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Composition dependence of phase structure and electrical properties of (1−y)Bi1−x Nd x FeO3−y BiScO3 ceramics
Abstract
In this work, we have studied a new lead-free ceramic of (1−y)Bi1−x
Ndx
FeO3-y
BiScO3 (0.05≤x≤0.15 and 0.05≤y≤0.15) prepared by a conventional solid-state method, and the influences of Nd and Sc content on their phase structure and electrical properties were investigated in detail. The ceramics with 0.05≤x≤0.10 and 0.05≤y≤0.15 belong to an R3c phase, and the rhombohedral-like and orthorhombic multiphase coexistence is established in the composition range of 0.125≤x≤0.15 and y=0. The electrical properties of the ceramics can be enhanced by modifying x and y values. The highest piezoelectric coefficient (d
33~51 pC/N) is obtained in the ceramics with x=0.075 and y=0.125, which is superior to that of a pure BiFeO3 ceramic. In addition, a lowest dielectric loss (tan δ~0.095%, f=100 kHz) is shown in the ceramics with x=0.15 and y=0 due to the involvement of low defect concentrations, and the improved thermal stability of piezoelectricity at 20–600°C is possessed in the ceramics. We believe that the ceramics can play a meaningful role in the high-temperature lead-free piezoelectric applications.
Among the different types of multiferroic compounds, bismuth ferrite (BiFeO3; BFO) stands out because it is perhaps the only one being simultaneously magnetic and strongly ferroelectric at room temperature. Therefore, in the past decade or more, extensive research has been devoted to BFO-based materials in a variety of different forms, including ceramic bulks, thin films and nanostructures. Ceramic bulk BFO and their solid solutions with other oxide perovskite compounds show excellent ferroelectric and piezoelectric properties and are thus promising candidates for lead-free ferroelectric and piezoelectric devices. BFO thin films, on the other hand, exhibit versatile structures and many intriguing properties, particularly the robust ferroelectricity, the inherent magnetoelectric coupling, and the emerging photovoltaic effects. BFO-based nanostructures are of great interest owing to their size effect-induced structural modification and enhancement in various functional behaviors, such as magnetic and photocatalytic properties. Although to date several review papers on BFO and BFO-based materials have been published, they were each largely focused on one particular form of BFO. There have been very few papers addressing the different forms of BFO in a comprehensive manner and providing a comparison across the different forms. As BFO has been extensively studied over the past more than one decade especially in the past several years, there have been new phenomena arising more recently. Naturally they were not included in the early reviews. Here, we provide an updated comprehensive review on the progress of BFO-based materials made in the past fifteen years in the different forms of ceramic bulks, thin films and nanostructures, focusing on the pathways to modify different structures and to achieve enhanced physical properties and new functional behavior. We also prospect the future potential development for BFO-based materials in the cross disciplines and for multifunctional applications. We hope that this comprehensive review will serve as a timely updating and reference for researchers who are interested in further exploring bismuth ferrite-based materials.
By means of the quadratic magnetoelectric effect the components of the non-linear magnetoelectric susceptibility tensor βijk of the antiferromagnetic ferroelectric ferroelastic phase of BiFeO3 have been determined at 4 K: β_111 =5.010^-19[sA^-1],β_113=8.110^-19[sA^-1], β_311 =0.310^-19[sA^-1],β_333=2.110^-19[sA^-1]
Eu substituted BiFeO3 (Bi1−xEuxFeO3; x=0–0.15) polycrystalline ceramics were synthesized by a solid state reaction method. Rietveld refinement of X-ray diffraction patterns reveals that samples crystallize in R3c structure for x≤0.10 and (R3c+Pn21a) phases coexist for x≥0.12–0.15. The magnetic measurements show weak ferromagnetic nature of Eu substituted BiFeO3 samples due to ferromagnetic coupling between Eu3+ and Fe3+ ions. The remnant magnetization is found to increase from 0.0003 emu/g for x=0.00 to 0.087 emu/g for x=0.15. The gradual change in line shape of electron spin resonance spectra has been attributed to local distortion induced by Eu substitution. UV–visible absorption spectra in the spectral range 1.12–3.5 eV were dominated by two charge transfer transitions and two doubly degenerate d–d transitions. The optical band gap is found to decrease from 2.25 to 2.16 eV with increasing Eu concentration. Improved dielectric properties with enhancement in frequency independent region of dielectric constant and loss have been observed.
