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The crystal structures and electrical properties of lead-free BiFeO3-BaTiO3 [(1-x)BFxBT] piezoelectric system are investigated as a function of BaTiO3 concentration. The well-saturated P-E hysteresis loop was observed in the 0.80BiFeO3–0.20BaTiO3 composition system, while a less hysteretic strain-electric field curve was exhibited by the 0.70BiFeO3–0.30BaTiO3 with a strain hysteresis of 16%, the value comparable to PZT-based piezoelectric ceramics. The crystal structures investigated under the synchrotron radiation X-ray diffraction exhibited a rhombohedral structure for BFBT system with x=0.10–0.25 and a pseudo-cubic structure for BFBT system with x=0.30–0.40. The structural phase diagram for the BiFeO3-BaTiO3 system is suggested based on the results of temperature-dependent synchrotron radiation X-ray diffraction measurement and investigated electrical properties. [ABSTRACT FROM AUTHOR]

We describe systematic studies on Nd and Mn co-doped BiFeO3, i.e., (Bi0.95Nd0.05) (Fe0.97Mn0.03)O3 (BNFM) polycrystalline electroceramics. Raman spectra and X-ray diffraction patterns revealed the formation of rhombohedral crystal structure at room temperature, and ruled out structural changes in BiFeO3 (BFO) after low percentage chemical substitution. Strong dielectric dispersion and a sharp anomaly around 620K observed near the Néel temperature (TN ~ 643K of BFO) support strong magneto-dielectric coupling, verified by the exothermic peak in differential thermal data. Impedance spectroscopy disclosed the appearance of grain boundary contributions in the dielectric data in the region, and their disappearance just near the Néel temperature suggests magnetically active grain boundaries. The resistive grain boundary components of the BNFM are mainly responsible for magneto-dielectric coupling. Capacitive grain boundaries are not observed in the modulus spectra and the dielectric behavior deviates from the ideal Debye-type. The ac conduction studies illustrate short-range order with ionic translations assisted by both large and small polaron hopping. Magnetic studies indicate that the weak antiferromagnetic phase of BNFM ceramics is dominated by a strong paramagnetic response (unsaturated magnetization even at applied magnetic field of 7 T). The bulk BNFM sample shows a good in-plane magnetoelectric coupling (ME) coefficient. [ABSTRACT FROM AUTHOR]

We describe systematic studies on Nd and Mn co-doped BiFeO3, i.e., (Bi0.95Nd0.05) (Fe0.97Mn0.03)O3 (BNFM) polycrystalline electroceramics. Raman spectra and X-ray diffraction patterns revealed the formation of rhombohedral crystal structure at room temperature, and ruled out structural changes in BiFeO3 (BFO) after low percentage chemical substitution. Strong dielectric dispersion and a sharp anomaly around 620K observed near the Néel temperature (TN ~ 643K of BFO) support strong magneto-dielectric coupling, verified by the exothermic peak in differential thermal data. Impedance spectroscopy disclosed the appearance of grain boundary contributions in the dielectric data in the region, and their disappearance just near the Néel temperature suggests magnetically active grain boundaries. The resistive grain boundary components of the BNFM are mainly responsible for magneto-dielectric coupling. Capacitive grain boundaries are not observed in the modulus spectra and the dielectric behavior deviates from the ideal Debye-type. The ac conduction studies illustrate short-range order with ionic translations assisted by both large and small polaron hopping. Magnetic studies indicate that the weak antiferromagnetic phase of BNFM ceramics is dominated by a strong paramagnetic response (unsaturated magnetization even at applied magnetic field of 7 T). The bulk BNFM sample shows a good in-plane magnetoelectric coupling (ME) coefficient. [ABSTRACT FROM AUTHOR]

Phase pure bismuth ferrite (BiFeO3) thin films with (001)-oriented epitaxial structure are realized on lanthanum strontium manganite (La0.67Sr0.33MnO3) buffered (001)-SrTiO3 substrates by chemical solution deposition. The annealing process is optimized such that a stoichiometric precursor can be used to accurately control the Bi:Fe ratio. Ferroelectric, dielectric, and resistive switching behaviours are investigated for 40 nm, 70 nm, and 150 nm BFO thin films. While the thinnest film (40 nm) shows very leaky loops, square and fully saturated polarization hysteresis loops are shown for the thicker films. The highest remanent polarization (2Pr=100 μC/cm²) and relative dielectric constant (ϵr=613) are obtained in the 150 nm BFO thin film. High cycle fatigue tests show that the thick films are resistant to polarization fatigue. Piezoresponse force microscopy results show that the domain structure varies with thickness. Resistive switching and polarization mediated diode effects are also observed. These robust properties suggest that chemical solution deposition derived BiFeO3 thin films can offer a viable low cost alternative. [ABSTRACT FROM AUTHOR]

Photovoltaic properties of multiferroic (Ce, Mn) codoped BiFeO3 (BCFMO) thin films grown on low cost ITO coated corning glass substrate have been investigated. The transient response of photovoltaic current of the BCFMO thin film in metal-multiferroic-metal (MMM) capacitor configuration is found to be strongly dependent on both the intensity of incident laser light (k = 405nm) varying from 15mW/cm² to 160mW/cm² and thickness of the BCFMO film (110 to 305 nm). Current density-voltage (J-V) measurement shows an exponential increase in photoinduced open circuit voltage and linear increase in short circuit photocurrent with increase in intensity of illuminating light. Almost 240 fold enhancement in photo-induced current is observed in BCFMO thin film of 110nm thickness. Present work suggests that multiferroic BCFMO thin film deposited on ITO coated corning glass substrate using chemical solution deposition technique exhibits strong photovoltaic response that can be exploited efficiently for the light harvesting and photosensitive device application. [ABSTRACT FROM AUTHOR]

