Bi5Ti3FeO15 Research Articles

Dielectric, ferroelectric and magnetic properties of La doped Bi5Ti3FeO15 ceramics

Aurivillius Bi5Ti3FeO15 (BTF) and Bi5−xLaxTi3FeO15 (BLTF) ceramics were successfully synthesized by a simple solid state reaction method. The samples were characterized by X-ray diffraction with no impurity phase identified. SEM micrographs show an evident decrease of grain size of La modified ceramics in comparison with pure BTF. Dielectric properties were investigated in a wide range of temperatures (300–1000 K) and frequencies (1 Hz–1 MHz). The Curie temperature was found to decrease in BLTF when compared to BTF ceramics. An energy bandgap of 1.83 and 1.77 eV for the BTF and BLTF ceramics, respectively was determined from UV–Vis diffuse absorption spectrum. Influence of La doping on ferroelectric and ferromagnetic measurements of both samples was also performed. Very weak ferromagnetism inside BTF can be observed while samples with La content showed complete paramagnetic behavior.

The effect of Mn doping contents on the structural, dielectric and magnetic properties of multiferroic Bi5Ti3FeO15 Aurivillius ceramics

Aurivillius Bi5Ti3FeO15 (BTFO) multiferroic ceramics with different Mn doping contents were synthesized through the conventional solid state reaction. The effect of Mn doping on the structural, magnetic and dielectric behaviors of BTFO ceramics is investigated in detail. All these Mn-doped BTFO ceramics are determined to be layered Aurivillius structure by X-ray diffraction. No microstructure variation of plate-like grains is obviously confirmed due to Mn doping through field emission scanning electron microscopy. Similar evolution of ε and tanδ with frequency is found both in BTFO and 10% Mn-doped BTFO ceramics. However, obvious dielectric dispersion phenomena are presented as the Mn-doping content is beyond 0.1, and this dispersion behavior becomes strong with increasing Mn-doping content, clearly indicated by the appearance of dielectric loss relaxation peaks. Finally, the same magnetic orders of 10% Mn-doped BTFO ceramics as those of the BTFO one are unambiguously found while weak ferromagnetism is observed in BTFO ceramics with Mn-doping content beyond 0.2.

Structural and electrical properties of Bi5Ti3FeO15 ceramics

Bi5Ti3FeO15 (BTF) is a multiferroic material of Aurivillius structural family with (perovskite) layered structure. This material has special interest and position in the family because it is a combination of multiferroic BiFeO3 and ferroelectric Bi4Ti3O12, and can be used as new magneto-electric material for devices. The compound (Bi5Ti3FeO15) was synthesized by a standard and widely used a high-temperature solid-state reaction method using high purity oxides. Preliminary structural analysis of the compound from the room temperature X-rays diffraction data confirmed the formation and good quality of the material. The nature of the microstructure (i.e., distribution, size and shape of grains, etc.) of sample recorded at room temperature using scanning electron microscopy exhibits formation of high-density sample. Studies of capacitive (permittivity and tangent loss) and resistive (impedance, electrical modulus and electrical conductivity) properties of the material as a function of frequency (1–1,000 kHz) at different temperatures (30–500 °C) using a complex impedance spectroscopy technique have provided many interesting and vital information on contribution of grains, grain boundary and interface in the material.

The Cr-substitution concentration dependence of the structural, electric and magnetic behaviors for Aurivillius Bi5Ti3FeO15 multiferroic ceramics