Investigation on structural, vibrational, dielectric and ferroelectric properties of Bi1−xPrxFeO3 (x = 0.0, 0.15, 0.25) ceramic samples has been carried out. Room temperature Rietveld-refined X-ray diffraction pattern shows the crystal structure of Bi1−xPrxFeO3 is rhombohedral for x = 0 and triclinic for x = 0.15, 0.25. The changes in Raman normal modes with increasing doping concentration infer the structural transformation is due to Pr substitution at A-site in BiFeO3. Raman spectra also reveal suppression of ferroelectric behavior due to Pr doping. The dielectric parameters, namely, dielectric permittivity (ε′) and loss tangent (tan (δ)) were evaluated as a function of frequency at room temperature. The ferroelectric polarization reduces in Pr doped bulk BFO samples due to structural change.
Recent research activities on the linear magnetoelectric (ME) effect---induction of magnetization by an electric field or of polarization by a magnetic field---are reviewed. Beginning with a brief summary of the history of the ME effect since its prediction in 1894, the paper focuses on the present revival of the effect. Two major sources for 'large' ME effects are identified. (i) In composite materials the ME effect is generated as a product property of a magnetostrictive and a piezoelectric compound. A linear ME polarization is induced by a weak ac magnetic field oscillating in the presence of a strong dc bias field. The ME effect is large if the ME coefficient coupling the magnetic and electric fields is large. Experiments on sintered granular composites and on laminated layers of the constituents as well as theories on the interaction between the constituents are described. In the vicinity of electromechanical resonances a ME voltage coefficient of up to 90 V cm-1 Oe-1 is achieved, which exceeds the ME response of single-phase compounds by 3-5 orders of magnitude. Microwave devices, sensors, transducers and heterogeneous read/write devices are among the suggested technical implementations of the composite ME effect. (ii) In multiferroics the internal magnetic and/or electric fields are enhanced by the presence of multiple long-range ordering. The ME effect is strong enough to trigger magnetic or electrical phase transitions. ME effects in multiferroics are thus 'large' if the corresponding contribution to the free energy is large. Clamped ME switching of electrical and magnetic domains, ferroelectric reorientation induced by applied magnetic fields and induction of ferromagnetic ordering in applied electric fields were observed. Mechanisms favouring multiferroicity are summarized, and multiferroics in reduced dimensions are discussed. In addition to composites and multiferroics, novel and exotic manifestations of ME behaviour are investigated. This includes (i) optical second harmonic generation as a tool to study magnetic, electrical and ME properties in one setup and with access to domain structures; (ii) ME effects in colossal magnetoresistive manganites, superconductors and phosphates of the LiMPO4 type; (iii) the concept of the toroidal moment as manifestation of a ME dipole moment; (iv) pronounced ME effects in photonic crystals with a possibility of electromagnetic unidirectionality. The review concludes with a summary and an outlook to the future development of magnetoelectrics research.
Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO1-xFx (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO1-xFx as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO1-xFx with other Fe-based superconductors suggests that the structural perfection of the Fe–As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.
Highly (111)-oriented rhombohedral BiFeO <sub>3</sub> (BFO) thin films were grown on (111) SrTiO <sub>3</sub> substrates by pulsed laser deposition. Polarized Raman-scattering study of the (111)-oriented epitaxial BFO thin film with rhombohedral R3c symmetry was carried out by employing two distinct backscattering geometries. The A<sub>1</sub> -symmetry transverse-optical [A<sub>1</sub>( TO )] phonons were selectively isolated from the E -symmetry transverse-optical [E( TO )] phonons by employing Y<sup>′</sup>(ZZ)Y<sup>′</sup> polarization configuration in a novel side-view backscattering. By comparing the Y<sup>′</sup>(ZZ)Y<sup>′</sup> spectrum with the Z(X<sup>′</sup>X<sup>′</sup>)Z polarization spectrum in a normal backscattering, we were able to assign most of A<sub>1</sub> and E -symmetry normal modes of R3c BFO. In addition, we found that there was a negligible LO-TO splitting in the A<sub>1</sub> -symmetry normal modes.
Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the
intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large
electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover
practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction
with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free
piezoelectric bismuth ferrite (BiFeO3) films. Electric field–dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like
phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based
data storage and actuator applications.
Ferroelectromagnets are an interesting group of compounds that complement purely (anti-)ferroelectric or (anti-)ferromagnetic materials--they display simultaneous electric and magnetic order. With this coexistence they supplement materials in which magnetization can be induced by an electric field and electrical polarization by a magnetic field, a property which is termed the magnetoelectric effect. Aside from its fundamental importance, the mutual control of electric and magnetic properties is of significant interest for applications in magnetic storage media and 'spintronics'. The coupled electric and magnetic ordering in ferroelectromagnets is accompanied by the formation of domains and domain walls. However, such a cross-correlation between magnetic and electric domains has so far not been observed. Here we report spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3, obtained by imaging with optical second harmonic generation. The coupling originates from an interaction between magnetic and electric domain walls, which leads to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.
Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet,
BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is
rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter)
almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement
is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small
changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These
enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices
that actively couple the magnetic and ferroelectric order parameters.
Adding both La3+ and Co3+ was used to tune the microstructure and electrical properties of BiFeO3 (BFO) thin films, and Bi1−xLaxFe0.90Co0.10O3 thin films were grown on the SrRuO3-buffered Pt-coated silicon substrates by a radio frequency sputtering. A polycrystalline structure with (110) orientation was shown in thin films, and their resistivity dramatically increases as the La3+ content increases. Their dielectric constant increases, and dielectric loss decreases with increasing La3+ content. In addition, their ferroelectric and fatigue properties were enhanced with rising La3+ content. The thin films with x = 0.03 have optimum electrical properties (e.g., remanent polarization 2Pr ~ 175.6 μC/cm2, coercive field 2Ec ~ 699.5 kV/mm, dielectric constant εr ~ 257 and tan δ ~ 0.038), together with a good fatigue behavior. The impendence analysis of the films was conducted to identify the defects type during conductivity, and both hopping electrons and single-charged oxygen vacancies are mainly responsible for the conduction of grain and grain boundaries regardless of La3+ content. As a result, the doping with both La3+ and Co3+ benefits the improvement in the electrical properties of BFO thin films. © 2014, Science China Press and Springer-Verlag Berlin Heidelberg.
In this work, the (1 – x)Bi1–ySmyFeO3–xBiScO3 lead-free ceramics were prepared by the rapid thermal quenching technique, and the effects of compositions and preparation processes on their phase structure, microstructure, and electrical properties were investigated. By tuning the compositions, a high d33 of ∼51 pC/N and a low dielectric loss of ∼0.25% can be attained in the ceramics with x = 0.05 and y = 0.05, which is superior to the previously reported results. In addition, a saturated P–E loop with a Pr of 14.2 μC/cm2 and an EC of 53.1 kV/cm can be witnessed in the ceramics with x = 0.05 and y = 0. By studying the relationships between d33 and different sintering methods, we can find that the quenching method can effectively promote the piezoelectricity of the ceramics. As a result, the systematic investigations on the (1 – x)Bi1–ySmyFeO3–xBiScO3 ceramics can benefit the developments of bismuth ferrite materials in the field of high-temperature piezoelectrics.
