Search Results (26)

Good piezoelectricity and high resistivity are prerequisites for high-temperature acceleration sensors to function correctly in high-temperature environments. Bismuth layered structure ferroelectrics (BLSFs) are promising candidates for piezoelectric ceramics with excellent piezoelectric performance at high temperatures, high electrical resistivity, and high Curie temperatures (T_c). In this study, (LiMn)⁵⁺ is substituted for Bi at the A-site, and Ce-doping is performed to replace Ti ions in Na_0.5Bi_4.5Ti₄O₁₅, which achieves the desired combination of high piezoelectric coefficients and high resistivity. Herein, we prepared Na_0.5Bi₃(LiMn)_0.9Ti_4−xCe_xO₁₅ high-temperature piezoelectric ceramics, achieving a high piezoelectric coefficient d₃₃ of 32.0 pC/N and a high resistivity ρ of 1.2 × 10⁸ Ω·cm (at 500 °C), and a high Curie temperature of 648 °C. It is important that the d₃₃ variation remains within 8% over a wide temperature range from 25 °C to 600 °C, demonstrating excellent thermal stability. Structural characterization and microstructure analysis showed that the excellent piezoelectric coefficient and high resistivity of cerium-doped Na_0.5Bi_4.5Ti₄O₁₅-based ceramics are attributable to the synergistic effects of structural characteristics, defect concentration, refined grain size and domain morphology. This study demonstrates that the superior properties of Na_0.5Bi₃(LiMn)_0.9Ti_4−xCe_xO₁₅ ceramics are crucial for the stable operation of high-temperature accelerometer sensors and for the development of high-temperature devices. Full article

The mechanical properties of Mn- and Fe-doped Na_0.5Bi_0.5TiO₃ ceramics in unpoled and poled states were examined and analyzed for the first time through measurements of Young’s modulus, the elastic modulus, Poisson’s number, compressibility modulus K, hardness, fracture toughness and bending strength on one hand and by stress–strain measurements on the other hand. It was found that both the introduction of Fe and Mn ions into Na_0.5Bi_0.5TiO₃ and E-poling lead to improvements in their mechanical properties. The additives also cause improvement of the piezoelectric properties. The stress–strain curves revealed a changing mechanical response with the Mn and Fe doping of the NBT. With the doping, there was a decrease in coercive stress, which enhanced the remnant strain. In contrast, the E-poling led to an increase in the coercive stress, which reduced the remnant strain. Induced internal stresses associated with non-180° domain switching were determined. It was found that the investigated materials displayed significant ferroelastic deformation and large remnant polarization even under external stress of 180–250 MPa. Modification of NBT by Mn and Fe ions and E-poling were found to be effective ways of improving actuator performance and controlling operating stresses in order to minimize irreversible fatigue damage. The results suggest that the investigated materials could replace PZT ceramics in actuator applications where high blocking stress is required. Full article

The organic pollutants discharged from industrial wastewater have caused serious harm to human health. The efficient photocatalytic degradation of organic pollutants under sunlight shows promise for industrial applications and energy utilization. In this study, a modified TiO₂ photocatalyst doped with bismuth (Bi) and fluorine (F) and composited with SnO₂ and SiO₂ was prepared, and its performance for the degradation of Rhodamine B (RhB) under simulated sunlight was evaluated. Through the optimization of the doping levels of Bi and F, as well as the ratio of SnO₂ and SiO₂ to TiO₂, the optimal catalyst reached degradation efficiency of 100% for RhB within 20 min under simulated sunlight, with a first-order reaction rate constant of 0.291 min⁻¹. This value was 15, 41, 6.5, and 3.3 times higher than those of TiO₂/SnO₂, Bi/TiO₂, Bi-TiO₂/SnO₂, and F/Bi-TiO₂/SnO₂, respectively. The active species detection showed that h⁺ was the most crucial active species in the process. The role of Bi and F addition and SnO₂-SiO₂ compositing was investigated by characterization. Bi formed a chemical bonding with TiO₂ by doping into TiO₂. The absorbance intensity in the UV and visible light regions was improved by SnO₂ and F modification. Composite with SiO₂ led to a larger surface area that allowed for more RhB adsorption sites. These beneficial modifications greatly enhanced the photocatalytic activity of the catalyst. Full article