Aurivillius Bi5Ti3FeO15 (BTFO) multiferroic ceramics with different Cr-doped concentrations have been synthesized by the conventional solid state reaction method. The influences of Cr-doping concentrations on the structural, magnetic, dielectric, and ferroelectric properties of BTFO ceramics are investigated in detail. All these sintered Cr-substituted BTFO ceramics are determined to be layered perovskite Aurivillius structure by X-ray diffraction, as well as the lattice parameters a, b, and c are in good accordance with Vegard's law along with the Cr-doping concentration. The lattice distortion a/b for Aurivillius family decreases with increasing Cr-doping concentration. Moreover, Cr-doping can promote greatly the grain growth of BTFO samples confirmed from field emission scanning electron microscopy characterization. However, no obvious signs of the improvement in ferroelectric properties are found in Cr-doped BTFO ceramics, and abnormal ferroelectric polarization versus electric field (P-E) loops are observed as Cr-doping content is beyond 0.1. Similar ε (tanδ) versus frequency plots to those of the BTFO sample are exhibited when Cr-doping concentration is less than 0.1. Nevertheless, obvious dielectric dispersion phenomena are shown as the Cr-doping concentration is beyond 0.1, and this dispersion behavior becomes strong with further increasing Cr-doping concentration, which are clearly indicated by the appearance of dielectric loss relaxation peaks in the measurement frequency from 102 Hz to 106 Hz. In addition, the corresponding frequency to relaxation peak shifts towards high frequencies with the Cr-doping concentration. Finally, the same magnetic orderings for all these Cr-doped BTFO ceramics as those of the BTFO one, i.e., superparamagnetic state dominated with antiferromagnetic interaction, are unambiguously found, signifying that the predicted Fe3+-O-Cr3+ 180° ferromagnetic superexchange interaction based on the Goodenough-Kanamori (G-K) rule might not be achieved in BTFO ceramics through Cr substitution by the conventional solid state reaction.

Epitaxial Bi5Ti3FeO15–CoFe2O4 Pillar–Matrix Multiferroic Nanostructures

Epitaxial self-assembled ferro(i)magnetic spinel (CoFe2O4 (CFO)) and ferroelectric bismuth layered perovskite (Bi5Ti3FeO15 (BTFO)) pillar-matrix nanostructures are demonstrated on (001) single-crystalline strontium titanate substrates. The CFO remains embedded in the BTFO matrix as vertical pillars (∼50 nm in diameter) up to a volume fraction of 50%. Piezoresponse force microscopy experiments evidence a weak out-of-plane and a strong in-plane ferroelectricity in the BTFO phase, despite previously reported paraelectricity along the c-axis in a pure BTFO film. Phenomenological Landau-Ginzburg-Devonshire-based thermodynamic computations show that the radial stress induced by the CFO nanopillars can influence these ferroelectric phases, thus signifying the importance of the nanopillars. The CFO pillars demonstrate robust ferromagnetic hysteresis loops with little degradation in the saturation magnetization (ca. 4 μB/f.u.). Thus BTFO-CFO nanocomposites show significant promise as a lead-free magnetoelectric materials system.

Room Temperature Magnetoelectric Coupling in Bi<sub>5</sub>Ti<sub>3</sub>FeO<sub>15</sub> Ceramics

Magnetoelectric(ME) coupling at room temperature(RT) in four-layered perovskite Bi5Ti3FeO15(BTFO) ceramics prepared by conventional solid state reaction method was observed. Unsaturated ferroelectric hysteresis loop with 2Pr=0.464 μC/cm2 and 2Ec=25 kV/cm at an applied electric field 58 kV/cm was obtained because of lower breakdown voltage which maybe induced by lower relative density of the sample. A weak ferromagnetic (Mr=0.122 memu/g, Hc=69 Oe) rather than an antiferromagnetic property was observed at RT by magnetic measurement. Significantly, the ME coupling between the electric dipoles and magnetic dipoles at RT was demonstrated by measuring the effect of magnetic and DC electric poling on ferroelectric and magnetic hysteresis loops, respectively. Both Pr and Mr decreased after magnetic and DC electric poling. And the rate of Pr change decreased with increasing measuring electric field.