Ni doped BiFeO3 (x=0, 0.05, 0.1 and 0.15) nanocrystalline ceramics were synthesized by the solution combustion method (SCM) to obtain optimal multiferroic properties. The effect of Ni doping on structural, morphological, ferroelectric, magnetic and dielectric properties of BiFeO3 was studied. The structural investigations by using X-ray diffraction (XRD) pattern confirmed that BiFe1−xNixO3 ceramics have rhombhohedral perovskite structure. The ferroelectric hysteresis measurements for BiFe1−xNixO3 (x=0, 0.05, 0.1, 0.15) compound at room temperature found to exhibit unsaturated behavior and presents partial reversal of polarization. The magnetic measurements demonstrated an enhancement of ferromagnetic property due to Ni doping in BiFeO3 when compared with undoped BiFeO3. The variation of dielectric constant with temperature in BiFe0.9Ni0.1O3 and BiFe0.85Ni0.15O3 samples evidenced an apparent dielectric anomaly around 350 °C and 300 °C which corresponds to antiferromagnetic to paramagnetic phase transition of (TN) of BiFeO3. The dependence of room temperature dielectric properties on frequency signifies that both dielectric constant (ε) and dielectric loss (tan δ) are the strong function of frequency. The results show that solution combustion method leads to synthesis of an excellent and reproducible BiFe1−xNixO3 multiferroic ceramics.
Bi1−xSmxFeO3 multiferroics (x = 0.0, 0.05 and 0.1 having code BF0/SM0, SM5 and SM10 respectively) were synthesized via stage solid-state reaction method and their detailed structural, magnetic and impedance measurements are performed. X-ray diffraction profile and Rietveld analysis indicates that the crystal structure is rhombohedral (R3c). Due to Sm doping, the weak ferromagnetism in BiFeO3 ceramics may be attributed to the improved crystallinity and non presence of secondary phases. Bi0.9Sm0.1FeO3 ceramic exhibited the highest value of remnant magnetization and coercive field. The values of dielectric constant and dielectric loss of SM5 and SM10 samples showed dispersion at low frequency region. The temperature dependence of electric modulus at different frequencies shows the presence of well defined peaks and thus gives the temperature at which the measuring frequency is equal to conductivity relaxation frequency. The typical features of jump relaxation model are obeyed in ac conductivity analysis. Frequency dependence of the conductivity follows the universal power law.
Multiferroic BiFe1-xScxO3 ceramics with x=0.00∼0.10 were synthesized by rapid liquid phase sintering. The influences of Sc doping on the crystalline structures, dielectric, ferroelectric, and magnetic behaviors of BiFeO3 ceramics were explored. The X-ray diffraction and the Raman spectrometric analysis revealed that all the samples are nearly single phase of rhombohedral structure with the incorporation of Sc ions into BiFeO3. With increase doping concentration of x, the dielectric constant, dielectric loss, and remenant polarization for the doped BiFeO3 increase first and then drop down with further rise of x. A saturated ferroelectric polarization can be achieved at a small amount of Sc doping concentration (x<0.03), with a optimized remanent polarization of 17.6 μC/cm2 at x=0.03. Meanwhile, the magnetization is also slightly increased by introducing Sc dopant, with a maximum remanent magnetization of 0.0105 emu/g at x=0.01. These results indicate that BiFeO3 ceramics with small amounts of Sc-doping may be promising for applications in magnetoelectric devices.
The polycrystalline Nd-modified bismuth ferrite BiFeO3 (Bi1−xNdxFeO3 (BNFO) (x=0, 0.05, 0.15, and 0.25)) were prepared in a single-phase using a standard and cost effective solid-state reaction method. In order to check the quality and formation of the compounds x-rays diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDAX) techniques were used. Preliminary structural analysis indicates that the crystal structure of BNFO is rhombohedra for its low content of Nd (x=0, 0.05, 0.15) whereas for higher content (x=0.25) it is tetragonal. The dielectric and ferroelectric properties of BiFeO3 (BFO) were dramatically enhanced on the above Nd- substitutions. Study of the frequency dependence of ac conductivity suggests that the materials obey Jonscher's universal power law. An increase in Nd-content in BNFO results in the enhancement of spontaneous magnetization of BFO because of the collapse of spin cycloid structure.
