Progress in BiFeO3-based heterostructures: materials, properties and applications

The Ferroelectric Effects of Rhombohedral and Tetragonal BiFeO3 in Photoelectrochemical Water Splitting

The phase of BiFeO3 (BFO) as well as its domain configuration can be tuned by strain engineering. Phase change may greatly influence the properties of the polarization field and hence charge separation. However, the photoelectrochemical properties of different BFO phases have rarely been addressed. Here, the photoelectrochemical study of tetragonal (T-) and rhombohedral (R-) phase BFO films was conducted under visible light illumination. The photocurrent density of R-BFO is 5 times that of T-BFO. A ferroelectric domain study shows that T-BFO features single domain structure in contrast to the polydomain structure of R-BFO. Higher charge separation efficiency is achieved in R-BFO, dominated by the domain walls as conducting pathways for efficient charge separation and transfer. This work provides a fundamental understanding of the photoelectrochemical properties of T- and R-BFO, offering valuable insights for the development of BFO-based materials for solar energy conversion.

Photovoltaic Effect of La and Mn Co-Doped BiFeO3 Heterostructure with Charge Transport Layers

Bismuth ferrite BiFeO3 (BFO)-based ferroelectrics have great potential as inorganic perovskite-like oxides for future solar cells applications due to their unique physical properties. In this work, La and Mn co-doped BFO thin films with compositions Bi0.9La0.1(Fe1-xMnx)O3 (x = 0, 0.05, 0.1, 0.15) (denoted as BLF, BLFM5, BLFM10, BLFM15, respectively) were prepared via a sol-gel technique on indium tin oxide (ITO) glass. All the films are monophasic, showing good crystallinity. The optical bandgap Eg was found to decrease monotonously with an increase in the Mn doping amount. Compared with other compositions, the BLFM5 sample exhibits a better crystallinity and less oxygen vacancies as indicated by XRD and XPS measurements, thereby achieving a better J-V performance. Based on BLFM5 as the light absorbing layer, the ITO/ZnO/BLFM5/Pt and ITO/ZnO/BLFM5/NiO/Pt heterostructure devices were designed and characterized. It was found that the introduction of the ZnO layer increases both the open circuit voltage (Voc) and the short circuit current density (Jsc) with Voc = 90.2 mV and Jsc = 6.90 μA/cm2 for the Pt/ BLFM5/ZnO/ITO device. However, the insertion of the NiO layer reduces both Voc and Jsc, which is attributed to the weakened built-in electric field at the NiO/BLFM5 interface.

Pressure-Induced Phase Diagram and Electronic Structure Evolves during the Insulator-Metal Transition of Bulk BiFeO3

BiFeO3 is the most widely known multiferroic at room temperature, possessing both ferroelectricity and antiferromagnetism. It has high Curie temperature and Néel temperature, i.e., 1103 and 643 K, respectively. Despite these unique properties, the pressure-induced phase diagram of bulk BiFeO3 has remained controversial. Based on the ab initio evolutionary algorithm, we systematically searched for the potential stable structures of bulk BiFeO3 at 0-50 GPa. It is identified that there are five pressure-induced phase transition sequences R3c-G-AFM →(5GPa) C2/m-G-AFM →(15GPa) Pnma-G-AFM →(24GPa) Pnma-FM →(35GPa) Imma-FM →(45GPa) Cmcm-FM, which provided a comprehensive pressure-induced phase diagram. As the pressure increases, we discovered an interesting phenomenon: a pressure-induced magnetic sequence transition, i.e., BiFeO3 transitions from an antiferromagnetic to a ferromagnetic sequence. Concurrently, the electronic structure evolves during the insulator-metal transition, influenced not only by the pressure but also by the phase transition. Our research has elucidated the long-standing question of the phase transition sequence of the BiFeO3 system under pressure and provided theoretical support for the insulator-metal transition.

