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Photovoltaic, photo-impedance, and photo-capacitance effects of the flexible (111) BiFeO <sub/>3</sub> film
摘要： Ferroelectric polarization allows a depolarization electric field to separate electron-hole pairs excited by lights, and thus, the photovoltaic properties of ABO3-type films on a hard SrTiO3 or Si substrate have been extensively studied recently. However, there are a few reports on the photocapacitance and photoimpedance of these oxide films, especially on flexible substrates. In this work, the strong photovoltaic, giant photocapacitance, and photoimpedance effects were observed in the flexible (111) BiFeO3 films with natural downward polarization. The flexible mica/SrRuO3/BiFeO3/Au cells show a maximum photovoltaic efficiency at 150 °C, a 95.5% decrease in photoimpedance effects, and a 316% increase in photocapacitance effects under 405-nm-wavelength light illumination at 25 °C. Most importantly, these properties do not show obvious degradation when the device is bent to 3 mm radius for 104 times. This work is of vital importance for us to develop new flexible photoelectronic devices.
关键词： photo-capacitance,photovoltaic,flexible,photo-impedance,BiFeO3 film
更新于2025-09-11 14:15:04
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Construction of high <i>T</i> <sub/>c</sub> BiScO <sub/>3</sub> -BiFeO <sub/>3</sub> -PbTiO <sub/>3</sub> and its enhanced piezoelectric properties by sintering in oxygen atmosphere
摘要： The high-temperature piezoelectric ceramics 0.36[(1 ? x)BiScO3-xBiFeO3]-0.64PbTiO3 was constructed by introducing BiFeO3 with a high Curie temperature (Tc ～ 830 °C) in the 0.36BiScO3-0.64PbTiO3 binary system. In terms of microstructure, low-melting BiFeO3 plays a role as a sintering aid, lowering the sintering temperature of the ceramic and signi?cantly increasing the grain size. At the same time, the crystal structure shifts from the initial morphotropic phase boundary to the tetragonal phase side, and the Tc increased gradually with increasing BiFeO3 content. Under the conventional air atmosphere sintering conditions, the Tc of the sample with x = 0.3 can reach ～500 °C, and the piezoelectric constant d33 is 125 pC/N. Compared with that, the d33 of the same composition sample sintered in an oxygen atmosphere is increased to 165 pC/N, which is mainly due to the decrease in the content of oxygen vacancies that helps to increase poling electrical ?eld. Moreover, the oxygen-sintered specimen exhibits an excellent thermal stability in a wide temperature range from room temperature to 450 °C, indicating that it is a promising candidate for ultra-high-temperature piezoelectric devices applications.
关键词： high-temperature piezoelectric ceramics,thermal stability,BiScO3-BiFeO3-PbTiO3,sintering in oxygen atmosphere,piezoelectric properties
更新于2025-09-11 14:15:04
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Oxygen vacancy induced photoconductivity enhancement in Bi <sub/> 1- <i>x</i> </sub> Ca <i> <sub/>x</sub></i> FeO <sub/>3-δ</sub> nanoparticle ceramics: A combined experimental and theoretical study
摘要： Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (OV) leads to large scale enhancement of photoconductivity in BiFeO3 (BFO). The OV concentration is increased by substituting an aliovalent cation Ca2+ at Bi3+ sites in the BFO structure. Furthermore, the OV concentration at the disordered grain boundaries can be increased by reducing the particle size. Photoconductivity studies carried out on spark plasma sintered Bi1-xCaxFeO3-δ ceramics show four orders of enhancement for x = 0.1. Temperature dependent Nyquist plots depict a clear decrease in impedance with increasing Ca2+ concentration which signi?es the role of OV. A signi?cant reduction in photoconductivity by 2 to 4 orders and a large increase in impedance of the air-annealed (AA) nanocrystalline ceramics suggest that OV at the grain boundaries primarily control the photocurrent. In fact, activation energy for AA samples (0.5 to 1.4 eV) is larger than the as-prepared (AP) samples (0.1 to 0.5 eV). Therefore, the room temperature J-V characteristics under 1 sun illumination show 2–4 orders more current density for AP samples. Density-functional calculations reveal that, while the defect states due to bulk OV are nearly ?at, degenerate, and discrete, the defect states due to surface OV are non-degenerate and interact with the surface dangling states to become dispersive. With large vacancy concentration, they form a defect band that enables a continuous transition of charge carriers leading to signi?cant enhancement in the photoconductivity. These studies reveal the importance of tailoring the microstructural features as well as the composition-tailored properties to achieve large short circuit current in perovskite oxide based solar cells.