Highlights • Synthesis of CoFe 2 O 4 @ BiFeO 3 and BiFeO 3 @ CoFe 2 O 4 by co-precipitation method. • Core-shell structure of developed nanocomposites is identified by HRTEM. • Highest magnetic and dielectric properties are observed in CoFe 2 O 4 @ BiFeO 3 sample. • Magnetoelectic coupling is observed in developed core-shell nanocomposites. • Interchanging core and shell position of developed materials is novelty of our work. Abstract Nano-sized CoFe 2 O 4 (CFO), BiFeO 3 (BFO) and their core-shell composites BFO@CFO and CFO@BFO were synthesized by chemical co-precipitation method. X-ray diffraction pattern confirmed the crystallinity and phase formation of bare CFO, BFO and their core-shell composites. Morphology and core-shell nature of these nanoparticles is justified by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Magnetization curve showed the weak ferromagnetic behaviour of BFO. Typical ferrimagnetic behaviour is shown by bare CFO and core-shell nanocomposites. The value of maximum magnetization, remanence magnetization and coercivity of CFO@ BFO were found to be greater than the BFO@ CFO. Also, CFO@ BFO showed the highest value of dielectric constant in the frequency range of 104–106 Hz. Dielectric constant versus temperature curve of BFO and core-shell composites exhibit incongruity close to the antiferromagnetic transition temperature (370 °C) of BFO indicating presence of magnetoelectric (ME) coupling. [ABSTRACT FROM AUTHOR]

Abstract Multiferroic Bi 1-x Gd x FeO 3 ceramics (with x = 0.0, 0.05 and 0.10 coded as BFO/GD0, GD5 and GD10, respectively) were synthesized via two stage solid-state reaction technique. Structural, magnetic and impedance measurements of prepared ceramics have been studied in a systematic way. X-ray diffraction studies and Rietveld analysis revealed a structure phase transition from rhombohedral (R 3 c) to orthorhombic (Pnma) at x ≥ 0.10. Due to the replacement of Fe3+ ions by Gd3+ ions (magnetically active), an increase in magnetization and coercive field is observed. For GD10 sample, a remnant magnetization (M r) of 30 memu/g and coercive field (H c) of 1.5 kOe were observed. The dielectric constant shows almost flat response with temperature for GD10 sample at different frequencies. Also at higher frequencies, the high values of εʹ and low values of tan δ for this material makes it suitable for device applications. The improvement in dielectric parameters and magnetic property is may be due to the presence of structural transformation resulting from the incorporation of Gd in the lattice of BFO. Highlights • Refinement has been done by assuming hexagonal representation of R3c space group. • Magnetic properties are improved by doping of Gd. • Impedance plots have revealed a non-Debye type of relaxation process. [ABSTRACT FROM AUTHOR]

Polycrystalline BiFeO3 (BFO) and Bi0.9Gd0.1Fe1−xCrxO3 (x = 0, 0.025, 0.05, 0.075, 0.10) multiferroic thin films were fabricated on quartz and Pt(111)/Ti/SiO2/Si(100) substrates using a sol-gel method. The effects of (Gd, Cr) co-doping on the microstructural, electrical and optical properties of BFO were studied. X-ray diffraction and micro-Raman measurements demonstrated that the phases of all films were a rhombohedral perovskite structure. The merging of (110) and (104) diffraction peaks demonstrated a structural transition in the Bi0.9Gd0.1Fe1−xCrxO3 thin films. The field emission scanning electron microscopy (FESEM) patterns exhibited that the grain sizes were decreased and the surface textures got denser and glossier with the increasing Cr content. The Bi0.9Gd0.1Fe0.95Cr0.05O3 showed a more uniform grain size distribution and denser surface. The leakage current densities and electrical polarizations of (Gd, Cr) co-doped BFO were improved. A minimum leakage current density (5.32 × 10−9 A/cm2) was obtained in Bi0.9Gd0.1Fe0.95Cr0.05O3 thin films at the electric field of 300 kV/cm, which decreased by four and five orders of magnitude compared to the BGFO thin film (4.17 × 10−5 A/cm2) and BFO thin film (6.5 × 10−4 A/cm2), respectively. And larger polarizations were observed in Bi0.9Gd0.1Fe0.95Cr0.05O3 thin film. Moreover, the leakage current mechanisms of all films have been studied. The optical band gaps (Eg) of Bi0.9Gd0.1Fe1−xCrxO3 thin films were blue-shift with the increasing of x value, which suggested a promising applications in the field of photocatalysis and power electronic devices. [ABSTRACT FROM AUTHOR]

The structural, magnetic, electronic and optical properties of Pbnm BiFeO (BFO), BiFeMnO (BFM), BiXFeMnO (XBFM) (X = Ce, Gd, Lu) have been investigated by the first principles within the PBE+U scheme. It is shown that the dopant Mn in the B sites and Ce (Gd, Lu) in the A sites improves the crystalline quality. The magnetic moments of BiCeFeMnO (CBFM) and BiGdFeMnO (GBFM) are 10 and 16 which mainly arises from the strongly localized unpaired 4 f electrons of Ce and Gd, 3 d electrons of Mn and Fe. While, as BFM, the magnetic moment of BiLuFeMnO (LBFM) is 9 indicating no effect on the magnetization is made by Lu for its full 4 f states. The densities of states of the five systems hint that CBFM is metallic and BFM, GBFM, LBFM are still semiconductors. The metallic properties of CBFM arise from the hybridization between Ce-4 f and Mn-3 d states which leads the Mn states to be split into and lowering the bottom of the conduction band to cross the Fermi level. Furthermore, we also study the optical properties of Pbnm BiFeO (BFO), BiFeMnO (BFM), BiXFeMnO (XBFM) (X = Ce, Gd, Lu). In this work, the optical properties including the absorption spectrum, loss function, refractive index and reflectivity spectrum are discussed in detail. [ABSTRACT FROM AUTHOR]

