Bi4Ti3O12 Research Articles

Double polarization hysteresis and dramatic influence of small compositional variations on the electrical properties in Bi4Ti3O12 ceramics

This work reports the existence of double polarization hysteresis (P–E) loop in Aurivillius-phase ferroelectric Bi4Ti3O12 (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P–E loop is recalled by Nb donor doping, and associated composition Bi4Ti2.97Nb0.03O12.015 (BiT-0.03Nb) shows high remnant polarization (Pr = 12.5 μC/cm2) and large field-induced strain (S33 = 5.6 × 10−4). In addition, this doping results in bulk conductivity (σb) of BiT decreasing dramatically and associated activity energy (Ea) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg2+ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ˜0.65 × 10−2 S cm−1 in the bulk.

Surface plasmon resonance effect of Ag nanoparticles for improving the photocatalytic performance of biochar quantum-dot/Bi4Ti3O12 nanosheets

Herein, we report a novel ternary material comprised of Ag nanoparticles and carbon quantum dots (CDs), which are co-loaded using 2D Bi4Ti3O12 (BIT) sheets. In this system, Ag can be applied as excited electron-hole pairs in the Bi4Ti3O12 by transferring the plasmonic energy from the metal to the semiconductor. The surface plasmon resonance of Ag can promote the electron transfer properties of the CDs, thereby improving the separation efficiency of the electron-hole pairs. Meanwhile, the CDs can act as an electron buffer to decrease the recombination rate of the electron hole. Moreover, CDs are prepared using a biomaterial, which can provide a chemical group to enhance the electron transfer and connection. The synergistic effects of CDs, Ag, and BIT enable the design of a photocatalytic application with a remarkably improved efficiency and operational stability.

Effect of vanadium doping on structural, dielectric and ferroelectric properties of bismuth titanate (Bi4Ti3O12) ceramics

Abstract The effect of vanadium doping on the structural, dielectric and ferroelectric properties of Bi4Ti3O12 (BTO) has been studied. Bi4–x/3Ti3–xVxO12 (x = 0, 0.006, 0.012, 0.018, 0.024 and 0.03 mol%) were prepared using a sol–gel synthesis method and calcined at 400 °C for 3 h. All samples were sintered at 950 °C for 3 h. The relative density of ceramic samples decreases with the addition of vanadium. The structural analysis confirms that no structural changes occur with doping of vanadium into BTO ceramics. Doping of vanadium into BTO ceramics improves its ferroelectric and dielectric properties.

Photocatalytic removal using g-C3N4 quantum dots/Bi2Ti2O7 composites.

In this work, a simple method to load of g-C3N4 quantum dots (CN QDs) onto Bi2Ti2O7 (BTO) microsphere with the amount of CN QDs (3, 7, 10 and 15%). The photocatalyst was used for the treatment of water pollutants under visible-light illumination, which proved that CNBTO composites showed improved photocatalytic activity matched up to pure BTO. Reformation of BTO with CN QDs enhanced the light assimilation capacity, and promoted the isolation of photo-induced electron-hole pairs. The trapping experiments and ESR were announced the holes (h+) and superoxide oxide (O2-) played the key role, and the relative mechanism of the photocatalytic process was proposed. Meanwhile, the effects of CN QDs content, pH and initial pollutant concentration on the removal efficiency of ciprofloxacin (CIP) were studied. Results showed that the CN QDs loaded on BTO presented higher photocatalytic efficiency, and an optimum value for the dosage of photocatalytic in pH 8.0.

Combustion synthesis, characterization and photocatalytic application of CuS/Bi4Ti3O12 p-n heterojunction materials towards efficient degradation of 2-methyl-4-chlorophenoxyacetic acid herbicide under visible light

