Bi4Ti3O12 Powders Research Articles

Dielectric, piezoelectric and ferroelectric anisotropy in grain oriented Aurivillius phase Sr2Bi4Ti5O18 processed by the reactive templated technique

ABSTRACTSr2Bi4Ti5O18 ceramics were fabricated using the pre-reacted Bi4Ti3O12 and SrTiO3 powders via solid-state reaction route. These in stoichiometric ratio were uniaxially pressed and sintered at 1130°C for 3 h to obtain textured ceramics. The obtained dense ceramics exhibited crystallographic anisotropy with prominent c-axis oriented grains (Lotgering factor of 0.62) parallel to the uniaxially pressed direction. The resulted anisotropy in the ceramic was attributed to the reactive template-like behavior of Bi4Ti3O12 that was used for making Sr2Bi4Ti5O18. Dielectric, ferro and piezoelectric properties measured on the ceramics in the direction perpendicular to the uniaxially pressed axis were found to be superior to that measured in the parallel direction.

Microstructure, ferroelectric and dielectric proprieties of Bi4Ti3O12 materials prepared by two methods

Bi4Ti3O12 (BTO) materials were prepared by the sol–gel method via the acetic acid method (AAM) or the ethylene glycol method (EGM). BTO powders prepared by EGM are composed of the main phase without purity phases when annealed at 650 °C. BTO powders prepared by AAM are composed of the main phase without secondary phases when annealed at 625 °C. BTO ceramics prepared by AAM have denser microstructure and greater grain size than those prepared by EGM. BTO ceramics prepared by two methods exhibit well typical P–E loops for ferroelectrics. The remnant polarization of BTO ceramics prepared by AAM is greater than those prepared by EGM. And the coercive field and dielectric loss of BTO ceramics prepared by AAM are smaller than those prepared by EGM. BTO ceramics prepared by AAM have better ferroelectric and dielectric properties than those prepared by EGM.

Formation Mechanism of Plate-like Bi4Ti3O12 Particles in Molten Salt Fluxes

The plate-like Bi4Ti3O12 particles were prepared by molten salt synthesis method. The influence of sintering temperature and cooling process on the microstructure of Bi4Ti3O12 powders was studied. Much larger particles were formed at higher temperatures. The particles could grow larger in slow cooling process. The formation mechanism of plate-like Bi4Ti3O12 particles in Na2SO4-K2SO4 system could be viewed as four processes: (1) solid reaction and nucleation, (2) plate-like structure formation, (3) diffusion and edge nucleation, (4) diffusion and epitaxial growth.

Effect of reductant type on phase composition and ferroelectric behavior of combustion-synthesized BaTiO3 and Bi4Ti3O12

Finely dispersed BaTiO3 and Bi4Ti3O12 powders were prepared by solution-combustion synthesis using glycine, carbamide, and glycerol as reducing agents. The use of glycine as a reducing agent was found to yield single-phase BaTiO3 and Bi4Ti3O12 without additional heat treatment. Explored was the influence of reductant type and process parameters on the phase composition, crystal structure, and dielectric properties of combustion-synthesized barium and bismuth titanates.

Hydrothermal Synthesis of Spherical Bismuth Titanate Crystals

Spherical bismuth titanate (Bi4Ti3O12) particles were synthesized by hydrothermal method using Bi(OH)3, Ti(SO4)2 and KOH as raw materials, using polyvinylpyrrolidone (PVP) as the surfactant. The effects of concentration of the alkali solution, the reaction temperature and soaking time on the bismuth titanate crystal structure and morphology have been analyzed. XRD, SEM were used to characterize the crystal structure and microstructure of the as-prepared Bi4Ti3O12.The results show that the temperature plays an important role on the morphology of the Bi4Ti3O12.As the increase of the hydrothermal temperature, the Bi4Ti3O12 has been transformed from the spherical morphology to fibrous morphology. The spherical Bi4Ti3O12 powders with uniform distribution can be obtained when the concentration of KOH is from 1mol/L to 2 mol/L,the reaction temperature and hydrothermal time are 160°C and 24h respectively. SEM observation showed that the diameter of spherical Bi4Ti3O12 is about 500 nm.