We have developed a novel synthetic route for the preparation of single phase NdxBi1−xFe0.95Sc0.05O3 (NBFSO) nanopowder materials by a surfactant-assisted combustion-derived method. Rietveld fitting of the Powder X-ray diffraction data showed the nanopowder structure evolves from a distorted rhombohedral BiFeO3 crystalline structure (R3c, x = 0) to a orthorhombic structure (Pbnm, x = 0.10). Differential thermal analysis and thermogravimetric analysis (DTA/TGA) showed a crystallization temperature of 200 °C. Transmission electron microscopy (TEM) images revealed the presence of clusters formed by fine nanoparticles less than 60 nm in diameter. From Raman spectroscopy, the change from rhombohedral structure to cubic structure was observed by a drastic intensity reduction of the A1−2 and A1−3 Raman modes, with the A1−1 and A1−2 modes gradually merging together, indicating the merge of the orthorhombic phase. Despite the antiferromagnetic nature of bulk BiFeO3, the NBFSO nanopowders obtained displayed a ferromagnetic hysteresis loop, with coercivities of 0.08 T and remanent magnetizations of 0.65–4.05 Am2/kg when measured at room temperature. The increasing and uncompensated spins at the surface of nanoparticles and the canted internal spin by the tilt of FeO6 octahedral units and the structure transition appear to be the main reason for observed this ferromagnetic behavior.
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 620 K observed near the Néel temperature (
T
N
∼ 643 K 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.
We have developed the high-temperature bismuth ferrite ceramics with enhanced piezoelectric activity by the chemical modifications, that is, the Bi1-x-ySmxLayFeO3 (0≤x≤0.30 and 0≤y≤0.15) lead-free ceramics were prepared by the conventional solid-state method. The influences of La & Sm content on their microstructure and electrical properties were systematically investigated. The ceramics with 0≤x<0.10 (y=0.05) or 0≤y≤0.15 (x=0.025) belong to a triclinic phase, and a mixed structure with rhombohedral-like and orthorhombic phases was found in the ones with 0.10≤x≤0.30 (y=0.05). The electrical properties of the ceramics can be operated by refining x and y values. A very low dielectric loss (tan δ~0.43%) was shown in the ceramics with x=0.025 and y=0.05 because of the involvement of low defect concentrations. In addition, the ceramics with x=0.025 and y=0.05 also possess a high piezoelectric activity (d33~50 pC/N), which is larger with the respect to the previously reported results in high-temperature piezoceramics with a Curie temperature of >600 oC, and the better thermal stability of piezoelectricity in 20~700 oC is also shown. We believe that this material system is suitable to the high-temperature piezoelectric applications.
The multiferroic properties of BiFeO3-based ceramics were improved through optimizing their sintering method and doping with certain rare earth elements in pure BiFeO3. Some methods, especially liquid-phase sintering method has largely decreased the densities of oxygen vacancies and Fe2+ in BiFeO3-based ceramics, and thus their resistivity became high enough to measure the saturated polarization and the large piezoelectric d
33 coefficient under the high electric field of >150 kV/cm. Besides, multiferroic properties were improved through the rare earth elements’ doping in pure BiFeO3. Magnetization commonly increases with the proportional increase of Nd, La, Sm and Dy contents up to ~30 %, while ferroelectric phase can transform to paraelectric phase at a certain proportion. An improved magnetoelectric coupling was often observed at ferroelectric phase with a relatively large proportion. Besides, an enhanced piezoelectric coefficient is expected in BiFeO3-based ceramics with morphotropic phase boundaries as they are already observed in thin epitaxial BiFeO3 films.
Dense Bi4Ti3O12 (BTO), Bi3.15La0.85Ti3O12 (BLaT) and Bi3.15Nd0.85Ti3O12 (BNdT) ferroelectric ceramics were synthesized by solid–state reaction method. All ceramics are orthorhombic bismuth-layered perovskite structure with plate-like grains of random orientation. The influences of La and Nd doping on the ferroelectric properties and leakage mechanism were investigated. The remanent polarizations (2P
r) were determined to be 13.4, 23.9 and 32.6 μC/cm2 for BTO, BLaT, and BNdT, respectively. The leakage current density decreased markedly with La and Nd doping. The dominant leakage mechanism in both BTO and BLaT ceramics has been found to be the ohmic mechanism and the space-charge-limited current mechanism in the low and high electric field region, respectively. While in BNdT ceramics a quasi-ohmic behavior was found in the high electric field region, following the ohmic behavior in the low electric field region and trapped filled limited behavior in the intermediate electric field region.
