Ferroelectric Bismuth Titanate Research Articles

Adaptation of the Crystal Structure to the Confined Size of Mixed-oxide Nanoparticles.

Chemical composition and crystal structure are central to defining the functional properties of materials. But when a material is prepared in the form of nanoparticles, the structure and, as a consequence, the composition will also frequently change. Understanding these changes in the crystal structure at the nanoscale is therefore essential not only for expanding fundamental knowledge, but also for designing novel nanostructures for diverse technological and medical applications. The changes can originate from two thermodynamically driven phenomena: (i) a crystal structure will adapt to the restricted size of the nanoparticles, and (ii) metastable structural polymorphs that form during the synthesis due to a lower nucleation barrier (compared to the equilibrium phase) can be stabilized at the nanoscale. The changes to the crystal structure at the nanoscale are especially pronounced for inorganic materials with a complex structure and composition, such as mixed oxides with a structure built from alternating layers of several structural blocks. In this article the complex structure of nanoparticles will be presented based on two examples of well-known and technologically important materials with layered structures: magnetic hexaferrites (BaFe12O19 and SrFe12O19) and ferroelectric Aurivillius layered-perovskite bismuth titanate (Bi4Ti3O12).

Structural and electrical characterizations of Gd doped NBT perovskite nanocrystals synthesized by mechanical alloying

Recently, a new family of oxide-ion conductors based on the ferroelectric perovskite Sodium Bismuth Titanate (Na0.5Bi0.5TiO3, NBT) has been reported. NBT has been investigated intensely as solid electrolytes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). This work focuses on the structural and electrical properties of Gadolinium doped Sodium Bismuth Titanate for its possible application as an electrolyte material in SOFCs. Gd doped nanomaterial has been synthesized by mechanical alloying. X-ray diffraction analysis confirms the formation of the rhombohedral phase of Gd doped NBT perovskite with space group R3c. FESEM micrograph confirms agglomerated spherical grains and EDX spectra confirms the existence of the major constituent atoms. Ac conductivity has been found to follow the universal Jonscher’s power law. Structural and electrical characterization of the sample provide its effectiveness as an electrolyte material in SOFCs.

Effect of fuel composition and concentration on dielectric properties of bismuth titanate (Bi4Ti3O12) synthesized by microwave-induced combustion method

In this work, ferroelectric bismuth titanate was prepared by a microwave-assisted auto-combustion method using different fuel agents (glycine, acetylacetone, and urea). X-ray diffraction patterns show that bismuth titanate with perovskite structure has been formed successfully in all cases. Although bismuth oxide as a major impurity is also identified, its quantitative amount has been minimized when glycine used as fuel in the combustion reaction. The effects of glycine concentration (fuel-deficient, stoichiometric, and fuel-rich) on the properties also have been evaluated. The results show that the degree of crystallinity increases when the fuel-rich reaction was used. Dielectric properties were measured as a function of frequency by means of an LCR meter. It is found that both parts of permittivity decrease with increasing frequency; conversely, AC conductivity rises with frequency. Furthermore, one semicircle is detected in the impedance spectra, demonstrating a significant contribution of the grain boundary. It is also observed that the higher the molar value of glycine, the greater the value of dielectric constant and the lower level of impurity.

Effect of pressure of pelletization on dielectric properties of Bismuth Titanate prepared by sol-gel synthesis

Ferroelectric Bismuth Titanate (Bi4Ti3O12) was prepared by sol-gel synthesis method. Bismuth nitrate and titanium isopropoxide were used as the starting precursors in isopropanol. The annealing of precipitate powders was done at 400 °C for 4 h. Effect of pressure of pelletization on the dielectric properties of Bi4Ti3O12 was studied. The pressure was varied from 585 MPa to 1365 MPa during pellet preparation. The orthorhombic structure of Bi4Ti3O12 was obtained after sintering at 800 °C for 4 h, which was confirmed by X-ray diffraction. Dielectric studies have been done in a wide frequency (20 Hz–20 MHz) and temperature (100–400 °C) range.