In this study, a series of CuS/Bi4Ti3O12 p-n heterojunction materials were synthesized by a two-step process. Initially, the Aurivillius phase Bi4Ti3O12 (BT) was synthesized by a facile combustion route using urea as a fuel. The Bi4Ti3O12 was subsequently modified by deposition of CuS (5–20 wt%) using a hydrothermal route to prepare the heterojunction materials. The methods of synthesis and calcination temperature were important factors which influenced the morphology, particle size and phase purity of Bi4Ti3O12 material. Phase pure BT nanoplates with planar dimension of 150–200 nm and thickness between 50 and 70 nm were obtained at a calcination temperature of 600 °C. Pure CuS prepared by hydrothermal method, contained hierarchical microspheres with diameter in the range of 1.2–1.6 μm. The heterostructure materials exhibited hierarchical flower like structure consisting of ultrathin CuS nanosheets and BT-nanoflakes. HRTEM and microstructural study revealed microscopic close interaction between the two phases. The optical and electrical measurement study suggested significant improvement in visible light absorption (400–800 nm) and charge carrier separation due to heterojunction formation. The CuS/Bi4Ti3O12 materials showed excellent photocatalytic activity for aqueous phase degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicide under visible light (>95% degradation in 3 h). The rate constant for CuS/Bi4Ti3O12 materials was 4.5 times higher than the pure BT material towards MCPA degradation. The OH and O2– radicals have been identified as the reactive species, the formation of which was confirmed by spectrometric method using terephthalic acid and nitroblue tetrazolium as molecular probes. The mechanism of MCPA degradation over the photocatalyst surface has also been elucidated using LC-ESI-MS, TOC and scavenger experiments.

Three-Dimensional Domain Patterns in Tetragonal-to-Monoclinic Bi 4ti 3O 12 Ceramics: Nonlinear Analysis and Piezoresponse Force Microscopy Imaging

Tetragonal-to-monoclinic Bi4ti3O12 (BIT) exhibits complicated domain patterns thanks to its two independently switchable spontaneous polarizations that lie in the ac plane of the monoclinic unit cell. Utilizing the nonlinear theory of ferroelectric phase transformation based on the deformation gradient tensor and spontaneous polarization, we systematically analyzed domain patterns in BIT, classifying its domain walls (DWs) into five different classes. Three-dimensional piezoresponse force microscopy (3D PFM) was then adopted to characterize the ceramic BIT, revealing intriguing domain patterns in planar, lateral, as well as tilted grains. Guided by the nonlinear theoretical analysis, 3D polarization distributions were successfully reconstructed, wherein 9°-, 90°-, 91°-, and 180°-DWs were observed along with 171°-charged DWs. The nonlinear analysis is thus confirmed by 3D PFM characterizations, and the combined theoretical analysis and experimental investigation contribute to our understanding on the 3D tetragonal-to-monoclinic ferroelectric domain patterns.

Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution

Bi4Ti3O12 (BIT), a typical Aurivillius ceramics with high Curie temperature (Tc ˜ 675 °C), has great potential for high temperature applications. This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO6 octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi4Ti2.98W0.01Nb0.01O12 possesses an optimum piezoelectric coefficient (d33) of 32 pC/N, a high Tc of 655 °C and a large resistivity of 3 × 106 Ω·cm at 500 °C. The maximum d33 reported here is approximately quadruple than that of pure BIT (˜7 pC/N). Moreover, the d33 of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.

Formation mechanism of A-site complex perovskite (Ba, Sr)TiO3 microplatelets

A-site complex perovskite (Ba, Sr)TiO3 microplatelets with high aspect ratio were synthesized successfully by molten salt synthesis (MSS) and topochemical microcrystal conversion(TMC) technique. In the process of synthesis, Bi4Ti3O12 (BiT) platelets firstly prepared by MSS method were used as precursor and powdered SrCO3-BaCO3 mixture were employed as reactants in NaCl flux at 1000 °C. The effects of BiT-to-SrCO3-to-BaCO3 molar ratios on phase and microstructure of the resultant products were investigated. The synthetic (Ba0.5Sr0.5)TiO3 platelets would be effective templates for producing highly textured ceramics using the templated grain growth(TGG) method.