Strategies for enhancing performance of perovskite bismuth ferrite photocatalysts (BiFeO3): A comprehensive review

Organic pollutants pose a significant threat to water safety, and their degradation is of paramount importance. Photocatalytic technology has emerged as a promising approach for environmental remediation, and Bismuth ferrite (BiFeO3) has been shown to exhibit remarkable potential for photocatalytic degradation of water pollutants, with its excellent crystal structure properties and visible light photocatalytic activity. This review presents an overview of the crystal properties and photocatalytic mechanism of perovskite bismuth ferrite (BiFeO3), as well as a summary of various strategies for enhancing its efficiency in photocatalytic degradation of organic pollutants. These strategies include pure phase preparation, microscopic modulation, composite modification of BiFeO3, and the integration of Fenton-like reactions and external field-assisted methods to improve its photocatalytic performance. The review emphasizes the impact of each strategy on photocatalytic enhancement. By providing comprehensive strategies for improving the efficiency of BiFeO3 photocatalysis, this review inspires new insights for efficient degradation of organic pollutants using BiFeO3 photocatalysis and contributes to the development of photocatalysis in environmental remediation.

Spray pyrolysis-derived robust ferroelectric BiFeO3 thin films

Scalable and low-cost synthesis of high-quality ferroic films is critical for the development of advanced electronic devices and sensors. Here, we employ solution-based spray pyrolysis to fabricate bismuth ferrite thin films on glass substrates and explore the impact of annealing conditions to attain functional thin films of superior quality and switchable polarization. Optimised thin films display polycrystalline nanostructured grains with the highest X-ray diffraction intensity along the (110) orientation and a mixed Fe2+/3+ valence suggesting the presence of oxygen vacancies. The optimized films show a complex ferroelectric domain microstructure and exhibit robust nanoscale polarization switching in the range of several volts. Domains are found to scale with the sizes of nanocrystalline grains, which points to the role of surface-energy-related mechanisms affecting the domain patterns. Our results demonstrate the potential of spray pyrolysis for the fabrication of high-quality ferroelectric thin films and provide new opportunities for the development of low-cost scalable advanced electronic devices.

Review on Resistive Switching Devices Based on Multiferroic BiFeO3

This review provides a comprehensive examination of the state-of-the-art research on resistive switching (RS) in BiFeO₃ (BFO)-based memristive devices. By exploring possible fabrication techniques for preparing the functional BFO layers in memristive devices, the constructed lattice systems and corresponding crystal types responsible for RS behaviors in BFO-based memristive devices are analyzed. The physical mechanisms underlying RS in BFO-based memristive devices, i.e., ferroelectricity and valence change memory, are thoroughly reviewed, and the impact of various effects such as the doping effect, especially in the BFO layer, is evaluated. Finally, this review provides the applications of BFO devices and discusses the valid criteria for evaluating the energy consumption in RS and potential optimization techniques for memristive devices.

How a Ferroelectric Layer Can Tune a Two-Dimensional Electron Gas at the Interface of LaInO3 and BaSnO3: A First-Principles Study

The emerging interest in two-dimensional electron gases (2DEGs), formed at interfaces between two insulating oxide perovskites, poses a crucial fundamental question in view of future electronic devices. In the framework of density-functional theory, we investigate the possibility to control the characteristics of the 2DEG formed at the LaInO₃/BaSnO₃ interface by including a ferroelectric layer. To do so, we consider BaTiO₃ as a prototype example and examine how the orientation of the ferroelectric polarization impacts density and confinement of the 2DEG. We find that aligning the ferroelectric polarization toward (outward) the LaInO₃/BaSnO₃ interface leads to an accumulation (depletion) of the interfacial 2DEG. Varying its magnitude, we find a linear effect on the 2DEG charge density that is confined within the BaSnO₃ side. Analysis of the optimized geometries reveals that inclusion of the ferroelectric layer makes structural distortions at the LaInO₃/BaSnO₃ junction less pronounced, which, in turn, enhances the 2DEG density. Thicker ferroelectric layers allow for reaching higher polarization magnitude. We discuss the mechanisms behind all these findings and rationalize how the characteristics of both 2DEGs and 2D hole gases can be controlled in the considered heterostructures. Overall, our results can be generalized to other combinations of ferroelectric, polar, and nonpolar materials.

