiO3. The signal is sufficient to study a single deposited layer (≥10 nm for the crystallized film) which then defines the interface between the substrate and thin film for the following layers. A protocol for processing the data is developed to account for a thermal shift of the entire setup, including the sample, to allow extraction of maximum information from the refinement, e.g. texture. The simplicity of the sample environment allows for the future development of even more advanced measurements during thin-film processing under non-ambient conditions.

Mechanisms for texture in BaTiO3 thin films from aqueous chemical solution deposition

The prototype piezoelectric material BaTiO3 is widely used in e.g., capacitators. Chemical solution deposition (CSD) of BaTiO3 films is a simple and environmentally friendly processing route, but insight in the crystallization process is crucial to tailor the film properties. In this work, the influence of the annealing conditions on the crystallization behavior of BaTiO3 thin films from aqueous chemical solution deposition is presented. In situ synchrotron X-ray diffraction was used to reveal the phase evolution, crystallization of the films, and to study how the degree of crystallographic texture in the polycrystalline films evolved. Our results revealed that the formation of an intermediate metastable oxycarbonate phase is critical for the formation of BaTiO3 thin films prepared by aqueous CSD. The pyrolysis products present in the film before crystallization determine the degree of preferential orientation and by tuning the heating program, especially the heating rate through nucleation (<0.2 °C/s), control of the microstructure and degree of preferential orientation in the films was demonstrated.In situ X-ray diffraction patterns of a BaTiO3 film, prepared by spin coating of an aqueous chemical solution, as a function of time and temperature, showing the phase evolution and crystallization of BaTiO3.

Synthesis of BaTiO3 nanoparticles by sol-gel assisted solid phase method and its formation mechanism and photocatalytic activity

In this paper, a new sol-gel assisted solid-phase method for the preparation of nano BaTiO3 ceramics is proposed to solve the shortcomings of too high temperature in solid-phase preparation and NO2 pollution produced by sol-gel method. The TiO2 precursor gel is used to encapsulate BaCO3, which can effectively reduce the temperature during calcination. In this study, XRD, FT-IR, XPS, TEM, SEM and TG-DSC were used to explore the structure and evolution of samples at different stages. In addition, the crystallization and growth process of BaTiO3 were further studied. Then the energy band structure and electron hole recombination of different samples were analyzed by UV–Vis and PL spectra. Finally, the photocatalytic activity of different samples was investigated by photolytic water experiment. The results showed that BaTiO3 was initially generated at 600 °C and pure phase BaTiO3 was generated at 800 °C. In the photolytic water experiment, the samples calcined at 700 °C showed the best photocatalytic performance, with a hydrogen production rate of 43.74 μmol/g/h.

Enhanced in-plane ferroelectricity in BaTiO3 thin films fabricated by aqueous chemical solution deposition

Ferroelectric BaTiO3 is widely used in capacitors, but the low Curie temperature limits a further use of BaTiO3. In this work we present an aqueous chemical solution deposition (CSD) route for BaTiO3 thin films, demonstrating that organic solvents are not required for CSD. Textured BaTiO3 thin films were deposited on SrTiO3 substrates. The in-plane dielectric properties were investigated using interdigitated electrodes and ferroelectric switching was observed up to 160±5 °C. The increased Curie temperature is proposed to result from thermal strain due to a mismatch in thermal expansion coefficient between the film and the substrate, and is in good agreement with the theory of strain engineering in BaTiO3. Finally, the decomposition and crystallization of BaTiO3 during thermal treatment were determined by the combination of thermal analysis, IR spectroscopy and X-ray diffraction of powder prepared from the solution.

Giant Strain and Induced Ferroelectricity in Amorphous BaTiO₃ Films under Poling.