Effect of dysprosium doping on structural and vibrational properties of lead-free (Na0.7K0.3)0.5Bi0.5TiO3 ferroelectric ceramics

Abstract This study describes the effect of Dy 3+ doping of lead-free ferroelectric sodium potassium bismuth titanate ((Na 0.7 K 0.3 ) 0.5 Bi 0.5 TiO 3 ; NKBT) ceramics on their structural, optical, and vibrational properties. X-ray diffraction and Rietveld refinement analyses revealed that NKBT samples exhibited a rhombohedral perovskite structure belonging to the R3c space group, with the incorporation of Dy 3+ resulting in structural parameter change and local atomic structure shift to tetragonal P4mm, as supported by the appearance of new Raman modes. Increased Dy 3+ content decreased the NKBT band gap from 3.4 to 3.3 eV, which was ascribed to the introduction of Dy 4 f levels between valence and conduction bands. Ferroelectric behavior studies combined with transport measurements explained the unexpected ferroelectric response weakening of Dy 3+ -modified NKBT by increased leakage current densities.

Integration and High-Temperature Characterization of Ferroelectric Vanadium-Doped Bismuth Titanate Thin Films on Silicon Carbide

4H-SiC electronics can operate at high temperature (HT), e.g., 300°C to 500°C, for extended times. Systems using sensors and amplifiers that operate at HT would benefit from microcontrollers which can also operate at HT. Microcontrollers require nonvolatile memory (NVM) for computer programs. In this work, we demonstrate the possibility of integrating ferroelectric vanadium-doped bismuth titanate (BiTV) thin films on 4H-SiC for HT memory applications, with BiTV ferroelectric capacitors providing memory functionality. Film deposition was achieved by laser ablation on Pt (111)/TiO2/4H-SiC substrates, with magnetron-sputtered Pt used as bottom electrode and thermally evaporated Au as upper contacts. Film characterization by x-ray diffraction analysis revealed predominately (117) orientation. P–E hysteresis loops measured at room temperature showed maximum 2Pr of 48 μC/cm2, large enough for wide read margins. P–E loops were measurable up to 450°C, with losses limiting measurements above 450°C. The phase-transition temperature was determined to be about 660°C from the discontinuity in dielectric permittivity, close to what is achieved for ceramics. These BiTV ferroelectric capacitors demonstrate potential for use in HT NVM applications for SiC digital electronics.

Fabrication and properties of Nd3+-doped ferroelectric barium bismuth titanate glass-ceramic nanocomposites

This paper demonstrates the synthesis of precursor glasses for ferroelectric barium bismuth titanate (BaBi4Ti4O15) (BBiT) by the melt-quench technique in the SiO2K2OBaOBi2O3TiO2 (SKBBT) glass system doped with Nd2O3. BBiT glass-ceramic (GC) nanocomposites have been derived from these precursor glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (TEM) and FTIR reflectance spectroscopy. The activation energy of crystallization of the precursor glass has been estimated using DSC data and found to vary in the range of 203–218 kJ/mol for three different models. The emission intensity of the 4F3/2 → 4I11/2 transition is enhanced by an increase in heat-treatment time and increases about 9-fold in the GC samples heat-treated for 60 h compared to the precursor glass. An increase in the dielectric constant with increase in ceramization time has been observed which suggests the formation of non-centrosymmetric BBiT ferroelectric crystals upon ceramization.

Improving the Electrical Properties of Zr-Doped Bi3.15Nd0.85Ti3O12 Thin Films by Engineering Polarization Rotation

Nd3+/Zr4+-cosubstituted bismuth titanate (BNTZx, x = 0, 0.05, 0.1, 0.3, and 0.5) thin films have been fabricated by chemical solution deposition and their polarization hysteresis loops, leakage current, and capacitance butterfly loops investigated. Results show that, at Zr content of x = 0.1, both capacitance and remanent polarization can be greatly improved. The BNTZ0.1 film also exhibits fatigue-free, excellent leakage current characteristics (I ≈ 9.44 × 10−9 A) at applied voltage of 3 V. High-quality c-axis-oriented BNTZx = 0.1 films with improved electrical properties were fabricated; this finding supports the feasibility of engineering polarization rotation in ferroelectric bismuth titanate (as suggested theoretically by Roy et al. in Appl. Phys. Lett. 102:182901, 2013).

