High temperature lead-free relaxor ferroelectric: intergrowth Aurivillius phase BaBi2Nb2O9−Bi4Ti3O12 ceramics

High temperature lead-free relaxor ferroelectric: intergrowth Aurivillius phase BaBi2Nb2O9−Bi4Ti3O12 ceramic

Microstructure and electrical properties of Aurivillius phase (CaBi2Nb2O9)1-x(BaBi2Nb2O9)x solid solution

Microstructure and electrical properties of Aurivillius phase (CaBi2Nb2O9)1-x(BaBi2Nb2O9)x solid solutio

Thermal depoling of high Curie point Aurivillius phase ferroelectric ceramics

Thermal depoling of high Curie point Aurivillius phase ferroelectric ceramic

Crystal structure and electrical properties of textured Ba2Bi4Ti5O18 ceramics

Highly textured Ba2Bi4Ti5O18 ceramic was prepared by spark plasma sintering (SPS). X-ray diffraction of the ceramics revealed the coexistence of a major ferroelectric phase (Space group, SG: B2cb) and a minor paraelectric phase (SG: I4/mmm) at room temperature. A diffused phase transition was observed at around 240 °C. The evolution of the switching current peaks in the electric current vs. electric field (I-E) loops with increasing temperature was interpreted by the structural changes and temperature dependent polarisation reversal processes. The slim polarisation vs. electric field (P-E) loops, the extra switching current peaks in the I-E loops and the non-zero piezoelectric d33 coefficient indicate that Ba2Bi4Ti5O18 is a relaxor ferroelectric material. The recoverable energy density (0.41 ± 0.01 J/cm3) of Ba2Bi4Ti5O18 ceramics in the perpendicular direction to the SPS pressing direction is close to that of Pb(Mg1/3Nb2/3)O3-based ceramics. The obtained results suggest Ba2Bi4Ti5O18 ceramics might be promising for energy storage applications

Textured high Curie point piezoelectric ceramics prepared by spark plasma sintering

Textured high Curie point piezoelectric ceramics prepared by spark plasma sinterin

Ferroelectric and photocatalytic properties of Aurivillius phase Ca₂Bi₄Ti₅O₁₈

Aurivillius phase Ca2Bi4Ti5O18 powders with micrometer size were produced by solidstate reaction. X-ray diffraction revealed that the powders had polar orthorhombic structure with space group of B2cb. Ca2Bi4Ti5O18 ceramic exhibited frequency independent dielectric anomaly at 774 °C. The piezoelectric coefficient d33 value of poled Ca2Bi4Ti5O18 pellets was 0.7±0.2 pC/N. Both frequency independent dielectric anomaly and detectable d33 value clearly indicated that Ca2Bi4Ti5O18 is a ferroelectric material with Curie point of 774 ℃. UV–vis absorption spectra revealed that Ca2Bi4Ti5O18 had a direct band gap of 3.2 eV. Photocatalytic activity of the Ca2Bi4Ti5O18 powders was examined by degradation of rhodamine B (RhB) under simulated solar light. 16% of RhB solution was degraded by Ca2Bi4Ti5O18 powders after 4 h UV-vis irradiation. With Ag nanoparticles deposited on the Ca2Bi4Ti5O18 powders surface, 50% of RhB were degraded under the same irradiation condition. The fitted degradation rate constant of Ag decorated Ca2Bi4Ti5O18 was 4 times higher than that of bare Ca2Bi4Ti5O18. This work suggested that the Aurivillius ferroelectric Ca2Bi4Ti5O18 is a promising candidate for photocatalytic applications

B-Site donor and acceptor doped Aurivillius phase Bi3NbTiO9 ceramics

B-Site donor and acceptor doped Aurivillius phase Bi3NbTiO9 ceramic

Effect of Phase Transitions on Thermal Depoling in Lead-Free 0.94(Bi_0.5Na_0.5TiO₃)–0.06(BaTiO₃) Based Piezoelectrics

0.94­(Bi0.5Na0.5TiO3)–0.06­(BaTiO3) (BNTBT) is a potential lead-free piezoelectric candidate to replace lead-based PZT ceramics. The thermal depoling temperature sets the upper limit for the high temperature application of piezoelectric materials. Recently, an interface model was proposed to explain the good resistance to thermal depoling of BNTBT-ZnO composite. However, we found that the presence of ZnO was not limited to the interface, but contributed intrinsically to the BNTBT lattice. This played a critical role in the structural changes of BNTBT, confirmed by a unit volume change supported by XRD, which was further proved by Raman, EDS, and dielectric characterization at different temperatures. The previous interface model is not correct because BNTBT shows thermally stable piezoelectric properties, even though there is no interface between BNTBT and ZnO. The thermal depoling behavior of BNTBT-based materials is directly related to the transition temperature from the rhombohedral phase to the tetragonal phase in our phase transition model, which is consistent with four current peaks in their ferroelectric loops close to the depoling temperature

Orientation dependence of dielectric and relaxor behaviour in Aurivillius phase BaBi2Nb2O9 ceramics prepared by spark plasma sintering

Grain-oriented Aurivillius phase BaBi2Nb2 O9 ceramics were fabricated using Spark Plasma Sintering (SPS). Their relaxor behaviour was confirmed by a strong frequency dispersion of the dielectric response. The dielectric behaviour has been fitted using different relaxor models. The relaxor parameters are isotropic, while the dielectric constants are highly anisotropic. The piezoelectric constant d33 is zero perpendicular and parallel to the hot pressing direction, and the P–E response is dominated by losses. The inability to pole the samples at room temperature is consistent with the Tf temperature (~115 K) estimated from fitting the experimental data to the Vogel–Fulcher model. This suggests that it may be possible to observe piezoelectric and ferroelectric properties at very low temperatures

Crystal Chemistry and Magnetic Properties of Gd-Substituted Aurivillius-Type Bi₅FeTi₃O₁₅ Ceramics

Aurivillius-phase ferroelectrics can be turned into multiferroic materials by incorporating magnetic ions. The four-layer Aurivillius-type system Bi₅FeTi₃O₁₅ is well-known to show a strong magnetoelectric effect; however, much controversy exists on its magnetic state and the possible multiferroicity at room temperature. In this paper, we report a detailed investigation on the interconnections between crystal chemistry and magnetic properties of Bi₅FeTi₃O₁₅ ceramics chemically modified by the A-site gadolinium substitution. The structural studies showed that all Bi_5–<i>x</i>Gd_<i>x</i>FeTi₃O₁₅ (0 ≤ <i>x</i> ≤ 1) samples adopt the polar orthorhombic space group symmetry <i>A</i>2₁<i>am</i> at room temperature. The unit cell volume and the orthorhombic distortion decrease alongside the reduction of octahedral tilts by increasing the amount of Gd added. The decrease in tilting distortion of the [Ti/Fe]­O₆ octahedra was further evidenced by the suppression of the Raman A₁[111] tilt mode at 233 cm^–1. By using superconducting quantum interference and vibrating sample magnetometry, it was demonstrated that all the ceramics are paramagnetic from 5 K up to 700 K. It was thus concluded that the A-site substitution of Bi₅FeTi₃O₁₅ with magnetic Gd ions brings about a slight structural relaxation of the parental orthorhombic lattice, but it is not an effective way to induce multiferroic properties in the Aurivillius compound. We suggest that the room-temperature (ferri/ferro/antiferro-) magnetism in Bi₅FeTi₃O₁₅ previously reported in the literature might be due to the presence of magnetic impurities or local short-range magnetic ordering formed during material processing under different conditions