Single phase multiferroic BiFeO3 (BFO) ceramics were synthesized with controllable amount of Fe2+ and oxygen vacancies in a very wide concentration range. Double ferroelectric hysteresis loops are observed in fresh BFO ceramics at room temperature without any aging processes. Detailed study shows that this is due to the defect dipoles which have preferential orientations antiparallel to the direction of spontaneous polarization, providing a driving force for domain back-switching. The dielectric constant of BFO could be enormously enhanced by 100 times by increasing the Fe2+ content, employing a polaronic relaxation process.
A giant remanent polarization of BiFeO3 thin films is obtained by introducing Zn and Mn, and Bi(Fe0.93Mn0.05Zn0.02)O3 (BFMZO) thin films were prepared on SrRuO3-buffered silicon substrates by the radio-frequency sputtering. An (111) orientation is induced in such a film because of the introduction of an SrRuO3 buffer layer. An enhanced ferroelectric behavior of 2Pr ∼ 235 μC/cm2 and 2Ec ∼ 612 kV/cm is observed in BFMZO thin films, together with a fatigue-free behavior. As a result, the introduction of Zn and Mn is a good way to improve the electrical behavior of BiFeO3 thin films.
Sb5+-doped (NaBi)0.38(LiCe)0.05[]0.14Bi2Nb2O9 (represented as NBNLCS-x, where [] represents A-site vacancies) ceramics were prepared by the conventional solid-state route. The ceramics well sintered to approach ∼98.5% theoretical density and the tetragonality of crystal structure increased with Sb5+ additions. However, the Curie temperature (TC) and the piezoelectric coefficient (d33) of Sb5+-modified ceramics gradually decreased. The 3 mol% Sb5+-doped samples exhibited optimum properties with a d33 value of ∼22 pC/N planar electromechanical coupling factor (kp) of ∼11.2% and relatively high TC of ∼765 °C. These results indicate that NBNLCS-x material is a promising candidate for high-temperature piezoelectric applications.
Insulated Bi1 − xDyxFeO3 (x = 0–0.2) were prepared to study their multiferroic properties at various temperatures. Bi1 − xDyxFeO3 (x = 0–0.08) shows rhombohedral phase, ferroelectric polarization of > 18 μC/cm2, and piezoelectric d33 value of > 35 pC/N at room temperature. After the polarized ceramics were annealed at various high temperatures, the piezoelectric d33 changes suggest that ferroelectric component exists below 700 °C. There are ferroelectric phase and PZT-like anti-polar orthorhombic phase together in Bi1 − xDyxFeO3 (x = 0.11–0.17), although only ferroelectric phase contributes polarization and d33 which decreases with Dy concentration at this two-phase coexistence region. Finally, Bi1 − xDyxFeO3 (x = 0.2) transforms to non-polar orthorhombic phase according to structural and electric measurements.
The effect of Bi{sub 0.90}La{sub 0.10}Fe{sub 0.90}Zn{sub 0.10}O{sub 3} (BLFZO) thicknesses on the microstructure and multiferroic properties of BiFeO{sub 3} (BFO) thin films was investigated, and all bilayered thin films were grown on Pt-coated silicon substrates without any buffer layers by a radio frequency sputtering. A (110) orientation is dominant in all the bilayers, and two grain growth modes are identified in these bilayers by using an atomic force microscope, where different grain growth modes significantly affect their leakage behavior. The dielectric constant ({epsilon}{sub r}) of bilayers gradually increases, and magnetic properties were deteriorated with the addition of BLFZO with a higher {epsilon}{sub r} and a weaker magnetic behavior. An enhanced ferroelectric behavior of 2P{sub r} {approx} 116.2 {mu}C/cm{sup 2} and 2E{sub c} {approx} 524 kV/cm could be observed in the BFO/BLFZO bilayered thin film with 80 nm BLFZO layer owing to a higher orientation degree of (110) and an interface coupling together with a lower leakage current density. As a result, electrical properties of BFO could be tailored by modifying the thicknesses of BLFZO.