Effect of thickness and crystalline morphology on electrical properties of rf-magnetron sputtering deposited Bi4Ti3O12 thin films

Bi4Ti3O12 (BiT) thin films with thicknesses ranging from 535 to 870 nm were deposited on Pt(111)/Ti/SiO2/Si substrates by rf-magnetron sputtering method. The films were crystallized by direct thermal annealing in air at 650 °C. The effects of film thicknesses and crystalline morphology on ferroelectric, leakage current conduction and dielectric properties were investigated. XRD and SEM analysises reveal that BiT thin film deposited at 400 °C is amorphous and exhibits a non-crystalline morphology. After annealing treatment, the amorphous film transformed into Aurivillius Bi4Ti3O12 crystalline phase with rodlike grains. The electrical properties show that the as-deposited thin film is a lossy dielectric with absence of ferroelectricity. The remnant polarization of crystalline BiT thin films increases slightly with decreasing thickness. The leakage currents of annealed BiT films exhibit ohmic behavior in low voltage region and Schottky emission conduction characteristic in high voltage region, respectively. For crystalline BiT films, the dielectric constant decreases significantly with increasing film thicknesses.

Sustainable yarn type-piezoelectric energy harvester as an eco-friendly, cost-effective battery-free breath sensor

A cost-effective layer-by-layer brush-coating technique was developed to fabricate a flexible yarn-based piezoelectric nanogenerator (FY-PNG) to harness abundant waste mechanical energy. A simple sol-gel method was used to synthesize the orthorhombic crystalline phase of bismuth titanate perovskite, i.e., Bi4Ti3O12 (BiTO). A single FY-PNG device generated a maximum peak-to-peak open-circuit voltage (VOC(P–P)), short-circuit current (ISC(P–P)), and instantaneous area power density of 60 V, 400 nA, and 18.5 mW/m2, respectively, upon application of a 1 N periodic mechanical load. The switching polarity of the FY-PNG demonstrated good phase shifting between the output signals and confirmed that the output derived from the device and not from any external sources. The working mechanism, electrical poling effect, force analysis, repeatability, stability, charging, energy storage analysis, and sensitivity to biomechanical force of the FY-PNG was thoroughly investigated. The FY-PNG device output was used to power five commercial green light-emitting diodes (LEDs) and a display system. Additionally, a non-invasive self-powered breathing sensor (SPBS) was developed to monitor human inhalation/exhalation. The repeatability and reproducibility of SPBS evaluated using different devices and test subjects demonstrated a good variation in output (i.e., 0.2–0.4 V) for inhalation/exhalation; the SPBS was also evaluated under slow/fast and constant breathing conditions. The proposed brush-coating technique for FY-PNGs is an efficient, cost-effective, eco-friendly, and easily scalable technique that can pave the way to the design of novel-shaped PNG devices for applications such as implantable self-powered biosensors and automotive electronic systems.

CaBi4Ti4O15-based lead-free sol–gel composites for high-temperature application

CaBi4Ti4O15 (CBiT)-based lead-free sol–gel composites were developed for high-temperature ultrasonic transducer application. In this study, two types of lead-free sol–gel solution, Ba0.7Sr0.3TiO3 (BST) and Bi4Ti3O12 (BiT), were used for consistency to fabricate ∼50-µm-thick CBiT/BST and CBiT/BiT films on 3-mm-thick titanium substrates by a sol–gel spray technique. BST and BiT were chosen because of their high dielectric constant and high Curie temperature, respectively, in addition to their being lead-free materials. A thermal cycle test was carried out between RT and 600 °C, and clear multiple echoes were confirmed during three thermal cycles for both materials. In addition, the sensitivity of CBiT/BiT was higher than that of CBiT/BST although a higher poling temperature is required for CBiT/BiT. Therefore, an ultrasonic transducer potential for high-temperature application was successfully demonstrated.

Some peculiarities at preparation of Bi4Ti3O12 films for bolometric applications

We discuss properties of Bi4Ti3O12 (BTO) films in BTO/CeO2/YSZ multilayered buffer system, on silicon and on silicon-on-insulator (SOI) substrates, employed for the preparation of epitaxial La0.67Sr0.33MnO3 (LSMO) films. We try to find a correlation between the parameters of film preparation and structural properties and morphology of the BTO films with the goal to eliminate defects. We also point out that many morphological defects observed on the final LSMO films prepared for bolometers originate in the bottom BTO layer. We have found out that the actual substrate temperature is a very important parameter during the process of BTO film deposition since deviations of only few degrees from the proper temperature can cause the growth of mixture crystal orientation.