Room temperature ferroelectric and magnetic properties of undoped BiFeO and (Nd, Co) codoped BiFeO are reported. The sol-gel synthesized BiNdFeCoO (x = 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06) ceramics were analysed by XRD pattern, Raman spectrum, X-ray photoelectron spectrum (XPS), ferroelectric loop and magnetic hysteresis loop. The evolution of the changes in the ferroelectric and magnetic properties with gradual tiny increase in the dopant concentration was investigated. XRD patterns and Raman spectra confirm the typical rhombohedral structure for all the samples. The oxidation states of Fe and the existence of oxygen vacancies studied through XPS reveal that enhanced ferroelectric properties of the doped samples are due to the presence of low Fe ions and reduction of oxygen vacancies. The remnant polarisation and maximum polarisation values of Nd 1-5% doped samples are remarkably enhanced compared to BFO. The highest Nd doping 6% showed reduced ferroelectric parameters due to the internal strain caused by the high doping, which was illustrated by its Raman spectrum. Well saturated magnetic hysteresis loops are obtained due to the doping of Nd and Co with significant magnetic parameters. A notable simultaneous improvement in both magnetic and ferroelectric properties has been illustrated for 1-5% of Nd doping. [ABSTRACT FROM AUTHOR]

ABSTRACT In this work, we prepared a series of poly(vinylidene fluoride) (PVDF)-surface functionalized BiFeO3 (h-BFO)-Sodium dodecyl sulfate (SDS) composite films by solvent casting method to investigate the effect of SDS in the composites. The X-ray diffraction confirmed that the structure of h-BFO significantly changed in the PVDF-(h-BFO)-SDS composite in comparison with the rhombohedral structure of pure BiFeO3. The microscopic study illustrated that the composite with a higher percentage of SDS content facilitated the dispersion as well as proper distribution of ceramic particles in the polymer matrix. The presence of different functionalities of respective polymer and the modified fillers was confirmed by FTIR Spectrophotometer. The dielectric and electrical study done by Impedance Analyzer revealed that the SDS treated surface functionalized composites showed relatively higher dielectric properties than that of two phase composites and pure polymer. Finally, the ferroelectric properties of the composite films done by P-E loop tracer revealed that the SDS-treated composites showed an enhanced remanent polarization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45040. [ABSTRACT FROM AUTHOR]

A two-step sintering method was employed to fabricate BiFeO 3 ceramics and the influences of sintering conditions on the structural, dielectric, ferroelectric, and piezoelectric properties were investigated. It was found that high-density and pure-phase BiFeO 3 ceramics could be successfully achieved through the two-step sintering method by optimizing the sintering conditions. Furthermore, ferroelectricity and piezoelectricity were also improved by the two-step sintering method. The pure-phase BiFeO 3 ceramics obtained at T 1 =850 °C and T 2 =750 °C exhibited high resistivity (1.57×10 6 Ω.m), large remanent polarization ( P r =0.80μC/cm 2 ) and strong piezoelectric activity ( d 33 =42pC/N). All these results indicated that the two-step sintering method was an effective way to improve the properties of the BiFeO 3 ceramics. [ABSTRACT FROM AUTHOR]

In ferroelectric tunnel junctions, the tunnel resistance depends on the polarization orientation of the ferroelectric tunnel barrier, giving rise to tunnel electroresistance. These devices are promising to be used as memristors in neuromorphic architectures and as non-volatile memory elements. For both applications, device scalability is essential, which requires a clear understanding of the relationship between polarization reversal and resistance change as the junction size shrinks. Here we show a robust tunnel electroresistance in BiFeO3-based junctions with diameters ranging from 1200 to 180 nm. We demonstrate that the tunnel electroresistance and the corresponding fraction of reversed ferroelectric domains change drastically with the junction diameter: while the micron-size junctions display a reversal in less than 10% of the area, the smallest junctions show an almost complete polarization reversal. Modeling the electric-field distribution, we highlight the critical role of the bottom electrode resistance which significantly diminishes the actual electric field applied to the ferroelectric barrier in the mixed polarization state. A polarization-dependent critical electric field below which further reversal is prohibited is found to explain the large differences between the ferroelectric switchability of nano- and micron-size junctions. Our results indicate that ferroelectric junctions are downscalable and suggest that specific junction shapes facilitate complete polarization reversal. [ABSTRACT FROM AUTHOR]

The Electrical properties of Bi 0.7 Dy 0.3 FeO 3 (BDFO) thin films deposited by pulsed laser deposition (PLD) on ZnO/Si films and its potential applications are discussed in this paper. MIS (metal/insulator/semiconductor) Capacitors of Cr-Au/BDFO/ZnO/p-Si structures have been fabricated and their interface traps and electrical properties have been investigated. To obtain the information about the interface trap states, systematic studies on the frequency-dependent capacitances and conductance measurement were performed. Frequency dependent analysis of the device was made in the frequency range of 10 kHz–500 kHz. It was observed that dispersion of the oxide capacitance was 2% per decade within this frequency range. When the sweeping voltage changes from − 3 to + 4 V the memory aperture was found to be increased from 300 to 850 mV. This significant hysteresis property in the C–V characteristics may be attributed to the slight ferroelectric behaviour of BDFO/ZnO film, which is essential for a memory device. It was also observed that density of trap state ( D it ) is found approximately 9 × 10 11 cm − 2 eV − 1 while increasing the frequency from 10 kHz to 500 kHz, the thickness of the oxide layer was 300 nm in this experiment. The calculated dielectric constant of device (~ 190) is much higher than that of BDFO (> 30). The dielectric loss tangent of the device was found to initially increase with voltage then decrease, whereas the ac conductivity depicted an opposite trend. Multiferroic BDFO is promising material shows the good coupling between ferroelectric and ferromagnetic properties and ideal behaviour at room temperature. Integration of BDFO films with ZnO piezoelectric can be used directly as electricity generator with enhanced output in MEMS applications as well as in Memory devices. [ABSTRACT FROM AUTHOR]