Thermal stabilities of electromechanical properties in cobalt-modified strontium bismuth titanate (SrBi4Ti4O15)

Bismuth layer-structured ferroelectric (BLSF) strontium bismuth titanate (SrBi4Ti4O15, SBT) ceramic oxides with B-site cobalt substitutions have been synthesized using conventional solid–state reaction. The dielectric, piezoelectric, and ferroelectric properties of cobalt-modified SBT are investigated in detail. The results indicate that cobalt is very effective in promoting the piezoelectric performance of SBT. The SBT modified with 3 mol% Co3+ (SBT-3Co) exhibits the optimized piezoelectric properties, with a piezoelectric constant d33 of 28 pC/N, which is the highest value among the modified SBT-based piezoelectric ceramics ever reported. The temperature-dependent electrical impedance, resonance frequencies, and electromechanical coupling factors (kp and kt) reveal that the cobalt-modified SBT ceramics have good thermal stabilities of electromechanical properties up to 300 °C. These results demonstrate that the cobalt-modified SBT ceramics are promising materials for high temperature piezoelectric sensors applications.

Bismuth Titanate Fabricated by Spray-on Deposition and Microwave Sintering For High-Temperature Ultrasonic Transducers.

Thick films of ferroelectric bismuth titanate (Bi4Ti3O12) have been fabricated by spray-on deposition in conjunction with microwave sintering for use as high-temperature ultrasonic transducers. The elastic modulus, density, permittivity, and conductivity of the films were characterized. Electro-mechanical properties of the films were estimated with a commercial d33 meter which gave 16 pC/N. This value is higher than typically reported for bulk bismuth titanate; however, these films withstand higher field strengths during poling which is correlated with higher d33 values. Films were capable of operating at 650 °C for roughly 5 min before depoling and can operate at 600 °C for at least 7 days.

Enhanced piezoelectric properties and excellent thermal stabilities of cobalt-modified Aurivillius-type calcium bismuth titanate (CaBi4Ti4O15)

Abstract Bismuth layer-structured ferroelectric (BLSF) calcium bismuth titanate (CaBi 4 Ti 4 O 15 , CBT) piezoelectric ceramics with 0.0–1.0 wt.% cobalt oxide (Co 2 O 3 ) have been prepared via a conventional solid-state reaction method. Microstructural morphology and electrical properties of cobalt oxide-modified CBT ceramics were investigated in detail. X-ray powder diffraction (XRPD) analysis revealed that the cobalt oxide-modified CBT ceramics have a pure four-layer Aurivillius-type structure. The piezoelectric properties of CBT ceramics were significantly enhanced by cobalt oxide modifications. The piezoelectric coefficient d 33 and Curie temperature T c of 0.2 wt. % cobalt oxide-modified CBT ceramics (CBT-Co4) are 14 pC/N and 782 °C, respectively. The DC resistivity and thermal depoling behavior at elevated temperature indicated that the CBT-Co4 ceramics exhibit good thermal stability, demonstrating that the CBT-Co4 ceramics are potential materials for high temperature piezoelectric applications.