This review summarizes the progress over the last fifteen years in visible light reactive photocatalysts for environmental arsenic remediation. The design and performance of several materials including (1) doped and surface functionalized TiO₂, (2) binary composites combining TiO₂ with another semiconductor that absorbs visible light radiation or a metal (Pt), (3) ternary composites incorporating TiO₂, a conductive polymer that can retard electron-hole recombination and an excellent adsorbent material for the removal of As(V), (4) tungsten, zinc, and bismuth oxides, (5) g-C₃N₄ based catalysts, and (6) M@AgCl core–shell structures. These results show that long reaction time remains a major challenge in achieving high As(III) oxidation. Full article

This work addresses the global sustainable development concerns by investigating the enhancement of piezo-photocatalytic efficiency in bismuth ferrite-based thin films synthesized using reactive high-power impulse magnetron sputtering. The influence of substrate type and Cr addition on structural, optical and ferroelectric properties of bismuth ferrite (BFO) based thin films was investigated. X-ray diffraction measurements showed the formation of different phases depending on the substrate used for sample growth. Compared to the BFO film deposited on FTO (F-SnO₂), the Cr-doped BFO (BFCO) sample on SrTiO₃ (STO) exhibits higher photodegradation efficiency (52.3% vs. 27.8%). The enhanced photocatalytic activity of BFCO is associated with a lower energy band gap (1.62 eV vs. 1.77 eV). The application of ultrasonic-wave vibrations simultaneously with visible light improved 2.85 times and 1.86 times the photocatalytic degradation efficiencies of BFO/FTO and BFCO/STO catalysts, respectively. The piezoresponse force microscopy (PFM) measurements showed that both catalysts exhibit ferroelectric behavior, but a higher piezoelectric potential was evidenced in the case of the BFO/FTO thin film. The enhancement of piezo-photodegradation efficiency was mainly attributed to the piezoelectric-driven separation and transport of photo-generated carriers toward the surface of the photocatalyst. Full article

Synthesis and study of materials based on bismuth cerates and titanates were carried out. Complex oxides Bi_1.6Y_0.4Ti₂O₇ were synthesized by the citrate route; Bi₂Ce₂O₇ and Bi_1.6Y_0.4Ce₂O₇—by the Pechini method. The structural characteristics of materials after conventional sintering at 500–1300 °C were studied. It is demonstrated that the formation of a pure pyrochlore phase, Bi_1.6Y_0.4Ti₂O₇, occurs after high-temperature calcination. Complex oxides Bi₂Ce₂O₇ and Bi_1.6Y_0.4Ce₂O₇ have a pyrochlore structure formed at low temperatures. Yttrium doping of bismuth cerate lowers the formation temperature of the pyrochlore phase. As a result of calcination at high temperatures, the pyrochlore phase transforms into the CeO₂-like fluorite phase enriched by bismuth oxide. The influence of radiation-thermal sintering (RTS) conditions using e-beams was studied as well. In this case, dense ceramics are formed even at sufficiently low temperatures and short processing times. The transport characteristics of the obtained materials were studied. It has been shown that bismuth cerates have high oxygen conductivity. Conclusions are drawn about the oxygen diffusion mechanism for these systems. The materials studied are promising for use as oxygen-conducting layers in composite membranes. Full article