Multiferroic BiFeO δ ( δ =2.67, 2.95 and 3.02) compound of various oxygen contents ( δ ) have been prepared by gel sol method. The influence of oxygen contents on the structure, electric and magnetic properties of BiFeO 3 compound has been investigated. X-ray diffraction (XRD) measurements indicate that all the samples of BiFeO δ have the same crystal structure regardless of oxygen content. The SEM micrograph reveals microstructures comprising of grains with various sizes from 200 nm to 1 µm. XPS study confirms the coexistence of Fe 3+ and Fe 2+ ions in BiFeO δ compound. The M ( H ) curves exhibit weak ferromagnetic behavior with unsaturated magnetization at room temperature, independent of the oxygen content. The M ( T ) curves of suggest anti-ferromagnetic behavior with Neel temperature of ~370 °C for BiFeO 2.95 and BiFeO 3.02 samples and paramagnetic behavior of BiFeO 2.67 sample from RT up to 500 °C. The experimental results show that the antiferromagnetic ordering is strongly correlated with the oxygen content and is almost entirely suppressed in BiFeO δ with δ =2.67. The effect of oxygen vacancies is to weaken the magnetic ordering rather than to enhance it as previously suggested in the literature. [ABSTRACT FROM AUTHOR]

Sulfurized BiFeO3 (BFO) thin films have been investigated with the purpose of reducing their band gap for photovoltaic applications. A strong dependence of the degree of sulfurization on the structure and optical properties of the BFO thin films was observed. The sulfurization process substantially reduced the optical band gap from 2.83 eV for the reference sample to ∼1.90 eV in a sample sulfurized at 200 °C, a temperature at which the BFO phase was still dominant. The existence of the secondary Bi2S3 phase was found to be initiated from the film surface and became dominant at higher temperatures. XPS analysis suggests potential Bi–Fe(iii)–Fe(ii)–S–O compounds as a result of the change of the oxidation state of Fe with the progress of sulfurization. The sulfurized BFO film exhibited relatively higher positively charged grain boundaries than the reference film, suggesting its improved applicability in photovoltaic devices. [ABSTRACT FROM AUTHOR]

Improvement in magnetic and electrical properties of multiferroic BiFeO3 in conjunction with their dependence on particle size is crucial due to its potential applications in multifunctional miniaturized devices. In this investigation, we report a study on particle size dependent structural, magnetic and electrical properties of sol-gel derived Bi0.9Ba0.1FeO3 nanoparticles of different sizes ranging from ~ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses oxygen vacancies, reduces leakage current density and Fe2+ state. An improvement in both magnetic and electrica properties is observed for 10% Ba-doped BiFeO3 nanoparticles compared to its undoped counterpart. The saturation magnetization of Bi0.9Ba0.1FeO3 nanoparticles increase with reducing particle size in contrast with a decreasing trend of ferroelectric polarization. Moreover, a first order metamagnetic transition is noticed for ~ 49 nm Bi0.9Ba0.1FeO3 nanoparticles which disappeared with decreasing particle size. The observed strong size dependent multiferroic properties are attributed to the complex interaction between vacancy induced crystallographic defects, multiple valence states of Fe, uncompensated surface spins, crystallographic distortion and suppression of spiral spin cycloid of BiFeO3. [ABSTRACT FROM AUTHOR]

Improvement in magnetic and electrical properties of multiferroic BiFeO3 in conjunction with their dependence on particle size is crucial due to its potential applications in multifunctional miniaturized devices. In this investigation, we report a study on particle size dependent structural, magnetic and electrical properties of sol-gel derived Bi0.9Ba0.1FeO3 nanoparticles of different sizes ranging from ~ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses oxygen vacancies, reduces leakage current density and Fe2+ state. An improvement in both magnetic and electrica properties is observed for 10% Ba-doped BiFeO3 nanoparticles compared to its undoped counterpart. The saturation magnetization of Bi0.9Ba0.1FeO3 nanoparticles increase with reducing particle size in contrast with a decreasing trend of ferroelectric polarization. Moreover, a first order metamagnetic transition is noticed for ~ 49 nm Bi0.9Ba0.1FeO3 nanoparticles which disappeared with decreasing particle size. The observed strong size dependent multiferroic properties are attributed to the complex interaction between vacancy induced crystallographic defects, multiple valence states of Fe, uncompensated surface spins, crystallographic distortion and suppression of spiral spin cycloid of BiFeO3. [ABSTRACT FROM AUTHOR]

Thin films of (Bi 2− x La x )Fe 4 O 9 ( x = 0 and x = 0.05) were prepared on Pt(1 1 1)/Ti/SiO 2 /Si(1 0 0) substrates by using a chemical solution deposition method to investigate structural, microstructural, electrical and multiferroic properties. Both the thin films were crystallized in mullite type phases with orthorhombic structures containing no secondary and impurity phases, which was confirmed by X-ray diffraction and Raman spectroscopy studies. The (Bi 1.95 La 0.05 )Fe 4 O 9 thin film exhibited improved electrical and multiferroic properties at room-temperature. The leakage current density of the (Bi 1.95 La 0.05 )Fe 4 O 9 thin film was one order of magnitude lower than that of the Bi 2 Fe 4 O 9 thin film. Furthermore, in the thin film form, (Bi 2− x La x )Fe 4 O 9 exhibited better stability against electrical breakdowns and enhanced multiferroic properties. [ABSTRACT FROM AUTHOR]