Piezoelectric properties and thermal stabilities of strontium bismuth titanate (SrBi4Ti4O15)

Bismuth layer-structured ferroelectric (BLSF) compound strontium bismuth titanate (SrBi4Ti4O15, SBT) with cerium modifications have been synthesized using conventional solid-state processing. X-ray powder diffraction (XRPD) analyses reveal that the cerium-modified SBT ceramics have a pure four-layer Aurivillius-type structure. The dielectric, ferroelectric, and piezoelectric properties of the cerium-modified SBT ceramics are investigated in detail. The results indicate that the cerium modifications into SBT increase the densities, decrease the sintering temperature, lower the dielectric loss tanδ, and reduce the coercive filed Ec. The piezoelectric measurements show that cerium is very effective in promoting the piezoelectric properties of SBT ceramics. The SBT ceramics modified with 4mol% CeO2 (SBT-4Ce) exhibit the optimized piezoelectric properties, with a piezoelectric constant d33 of 27pC/N, which is the highest value among the modified SBT-based piezoelectric ceramics ever reported. The temperature-dependent electrical impedance and electromechanical coupling coefficients (kp and kt) reveal that the electromechanical coupling characteristics have a significant deterioration at ~400°C because of the high conductivity at high temperature. But the temperature-dependent frequency constants (Np and Nt) and thermal annealing analyses indicate the cerium-modified SBT ceramics have good thermal stabilities of piezoelectric properties up to 450°C. These results demonstrate that the cerium-modified SBT ceramics are promising materials for high temperature piezoelectric sensors applications.

Characterization of Bi4Pb2Ti3FeNbO18 nanoplates

Existence of functional ferroic properties in materials of potential application has become a subject of vast interest these days. The occurrence of electric and magnetic orders in a single phase makes the materials to work in multifaceted tasks. A relaxor ferroelectric, lead iron niobate (PFN) i.e., Pb(Fe1/2Nb1/2)O3 and the layered Aurivillius ferroelectric bismuth titanate (BTO), i.e., Bi4Ti3O12 are the two well-known dielectric materials. Some of the challenges during the formation of PFN limit the applicability of the PFN ceramics. To overcome the practical limitations, this work was done to optimize the operative conditions and to examine the influence of another novel material on the structure – property variations/relations. For this purpose, polycrystalline sample of a mixed compound Bi4Ti3O12 – 2Pb(Fe0.5Nb0.5)O3 (Bi4Pb2Ti3FeNbO18) was prepared using a conventional solid-state reaction technique. An analysis of X-ray diffraction with FESEM image confirms the formation a single-phase compound in orthorhombic crystal structure in the form of nanoplates. To accolade the useful features of the new compound, we studied the ferroelectric, dielectric, magnetic and electrical properties.

First-principles study of A-site substitution in ferroelectric bismuth titanate

We employ density functional theory to investigate the effect of A-site rare earth substitution on the point defect formation in bismuth titanate (BIT) in the dilute substitution limit. Despite previous claims that the formation energy of neutral oxygen vacancies in La-substituted BIT (BLT) is higher than in pure BIT, our calculations show that this is only true for four out of the six distinct oxygen sites. Of these four sites, in two the difference is <0.1 eV while in the other two the difference is ~0.25 eV. In the case of +2 charged oxygen vacancies, in only two of the six distinct oxygen sites is the formation energy of the oxygen vacancy higher in BLT than in BIT, where they differ by ~0.14 eV. These results do not support the traditional explanation for the fatigue-free characteristic of BLT, which states that La substitution might avoid the ferroelectric fatigue of BIT by simply suppressing the formation of oxygen vacancies.

Synthesis of bismuth titanate with urea as fuel by solution combustion route and its dielectric and ferroelectric properties

Preparation of ferroelectric bismuth titanate (Bi4Ti3O12) is carried out by solution combustion route with urea as fuel at much lower calcinations temperatures. The single phase bismuth titanate was obtained after calcinations at 800°C. SEM micrographs of the calcined powders show agglomerated, flaky and foamy morphology, which is typical of combustion synthesis and that of sintered ceramics shows the grain formation. Behavior of dielectric constant and dielectric loss as a function of temperature of as-prepared sample are reported in this communication. Ferroelectric to paraelectric phase transition occurs at the temperature Tc∼660°C. Its remnant polarization (2Pr) is very less of the order of 0.012μC/cm2.