Processing optimization and sintering time dependent magnetic and optical behaviors of Aurivillius Bi5Ti3FeO15 ceramics

Aurivillius Bi5Ti3FeO15 (BTF) ceramics were synthesized using the conventional solid state reaction method by optimizing excess of Bi2O3 and sintering time. Their structures, magnetic, and optical properties were investigated in detail. The optimum process to sinter pure Aurivillius BTF ceramics was confirmed to be 3 wt. % excess Bi2O3 to compensate the Bi volatilization at 1050 °C for 240 min (BTF-240M). The microstructure and crystalline structure of the BTF ceramics had little dependence on the sintering time from the x-ray diffraction (XRD) and scanning electron microscopic data. Nevertheless, the magnetic and optical properties were closely related with the sintering time. The overall magnetic behavior of these BTF ceramics was superparamagnetic (SPM), whereas there were unambiguous clues for the existence of antiferromagnetic (AFM) interactions. However, whether the SPM behavior was intrinsic or arised from a tiny amount of spinel Fe3O4 impurity phase cannot be thoroughly ruled out in the XRD detection limit in the present stage. The AFM interactions were weakened upon extending the sintering time. The effective magnetic moment (μeff), however, demonstrated different dependency on the sintering time. It increased with the sintering time from 80 min to 240 min, and then dropped with further extending the sintering time. Compared with other BTF ceramics, the BTF-240M ceramic showed the highest values of the refractive index n and real part ε1, as well as the lowest ones of the extinction coefficient k and imagine part ε2 in whole photon energy range. Finally, a direct inter-band transition was confirmed for these BTF ceramics and optical energy band gaps were determined to be about 3.08, 3.18, and 3.39 eV for 80 min, 150 min, and 240 min sintered BTF ceramics, respectively, yet abnormal optical behavior was observed in BTF-360M ceramic.

The structural and piezoresponse properties of c-axis-oriented Aurivillius phase Bi5Ti3FeO15 thin films deposited by atomic vapor deposition

The deposition by atomic vapor deposition of highly c-axis-oriented Aurivillius phase Bi5Ti3FeO15 (BTFO) thin films on (100) Si substrates is reported. Partially crystallized BTFO films with c-axis perpendicular to the substrate surface were first deposited at 610 °C (8% excess Bi), and subsequently annealed at 820 °C to get stoichiometric composition. After annealing, the films were highly c-axis-oriented, showing only (00l) peaks in x-ray diffraction (XRD), up to (0024). Transmission electron microscopy (TEM) confirms the BTFO film has a clear layered structure, and the bismuth oxide layer interleaves the four-block pseudoperovskite layer, indicating the n = 4 Aurivillius phase structure. Piezoresponse force microscopy measurements indicate strong in-plane piezoelectric response, consistent with the c-axis layered structure, shown by XRD and TEM.

Effects of annealing temperature on the structures, ferroelectric and magnetic properties of Aurivillius Bi5Ti3FeO15 polycrystalline films

The effects of annealing temperature on the structures, ferroelectric and magnetic properties of Aurivillius layer-structured Bi5Ti3FeO15 (BTF) films were investigated. It was found that an annealing temperature above 625°C can lead to the appearance of Bi4Ti3O12 (BiT) secondary phase on Pt substrates. The reduction of the grain sizes was simultaneously confirmed by X-ray diffraction and atomic force microscopy with the introduction of the BiT phase. Moreover, the remanent polarization and coercive field of the BTF films were dramatically enhanced with the introduction of the BiT phase. Improved ferromagnetism for the BTF films was demonstrated upon increasing annealing temperature. Our data indicated that the ferroelectricity strongly correlated with the growth orientation of the BTF films. Finally, the possible factors for the obvious increase of the remanent polarization and coercive field, and the possible reasons for the enhanced ferromagnetic properties were discussed with increasing annealing temperature.