Lead-based electro-ceramic compositions are excellent energy storage materials used for high-energy storage density applications in dielectric ceramic capacitors. However, these materials have lead contents in their compositions, making them toxic, with a negative impact on human health and the environment. For this reason, we synthesized a lead-free bismuth-based electro-ceramic perovskite, 0.80(0.92Bi_1/5Na_1/5TiO₃-0.08BaTiO₃)-0.20(Na_0.73Bi_0.09NbO₃₋xTa₂O₅), abbreviated (BNT-BT-NBN_1−xT_x), from mixed oxides with doping of tantalum (Ta) at different concentrations, using a conventional solid-state reaction method. The effects of Ta doping on the phase evolution, microstructure development, and energy storage applications were investigated. Detailed powder X-ray diffraction analysis revealed a pure perovskite phase with Ta doping at ≤0.05. Furthermore, it was observed that excessive addition of Ta has been resulted in secondary phase generation. Scanning electron microscopy validated the development of dense microstructures with a reduced grain size for the Ta concentration of ≤0.01. Electrochemical analysis revealed a maximum polarization (P_m) of ~22 µC/cm² and a recoverable energy density of 1.57 J/cm³ with 80% efficiency for Ta doping at 0.05 with an applied field of 175 kV/cm. These results demonstrate the development of enhanced ferroelectric characteristics in an as-synthesized electro-ceramic perovskite for high-energy storage density applications in electro-ceramic capacitors. Full article

In this study, composite materials based on nanocrystalline anatase TiO₂ doped with nitrogen and bismuth tungstate are synthesized using a hydrothermal method. All samples are tested in the oxidation of volatile organic compounds under visible light to find the correlations between their physicochemical characteristics and photocatalytic activity. The kinetic aspects are studied both in batch and continuous-flow reactors, using ethanol and benzene as test compounds. The Bi₂WO₆/TiO₂-N heterostructure enhanced with Fe species efficiently utilizes visible light in the blue region and exhibits much higher activity in the degradation of ethanol vapor than pristine TiO₂-N. However, an increased activity of Fe/Bi₂WO₆/TiO₂-N can have an adverse effect in the degradation of benzene vapor. A temporary deactivation of the photocatalyst can occur at a high concentration of benzene due to the fast accumulation of non-volatile intermediates on its surface. The formed intermediates suppress the adsorption of the initial benzene and substantially increase the time required for its complete removal from the gas phase. An increase in temperature up to 140 °C makes it possible to increase the rate of the overall oxidation process, and the use of the Fe/Bi₂WO₆/TiO₂-N composite improves the selectivity of oxidation compared to pristine TiO₂-N. Full article

In order to meet the urgent need for high temperature piezoelectric materials with a Curie temperature over 400 °C, the Mn/Nb co-doped strategy has been proposed to improve the weak piezoelectric performance of the Aurivillius-type Na_0.5Bi_4.5Ti₄O₁₅ (NBT) high temperature piezoelectric ceramics. In this paper, the crystal structure, electrical properties, and thermal stability of the B-site Mn/Nb co-doped Na_0.5Bi_4.5Ti_4-x(Mn_1/3Nb_2/3)_xO₁₅ (NBT-100x) ceramics were systematically investigated by the conventional solid-state reaction method. The crystal structural analysis results indicate that the NBT-100x ceramics have typical bismuth oxide layer type phase structure and high anisotropic plate-like morphology. The lattice parameters and the grain sizes increase with the B-site Mn/Nb co-doped content. The electrical properties were significantly improved by Mn/Nb co-doped modifications. The maximum of the piezoelectric coefficient d₃₃ was found to be 29 pC/N for the NBT-2 ceramics, nearly twice that of the unmodified NBT ceramics. The highest values of the planar electromechanical coupling factor k_p and thickness electromechanical coupling factor k_t were also obtained for the NBT-2 ceramics, at 5.4% and 31.2%, respectively. The dielectric spectroscopy showed that the Curie temperature Tc of the Mn/Nb co-doped NBT-100x ceramics is slightly higher than that of unmodified NBT ceramics (646 °C). The DC resistivity of the NBT-2 ceramics is higher than 10⁶ Ω∙cm at 500 °C. All the results together with the good thermal stability demonstrated the Mn/Nb co-doped ceramics as an effective method to improve the NBT based piezoelectric ceramics and the potential candidates of the Mn/Nb co-doped NBT-100x ceramics for high temperature piezoelectric applications. Full article