The ultrafine of Bi 1− x Gd x FeO 3 with x =0, 0.05, 0.1, 0.15 were synthesized by the co-precipitation method. These powders were defined by the X-ray diffraction analysis, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). The dielectric constant and dielectric loss were measured by an inductance–capacitance–resistance (LCR) meter. The X-ray diffraction analysis showed that increasing the asymmetry and decreasing the second phases occur by increasing the amount of gadolinium. A phase transformation began from the rhombohedral phase to the orthorhombic one by adding gadolinium in about x =0.15. Gd-doping improved the magnetic properties because the cycloid spins were distorted by adding Gd instead of Bi. Furthermore, the dielectric properties were improved as a result of the reduction in Fe 2+ and oxygen vacancies. The microwave sintering method was used to densify the compact pellets for electrical tests. FESEM images showed that microwave sintering leads to the enhancement of ferroelectric properties due to the high densities of the sintered pellets and the prevention of grain growth. [ABSTRACT FROM AUTHOR]

0.70BiLaFeO-0.30BaTiO + 1 mol% MnO multiferroic ceramics were prepared by using the solid state reaction and their phase structure, dielectric, ferroelectric and ferromagnetic properties were studied. All the ceramics possess perovskite structure and exhibit good insulation and densification. A morphotropic phase boundary of rhombohedral and tetragonal phases is formed at x = 0.02. As the concentration of La is increased, the ferroelectric-paraelectric phase transition of the ceramics at Curie temperature becomes gradually more diffusive. A small amount of the substitution of La for Bi improves effectively the ferroelectricity of the ceramics and the optimum remanent polarization of 27.2 μm/cm reaches at x = 0.04. After the addition of La, the ferromagnetism of the ceramics is greatly enhanced and the remanent magnetization M monotonously increases from 0.0321 to 0.147 emu/g with x increasing from 0 to 0.10. Our results show that the ceramics possess simultaneously improved ferroelectric and ferromagnetic properties and may a promising candidate for room-temperature multiferroic materials. [ABSTRACT FROM AUTHOR]

BiFeO3(BFO), Bi0.8Er0.2FeO3 (BEFO), Bi0.8Er0.2Fe0.9Mn0.1O33 (BEFMO) and Bi0.8Er0.2Fe0.9Co0.1O3(BEFCO) nanoparticles were prepared by sol-gel method having an average size of 200 nm for BFO, under100 nm for BEFO and under 60 nm for BEFMO and BEFCO. Phase transition from a rhombohedral symmetry (R3c) for BFO to an orthorhombic symmetry (Ibmm) for BEFO, BEFMO and BEFCO has been observed. The phase transformation combined with size reduction has significantly improved both ferroelectric and ferromagnetic behaviors of the doped samples in a similar way. The formation of dipolar defect complexes (DDCs) in the doped samples also contributes to the improved ferroelectric property with saturated polarization (Ps) of 0.375 μC/cm² and remanent polarization (Pr) of 0.244 μC/cm² for BEFMO. Size effect may also impact the simultaneously developed Pr for BEFMO and BEFCO. Owning to the interactions between the ferromagnetic and antiferromagnetic microdomains, improved saturated magnetization (Ms) and remanent magnetization (Mr) are also observed in BEFMO. [ABSTRACT FROM AUTHOR]

Inorganic-organolead halide perovskite CH3NH3PbI3 modified BiFeO3 polycrystalline film has been established. The composite photoelectrode presents much larger open voltage and several magnitudes superior photoelectric conversion performance in comparison to the ordinary BiFeO3 polycrystalline film. The I-V curve shows that the short-circuit current (Jsc) is 1.74mA·cm-2 and open-circuit voltage (Voc) is 1.62V, the device's photon to current efficiency is over 1%. The large open voltage and high photovoltaic efficiency is believed to attributed to the spontaneous polarization of composite perovskite induced by BiFeO3 lattice and modified reduced work function of the modified BiFeO3 surface. Our results clearly show that the present BiFeO3-CH3NH3PbI3 planar device is capable to generate a large voltage in macro scale under visible light, leading an approach to further applications on photodetectors and optoelectronic switch. [ABSTRACT FROM AUTHOR]

Abstract: The polycrystalline samples of dysprosium (Dy)-modified bismuth ferrite (i.e., Bi1−x Dy x FeO3; x=0–0.2 with the interval of 0.05) (BDFO) were synthesized using a high-temperature solid-state reaction method. Preliminary X-ray structural analysis showed that the reported crystal structure of BiFeO3 (rhombohedral) is invariant even with Dy-substitution at the Bi-site upto x=0.2. The scanning electron micrograph of the compounds showed (i) the uniform distribution of grains on the sample surface with high density and (ii) reduction of grain size on increasing Dy content in BiFeO3 (BFO). Studies of impedance, electrical modulus and electric conductivity of the materials in wide frequency (10–1000kHz) and temperature (30–500°C) ranges using a complex impedance spectroscopy technique have provided new and interesting information on the contribution of grains, grain boundary and interface in these parameters. Detailed studies of impedance spectroscopy clearly exhibit the dielectric relaxation of non-Debye type. The ac conductivity of the Dy-substituted BFO obeyed Jonscher's universal power law. An increase in Dy-content in BDFO results in the increase of spontaneous magnetization of BFO due to the collapse of spin cycloid structure. [Copyright &y& Elsevier]