A simple method for fabricating p–n junction photocatalyst CuFe2O4/Bi4Ti3O12 and its photocatalytic activity

The synthesis of Bi4Ti3O12 and CuFe2O4 powders was achieved using a conventional solid-state reaction and the Sol–Gel method, respectively. A novel p–n heterojunction photocatalyst CuFe2O4/Bi4Ti3O12 was subsequently prepared through ball milling. The structures, morphologies, and optical properties of the photocatalysts were comprehensively characterized. The transmission electron microscopy (TEM) images showed a clear interface between CuFe2O4 and Bi4Ti3O12, indicating that a heterojunction between CuFe2O4 and Bi4Ti3O12 was formed during ball milling. In addition, the photocatalytic activity was evaluated based on the photocatalytic degradation of methyl orange (MO). The results indicated that the photocatalytic activity of the p–n heterojunction photocatalyst CuFe2O4/Bi4Ti3O12 was higher than that of Bi4Ti3O12 alone. The enhanced photocatalytic activity could be attributed to the formation of a heterojunction between CuFe2O4 and Bi4Ti3O12, which suppressed the recombination of photogenerated electron–hole pairs. We also investigated the effects of procedure time and dispersant (H2O) during ball milling on the photocatalytic activity. The mechanisms underlying the observed photocatalytic activity were also described based on the semiconductor energy band theory and p–n junction principle. Moreover, the analysis of the radical scavengers confirmed that •O2− and h+ were the primary reactive species to cause the degradation of the MO.

Preparation of Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> (BIT) Ceramics via a High-Energy Ball Milling Process Doped with Multi-Walled Carbon Nanotubes (MWNTs)

We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With an increasing milling time, this particle size of mixture is gradually reduced, thus, we have mostly an amorphous phase. The BIT ceramics were duly obtained by sintering the synthesized powders at temperatures ranging from 850°C to 1000°C. The BIT ceramics sintered at 1020°C for 1 h, exhibiting a density with 7.52 g/cm3 of a crystaline phase and a dielectric of K = 288.11 (100 Hz), as well as a dielectric loss of 0.05 (100 kHz). The High-energy ball milling process is a promising way to prepare BIT ceramics. After the preparation of the BIT, we doped it with the Multi-Walled Carbon Nanotubes which are properly obtained by a chemical vapour deposition (CVD), using nickel as a catalyst, as well as using acetilene at 720°C, and then proceeded with the dielectric and optical measurements.

Fabrication and electrical properties of 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 textured ceramics by RTGG method using micrometer sized BaTiO3 plate-like templates

Two-step molten salt driven micrometer-scaled tabular (100) BaTiO3 (BT) template seeds were used for the first time to make 〈100〉 textured 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 (NBT–BT) piezoelectric ceramics. The use of platelet Bi4Ti3O12 powders instead of Bi2O3 and TiO2 as raw chemicals would not only benefit to the alignment of BT templates during tape casting, but also avoid the dissolution of BT seeds in liquid Bi2O3 during sintering. The results also proved that a pre-reaction procedure at a low temperature is unnecessary during reactive templated grain growth owing to the structure similarity between BT seeds and target compound. Well-textured NBT–BT lead-free piezoelectric ceramics (f∼91%) show excellent dielectric and piezoelectric properties of dielectric constant ɛr∼1300 and piezoelectric charge constant d33=260pC/N.

Microwave assisted hydrothermal synthesis of Bi4Ti3O12 nanopowders from oxide as raw materials

Abstract An alternative method to obtain Bi4Ti3O12 nanosized powders synthesized using microwave assisted hydrothermal treatment is proposed. Initially, the Bi4Ti3O12 powder was synthesized via solid-state reaction. Transparent aqueous solution of powder dissolved into hydrochloric acid was obtained and the pH adjustment was performed to the hydrothermal method. In order to show the viability of the proposed method, synthesis treatments at 160 °C with different hold times were carried out. The powders were characterized by differential thermal analyses, x-ray diffraction, scanning electron microscopy and infrared spectroscopy.

Soft combustion technique: Solution combustion synthesis and low-temperature combustion synthesis; to prepare Bi4Ti3O12 powders and bulk ceramics

Bi4Ti3O12 (BTO) powders were synthesized using soft combustion techniques, specifically known as Solution Combustion Synthesis (SCS) and Low-temperature Combustion Synthesis (LCS). XRD results showed that the single phase BTO was obtained following calcinations at 800?C for the sample prepared using SCS; compared to after combustion, for the sample prepared using LCS. The TG/DTA showed a combustion temperature of around 252 - 280?C, which became stable with a single phase BTO at 500?C and above. Sintering was carried out at 1,100?C for 3 h, to determine the microstructures, grain orientation, relative density, dielectric, and ferroelectric properties, of the bulk ceramics. It was found that the bulk ceramics prepared using SCS exhibited elongated-like grains, strong (117)-preferred grain orientation, a relative density of 93.3%, ?r = 320 - 360, tan ? = 0.03 - 0.1, Pr = 6.8 ?C/cm2, and Ec = 20 kV/cm. Meanwhile, the bulk ceramics prepared using LCS showed plate-like grains, strong c-preferred grain orientation, a relative density of 83%, ?r = 143 - 195, tan ? = 0.01 - 0.38, Pr = 5.9 ?C/cm2, and Ec = 30 kV/cm.