With the ever-increasing demand for energy, research on energy storage materials is imperative. Thereinto, dielectric materials are regarded as one of the potential candidates for application in advanced pulsed capacitors by reason of their ultrahigh energy-storage density, low energy loss, and good thermal stability. Among the numerous dielectric materials for energy storage, sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT) with high saturation polarization, as one of the successful alternatives to lead-based materials, has been extensively studied. However, degraded dielectric and ferroelectric properties as a consequence of chemical alterations usually produced by inhomogeneity in microstructure and composition due to the ion volatilization during preparing, thus affecting performance of devices. Hence, this review served to encompass the current state and progress on the optimization of energy storage performance in lead-free BNT-based materials over the past few years, including ceramics, multilayer ceramics, thin films, and thick films, involved in solid solution modification, metal/metallic oxide doping, process optimization and other related aspects to optimize energy storage performance. Furthermore, some prospective approach in the improvement of energy storage performance for BNT-based materials were also provided in this work according to the existing theoretical and experimental results, to impel their practical application. Full article

Bismuth-deficient sodium bismuth titanate (nominal Na_0.5Bi_0.49TiO_2.985, NB_0.49T) presents high oxide ion conductivity, which makes it a potential electrolyte material for intermediate-temperature solid oxide fuel cells. Acceptor doping has been proven an effective approach to enhance the bulk conductivity (σ_b) of NB_0.49T. Here, divalent Ca²⁺ ions were selected to partially replace Bi³⁺ on the A-site of NB_0.49T, and the temperature and composition dependences of σ_b and permittivity were investigated. Results showed that Ca²⁺ doping was effective for enhancing σ_b of NB_0.49T by creating oxygen vacancies. The highest σ_b (0.006 S·cm⁻¹ at 500 °C) was achieved by 2% Ca²⁺ doping. Further increase in the doping level decreased σ_b, which was more pronounced at temperatures below ~350 °C. Most importantly, Ca doping increased the temperature at which the activation energy for bulk conduction changed from ~0.80 eV (at low temperatures) to ~0.40 eV (at high temperatures), and reduced the temperature dependence of permittivity of NB_0.49T. Results from the average structural parameters and the local defect associates are discussed. The findings of this work are helpful for understanding the defect and conduction mechanisms for acceptor-doped NB_0.49T, and are also useful for developing NBT-based dielectrics with temperature-independent permittivity. Full article

In this work, we reported obtaining mesoporous Bi-doped TiO₂ by mechanosynthesis and bismuth loading of 0%, 1%, 3%, 5%, and 10% (milled TiO₂, TiO₂ Bi 1%, TiO₂ Bi 3% TiO₂ Bi 5%, and TiO₂ Bi 10%, respectively). The effect of bismuth doping and ball milling on the crystal structure, optical properties, and photocatalytic performance of Bi-doped TiO₂ mesoporous samples under UV, visible, and sun irradiation was investigated. According to the results of the Rietveld refinement, the estimated chemical formulas for the TiO₂ Bi 1%, TiO₂ Bi 3%, TiO₂ Bi 5%, and TiO₂ Bi10% samples were Ti_0.99Bi_0.01O₂, Ti_0.97Bi_0.03O₂, Ti_0.96Bi_0.04O₂, and Ti_0.91Bi_0.09O₂ respectively. The incorporation of Bi into the TiO₂ lattice causes the crystallite size to decrease and, consequently, the absorption spectrum of TiO₂ to extend into the visible region of the electromagnetic spectrum, resulting in a lower band gap (E_g) value. Bi-doped TiO₂ mesoporous samples had E_g values of 2.90 eV, 2.83 eV, 2.77 eV, and 2.70 eV for the TiO₂ Bi 1%, TiO₂ Bi 3%, TiO₂ Bi 5%, and TiO₂ Bi 10% samples, respectively. Photocatalytic removal of methylene blue (MB) data fit well for second-order kinetics. Photocatalytic activity increase followed the order of TiO₂ Bi 5% > TiO₂ Bi 10% > TiO₂ Bi 3% > TiO₂ Bi 1% > pristine TiO₂. The TiO₂ Bi 5% sample exhibited excellent photocatalytic performance for MB photodegradation under natural sunlight (89.2%). Full article