Investigation of crystal structure, magnetic and local ferroelectric properties of the diamagnetically-doped Bi1−xAxFeO3 (A=Ca, Sr, Pb, Ba; x=0.2, 0.3) ceramic samples has been carried out. It has been shown that the solid solutions have a rhombohedrally distorted perovskite structure described by the space group R3c. Piezoresponse force microscopy data have revealed the existence of the spontaneous ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO3 and to result in the appearance of weak ferromagnetism. The magnetic properties have been discussed in terms of doping- induced changes in the magnetic anisotropy.
The effects of modifying the well-known multiferroic BiFeO3 by substituting Fe by Mn and Bi by La have been investigated. It is shown that both the substitutions have a favourable effect on the multiferroic properties of BiFeO3. Thus, both BiFe1−xMnxO3 and Bi1−xLaxFeO3 (x=0.0–0.3) show increased magnetization accompanied by hysteresis loops as well as improved dielectric properties. The ferroelectric transition temperature is lower than that of BiFeO3, but is in a more accessible range. In Bi1−xLaxFeO3, there is a change in structure at x=0.2.
The entire zone-center phonon spectrum of the R3c ferroelectric antiferromagnetic phase of bismuth ferrite is computed using a first-principles approach based on density functional theory. Two phonon modes exhibiting eigendisplacement vectors that strongly overlap with the atomic distortions taking place at the ferroelectric structural phase transition are identified and give support to a transition with displacive character. Both Raman and infrared reflectivity spectra are also computed, providing benchmark theoretical results for the assignment of experimental spectra.
Dense CaBi4Ti4O15 (CBT) and
Na0.475Ca0.05Bi4.475Ti4O15
(NCBT) ceramics with a highly preferred {001} orientation were prepared
by the reactive templated grain growth (RTGG) method. Plate-like
Bi4Ti3O12 (BIT) particles were
synthesized by a molten salt technique and used as the reactive
template. The template particles were mixed with other oxide and
carbonate powders and aligned by tape-casting. During the sintering,
oriented CBT and NCBT were formed in situ topotaxially on the oriented
BIT particles, and textured CBT and NCBT ceramics were eventually
fabricated by the templated grain growth and densification. The
Lotgering {001} orientation degree of the textured ceramics exceeded 90%
for secondary-laminate sintered specimens. Textured CBT and NCBT
ceramics poled in the perpendicular direction to the preferred
<001> axis exhibited electromechanical coupling coefficient
(k33) and piezoelectric coefficients (d33 and
g33) three times higher than the values for nontextured
ceramics with the same composition.
Studies of a BiFeO3 synthesis were performed to identify reasons for the appearance of secondary phases, the Bi25FeO39- and Bi2Fe4O9-type phases, in the reaction product. X-ray diffraction and microstructural analyses, performed on samples with different concentrations of impurities, showed that the impurities in the starting material crucially influence the phase composition of the reaction product. A fraction of the generated secondary phases strongly depends on the nature and concentration of the impurities. The experimental results can be explained by the theoretical consideration of ternary phase relations between Bi2O3, Fe2O3, and an impurity oxide. Single-phase polycrystalline BiFeO3 was synthesized from ultrapure starting oxides. To avoid using the expensive ultrapure oxides, techniques for reducing the fraction of the secondary phases in the reaction products were developed.
Pristine (BiFeO3), Pr and Sc co-substituted Bi0.9Pr0.1Fe1−xScxO3 (0.01 ≤ x ≤ 0.07) ceramics have been investigated for their structural (including x-ray diffraction and Raman), morphological and piezoresponse behaviour. Secondary phases observed in pristine BiFeO3 (BFO) ceramic were significantly suppressed in the co-substituted samples. Grain size decreased in the co-substituted samples. Raman study revealed ten active phonon modes which remained almost invariant with co-substitution. Out-of-plane piezoresponse (OPP-PFM) exhibited negative self-polarization effect in the virgin state (without any poling) which has been explained in terms of built-in electric field. The self-polarization effect is largest in 3% Sc co-substituted sample. Poling with ±30 V dc voltage demonstrated both positive and negative domains. Maximum difference in the peak values (from histograms) of such opposite domains was observed in the Bi0.9Pr0.1Fe0.99Sc0.01O3 sample. Information from local measurements (such as PFM) should be useful in deciding such multiferroic materials for device application.