Prediction of the hardest BiFeO3 from first-principles calculations

BiFeO₃ is the only material with ferroelectric Curie temperature and Néel temperature higher than room temperature, making it one of the most well-studied multiferroic materials. Based on an ab initio evolutionary algorithm, we predicted a new cubic C-type antiferromagnetic structure (Fd3̄m-BiFeO₃) at ambient pressure. It was found that Fd3̄m-BiFeO₃ is the hardest BiFeO₃ (Vickers hardness ∼ 9.12 GPa), about 78% harder than R3c-BiFeO₃ (the well-known multiferroic material), which contributes to extending the life of BiFeO₃ devices. In addition, Fd3̄m-BiFeO₃ has the largest shear modulus (83.74 GPa) and the largest Young's modulus (214.72 GPa). Besides, we found an interesting phenomenon that among the common multiferroic materials (BiFeO₃, BaTiO₃, PbTiO₃, SrRuO₃, KNbO₃, and BiMnO₃), Pnma-BiMnO₃ has the largest bulk modulus, and its bulk modulus is about 15% larger than that of Fd3̄m-BiFeO₃. However, its Vickers hardness (4.47 GPa) is much smaller than that of Fd3̄m-BiFeO₃. This is because the Vickers hardness is proportional to the shear modulus and the shear modulus of Fd3̄m-BiFeO₃ is larger than that of Pnma-BiMnO₃. This work provides a deeper and more comprehensive understanding of BiFeO₃.

Bulk Photovoltaic Current Mechanisms in All-Inorganic Perovskite Multiferroic Materials

After the discovery of bulk photovoltaic effect more than half a century ago, ferro-electrical and magneto-optical experiments have provided insights into various related topics, revealing above bandgap open voltages and non-central symmetrical current mechanisms. However, the nature of the photon-generated carriers responses and their microscopic mechanisms remain unclear. Here, all-inorganic perovskite Bi0.85Gd0.15Fe1-xMnxO3 thin films were prepared by a sol-gel process and the effects of Gd and Mn co-doped bismuth ferrites on their microtopography, grain boundries, multiferroic, and optical properties were studied. We discovered a simple "proof of principle" type new method that by one-step measuring the leakage current, one can demonstrate the value of photo generated current being the sum of ballistic current and shift current, which are combined to form the so-called bulk photovoltaic current, and can be related to the prototype intrinsic properties such as magneto-optical coupling and ferroelectric polarization. This result has significant potential influence on design principles for engineering multiferroic optoelectronic devices and future photovoltaic industry development.

Highly Sensitive Acetone Gas Sensors Based on Erbium-Doped Bismuth Ferrite Nanoparticles

The acetone-sensing performance of BiFeO₃ is related to structural phase transformation, morphology and band gap energy which can be modulated by rare-earth ions doping. In this work, Bi_1-xEr_xFeO₃ nanoparticles with different amounts of Er doping were synthesized via the sol-gel method. The mechanism of Er doping on acetone-sensing performance of Bi_1-xEr_xFeO₃ (x = 0, 0.05, 0.1 and 0.2) sensors was the focus of the research. The optimal working temperature of Bi_0.9Er_0.1FeO₃ (300 °C) was decreased by 60 °C compared to BiFeO₃ (360 °C). The Bi_0.9Er_0.1FeO₃ sample demonstrated the optimal response to 100 ppm acetone (43.2), which was 4.8 times that of pure BFO at 300 °C. The primary reason, which enhances the acetone-sensing performance, could be the phase transformation induced by Er doping. The lattice distortions induced by phase transformation are favorable to increasing the carrier concentration and mobility, which will bring more changes to the hole-accumulation layer. Thus, the acetone-sensing performance of Bi_0.9Er_0.1FeO₃ was improved.