This work presents optical and multiferroic properties of bismuth ferrite thin films that are affected by zirconium and dysprosium substitution. Non-centrosymmetric BiFeO₃,Bi_0.95Zr_0.05FeO₃, and Bi_0.95Dy_0.05FeO₃ thin films were coated on Pt/TiO₂/SiO₂/Si substrates using the spin coating method. The crystal structure, optical properties, microstructural, ferromagnetic, and ferroelectric properties of doped bismuth ferrite thin films were systematically investigated. From the XRD patterns, all the prepared thin films matched well with the rhombohedral structure with R3c space group with no observed impurity phases. The average crystallite size of the bismuth ferrite thin films were between 35 and 47 nm, and the size depended on the type of dopant. The determined energy band gap values of BiFeO₃, Bi_0.95Dy_0.05FeO₃, and Bi_0.95Zr_0.05FeO₃ thin films were 2.32 eV, 2.3 eV, and 2 eV, respectively. Doping of Dy and Zr at the Bi site led to reduced surface roughness. The prepared thin films exhibited enhanced ferromagnetic and ferroelectric properties. The remnant magnetization of Zr-doped BiFeO₃ was greater than that of the BiFeO₃ and Dy-doped BiFeO₃ thin films. From the obtained results, it was concluded that Zr-doped BiFeO₃ thin films are suitable for solar cell fabrication. Full article

Over the past decades, ferroelectric photovoltaic (FE-PV) systems, which use a homogenous ferroelectric material as a light-absorbing layer, have been studied using ferroelectric oxides. The PV activity of materials can be enhanced by adjusting the bandgap of materials, and it would have a large effect on the ferroelectric complex oxides. This phenomenon in epitaxial thin films of ferroelectric complex oxide, Bi_3.25La_0.75Ti₃O₁₂ (BLT), Fe- and Co-doped films were observed. Compared with undoped BLT, Co-(BLCT) doping and Fe and Co combined (BLFCT) doping resulted in the gradual reduction in the bandgap and efficient visible light absorption. The reduction in the bandgap to 11.4% and 18.1% smaller than the experimentally measured Eg of the bismuth titanate-based film using a simple Fe- and Co-doping method was performed, while maintaining ferroelectricity by analyzing the BLCT and BLFCT films based on polarization loops, and the temperature range of the out-of-plane lattice parameters and the photocurrent density of the BLFCT film was 32.2 times higher than that of the BLT film, which was caused by the decrease in the bandgap. This simple doping technique can be used to tune additional wide-bandgap complex oxides so that they can be used in photovoltaic energy conversion or optoelectronic devices. Full article

Sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT) has attracted much attention because of its excellent dielectric, piezoelectric and electromechanical properties. The microstructure of sodium bismuth titanate-doped ferrum niobium material (Bi_0.5Na_0.5TiO₃ doped (Fe_0.5Nb_0.5)⁴⁺, BNT-xFN) shows a triangle as its typical defect shape. Since piezoelectric devices usually operate under dynamic loads, they fail easily owing to dynamic stress concentration or dynamic fracture. Elastic waves can simulate many types of dynamic loads, and the dynamic stress concentration caused by an anti-plane shear wave is the basis for the calculation of the stress field strength factor of type Ⅲ-dynamic fractures. In this study, the electroelastic coupled-wave diffraction and dynamic stress concentration of BNT-xFN materials with triangular defects under the incidence of anti-plane shear waves were studied. Maxwell equations are decoupled by auxiliary functions, and the analytical solutions of the elastic wave field and electric field are obtained. Based on the conformal mapping method, the triangle defect was mapped to the unit circle defect, and the dynamic stress concentration coefficient around the triangle defect was obtained by calculating the undetermined mode coefficients in the expression through boundary conditions. The numerical calculation shows that the size of the triangular hole, the frequency of the applied mechanical load, the incidence angle of mechanical load and the amount of FN doping have a great influence on the stress concentration of BNT-xFN materials. Full article