We have investigated the structural, vibrational, ferroelectric, magnetic and dielectric properties of (0.95)PbZrTiO-(0.05)BiFeO (x = 0.51, 0.53 and 0.55) ceramics, prepared by the sol-gel route. Rietveld refined X-ray powder diffraction patterns of these samples confirm the single phase formation with a tetragonal structure (P4mm) symmetry at room temperature. The Williamson-Hall analysis was used to study the contributions of crystallite size and lattice strain on the peak broadening in the different patterns. Reduction in c/a ratio with x indicates poor ferroelectric behaviour for x = 0.55. Infrared spectroscopy revealed the slight shift of phonon modes towards the lower wave number side and increase in the bond length with increasing x which is in good agreement with the Rietveld analysis. Room temperature dielectric measurements of these samples show dispersion in ε which is associated with a peak in tanδ versus logf plots. M-H hysteresis loops exhibit weak ferromagnetism for x = 0.51 and almost anti-ferromagnetic behaviour for x = 0.55. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nd–Co and Gd–Co codoped BiFeO3 thin films are synthesized by chemical solution deposition method. [•] Enhanced magnetic property is observed in BGFC thin film at room temperature. [•] The onset electric field of FN tunneling of the films is associated with band gaps. [•] Both ferromagnetism and diamagnetism coexist in the BNFC film. [ABSTRACT FROM AUTHOR]

We report visible light detection with in-plane BiFeO3 (BFO) thin films grown on pre-patterned inter-digital electrodes. In-plane configured BFO film displayed photocurrents with a 40:1 photo-to-dark-current ratio and improved photo-sensing ability for >15 000 s (4 h) under small bias voltage (42 V). Nearly, sixty percent of the photo-induced charge carriers decay in 1.0 s and follow a double-exponential decay model. At 373 K, the effect of light does not significantly increase the dark current, probably due to reduced mobility. Sub-bandgap weak monochromatic light (1 mw/cm2) shows one fold increase in photo-charge carriers. [ABSTRACT FROM AUTHOR]

The ferroelectric switchable diode induced resistive switching behavior at low temperature has been investigated in the epitaxial BiFeO3 (BFO) thin films. The switchable diode can be tuned using a higher voltage at low temperatures. The diode barrier is determined to be ~0.55 eV at the interface between BFO and electrode. The resistive switchable barrier with respect to the ferroelectric domain switching has been systematically characterized at various low temperatures. The temperature dependent conduction and leakage mechanisms have also been identified. These results can advance our understanding of resistive switching based on ferroelectric switchable diode at low working temperatures and potentially extend the applications of memristor to a larger temperature scale. [ABSTRACT FROM AUTHOR]

B-site complex ion (MgNb)-modified high-temperature ceramics 0.71BiFeO-0.29BaTi(MgNb)O (BF-BTMN x) have been fabricated by the conventional solid-state reaction method. The compositional dependence of the␣phase structure, electrical properties, and depolarization temperature of the ceramics was studied. The main phase structure of BF-BTMN x ceramics is perovskite phase with pseudocubic symmetry. The experimental results show that the dielectric and piezoelectric properties, and temperature stability strongly depend on the (MgNb) content. The optimum (MgNb) content enhances the piezoelectric properties, Curie temperature, and depolarization temperature. The ceramic with x = 1% exhibited enhanced electrical properties of d = 158 pC/N and k = 0.322, combined with high-temperature stability with Curie temperature of T = 453°C and depolarization temperature of T = 400°C. These results show that the ceramic with x = 1% is a promising lead-free high-temperature piezoelectric material. [ABSTRACT FROM AUTHOR]

Artificial multiferroic superlattices (SL), consisting of BiFeO (16 nm)/BiNaTiO (5 nm) (BFO/BNT SL), were grown on (001) SrTiO single crystal by pulsed laser deposition method. The cross-sectional, surface morphology, and crystallographic structure of BFO/BNT SL and BFO single layer were investigated. It was found that the electrical, ferroelectric, and magnetic properties of BFO/BNT SL exhibit a remarkably enhancement compared with BFO single layer. The influence of BNT buffering layer, lattice strain, and interfaces interplay of the SL structure are supposed to benefit their ferroelectric and ferromagnetic properties. Our works suggested the BFO/BNT SL with an improved multiferroic characteristics have a promising application for the future informational storage devices. [ABSTRACT FROM AUTHOR]

BiInFeCoO (0 ≤ x ≤0.1, 0 ≤ y ≤ 0.05) nanoparticles have been successively synthesized by low temperature ethylene glycol based solution combustion method. The XRD patterns reveal the single phase rhombohedral distorted perovskite structure for pure BiFeO (BFO), and In doped BFO sample which is further confirmed from FTIR spectra. The co-doping of In and Co at A-B-sites of BFO results in structural distortion, improves the particles surface morphology in term of porosity, homogeneity, and density with further reduction of grain sizes. The TEM images also confirm the reduction, the average particle size showing particles size of 52 nm for BFO to around 12 nm for codoped BFO sample. All samples show ferromagnetic behavior at room temperature which further improves upon codoping with maximum saturation magnetization of 6.30 emu/gm. The codoping further follows a direct correspondence among lowering of Neel transition temperature (T ~ 240 °C), improvement in resistive behavior and enhancement of magnetoelectric effect ( α ~ 4.92 mV/cmOe) at room temperature. The possible origin of improvement in these properties has been explained on the basis of size effect and nature of the dopants. [ABSTRACT FROM AUTHOR]

Magnetic domains at the surface of a ferroelectric monodomain BiFeO3 single crystal have been imaged by hard x-ray magnetic scattering. Magnetic domains up to several hundred microns in size have been observed, corresponding to cycloidal modulations of the magnetization along the wave vector k = {δ, δ, 0) and symmetry equivalent directions. The rotation direction of the magnetization in all magnetic domains, determined by diffraction of circularly polarized light, was found to be unique and in agreement with predictions of a combined approach based on a spin-model complemented by relativistic density-functional simulations. Imaging of the surface shows that the largest adjacent domains display a 120° vortex structure. [ABSTRACT FROM AUTHOR]