关键词： density functional theory,BiFeO3,spark plasma sintering,Ca doping,oxygen vacancies,photoconductivity
更新于2025-09-11 14:15:04
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Understanding and predicting geometrical constraint ferroelectric charged domain walls in a BiFeO <sub/>3</sub> island via phase-field simulations
摘要： It has been known that ferroelectric charged domain walls (CDWs), which break the polarization continuity, may be electrically active with an elevated conductivity. However, the bound charge at CDWs may render them energetically unstable, and thus, forming CDWs naturally and manipulating them electrically is still challenging. Here, we theoretically utilize phase-field simulations to design spontaneously generated CDWs with center-type quad-domains in a single square-shaped BiFeO3 nanoisland. It is shown that the stability of the spontaneously emerging head-to-head domain walls with center-convergent quad-domains is mainly determined by three contributions, namely, the geometrical constraint from approximately 45°-tilted bottom edges, the electric boundary condition, and the necessary screening free charges to compensate head-to-head domain walls. It is demonstrated that the center-convergent quad-domains with head-to-head CDWs can be electrically switched to the center-divergent one with tail-to-tail CDWs, providing guidance for achieving ferroelectric domain-wall-based nanodevices with low-power dissipation.
关键词： phase-field simulations,electric boundary condition,ferroelectric charged domain walls,BiFeO3,screening free charges,geometrical constraint
更新于2025-09-10 09:29:36
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Synergistically Catalytic Activities of BiFeO3/TiO2 Core-Shell Nanocomposites for Degradation of Organic Dye Molecule through Piezophototronic Effect
摘要： The BiFeO3/TiO2 core-shell nanocomposites with the R3C space group is demonstrated to exhibit the superior synergistically catalyst activities, which is a combination of the piezo- and photo-catalytic activities (referred to as the piezophototronic effect). With the application of an ultrasonification and light irradiation, the degradation activity for the decomposition of the dye molecules by the piezoelectric polarization of the BiFeO3/TiO2 core-shell nanocomposites (referred to as the hybrid catalyst, BiFeO3/TiO2 NCs-P) is 432% higher than that of the un-poling BiFeO3/TiO2 nanocomposites (BiFeO3/TiO2 NCs). In responding to the excitation of the mechanical force (ultrasonic vibration), the results demonstrate that the BiFeO3 nanoparticles can effectively reduce the recombination rate of the carriers by the built-in electric field. Subsequently, the redox reaction has taken place on the surface of the hybrid catalyst in the solution to generate the powerful oxidizing radicals and further dissociate the organic dyes. The reaction k constant of the piezophototronic effect is 566% and 388% higher than that of the sole piezocatalytic and the photocatalytic process, respectively. After four consecutive cycling degradation tests, the hybrid catalyst still reaches ~ 85% of the degradation activity by the piezophototronic effect. Based on the fluorescence luminescence (FL) analysis, the signals associated to the hydroxyl radicals elevate with the increase of the catalysts’ concentration and the ultrasonic vibration time. This work reveals that the hybrid catalysts contains the ferroelectric material, which provides a new catalyst design strategy in the industrial application.
关键词： piezocatalysis,piezophototronic,TiO2,BiFeO3,photocatalysis,nanocomposite
更新于2025-09-10 09:29:36
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Frequency-dependent decoupling of domain-wall motion and lattice strain in bismuth ferrite
摘要： Dynamics of domain walls are among the main features that control strain mechanisms in ferroic materials. Here, we demonstrate that the domain-wall-controlled piezoelectric behaviour in multiferroic BiFeO3 is distinct from that reported in classical ferroelectrics. In situ X-ray diffraction was used to separate the electric-field-induced lattice strain and strain due to displacements of non-180° domain walls in polycrystalline BiFeO3 over a wide frequency range. These piezoelectric strain mechanisms have opposing trends as a function of frequency. The lattice strain increases with increasing frequency, showing negative piezoelectric phase angle (i.e., strain leads the electric field), an unusual feature so far demonstrated only in the total macroscopic piezoelectric response. Domain-wall motion exhibits the opposite behaviour, it decreases in magnitude with increasing frequency, showing more common positive piezoelectric phase angle (i.e., strain lags behind the electric field). Charge redistribution at conducting domain walls, oriented differently in different grain families, is demonstrated to be the cause.