Giant Negative and Positive Electrocaloric Effects Coexisting in Lead‐Free Na0.5Bi4.5Ti4O15 Films Over a Broad Temperature Range

Giant negative and positive electrocaloric effects (ECEs) coexist in lead‐free Na0.5Bi4.5Ti4O15 (NBTO) ferroelectric films with layered perovskite structure over a broad temperature range, with ΔT peaks of −14.8 °C (at 273 K) in the negative electrocaloric (EC) region (273–328 K), of 3.45 °C (at 373 K) in the positive EC region (328–418 K) and of −6.76 °C (at 483 K) in another negative EC region (418–513 K), respectively, under the electric field of 900 kV cm−1. Such giant ECEs are attributed to both the high break‐down electric field and prominent ferroelectricity. And the coexistence originates in the competition of the dipole polarization between both Na0.5Bi0.5TiO3 (NBT) and Bi4Ti3O12 (BTO) cells of NBTO films over the whole temperature region. Furthermore, the outstanding anti‐fatigue features with temperature stability for NBTO films ensure the durability of EC refrigeration. This work will prompt a novel technology for next generation of environmental‐friendly solid‐state cooling devices.

Stoichiometric control in Bi4Ti3O12 synthesis by novel hybrid solid state reaction

The synthesis of bismuth titanate Bi4Ti3O12 (BiT) is performed via a novel solid state reaction. The reaction is designed to control the stoichiometric content of the highly volatile element, i.e. Bi. The chemical route consists in trapping bismuth oxide colloids in a stabilized titanium based sol gel solution. The resulting colloidal-solution hybrid ink can be processed via various ceramic processes. After gelation of TiO2 in the sol-gel component the mixture reacts at high temperature (850 °C) to yield the BiT phase. The obtained material is c-axis oriented, and its lattice parameters, shrinkage and density matches the pure Bi4Ti3O12 phase. The sintered material exhibits enhanced higher dielectric constant (2 3 2) than usually reported for this phase.

Thickness Effect on (La0.26Bi0.74)2Ti4O11 Thin-Film Composition and Electrical Properties**Supported by the Basic Research Project of Shanghai Science and Technology Innovation Action under Grant No 17JC1400300, the National Key Basic Research Program of China under Grant No 2014CB921004, the National Natural Science Foundation of China under Grant No 61674044, and the Program of Shanghai Subject Chief Scientist under Grant No 17XD1400800.

Highly oriented (00l) (La0.26Bi0.74)2Ti4O11 thin films are deposited on (100) SrTiO3 substrates using the pulsed laser deposition technique. The grains form a texture of bar-like arrays along SrTiO3 ⟨110⟩ directions for the film thickness above 350 nm, in contrast to spherical grains for the reduced film thickness below 220 nm. X-ray diffraction patterns show that the highly ordered bar-like grains are the ensemble of two lattice-matched monoclinic (La,Bi)4Ti3O12 and TiO2 components above a critical film thickness. Otherwise, the phase decomposes into the random mixture of Bi2Ti2O7 and Bi4Ti3O4 spherical grains in thinner films. The critical thickness can increase up to 440 nm as the films are deposited on LaNiO3-buffered SrTiO3 substrates. The electrical measurements show the dielectric enhancement of the multi-components, and comprehensive charge injection into interfacial traps between (La,Bi)4Ti3O12 and TiO2 components occurs under the application of a threshold voltage for the realization of high-charge storage.

Enhanced photocatalytic performance of g-C3N4/Bi4Ti3O12 heterojunction nanocomposites

Two types of g-C3N4/Bi4Ti3O12 p-n heterostructures were prepared by a simple mixing–calcining method. One is constructed from Bi4Ti3O12 (BTO) nanoparticles and g-C3N4 nanosheets (NS), and the other is constructed from BTO nanoparticles and g-C3N4 nanoparticles (NP). The structures, morphologies, optical and electrochemical properties of the samples were systematically characterized. PL spectra, EIS spectra and photocurrent responses demonstrate an effective separation of photogenerated electron-hole pairs for the composites. The photocatalytic performance of the composites was evaluated by the degradation of rhodamine B (RhB) under simulated-sunlight irradiation, revealing that they exhibit an enhanced photocatalytic activity compared to bare BTO and g-C3N4. The highest photocatalytic activity is observed for the composites with g-C3N4 content centered around 10%. Furthermore, g-C3N4(NP)/BTO composites integrated from BTO and g-C3N4 nanoparticles possess a superior photocatalytic activity compared to those integrated from BTO nanoparticles and g-C3N4 nanosheents.