Structurally tuned multiferroic state is demonstrated for BiFeO-based compounds. The electric and magnetic orders are strongly affected by the coexistence of R3c and Cm phases, i.e., by structural softness through monoclinicity, which leads the multiferroism to be driven by the same cation. The Cm phase enhances the ferroelectric and magnetic responses through Bi/Ba-O and Fe/Ti-O bonds by influencing structural distortions and ion valence. We also show the strong correlations between ferroic orders, structural arrangements, and tuning of the ion valence in the perovskite B site. [ABSTRACT FROM AUTHOR]

Abstract: This report underlines the systematic studies of crystalline structure, magnetic and ferroelectric properties of polycrystalline Bi1− x − y La x Pr y FeO3 ceramic samples, in which x changes continuously from 0 to 0.2 for y =0 and y from 0 to 0.2 for x =0.2. X-ray diffraction (XRD) patterns revealed that La and Pr substitution at Bi site in the ceramic eliminates the usual impurity phases completely. Rietveld refinement of the XRD patterns shows that the crystal structure changes gradually from Rhombohedral (R3c) to Orthorhombic (pbnm) with increasing La and Pr concentration. This transition has significant effects on the multiferroic properties of Bi1− x − y La x Pr y FeO3 ceramics. Substantial enhancement in magnetization of Bi1− x − y La x Pr y FeO3 has been observed and this is found to be correlated with the evolution of structural phase change with doping of Pr in samples having lanthanum concentration of x =0.2. This leads to the suppression of helical spin order. However, the enhancement in magnetic behavior also takes place due to nanocrystallite nature of Bi1− x − y La x Pr y FeO3 (x =0.2, y =0.05–0.2). For the nanocrystallites having sizes lower than 62nm, which is the period of spin cycloid, this spin configuration will get destroyed resulting in the enhancement of magnetization. The studies of microstructures employing SEM and TEM revealed that Bi1− x − y La x Pr y FeO3 consists of nano size grained microstructures. It is also found that dielectric constant and dielectric loss get improved by La and Pr co-substitution. The dielectric constant for x =0.0, y =0.0 is 81 which changes to 354 for x =0.2, y =0.15 at 100Hz. Dielectric losses are strongly diminished from 0.960 for x =0.0, y =0.0, 0.321 for x =0.2, y =0.0 and to 0.20 for x =0.2, y =0.05 at 100Hz. This improvement in dielectric properties is likely due to the changes of lattice parameters and suppression of oxygen vacancies caused by La and Pr co substitution. [Copyright &y& Elsevier]

Abstract: Dense (1−y)BiFe1−x Co x O3–yBaTiO3 (BFC–BTx, y=0.29, x=0–0.012) high-temperature lead-free ceramics were prepared by the conventional oxide-mixed method and the effects of BiCoO3 modification on microstructural, electrical properties and their Curie temperatures were investigated. The solid solutions show a single phase perovskite structure, and the content of BiCoO3 has a significant effect on the microstructure of ceramics. The BFC–BTx ceramics exhibit improved Curie temperature T c, together with increased piezoelectric properties. In particular, x=0.6% BFC–BTx ceramics, with a Curie temperature, T c, of ∼488°C, show optimum piezoelectric properties of d 33=167pC/N, k p=0.32. The combination of good piezoelectric properties and high T c makes these ceramics suitable for elevated temperature piezoelectric devices. [Copyright &y& Elsevier]

Abstract: Nano-sized BiFeO3 powders were prepared by co-precipitation and then the obtained powders with a density higher than 90% of the theoretical density were fabricated by sintering at 825°C. The structural and micro-structural studies were investigated by the X-ray diffraction, field emission scanning electron microscope and transmission electron microscope. The dielectric constant and dissipation factor of the bulk samples were tested between 100Hz and 5MHz at several temperatures by an inductance–capacitance–resistance (LCR) meter. The magnetic properties of nanoparticles were measured by a vibrating sample magnetometer (VSM). As compared to bulk samples, the nanoparticles (36nm) exhibit small magnetization (weak ferromagnetism) as a result of the spiral spin structure collapse. The electrical properties show the acceptable values for the sintered sample with a relatively high density at 825°C and high amounts of BiFeO3, as compared to the other samples. [Copyright &y& Elsevier]

Polycrystalline BiFeO3 films have been magnetron sputter deposited at room temperature and subsequently heat-treated ex situ at temperatures between 400 and 700°C. The deposition was done in pure Ar atmosphere, as the use of oxygen-argon mixture was found to lead to nonstoichiometric films due to resputtering effects. At a target-to-substrate distance d = 2n the BiFeO3 structure can be obtained in larger range process gas pressures (2-7m Torr) but the films do not show a specific texture. At d = 6n3 codeposition from BiFeO3 and Bi2O3 has been used. Films sputtered at low rate tend to grow with the (001) texture of the pseudocubic BiFeO3 structure. As the film structure does not depend on epitaxy similar results are obtained on different substrates. A result of the volatility of Bi, Bi rich oxide phases occur after heat treatment at high temperatures. A Bi2SiO5 impurity phase forms on the substrate side, and does not affect the properties of the main phase. Despite the deposition on amorphous silicon oxide substrate weak ferromagnetism phenomena and displaced loops have been observed at low temperatures showing that their origin is not strain. Ba, La, Ca, and Sr doping suppress the formation of impurity phases and leakage currents. [ABSTRACT FROM AUTHOR]

Major ways to improve the magnetic and electrical properties of promising multiferroic BiFeO and optimize its synthesis have been studied, and its applications in spintronics, photonics, and magnonics have been discussed. [ABSTRACT FROM AUTHOR]