Strong up conversion photoluminescence in Er3+ doped Bi4Ti3O12 ferroelectric materials prepared by sol–gel method

Bi4Ti3O12 (BTO) doped with different concentrations of Er3+ was prepared using sol–gel method. Their structures and surface morphology were examined by X-ray diffraction, Raman spectroscopy and scanning electron microscopy, respectively. All XRD peaks can be indexed according to orthorhombic BTO phase, which is consistent with Raman measurement results. Strong upconversion green luminescence is observed in the Er3+ doped BTO powders pumped by 980 nm at room temperature. Three upconversion emission bands centered at about 525, 550 and 662 nm are due to the radiative relaxation of Er3+ from 2H11/2, 4S3/2 and 4F9/2 to the ground level 4I15/2, respectively. The upconversion emission mechanism of the samples were identified and analyzed. In addition, the doped BTO ceramics show obvious hysteresis loops, demonstrating the ferroelectric properties of the samples. These results illustrate the potential of this class of materials for photonic applications in optoelectronics devices.

Hydrothermal synthesis and characterization of Bi4Ti3O12 powders

The Bi4Ti3O12 powders were synthesized by a hydrothermal route. The influence of hydrothermal conditions on crystal structures and morphologies of Bi4Ti3O12 particles was studied. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy and ultraviolet visible (UV-vis) spectroscopy. These results revealed that the Bi4Ti3O12 powders prepared thus possessed a plate-like shape, a typical bismuth layered perovskite structure, and a wide UV-vis absorption peak. Additionally, the formation mechanism of the Bi4Ti3O12 nanoplates was also discussed.

Microstructural, Raman and XPS properties of single-crystalline Bi3.15Nd0.85Ti3O12 nanorods

Bi3.15Nd0.85Ti3O12 (BNT) nanorods were successfully synthesized first time by hydrothermal method. The nanorods are uniform along their length, and are composed of single-crystalline BNT with orthorhombic structure. The diameters of BNT nanorods are about 30–120nm and growth along the [104] direction, which are promising candidate for nanoscale ferroelectric sensors. Ten Raman active modes were observed for orthorhombic phase BNT nanorods, which are overdamped and highly shifted compare to that of Bi4Ti3O12 (BIT) powders. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy.

Lead-Free Ferroelectric Material: Dysprosium Doped Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub>

This study investigated fundamental of phase formation, crystal structure and calcination process for bismuth dysprosium titanate (Bi4-xDyxTi3O12; BDT) powders when x = 0, 0.25, 0.5, 0.75 and 1.0. BDT powders were prepared using a simple solid-state reaction on mixtures of reagent grade Bi2O3, Dy2O3 and TiO2 powders. The mixtures were calcined at temperature in the range of 500-800°C for 4 h at a heating/cooling rate of 5°C/min. Thermal characteristics of powders were studied using thermogravimetric/differential thermal analyses which indicated that the formation of Bi4Ti3O12 and Bi3Dy1Ti3O12 powders occurred at ~500oC. Effect of Dy3+ concentration on phase and crystal structure was investigated using X-ray diffractometry. The results revealed that at small concentration of Dy dopant (x £ 0.25), optimum calcination temperature for providing bismuth titanate-based phase was 650oC. Increasing content of Dy dopant seemed to reduce calcination temperature to 600oC. This study suggested the alternative environmental friendly BDT materials which may be used as starting powders for production of high quality BDT ceramics.

Preparation and Characterization of Nanosized Bi4Ti3O12 Powders

Nanosized Bi4Ti3O12 (BIT) powders were prepared by a simple coprecipitation process. Differential scanning calorimetry (DSC) measurement was carried out to estimate the phase transition temperatures of the BIT powders calcined at different temperatures. The results showed a range of coexistence of the BIT and Bi2Ti2O7 phases at calcination temperatures from 600 to 650 °C. The dielectric constants of ball-milled BIT powders calcined at different temperatures were measured. It was found that the samples had a value of around 190, which is higher than that of BIT bulk ceramics.

Hydrothermal Preparation of Bismuth Titanate Nanopowders

Bismuth titanate nanopowders were prepared by the hydrothermal method from Bi(NO3)3·5H2O, TiCl4 and KOH aqueous solution. The influences of reaction temperature and KOH concentration on the crystalline phase, morphology, and grain size of the prepared Bi4Ti3O12 powders were investigated. The results showed that well-crystallized, dispersive Bi4Ti3O12 nanopowders could be prepared by the hydrothermal treatment at 220–260°C for 6 h, in the case of [Ti]= 0.1 M, Bi:Ti = 4:3 and [KOH]=1.0–2.0 M. The prepared Bi4Ti3O12 powders of the orthorhombic structure were observed to be rectangle slice-shaped, and the grain sizes were about 30 nm in width and above100 nm in length. It was also confirmed that the desired concentration of KOH decreased with increasing of the treatment temperature.