Dielectric and Structural Properties of Bi5Ti3FeO15 Ceramics Obtained by Solid-State Reaction Process from Mechanically Activated Precursors

Bi5Ti3FeO15 (BTFO), an Aurivillius compound, was synthesized via sintering the Bi2O3 and Fe2O3 mixture and TiO2 oxides. The precursor material was ground in a high-energy attritorial mill for (1, 3, 5, and 10) h. The orthorhombic system Bi5Ti3FeO15 ceramics was obtained by a solid-state reaction process at 1313 K. Phase formation behavior was investigated using differential thermal analysis (DTA), thermal gravimetric (TG), and X-ray diffraction (XRD) techniques. The frequency-dependent properties of the material were investigated by impedance spectroscopy. The impedance spectroscopic method is widely used to characterize electrical properties of materials and their interfaces with electronically conducting electrodes. These studies indicate that 1h, 3h, and 5h primary high-energy ball milling followed by sintering is a promising technique for pure Bi5Ti3FeO15 ceramic preparation, whereas the ceramics obtained from the substrates after 10h milling is a two-phase material. As the result of this investigation, the model of adjusting the Nyquist charts with a three-element R-CPE (constant phase element) series connection was proposed. It was found that the value of the dielectric constant at the Curie temperature decreases when the milling time of the substrates increases. The decrease in the dielectric constant is influenced by the great dispersion of the grains, their dense packing, and location of particular grains in relation to other grains. Moreover, the change of resistivity with frequency indicates that relaxation processes take place in the material. In conclusion, it was reported that the optimal milling time of precursor oxide powders for carrying out the sintering process is equal to 5 h. Then the obtained ceramics contain one phase and exhibit the highest dielectric properties for practical applications.

Electrical, magnetic, and optical properties in multiferroic Bi5Ti3FeO15 thin films prepared by a chemical solution deposition route

Perovskite Aurivillius structure Bi5Ti3FeO15 (BTF) polycrystalline thin films were prepared by a chemical solution deposition route. The microstructure, electrical, and magnetic properties were investigated and in particular the optical properties of the BTF films were addressed. The coexistence of the ferroelectric and weak ferromagnetic properties at room temperature demonstrates the multiferroic behavior of the BTF films. The optical dielectric functions in the photon energy range of 1.13–4.13 eV have been extracted by fitting the experimental data in terms of the Tauc-Lorentz and Cauchy models. A direct interband transition is allowed and the energy bandgap is determined to be ∼3.3 eV for the BTF films. The weak absorption below the bandgap edge was observed and described by the Urbach band tail rule. Finally, the optical dispersion behaviors of the BTF films in the transparent region were explained using a single oscillator model.

Structural and ferroelectric properties of epitaxial Bi5Ti3FeO15 and natural-superlattice-structured Bi4Ti3O12–Bi5Ti3FeO15 thin films

Bismuth-layer-structured multiferroic Bi5Ti3FeO15 (BTFO15) (number of pseudoperovskite blocks, m=4) and natural-superlattice-structured Bi4Ti3O12–Bi5Ti3FeO15 (BIT-BTFO15) (m=3 or 4) thin films were prepared on (001)-oriented and (110)-oriented La-doped (3.73 wt %) SrTiO3 (La-STO) single-crystal substrates using pulsed laser deposition. X-ray diffraction patterns of these thin films on (001) La-STO single crystals indicated that the obtained thin films were single-phase (00l)-oriented layered perovskite, and that the BIT-BTFO15 (m=3 or 4) natural-superlattice structure was also obtained. On (110) La-STO single crystal, layered perovskite (11l)-oriented thin films were also obtained. Moreover, cross-sectional transmission electron microscope images of these thin films revealed four pseudoperovskite blocks (m=4) in the BTFO15 thin films, and an intergrowth structure of three and four pseudoperovskite blocks (m=3 or 4) in BIT-BTFO15 sandwiched by two (Bi2O2)2+ layers. In ferroelectric D-E hysteresis loop measurements, BTFO15 (m=4) and BIT-BTFO15 (m=3 or 4) thin films on (110) La-doped STO single crystals produced clear ferroelectric hysteresis loops with double remanent polarizations (2Pr) of 49 μC/cm2 and 44 μC/cm2, respectively. However, BTFO15 and BIT-BTFO15 thin films on (001) La-doped STO single crystals had paraelectric characteristics. These results demonstrate that the spontaneous polarization vectors of the BTFO15 and BIT-BTFO15 thin films were parallel to the a axis of their unit cells.