Enhancement of Efficiency of a TiO2-BiFeO3 Dye-Synthesized Solar Cell through Magnetization

Enhancement in the efficiency of a TiO₂ dye-sensitized solar cell (DSSC) has been demonstrated by introducing ferromagnetic perovskite BiFeO₃ and controlling the magnetic field, which induces two-dimensional material-like properties in the bulk of the TiO₂-BiFeO₃ DSSC (a 3-dimensional material). The effect of the concentration of BiFeO₃ as well as the magnetization direction on the performance of the TiO₂-BiFeO₃ DSSC has been investigated. After magnetization, it was confirmed that the current density, efficiency, and open circuit voltage of the TiO₂-BiFeO₃ DSSC were increased. The observed phenomena have been explained in terms of the Hall effect which is responsible for the reduction of the degree of freedom of the electron movement resulting in the two-dimensional material-like properties in the bulk of the TiO₂-BiFeO₃ DSSC.

Surface and Electrical Characterization of Bilayers Based on BiFeO3 and VO2

Thin films of BiFeO₃, VO₂, and BiFeO₃/VO₂ were grown on SrTiO₃(100) and Al₂O₃(0001) monocrystalline substrates using radio frequency and direct current sputtering techniques. To observe the effect of the coupling between these materials, the surface of the films was characterized by profilometry, atomic force microscopy, and X-ray photoelectron spectroscopy. The heterostructures, monolayers, and bilayers based on BiFeO₃ and VO₂ grew with good adhesion and without delamination or signs of incompatibility between the layers. A good granular arrangement and RMS roughness between 1 and 5 nm for the individual layers (VO₂ and BiFeO₃) and between 6 and 18 nm for the bilayers (BiFeO₃/VO₂) were observed. Their grain size is between 20 nm and 26 nm for the individual layers and between 63 nm and 67 nm for the bilayers. X-ray photoelectron spectroscopy measurements show a higher proportion of V⁴⁺, Bi³⁺, and Fe³⁺ in the films obtained. The homogeneous ordering, low roughness, and oxidation states on the obtained surface show a good coupling in these films. The I-V curves show ohmic behavior at room temperature and change with increasing temperature. The effect of coupling these materials in a thin film shows the appearance of hysteresis cycles, I-V and R-T, which is typical of materials with high potential in applications, such as resistive memories and solar cells.

Ca Solubility in a BiFeO3-Based System with a Secondary Bi2O3 Phase on a Nanoscale

In BiFeO₃ (BFO), Bi₂O₃ (BO) is a known secondary phase, which can appear under certain growth conditions. However, BO is not just an unwanted parasitic phase but can be used to create the super-tetragonal BFO phase in films on substrates, which would otherwise grow in the regular rhombohedral phase (R-phase). The super-tetragonal BFO phase has the advantage of a much larger ferroelectric polarization of 130-150 μC/cm², which is around 1.5 times the value of the rhombohedral phase with 80-100 μC/cm². Here, we report that the solubility of Ca, which is a common dopant of bismuth ferrite materials to tune their properties, is significantly lower in the secondary BO phase than in the observed R-phase BFO. Starting from the film growth, this leads to completely different Ca concentrations in the two phases. We show this with advanced analytical transmission electron microscopy techniques and confirm the experimental results with density functional theory (DFT) calculations. At the film's fabrication temperature, caused by different solubilities, about 50 times higher Ca concentration is expected in the BFO phase than in the secondary one. Depending on the cooling rate after fabrication, this can further increase since a larger Ca concentration difference is expected at lower temperatures. When fabricating functional devices using Ca doping and the secondary BO phase, the difference in solubility must be considered because, depending on the ratio of the BO phase, the Ca concentration in the BFO phase can become much higher than intended. This can be critical for the intended device functionality because the Ca concentration strongly influences and modifies the BFO properties.

Neutron powder-diffraction study of phase transitions in strontium-doped bismuth ferrite: 1. Variation with chemical composition

We report results from a study of the crystal and magnetic structures of strontium-doped BiFeO₃using neutron powder diffraction and the Rietveld method. Measurements were obtained over a wide range of temperatures from 300-800 K for compositions between 10%-16% replacement of bismuth by strontium. The results show a clear variation of the two main structural deformations-symmetry-breaking rotations of the FeO₆octahedra and polar ionic displacements that give ferroelectricity-with chemical composition, but relatively little variation with temperature. On the other hand, the antiferromagnetic order shows a variation with temperature and a second-order phase transition consistent with the classical Heisenberg model. There is, however, very little variation in the behaviour of the antiferromagnetism with chemical composition, and hence with the degree of the structural symmetry-breaking distortions. We therefore conclude that there is no significant coupling between antiferromagnetism and ferroelectricity in Sr-doped BiFeO₃and, by extension, in pure BiFeO₃.