We report an effect of giant surface modification of a 5.6 nm thick BaTiO3 film grown on Si (100) substrate under poling by conductive tip of a scanning probe microscope (SPM). The surface can be locally elevated by about 9 nm under −20 V applied during scanning, resulting in the maximum strain of 160%. The threshold voltage for the surface modification is about 12 V. The modified topography is stable enough with time and slowly decays after poling with the rate ~0.02 nm/min. Strong vertical piezoresponse after poling is observed, too. Combined measurements by SPM and piezoresponse force microscopy (PFM) prove that the poled material develops high ferroelectric polarization that cannot be switched back even under an oppositely oriented electric field. The topography modification is hypothesized to be due to a strong Joule heating and concomitant interface reaction between underlying Si and BaTiO3. The top layer is supposed to become ferroelectric as a result of local crystallization of amorphous BaTiO3. This work opens up new possibilities to form nanoscale ferroelectric structures useful for various applications.

Phase composition identification and microstructure of BaTiO3-containing sodium-aluminoborosilicate glass-ceramics

Bulk glasses with a composition 20.1Na2O/23.1BaO/23.0TiO2/7.6B2O3/17.4SiO2/3Al2O3/5.8Fe2O3 containing less than 30 mol% glass-forming oxides are synthesized. Information on the valency of the glass constituents is obtained by x-ray photoelectron spectroscopy and it is concluded that all species are predominantly present in their oxidized state. Glassy samples are annealed above the glass transition temperature which leads to the crystallization of BaTiO3 for all time-temperature applied schedules. The phase composition of the glass-ceramics is studied by x-ray diffraction and the formation of cubic BaTiO3 is suggested. Temperature-dependent Raman spectroscopy confirms the presence of solely cubic BaTiO3. The microstructures of all annealed samples are similar and consist of globular interconnected particles in which nanosized BaTiO3 crystals grow randomly. The mean size of the spherical formations increases with the increasing annealing time from 200 to 600 nm. Electron microscopy suggests that during the annealing process first phase separation and then crystallization of BaTiO3 occurs.

Facile synthesis of nanorods of tetragonal barium titanate using ethylene glycol

Tetragonal barium titanate (BaTiO3) nanorods were synthesized from hydroxide precursor by a hydrothermal/solvothermal method with 10vol% ethylene glycol as solvent. The hydroxide precursor slurry was prepared by the addition of 10M NaOH to a mixed solution of BaCl2 and TiCl4. When the above aqueous slurry was heated with water only at 200°C, cubic BaTiO3 nanocrystals formed, whereas tetragonal BaTiO3 nanorods were obtained when heated with 10vol% ethylene glycol. The crystallization of cubic BaTiO3 via dissolution–reprecipitation of precursor could be suppressed by the addition of ethylene glycol, resulting in the formation of tetragonal BaTiO3 under hydrothermal treatment at 200°C.

Crystallization behavior of a barium titanate tellurite glass doped with Eu3+ and Er3+

The main objective of this work has been to investigate the crystallization behavior of the glass composition 70TeO2–15BaO–15TiO2 doped with Eu3+ and Er3+ in order to check the possibility of obtaining transparent glass–ceramics containing rare earth-doped BaTiO3 nanocrystals. Glass samples with the ternary composition 70TeO2–15BaO–15TiO2 were synthesized by the melt-quenching method and doped with 0.1% of Eu3+ and Er3+. Thermal properties were investigated by DTA and heat-treatments were applied between Tg and Tx to induce the controlled crystallization of these glasses. One-step and two-step heat treatments were tested and the final glass–ceramics characterized by X-ray diffraction and UV–Vis absorption. It has been shown that transparent glass–ceramics can be obtained after heat-treatment but barium titanate BaTiO3 is hardly precipitated without coprecipitation of another crystalline phase identified as an isostructure of lanthanum tellurate. In addition, the crystalline volume fraction is relatively small in these transparent samples. Finally, Gold doping has been shown to be very effective to promote a volume nucleation and preferential crystallization of BaTiO3 over the other crystalline phases.

Effect of temperature and time on solvothermal synthesis of tetragonal BaTiO3

Tetragonal BaTiO3 nanoparticles are synthesized via solvothermal route in an ethanol water mixture. Ba(OH)2·8H2O is used as Ba precursor and TiO2 (P25 Degussa ∼25 nm, 30% anatase, 70% rutile) is used as Ti precursor in the Ba : Ti molar ratio 2 : 1. Effect of temperature and time study on solvothermal synthesis of BaTiO3 revealed that a moderate reaction temperature i.e. 185°C and longer reaction time favour tetragonal phase stabilization. Dissolution–precipitation appears to be the transformation mechanism for the crystallization of BaTiO3 from particulate TiO2 precursor.