Processing and some properties of biferroic Bi5 Ti3 FeO15 ceramics

Bi 5 Ti 3 FeO 15 (BTF) is an example of bifferoic Aurivillius phase with perovskite layered structure. Materials on the basis BTF are of substantial interest for new types of magnetoelectric device applications. In this review we discuss technology of preparation biferroic ceramic with composition Bi 5 Ti 3 FeO 15 . The ferroelectric layered Bi 5 Ti 3 FeO 15 (BTF) Aurivillius phases were synthesized by solid-phase synthesis reaction from the conventional mixture of oxides, viz. Bi 2 O 3 , Fe 2 O 3 , TiO 2 . Thermal analysis and mass change efect were used to investigate synthesis effects in the stoichiometric mixture of powders. The crystalline structure was checked by X-ray diffraction method at room temperature. Microstructure was investigated by scanning electron microscopy.

Preparation and Characterization of Bi-Layer-Structured Multiferroic Bi5Ti3FeO15 Thin Films Prepared by Pulsed Laser Deposition

Bi-layer-structured multiferroic Bi5Ti3FeO15 (BTFO15) thin films have been fabricated on the Pt/TiO2/SiO2/Si substrate at a low temperature of ∼520 °C and various O2 pressures of 0.01–0.12 Torr by pulsed laser deposition, and their dielectric, ferroelectric, and magnetic properties have been characterized. The X-ray diffraction patterns of the BTFO15 thin films indicate the mixed phases of Bi5Ti3FeO15 and pyrochlore Bi2Ti2O7. The BTFO15 thin films (520 °C and 0.12 Torr) show a good ferroelectric hysteresis loop, and a large double remanent polarization (2Pr) of 32 µC/cm2 was obtained at a maximum applied electric field of 1120 kV/cm (40 V) despite the coexistence of the Bi5Ti3FeO15 and pyrochlore Bi2Ti2O7 phases. The magnetic M–H hysteresis measurement shows that a weak ferromagnetic characteristic was also obtained.

Characterization of Epitaxial Bi-Layer-Structured Bi5Ti3FeO15 (m = 4) and Bi4Ti3O12-Bi5Ti3FeO15 (m = 3-4) Natural-Superlattice-Structured Multiferroic Thin Films Prepared by Pulsed Laser deposition

AbstractBi-layer-structured mutiferroic Bi5Ti3FeO15 (BTFO15) (m = 4) and natural-superlattice-structured Bi4Ti3O12- Bi5Ti3FeO15 (BIT-BTFO15) (m = 3-4) thin films have been prepared on (001) and (110) oriented SrTiO3 (STO) single crystal substrates by using pulsed laser deposition. X-ray diffraction patterns of these thin films on (00l) STO single crystals shows the obtained thin films were (00l)-oriented layer-perovskite single phase, and BIT-BTFO15 (m = 3-4) natural-superlattice-structure has also obtained. On (110) STO single crystal, layer perovskite (11l) oriented thin films have been also obtained. For characterizing ferroelectric properties, these thin films have been prepared on (001) and (110) oriented La-doped (3.73 wt%) STO single crystal substrates. From ferroelectric D-E hysteresis loops measurements, BTFO15 (m = 4) and BIT-BTFO (m = 3-4) thin films on (110) La-doped STO single crystals shows good ferroelectric hysteresis loops and their double remanent polarizations (2Pr) were 47 μC/cm2 and 44 μC/cm2, respectively. However, these thin films on (001) La-doped STO single crystals do not show ferroelectric characteristics.