Influence of Ce3+ on the Structural, Morphological, Magnetic, Photocatalytic and Antibacterial Properties of Spinel MnFe2O4 Nanocrystallites Prepared by the Combustion Route

The present work describes the effect of Ce3+ ion doping on the structural, morphological, and magnetic properties of spinel manganese ferrite (MnFe2O4) nanocrystallites (NCs) using various instrument techniques. Rare earth element (REE) Cerium (Ce3+) doped MnFe2O4 NCs were prepared by a simple microwave combustion technique. In the present scenario, ferrites are widely used for photocatalytic dye degradation and antibacterial applications. Aiming to achieve this, we prepared Ce3+ doped MnFe2O4 NCs by microwave combustion method and urea as burning agent and the obtained powder samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), high resolution scanning electron microscope (HR-SEM), high resolution transmission electron microscope (HR-TEM) and vibration sample magnetometer (VSM) techniques. The pure spinel phase formation was confirmed by XRD analysis. FTIR spectra show two prominent absorption bands under 1000 cm−1, which confirms the formation of the spinel structure. HR-SEM and HR-TEM pictures demonstrated a sphere-shaped morphology and also expose the combination and agglomeration of grains, which are mostly due to the magnetic characteristics of the samples. The magnetic properties of the synthesized MnCexFe2−xO4 (x = 0.0, 0.1, 0.3, and 0.5) NCs were studied by VSM analysis at room temperature (RT) shows ferromagnetic behavior. The photodegradation results showed that MnFe2O4 and Ce doped MnFe2O4 NCs have a higher potential to degrade methylene blue (MB) and the sample MnCe0.3Fe1.7O4 NCs showed superb photocatalytic performance (91.53%) compared to other samples. The antibacterial activities of Gram-positive S. aureus, B. subtilis and Gram-negative K. pneumonia and E. coli were investigated using pure and Ce3+ substituted MnFe2O4 NCs and a higher activity for MnCe0.3Fe1.7O4 NCs than other samples was observed, which indicated that they can be used in biomedical applications.

New multiferroic BiFeO3 with large polarization

BiFeO3 is one of the most widely studied multiferroic materials, because of its large spontaneous polarization at room temperature, as well as ferroelasticity and antiferromagnetism. Using ab initio evolutionary algorithm,...

Magnetic Field-Assisted Photocatalytic Degradation of Organic Pollutants over Bi1-xRxFeO3 (R = Ce, Tb; x = 0.00, 0.05, 0.10 and 0.15) Nanostructures

Magnetic-field-accelerated photocatalytic degradation of the phenol red (PR) as a model organic pollutant was studied using rare-earth elements modified BiFeO3 (Bi1-xRxFeO3 (R = Ce, Tb; x = 0.0, 0.05, 0.10 and 0.15); BFO: RE) nanostructures. The nanostructures were prepared via the hydrothermal process and their morphological, structural, functional, optical and magnetic features were investigated in detail. The effect of magnetic fields (MFs) on photocatalysis were examined by applying the different MFs under visible light irradiation. The enhanced photodegradation efficiencies were achieved by increasing the MF up to 0.5T and reduced at 0.7T for the compositions x = 0.10 in both Ce and Tb substituted BFO. Further, mineralization efficiencies of PR, reproducibility of MF-assisted photocatalysis, stability and recyclability of BFO: RE nanostructures were also tested.