Properties of BaTiO3 confined in nanoporous Vycor and artificial opal silica

Using the sol-gel technique, BaTiO3 was embedded into nanoporous Vycor and artificial vitreous opal silica for the first time. About 50 vol% of the pores was filled. In case of the Vycor glass (pore diameter 4-6 nm) only amorphous phase was revealed by XRD, IR reflectivity and Raman spectra. After additional gradual annealing, no crystallization was achieved. Chemical reaction with the SiO2 skeleton started at ~1000 K. The room-temperature IR and Raman spectra clearly show characteristic vibrational modes of the ferroelectrically distorted TiO6 octahedra without any long-range order. In case of the opal matrix (densely packed silica spheres, pore diameter up to ~50 nm), crystallization of the ferroelectric BaTiO3 appeared in coexistence with the amorphous phase, but the penetration depth of the crystalline BaTiO3 was limited. From the apparent temperature independence of the effective wide-frequency dielectric response due to the essentially temperature independent effective soft mode stiffened to ~100 cm-1, we can deduce that no macroscopic percolation of the crystalline BaTiO3 has appeared in our opal matrix. Nevertheless, Raman spectra bring evidence of a diffuse ferroelectric phase transition in the opal-BaTiO3 composite.

Effect of the Ba/Ti Ratio on the Microstructures and Dielectric Properties of Barium Titanate‐Based Glass–Ceramics

A series of BaTiO3 (BT)‐based ferroelectric glass–ceramics have been prepared via controlled crystallization by varying the Ba/Ti ratio in an aluminum silicate glass composition, and the subsequent microstructure, phase evolution, and dielectric properties have been investigated. X‐ray diffraction indicated that an increasing Ba/Ti ratio promoted the crystallization of BaTiO3 and BaAl2Si2O8 from the glass matrix, and the cracking of glass–ceramics appears to be correlated to mismatch in the thermal expansion coefficient among BaTiO3, BaAl2Si2O8, and the glass matrix. In addition, it was found that increasing the Ba/Ti ratio facilitated the formation of a dendrite structure with obvious porosity. The change in the Ba/Ti ratio in the glass notably modified the dielectric properties: a high Ba/Ti ratio in the glass resulted in an increased dielectric constant and decreased breakdown strength.

Formation of BaTiO3from Barium Oxalate and TiO2

Barium titanate powder has been prepared via a semi-oxalate method that uses barium oxalate and TiO2 precursors, instead of titanyl oxalate. Barium oxalate was precipitated from nitrate solution onto the surface of TiO2 powders. Crystallization of BaTiO3 from the precursors was investigated by TGA, DTA and XRD analysis. It is evident that an intermediate barium oxycarbonate along with BaCO3, forms between 450–500°C and that decomposes to BaCO3 again at high temperature. Decomposition of BaCO3 occurs at much lower temperature, from 600°C onwards, due to the presence of TiO2. The precursor completely transforms into BaTiO3 at 900°C. Nanometer size BaTiO3 crystallites are produced during this synthesis due to the lower calcination temperature. The crystalline morphology of BaTiO3 is controlled mainly by the morphology of BaCO3, which formed in the intermediate stage.

Crystallization of BaTiO3 Thin Films Prepared by Metalorganic Decomposition with Hydrothermal Treatment at 140°C

AbstractBaTiO3 (BTO) thin films with perovskite structure have been prepared on Pt/Ti/SiO2/Si substrates using a combined process of a conventional MOD (metal organic decomposition) process and a hydrothermal treatment. The BTO thin films with polycrystalline structure are grown on Pt/Ti/SiO2/Si substrates at a processing temperature of 140°C. The structural development, stoichiometry, spectroscopic, and dielectric properties of the BTO thin films have been systematically investigated. X-ray diffraction patterns show that well-developed crystallites with a pure perovskite phase have been formed. ICP (Inductively coupled plasma) and XPS (x-ray photoelectron spectroscopy) results show that stoichiometric BTO thin films were obtained.

