The temperature-dependent piezoelectric and electromechanical properties of cobalt-modified sodium bismuth titanate

Lightly cobalt-modified, Aurivillius-type, sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) ceramics were synthesized by substituting a small amount of cobalt ions onto the Ti⁴⁺ sites using conventional solid-state reaction. X-ray photoelectron spectroscopy (XPS) analysis coupled with bond valence sum calculations show that the dopant cobalt ions substitute for Ti⁴⁺ ions in the form of Co³⁺. The resultant cobalt-modified NBT ceramics (NBT-Co) exhibit better piezoelectric and electromechanical properties by comparison with pure NBT. With only 0.3 wt% Co³⁺ substitution, the piezoelectric properties of the NBT-Co ceramics are optimal, exhibiting a high piezoelectric coefficient (d₃₃~33 pC/N), a low dielectric loss tan δ (~0.1% at 1 kHz), a high thickness planar coupling coefficient (k_t~34%) as well as a high Curie temperature (T_c~663 °C). Such NBT-Co ceramics exhibit nearly temperature-independent piezoelectric and electromechanical properties up to 400 °C, suggesting that these cobalt-modified NBT ceramics are promising materials for high temperature piezoelectric applications.     

Studies on electrical and dielectric properties of co-precipitated Aurivillius phase Ca1−xBaxBi2Nb2O9 ceramics

Polycrystalline samples of lead free Ca_1−xBa_xBi₂Nb₂O₉ ceramics has been synthesized by simple chemical co-precipitation method. Single phase layered perovskite structure was confirmed by X-ray diffraction with average crystallite size in the range of 46–57 nm. Randomly oriented grains with inhomogeneous morphology was observed by scanning electron microscopy. Study of dielectric constant and corresponding tangent loss was carried out in the frequency range of 1 Hz to 5 MHz at room temperature. Ca_1−xBa_xBi₂Nb₂O₉ shows maximum value of dielectric constant of 535 at 1 Hz. The highest polarization of 0.026 μC/cm² was obtained at an applied electric field of 10 kV/cm using PE loop measurement.     

Lattice Dynamics,Dielectric Constants,and Phase Diagram of Bismuth Layered Ferroelectric Bi3Ti1−xWxNbO9+δ Ceramics

Lattice dynamics and phase transitions of Aurivillius ferroelectric Bi₃Ti_1?xW_xNbO_9+δ (BTWN100x, 0 ≤ x ≤ 15%) ceramics have been investigated by temperature‐dependent Raman spectra (80–800 K) and far‐infrared (FIR) reflectance spectra (6–300 K). The frequency, intensity, and line width of phonon modes as well as complex dielectric functions of BTWN100x ceramics have been extracted by fitting Raman and FIR reflectance spectra with the multi‐Lorentzian oscillator model. It was found that the dielectric constants at a certain frequency region become lower with increasing W compositions at room temperature due to the compressive stress on W–O bands. Moreover, the temperature‐dependent behavior of optical phonon modes in BTWN100x ceramics indicates that there are two intermediate phases during the phase transition from paraelectric I4/mmm to ferroelectric A2₁am phase on cooling. The phase diagram of BTWN100x ceramics as a function of W composition has been improved.     

Enhanced electrical properties of NaBi modified CaBi2Nb2O9-based Aurivillius piezoceramics via structural distortion

Two-layer structured ferroelectric ceramics, Ca_1-x(NaBi)_0.5xBi₂Nb₂O₉ (x?=?0.0–0.5; CNBN-x), were prepared by solid-state sintering. An artificial pseudo-morphotropic phase boundary was formed by the substitution of Ca with NaBi, and the crystal structure tended to crystallise in the pseudo-tetragonal phase as the increase of NaBi content. Curie temperature (T_c) slightly reduce and remain high value with the increase of NaBi content, which is in the range of 880–935?°C. Moreover, enhanced piezoactivity (d₃₃) and ferroelectricity (P_r) accompanying with decreased dielectric loss can be acquired in NaBi-modified CaBi₂Nb₂O_9. The CNBN-0.1 had the best performance, and its T_c, d₃₃ and P_r was 925?°C, 14.4 pC/N and 6.0 μC/cm², respectively. Thermal annealing measurement exhibited that the piezoelectric properties of Ca_1-x(NaBi)_0.5xBi₂Nb₂O₉ had good temperature stability up to 800?°C. Therefore, the NaBi-modified CaBi₂Nb₂O₉ ceramics are perceived to be of promising candidates for high-temperature applications.     

Structural,magnetic, and dielectric properties in Aurivillius phase SrxBi6-xFe1-x/2Co1-x/2Ti3+xO18

Sr_xBi_6-xFe_1-x/2Co_1-x/2Ti_3+xO₁₈ (x = 0, 0.25, 0.5, 0.75, 1)(SBFCT-x) ceramics were prepared by the sol-gel auto-combustion method, and their microstructures, ferroelectric, magnetic and dielectric properties were investigated. All samples show layer-perovskited Aurivillius phase, which confirms that Sr doping does not affect the structure of SBFCT ceramics. The coexistence of ferroelectricity and ferromagnetism were observed at room temperature for all the samples. The largest remnant polarization (2P_r ˜ 17.4 μC/cm²) is observed in the SBFCT-1 ceramic, while the SBFCT-0.5 ceramic shows the highest remnant magnetization (2M_r ˜ 0.74 emu/g). To explore the effect of valance states of magnetic ions on the properties, we analysed the content variation of Fe²⁺, Co²⁺, and oxygen vacancies by the X-ray photoelectron spectroscopy results. Furthermore, dielectric anomalies have been found around 400 K, which can be ascribed to the hopping process of oxygen vacancies. The effects of Sr and Ti substitution on ferroelectric and magnetic properties have been investigated and discussed.     

Lead-free and flexible piezoelectric nanogenerator based on CaBi4Ti4O15 Aurivillius oxides/ PDMS composites for efficient biomechanical energy harvesting

The development of a new class of perovskite materials and enhancing its capability as an energy harvester that scavenges energy from various sources to power electronics systems has attracted significant attention. Herein, we report a cost-effective approach to synthesize a perovskite material, explore its properties, and further develop a high-performance flexible nanogenerator based on hybrid piezoelectric composite. The Aurivillius-based oxide, CaBi₄Ti₄O₁₅ (CBTO) was fabricated via a mixed oxide reaction and crystallized in an orthorhombic symmetry at room temperature. The material properties were elucidated to act as a parallel plate capacitor that will further act as a base for the development of filter circuits. Aurivillus/PDMS composite films were used to fabricate a flexible Aurivillus-based piezoelectric nanogenerator (A-PENG) to act as a self-powered exercise counter and power the electronics. The A-PENG was systematically analyzed under different conditions such as weight percentage, before and after poling, and acceleration effects. In addition, device stability, and capacitor charging-discharging tests were performed. This study elucidated the formation of lead-free ceramic materials that were used to make a flexible composite film for the realization of a piezoelectric harvester acting as a sustainable energy source.