Reversible Rectification of Microscale Ferroelectric Junctions Employing Liquid Metal Electrodes

Both ferroelectric crystals and liquid metal electrodes have attracted extensive attention for potential applications in next-generation devices and circuits. However, the interface information between ferroelectric crystals and liquid metal electrodes has so far been lacking. To better understand the optoelectronic properties of microscale ferroelectric crystals (potassium tantalate niobate, KTN) and its potential integration with liquid metal electrodes (a "printing ink" for flexible electric circuit production), microscale KTN crystals sandwiched by eutectic gallium indium (EGaIn, a liquid metal) with varied contact geometries were studied. Unlike the bulk KTN crystal junctions, the microscale KTN junctions show electrical rectifying characteristics upon light illumination, and the directionality of the rectification can be reversed by increasing the ambient temperature to a few degrees. Furthermore, a strong suppression of the current upon increasing voltage, that is, the quasi-negative differential resistance, is observed when the microscale KTN is half-enclosed by the EGaIn electrode. Our results show that trapping/detrapping of carriers affected by the crystal size and the ambient temperature is the dominant physical mechanism for these observations. These results not only facilitate a better understanding of charge transport through the microscale ferroelectric crystals but also advance the design of miniaturized hybrid devices.

Low-Temperature Tunneling Electroresistance in Ferromagnetic Metal/Ferroelectric/Semiconductor Tunnel Junctions

Ferroelectric tunnel junctions (FTJs) as artificial synaptic devices are promising candidates for the building block of nonvolatile data storage devices. However, a small ON/OFF ratio of FTJs limits their application in low-temperature operations. In this work, the influence of quantum interference effects on tunneling electroresistance in the La_0.7Sr_0.3MnO₃/BaTiO₃/Nb:SrTiO₃ (ferromagnetic metal/ferroelectric/semiconductor) FTJ at low temperatures is investigated. The Current-voltage curves are observed in the tunnel junction from 300 to 10 K with a six-unit-cell thick BaTiO₃ film by the ferroelectric polarization effect. First, the ON/OFF current ratio increases from 300 to 30 K due to the increase of polarization in the ferroelectric barrier, and then, it gradually decreases when the temperature drops below 30 K. An anomalous ON/OFF current ratio of ∼10⁵ is obtained at 30 K. The low-temperature tunneling properties in the FTJ are associated with a low-temperature resistivity minimum in the ferromagnetic metal layer by the electron-electron interaction, which increases the La_0.7Sr_0.3MnO₃/BaTiO₃ interface resistance, leading to a higher resistance state and lower I_OFF for the OFF state. As a result, the ON/OFF current ratio is abruptly enhanced at 30 K. Our results emphasize the crucial role of transport properties of La_0.7Sr_0.3MnO₃ in FTJs and pave the way for the design and application of FTJs at low temperatures.

The CdTiO3/BaTiO3 superlattice interface from first principles

The oxide interface has been studied extensively in the past decades and exhibits different physical properties from the constituent bulks. Using first-principles electronic structure calculations, we investigated the interface of CdTiO₃/BaTiO₃ (CTO/BTO) superlattice with ferroelectric BaTiO₃. In this case, the conduction bands of CdTiO₃ are composed of Cd-5s orbitals with low electron effective mass and nondegenerate dispersion, and thus expected to have high mobility. We predicted a controllable conductivity at the interface, and further analyzed how the polarization direction and strength affect the conductivity. We also explored the relationship between two components: thickness and polarization. Intriguingly, the total polarization in CTO/BTO might be even larger than that of ferroelectric bulk BaTiO₃. Therefore, we found a way to maximize the superlattice polarization by increasing the fraction of the CdTiO₃ layers, based on the interesting dependence of the total polarization and CTO/BTO ratio.

Magnetoelectric effect in flexible nanocomposite films based on size-matching

Flexible magnetoelectric (ME) nanocomposites with a strong coupling between ferromagnetism and ferroelectricity are of significant importance from the point of view of next-generation flexible electronic devices. However, a high loading of magnetic nanomaterials is needed to achieve preferable ME response due to the size mismatch of the magnetostrictive phase and piezoelectric phase. In this work, ultra-small CoFe2O4 nanoparticles were prepared to match the size of the polar crystal in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) is introduced to enhance the interplay between P(VDF-TrFE) and CoFe2O4. The above multiple effects promote a good connection between the magnetostrictive phase and the piezoelectric phase. Therefore, an effective transference of stress from CoFe2O4 to P(VDF-TrFE) can be achieved. The as-prepared P(VDF-TrFE)/CoFe2O4@POTS exhibits a high ME coupling coefficient of 34 mV cm-1 Oe-1 when the content of CoFe2O4@POTS is 20 wt%. The low loading of fillers ensures the flexibility of ME nanocomposite films.