关键词： frequency dispersion,BiFeO3,domain walls,piezoelectric,lattice strain
更新于2025-09-10 09:29:36
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Symmetry Modulation and Enhanced Multiferroic Characteristics in Bi <sub/>1-</sub><i> <sub/>x</sub></i> Nd <i> <sub/>x</sub></i> FeO <sub/>3</sub> Ceramics
摘要： BiFeO3 is recognized as the most important room temperature single phase multiferroic material. However, the weak magnetoelectric (ME) coupling remains as a key issue, which obstructs its applications. Since the magnetoelectric coupling in BiFeO3 is essentially hindered by the cycloidal spin structure, here efforts to improve the magnetoelectric coupling by destroying the cycloidal state and switching to the weak ferromagnetic state through symmetry modulation are reported. The structure is tuned from polar R3c to polar Pna2 1, and finally to nonpolar Pbnm by forming Bi1-xNdxFeO3 solid solutions, where two morphotropic phase boundaries (MPBs) are detected. Greatly enhanced ferroelectric polarization is obtained together with the desired weak ferromagnetic characteristics in Bi1-xNdxFeO3 ceramics at the compositions near MPBs. The change of magnetic state from antiferromagnetic (cycloidal state) to ferromagnetic (canted antiferromagnetic) is confirmed by the observation of magnetic domains using magnetic force microscopy. More interestingly, combining experiments and first-principles-based simulations, an electric field-induced structural and magnetic transition from Pna21 back to R3c is demonstrated, providing a great opportunity for electric field-controlled magnetism, and this transition is shown to be reversible with additional thermal treatment.
关键词： multiferroics,symmetry modulation,electric field-controlled magnetism,BiFeO3
更新于2025-09-10 09:29:36
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Growth of pure and BFO doped KCl crystals by Czochralski technique and fabrication of microstrip patch antenna for GHz applications
摘要： Large sized pure and 0.1 mol% BiFeO3 (BFO) doped KCl single crystals were grown by Czochralski technique. Structural parameters were confirmed by powder XRD and single crystal XRD. EDX analysis was used to determine the elemental composition of BFO and KCl crystal. Photoluminescence confirmed that BFO acts as defect quenching agent for KCl single crystal which improved its optical transparency. Doping of BFO in KCl single crystal increased its hardness as measured by a Vicker’s microhardness test. The effect of BFO on dielectric constant and dielectric loss of KCl crystal, at various temperature and frequencies was studied. The low dielectric constant viz. 4.5 and 5.8 for pure and BFO doped KCl was helpful in designing and fabricating patch antenna in GHz frequency. As a result of BFO doping, the resonant frequency of microstrip patch antenna can be tuned at 5.40 GHz from 6.01 GHz for the KCl single crystal.
关键词： Czochralski technique,GHz applications,microstrip patch antenna,BiFeO3 (BFO),KCl single crystal
更新于2025-09-10 09:29:36
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Two-level hierarchical stripe domains and enhanced piezoelectricity of rapid hot-press sintered BiFeO <sub/>3</sub> ceramics
摘要： BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples.
关键词： ferroelectric,hot-press sintering,BiFeO3,multiferroic,domain structure,piezoelectric
更新于2025-09-10 09:29:36
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Enhanced Photoelectrochemical Performance of BiFeO <sub/>3</sub> Doped with Calcium: Doping Induced Heterojunction Through Phase Separation
摘要： Here we report on considerable enhancement in photoelectrochemical, PEC, performance of BiFeO3 induced by 20% Ca doping. We demonstrate that although doping is commonly carried out in low concentration of the dopants, order of few percentages, what we can call heavy doping, 20%, used in this work proven to be advantageous and serve as an efficient charge separation mechanism. At such high Ca percentage, phase separation takes place and other phases, mainly Fe2O3 (α/γ Fe2O3), are introduced into the material forming heterostructured photocatalyst with improved properties. This is carried out without resolving to the use of expensive rare earth cocatalyst. Polycrystalline BFO and 20% Ca doped photoelectrodes were synthesized by doctor blading. XRD showed the formation of Fe2O3 phase along with the BFO one. Particle size decreased significantly upon Ca doping promoting concomitant enhancement of ferromagnetism. The photocurrent density at 0.75 V showed fivefold increase upon 20% Ca doping. The enhancement in the photocurrent, charge carriers density and the reaction rate at the surface of the electrode deduced from electrochemical impedance spectroscopy recommend that Ca doping at such high percentage provide a mechanism for the separation of photogenerated charges. Elemental mapping suggested the non-perfect correlation between Bi and Fe as expected for a phase separated system. Band alignment of the different phases existing in the system could imply the formation of nanojunctions formed between BFO and α/γ Fe2O3 leading to increase in carrier lifetime. It is low cost approach to improve the performance of the multiferriocs photoelectrode towards the production of clean solar energy.
关键词： Photoelectrochemical,Hetero-Structure,Multiferriocs,BiFeO3
更新于2025-09-10 09:29:36