Poling-induced crystallization of tetragonal BaTiO3 and enhancement of optical second-harmonic intensity in BaO–TiO2–TeO2 glass system

Effect of poling on surface crystallization behavior of BaTiO3 in 15BaO–15TiO2–70TeO2 glass and on second-harmonic generation of the resultant glass ceramics has been examined. A direct current voltage in a range of 0.3–1 kV was applied to the original glass at around 400 °C, which is above its glass transition temperature, followed by cooling of the sample to room temperature with the voltage kept constant. X-ray diffraction patterns indicate that the poling increased the fraction of crystalline phases precipitated at the glass surface and that BaTiO3 crystallites were precipitated preferentially with (101)- or (110)-orientation. It is also observable that the x-ray diffraction line assigned to BaTiO3 shifted from the position corresponding to bulk cubic crystal to that of ferroelectric tetragonal one when the applied voltage was increased. In other words, the poling treatment stabilizes the tetragonal BaTiO3 phase, leading to a larger optical second-order nonlinear susceptibility. In fact, the second-harmonic intensity for the glass ceramic poled at 420 °C was enhanced by a factor of ten compared with the glass ceramic heat treated without an external electric field.

Preparation and Properties of Ferroelectric BaTiO3 Thin Films by Sol-Gel Process

Ferroelectric BaTiO3 thin films have been successfully prepared by sol-gel process using barium and titanium isopropoxides as precursor solutions for dip-coating. Homogeneous BaTiO3 thin films have been obtained on various substrates by preheating gel films at 120°C in a flow of oxygen/water vapor mixed gas, and successive heating at 650°C in oxygen atmosphere. The introduction of water vapor during preheating is very effective for the crystallization of BaTiO3 at relatively low temperatures. These films exhibit good crystallinity and smooth surfaces with grains as small as about 50 nm. BaTiO3 thin films prepared on Pt/SiO2/Si substrates with a thickness of about 0.5 µm show dielectric constants of 800∼1000 and loss tangents of 0.07∼0.09 at 1 kHz. Ferroelectric hysteresis loops were observed for these thin films which possessed the remanent polarization of 8 µC/cm2 and the coercive field of 25 kV/cm.

Metal Organic Resin Derived Barium Titanate: I, Formation of Barium Titanium Oxycarbonate Intermediate

Crystallization of BaTiO3 from an X‐ray amorphous, metal organic precursor was investigated by comparing samples heated in O2, air, argon, and CO2. It is evident that an intermediate barium titanium oxycarbonate phase forms between 500° and 620°C and that BaTiO3 forms directly by the endothermic decomposition of this phase between 635° and 700°C. From thermodynamic calculations, thermal analysis, X‐ray diffraction, and Raman spectroscopy, it is concluded that the intermediate oxycarbonate is a highly disordered, metastable, and weakly crystalline phase with a stoichiometry close to Ba2Ti2O5CO3.

Microcrystalline BaTiO3 by Crystallization from Glass

The properties and composition of glasses suitable for crystallization of BaTiO3 are described. The crystallization of certain glasses results in a nearly complete recovery of BaTiO3, besides the feldspar BaAl2SiO3 as a minor phase. The mechanism of crystallization was investigated by thermal analysis, viscosity, and grainsize measurements as a function of the temperature whereas density data were used for evaluation of the BaTiO3 content. Within the range 30 to 60% by volume of BaTiO3 at about 1μ grain size, the measured dielectric constant increased from 100 to 1200. The calculated partial dielectric constant of the Titanate phase at this grain size was about 3500. As the grain size approached 0.1μ, the dielectric constant decreased and became nearly independent of the temperature because of the predominance of surface states. Other effects were attributed to special structural characteristics, such as absence of porosity and clamping of the titanate particles within the microcrystalline matrix. Data are also presented on dielectric constant and loss tangent at different frequencies, dc breakdown strength, dc resistivity, and ferroelectric properties as a function of the grain size of the crystallized material.