Photovoltaic properties in an orthorhombic Fe doped KTN single crystal

Since the domain wall photovoltaic effect (DW-PVE) is reported in BiFeO₃ film, the investigations on photovoltaic properties in ferroelectrics have appealed more and more attention. In this work, we employed two Fe doped KTa_1-xNbxO₃ (Fe:KTN) single crystals in tetragonal phase and orthorhombic phase, respectively, possessing similar net polarization along [001]_C direction, to quantize the contribution on photovoltaic properties from bulk photovoltaic effect (BPVE) and DW-PVE in Fe:KTN. The results show that there are significant enhancements of open-circuit voltages (V_OC = -6.0 V, increases over 440%) and short-circuit current density (J_SC = 18.5 nA cm^-2, increases over 1580%) in orthorhombic Fe:KTN with engineer-domain structure after poled, corresponding to 14.2 mV and 2.2 mV for the single domain wall and bulk region under illumination of 405 nm light (100 mW). It reveals that DW-PVE plays a major role in KTN-based ferroelectrics, indicating an orthorhombic Fe:KTN single crystal is one of the potential photovoltaic materials.

Nonvolatile Multistates Memories for High-Density Data Storage

In the current information age, the realization of memory devices with energy efficient design, high storage density, nonvolatility, fast access, and low cost is still a great challenge. As a promising technology to meet these stringent requirements, nonvolatile multistates memory (NMSM) has attracted lots of attention over the past years. Owing to the capability to store data in more than a single bit (0 or 1), the storage density is dramatically enhanced without scaling down the memory cell, making memory devices more efficient and less expensive. Multistates in a single cell also provide an unconventional in-memory computing platform beyond the Von Neumann architecture and enable neuromorphic computing with low power consumption. In this review, an in-depth perspective is presented on the recent progress and challenges on the device architectures, material innovation, working mechanisms of various types of NMSMs, including flash, magnetic random-access memory (MRAM), resistive random-access memory (RRAM), ferroelectric random-access memory (FeRAM), and phase-change memory (PCM). The intriguing properties and performance of these NMSMs, which are the key to realizing highly integrated memory hierarchy, are discussed and compared.

Ethylene glycol assisted three-dimensional floral evolution of BiFeO3-based nanostructures with effective magneto-electric response

Controlled growth of nanostructures plays a vital role in tuning the physical and chemical properties of functional materials for advanced energy and memory storage devices. Herein, we synthesized hierarchical micro-sized flowers, built by the self-assembly of highly crystalline, two-dimensional nanoplates of Co- and Ni-doped BiFeO3, using a simple ethylene glycol-mediated solvothermal method. Pure BiFeO3 attained scattered one-dimensional nanorods-type morphology having diameter nearly 60 nm. Co-doping of Co and Ni at Fe-site in BiFeO3 does not destabilize the morphology; rather it generates three-dimensional floral patterns of self-assembled nanoplates. Unsaturated polarization loops obtained for BiFeO3 confirmed the leakage behaviour of these rhombohedrally distorted cubic perovskites. These loops were then used to determine the energy density of the BiFeO3 perovskites. Enhanced ferromagnetic behaviour with high coercivity and remanence was observed for these nanoplates. A detailed discussion about the origin of ferromagnetic behaviour based on Goodenough-Kanamori's rule is also a part of this paper. Impedance spectroscopy revealed a true Warburg capacitive behaviour of the synthesized nanoplates. High magneto-electric (ME) coefficient of 27 mV cm-1 Oe-1 at a bias field of -0.2 Oe was observed which confirmed the existence of ME coupling in these nanoplates.