Structural and ferroelectrical properties of bismuth titanate ceramic powders prepared by mechanically assisted synthesis

Nanosized bismuth titanate, Bi4Ti3O12, was prepared via a high-energy ball milling process through mechanically assisted synthesis directly from the oxide mixture of Bi2O3 and TiO2. The Bi4Ti3O12 phase started to form after 1 h of milling. With increasing the milling time from 3 to 12 h, the particle size of formed Bi4Ti3O12 did not reduce significantly. The grain size was less than 16 nm and showed a strong tendency to agglomeration. The nucleation and phase formation of Bi4Ti3O12, crystal structure, microstructure, powder grain size and specific surface area were followed by XRD, Rietveld refinement analysis, SEM and the BET specific surface area measurements. Raman spectroscopy was used to explain the structural properties of Bi4Ti3O12 powder, prepared by mechanically assisted synthesis. Reduction in grain size with the increase of milling time was also noted (change in the position and relative intensity), which indicated changes in the structure, caused by nanodimension grains. The sample milled for 12 h and subsequently sintered at 1000?C for 24 h exhibited a hysteresis loop, confirming that the synthesized material possesses ferroelectric properties. .

Spectroscopy study of Bi4Ti3O12 obtained from mechanically activated Bi2O3–TiO2 mixtures

Bismuth titanate, Bi4Ti3O12 powders were prepared by mechanically assisted synthesis from their oxides. The diameter of obtained particles depends on time of milling. In order to understand the grain size effects on the crystal structure we measured X-ray, TEM analysis and Raman spectra. The effect of mechanical treatment on the grain size is quite evident: as the milling time increases (3, 6, 12h), the powder becomes more activated and grain size decrease (7.3, 7.2, 6.9nm). With reducing the grain size, quantum effects at the Raman spectra, is reflected in the mode position change against balk crystal. And also, coagulation of each line appears, as well as a significant asymmetry of certain modes.

The evolution of structure induced by intensive milling in the system 2Bi2O3 · 3TiO2

Concurrent mechanochemical treatment of either a stoichiometric 2Bi2O3·3TiO2 powder mixture or (pulverized) Bi4Ti3O12 compound was performed in a planetary ball mill. Relevant structural parameters: crystallite size, amount of amorphous phase and the transformed fraction (as a result of chemical reaction between Bi2O3 and TiO2) of the powders milled for various milling times and intensities were derived from X-ray powder diffraction data. The obtained structural parameters were used to follow the kinetics of the reduction of crystallite size, amorphous phase formation and chemical reaction. In the powder mixture, during the early stage of mechanochemical treatment the Bi2(CO3)O2 phase was found as an intermediate product which transformed into the highly amorphized Bi4Ti3O12 phase as the milling progressed. On the other hand, mechanochemical treatment of Bi4Ti3O12 powder induced a gradual deformation of the crystal lattice and destruction of the perovskite-type structure. However, in both cases, after a certain milling time, a very disordered, amorphous/nanocrystalline structure was obtained. It was demonstrated that in the steady state, the amorphous/nanocrystalline phase ratio depends on the milling conditions. Higher milling intensities induce ‘nanocrystallization’ of the amorphous phase, i.e., precipitation of crystallites with an average size below 20nm. A kinetic model involving a nanocrystalline↔amorphous reaction, in which the forward and reverse reaction were first-order was postulated and used to analyze the formation of an amorphous phase.

Synthesis of Ferroelectric Bi4Ti3O12 by Alternative Routes: Wet No-Coprecipitation Chemistry and Mechanochemical Activation

Novel synthesis methods have been investigated for the preparation of Bi4Ti3O12 ferroelectric Aurivillius-type powders, namely, the wet no-coprecipitated chemistry using a n-butylamine aqueous solution and two mechanochemical activation techniques (vibrating and planetarium mills). For the sake of comparison, Bi4Ti3O12 powders were also produced by the traditional ceramic route. The syntheses of the crystalline phases were obtained by annealing of the precursors at different temperatures and times. Both the precursors and the thermally treated products were characterized by means of X-ray powder diffraction, thermal analysis, and scanning electron microscopy. The Aurivillius phase was found to appear at 600 °C for vibrating and 500 °C for planetarium-milled precursors. These temperatures are 250−350 °C lower than those reported for the traditional ceramic route (850 °C). Moreover, the stabilization at room temperature of a new fluorite Bi−Ti−O structure was obtained by use of the planetarium milling precu...