Thermally-induced loss of piezoelectricity in ferroelectric Na0.5Bi0.5TiO3–BaTiO3

The loss of piezoelectricity in ferroelectric sodium bismuth titanate (NBT) in solid solution with barium titanate ((1−x)NBT−xBT) is studied by means of thermal depoling and Raman spectroscopy. In the range 0≤x≤13%, the highest thermal stability of the piezoelectric coefficients is found in x=13%, for which a longitudinal piezoelectric coefficient of 118pC/N was nearly temperature-independent up to a maximum temperature of 165°C. The composition nearest the morphotropic phase boundary, x=6%, exhibited the lowest thermal depoling temperature of 107°C. Depoling of this composition is suggested to arise from a second order phase transition evidenced in the temperature-dependent Raman spectra.

Processing and Properties of Eu3+‐Doped Barium Bismuth Titanate (BaBi4Ti4O15) Glass–Ceramic Nanocomposites

Precursor glasses for the ferroelectric barium bismuth titanate (BaBi4Ti4O15) (BBiT) have been prepared by the melt‐quench technique in the SiO2–K2O–BaO–Bi2O3–TiO2 (SKBBT) glass system with and without Eu2O3 doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X‐ray diffraction (XRD), electron microscopy (FE‐SEM, TEM), and FT‐IR reflectance spectroscopy. FE‐SEM images show the formation of randomly oriented hexagonal rod‐shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT‐IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm−1. The activation energy of crystallization (Ec) varies from 295 to 307 kJ/mol. The dielectric constants (εr) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat‐treated GCs show higher εr values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5D0 → 7F2 transition. An intense 466 nm excitation band corresponding to the 7F0 → 5D2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat‐treatment times led to a 15‐fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam0.5) values obtained in the GCs are high and suitable for structural applications.

Atomic vapor deposition of bismuth titanate thin films

c-axis oriented ferroelectric bismuth titanate (Bi4Ti3O12) thin films were grown on (001) strontium titanate (SrTiO3) substrates by an atomic vapor deposition technique. The ferroelectric properties of the thin films are greatly affected by the presence of various kinds of defects. Detailed x-ray diffraction data and transmission electron microscopy analysis demonstrated the presence of out-of-phase boundaries (OPBs). It is found that the OPB density changes appreciably with the amount of titanium injected during growth of the thin films. Piezo-responses of the thin films were measured by piezo-force microscopy. It is found that the in-plane piezoresponse is stronger than the out-of-plane response, due to the strong c-axis orientation of the films.

Engineering polarization rotation in ferroelectric bismuth titanate

We report a combined experimental-theoretical study showing that collective application of rare earth doping on Bi-site of ferroelectric bismuth titanate (Bi4Ti3O12) and epitaxial strain leads to only a small increase in c-axis polarization, resolving conflicts of previous experimental data on c-axis oriented thin films. However, as shown by our first principles calculations, a modest c-axis polarization can be induced by simultaneous Bi(A) and Ti(B) site doping in bismuth titanate. This approach, correlating doping, epitaxial strain, and polarization in ferroic oxides, could be useful to tailor oxide compositions, assisting in the growth of epitaxial films along easy growth directions yielding reasonable polarization.

Dielectric properties of Bismuth Titanate (Bi4Ti3O12) synthesized using solution combustion route

Ferroelectric Bismuth Titanate (Bi 4 Ti 3 O 12 ) was prepared by solution combustion route with glycine as fuel. The single phase Bismuth Titanate was obtained after calcination at 800 °C, which was confirmed with the help of X-ray diffraction studies and EDS analysis. SEM micrographs of the calcined powders show agglomerated particles, which is typical of combustion synthesis. Behavior of dielectric constant and dielectric loss as a function of temperature of as prepared sample are reported here. Ferroelectric to paraelectric phase transition occurs at the temperature T c ∼650 °C. Impedance studies were made in the frequency range from 1 KHz to 1 MHz. The semicircles observed in the complex impedance diagrams indicate deviation from the Debye behavior. Activation energy of the sample around T c is found to be ∼0.35 eV and below T c is ∼0.13 eV, which was calculated using the Arrhenius plots.