Effects of Nb Content on the Ferroelectric and Dielectric Properties of Nb/Nd-Co-doped Bi4Ti3O12 Thin Films

Nd/Nb-co-substituted Bi3.15Nd0.85Ti3−x Nb x O12 (BNTN x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO2/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN x thin films were investigated. A low-concentration substitution with Nb ions in BNTN x can greatly enhance its remanent polarization (2P r) and reduce the coercive field (2E c) compared with those of Bi4Ti3O12 (BIT) thin film. The highest 2P r (71.4 μC/cm2) was observed in the BNTN0.03 thin film when the 2E c was 202 kV/cm. Leakage currents of all the films were on the order of 10−6 to 10−5 A/cm2, and the BNTN0.03 thin film has a minimum leakage current (2.1 × 10−6 A/cm2) under the high electric field (267 kV/cm). Besides, the C–V curve of the BNTN0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.

Ferroelectric properties of highly a-oriented polycrystalline Bi4Ti3O12 thin films grown on glass substrates

Thin films of highly a-oriented polycrystalline Bi4Ti3O12 (BTO) were deposited on Pt/Ta/glass substrates via pulsed laser deposition. X-ray diffraction experiments confirmed that the BTO thin films were preferentially oriented along the (104) direction. As a ferroelectric thin film, the BTO thin films exhibited good ferroelectric properties with a remanent polarization of 13.8 μC/cm2. The fatigue resistance test revealed that owing to their crystal orientation along the (104) direction, the BTO thin films significantly degrade after being subjected to ferroelectric polarization after around 108 switching cycles.

Fe3+/Nb5+ co-doping effects on the properties of Aurivillius Bi4Ti3O12 ceramics

Bi4Ti3-x(Nb0.5Fe0.5)xO12 (BTFNx) ceramics with 0 ≤ x ≤ 2 were synthesized to evaluate the effect of Fe3+/Nb5+ co-substitution into the B-site of Bi4Ti3O12 (BIT). We show that the XRD pattern for the compounds with x ≤ 1 is the characteristic one of a layered perovskite structure belonging to the n = 3 member of the Aurivillius family. Impurity peaks assigned to a pyrochlore phase are detected at higher concentrations. Raman measurements corroborated that Fe3+and Nb5+ ions are incorporated into the Ti sites of the Aurivillius compound. Frequency dependent dielectric studies at room-temperature displayed the reduction of both dielectric constant and loss tangent with substitution, while the electric-field-induced polarization switching behavior indicates ferroelectric character. It is observed that the ferroelectric transition temperature decreases with increasing Fe/Nb content. Magnetic measurements indicated no evidence of ferromagnetic ordering, but antiferromagnetic spin correlations between Fe3+ ions.

Bismuth titanate as an infrared reflective pigment for cool roof coating

A pale-yellow color nano pigment Bi4Ti3O12 (BTO) with impressive infrared (IR) reflectance (R = 95%) was synthesized using a simple hydrothermal method and characterized its crystalline nature, structural property, morphology and optical properties using X-ray diffraction technique (XRD), Raman spectroscopy, Fourier Transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV–Vis–NIR spectrophotometer. The Near infrared (NIR) reflectance was measured using UV–Vis–NIR diffuse reflectance spectrophotometer at a wavelength range of 700–2500nm. The band gap of the synthesized BTO nano pigment increases from 2.74 to 3.05eV by increasing the calcination temperature from 600°C to 800°C. For comparison study, the IR reflectance property and the thermal performance of synthesized BTO nano pigment was compared with the conventional infrared reflective white pigment TiO2. The BTO nano pigment shows higher NIR reflectance property and better thermal performance than the TiO2 pigment. The potential application of the BTO nano pigment as the “cool pigment” was also demonstrated by coating on to the steel substrate for the energy saving application.