Abstract: Bi1–x Ba x FeO3 (0.0≤x≤0.25) ceramics are prepared by chemical synthesis route. At room temperature, antiferromagnetic BiFeO3 is converted to ferromagnetic on doping Ba. A large change in the magnetization is observed around 370°C which is close to the Neel temperature (T N) of parent compound. Another magnetic transition is also observed near 600°C. Spin canting or impurity phase could be a probable reason for the origin of ferromagnetism in both cases. Ferroelectric and magnetic transitions of the compounds shift towards higher temperature with Ba-doping concentration. Anomaly in the dielectric constant is also observed near the T N of BiFeO3. The composition x=0.15 shows the maximum magnetic moment at room temperature while better fatigue resistance and maximum magnetoelectric coupling are observed for x=0.20 composition. [Copyright &y& Elsevier]

BiFeO-modified lead-free piezoceramics Li(NaK)NbTaO (LKNNT) were successfully fabricated by conventional method to investigate its influences on phase structure and electricity as well as mechanical properties. A tiny amount of BiFeO (BF) changes the phase structure of LKNNT to tetragonal and further to pseudocubic, and also effectively improves the sintering ability and densification of LKNNT which enhances the mechanical property. The LKNNT piezoceramics with the addition of 1 mol% BF has the bulk density of 5.02 g/cm and an enhanced fracture strength of 142 MPa which is even higher than that of the sample of similar composition prepared by spark plasma sintering, also possesses room temperature electric properties of d* ~ 225 pm/V, k ~ 36.3%, ε ~ 1140, tgδ ~ 0.018, T ~ 305 °C and Q ~ 80. The d* remains constant up to 150 °C and the change ratio of dielectric property largely decreases over the temperature range of −50-150 °C, which can be attributed to the temperature-independent phase structure of LKNNT piezoceramics, making the ceramics as a promising candidate for actual applications. [ABSTRACT FROM AUTHOR]

Abstract: BiFeO3/[0.93(Bi0.50Na0.50TiO3)–0.05BaTiO3–0.02K0.50Na0.50NbO3] (BFO/BNBTKNN) bilayered thin films were fabricated on Pt/TiO2/SiO2/Si substrates without any buffer layers by a combined sol–gel and radio frequency sputtering route. Effect of BNBTKNN on electrical properties of BFO/BNBTKNN thin films was investigated. A higher phase purity and a denser microstructure are induced for the BFO/BNBTKNN bilayered thin film by using the bottom BNBTKNN layer, resulting in its lower leakage current density. Moreover, the enhancement in dielectric behavior is also demonstrated for such a bilayer, where a high dielectric constant and a low dielectric loss are obtained. The BFO/BNBTKNN bilayered thin film has an improved multiferroic behavior: 2P r ∼76.8μC/cm2, 2E c ∼378.1kV/cm, 2M s ∼52.6emu/cm3, and 2H c ∼453.6Oe, together with a low fatigue rate up to ∼1×109 switching cycles. [Copyright &y& Elsevier]

BiFeO3 thin films were fabricated by pulsed laser deposition on Nb–SrTiO3 (0 0 1), La2/3Sr1/3MnO3/SrTiO3 (0 0 1), and SrRuO3/SrTiO3 (0 0 1) electrode surfaces. All films grew epitaxially along the substrates and were fully strained. The current–voltage curves of the structures revealed that the current level depended on the barrier height at the ferroelectric/bottom electrode interface. Resistive switching behavior was observed in the BiFeO3 films grown on all electrodes, which was rationalized in terms of conductive filaments and the variation of the Schottky barrier at the ferroelectric/electrode interfaces due to ferroelectric polarization. The conductive filament model and modulation of the Schottky barriers at film/electrode interfaces due to ferroelectric polarization applied to BiFeO3 films on SrRuO3 and La2/3Sr1/3MnO3 electrodes, respectively, while a combination of these two mechanisms was suggested to be responsible for the observed resistive switching of BiFeO3 film on Nb–SrTiO3. [ABSTRACT FROM AUTHOR]

In this work, Sm and Sc co-doped Bi1−xSmxFe1−yScyO3 (x  =  0.00–0.20; y  =  0.03) ceramics are fabricated by a rapid liquid phase sintering method, in order to develop single-phase multiferroics with large magnetization and polarization. X-ray diffraction and Raman spectroscopic studies reveal that the ceramics are single-phase with a structural transition from rhombohedral to orthorhombic structures near x  = 0.15. Electric and magnetic measurement results indicate that the transition significantly enhances the multiferroic properties, which stems from the Sm/Sc doping induced collapse of space-modulated spin structure and internal structural distortion. At an optimized composition of Bi0.85Sm0.15Fe0.97Sc0.03O3 (x  =  0.15), a remanent polarization of 16.5 μC cm−2, a magnetization 0.2020 emu g−1, and a magnetodielectric effect of 0.46% can be obtained. These results clearly demonstrate a potential application for Sm/Sc doped BiFeO3 ceramics in the field of multiferroic devices. [ABSTRACT FROM AUTHOR]

La3+ and V5+ co-doped BiFeO3 ceramics are synthesized by rapid liquid sintering technique. The modulated structure in Bi0.85La0.15Fe0.97V0.03O3 is investigated by using transmission electron microscopy (TEM). Two kinds of superstructures are observed in the samples. One is the component modulated superstructure and twin-domain, which is generated by La3+ ordered substitution for Bi3+ and frequently appears. The chemical composition of the superstructure is explored by x-ray energy dispersive spectroscopy (EDS). The model of the ordered structure is proposed. Simulation based on the model is conducted. The second is the fluorite-type δ-Bi2O3 related superstructure. The relation between the ferroelectric property and the microstructure of the sample is also discussed. [ABSTRACT FROM AUTHOR]