La3+ and V5+ co-doped Bi0.85La0.15Fe1−xVxO3 (BLFVx, x = 0–0.1) ceramics were prepared by a rapid liquid sintering technique. The effects of the V5+-doping content on the structure and electrical properties of BLFVx ceramics were investigated. In the range of the V5+ content x from 0 to 0.03, BLFVx ceramics had a polycrystalline perovskite structure with tiny residual Bi2O3, while an impurity phase appeared for x > 0.03. As the x increased from 0 to 0.1, both the leakage current density and the dielectric loss (tan δ) for BLFVx ceramics decreased gradually, while the dielectric constant (εr) first increased and then decreased gradually in this process, reaching a maximum value of 273 for x = 0.03. Among the BLFVx ceramics, the BLFVx=0.01 ceramic showed a well-saturated hysteresis loop with large remanent polarization (Pr) of 39.4 µC cm−2 and a low coercive electric field (Ec) of ±43.1 kV cm−1 under an applied electric field of ±75 kV cm−1. In addition, these ceramics exhibited good anti-fatigue characteristics after 2 × 1010 read/write polarization cycles. These suggested that La3+ and V5+ co-doping was beneficial for enhancing the dielectric, ferroelectric and anti-fatigue properties of the BLFVx ceramics.
BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.
In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle α R (associated with an inflection in the lattice constant a R ) near 400 and 350 °C in BiFeO 3 (BFO) and (BiFeO 3 ) 0.95 (BaTiO 3 ) 0.05 (BFO–5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)–orthorhombic (O)–cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO–5%BT exhibits a R–C transition near 830 °C. The BaTiO 3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO–5%BT remains less than 0.04 below 150 °C.
Single phase Bi <sub>0.9- x </sub> La <sub>0.1</sub> Nd <sub> x </sub> FeO <sub>3</sub> ( BLNFO <sub> x </sub>) ( x =0.05 , 0.07, and 0.1) multiferroic ceramics were prepared to study the effect of combine substitution of La and Nd in BiFeO <sub>3</sub> (BFO). X-ray diffraction studies revealed phase transition from rhombohedral (R3c) to triclinic (P1) on substitution of 05 and 07 mol % of Nd and subsequent transition to monoclinic C2/c with 10 mol % of Nd along with 10 mol % of La. These structural phase transitions and weakening of long range ferroelectric order with increasing x are also confirmed from Raman spectra. The existence of ferroelectricity and the corresponding Curie temperature for all noncentrosymmetric composition were determined using differential thermal analysis. Small remnant magnetization of 0.067 emu/g is observed in ( BLNFO )<sub> x =0.07</sub> as a result of collapse of space modulated spin structure. For pure BFO dielectric anomaly was observed at 355 ° C corresponding to Neel temperature. Due to coexistence of long range ferroelectric order and canted antiferromagnetic orders in ( BLNFO )<sub> x =0.05 and 0.07</sub> the magnetoelectric effects were observed below Neel temperature at 302 and 294 ° C , respectively, near which magnetoelectric coupling is obvious.
Gd-doped BiFeO3 polycrystalline ceramics were synthesized by solid-state reaction method and their dielectric and magnetic properties were investigated. X-ray diffraction pattern showed that Bi1 − xGdxFeO3 (x = 0, 0.05 and 0.1) ceramics were rhombohedral. The Gd substitution has suppressed the usual impurity peaks present in the parent compound and we obtained single phase Bi0.9Gd0.1FeO3 ceramic. Gd substitution reduced the antiferromagnetic Néel temperature (TN) in Bi1 − xGdx FeO3. An anomaly in the dielectric constant(ε) and dielectric loss(tan (δ)) in the vicinity of the antiferromagnetic Néel temperature (TN) was observed. Ferroelectric and magnetic hysteresis loops measured at room temperature indicated the coexistence of ferroelectricity and magnetism. The room temperature magnetic hysteresis loops were not saturated, but the magnetic moment was found to increase with increase in Gd concentration.
Ferroelectric BiFeO3 is rhombohedral with lattice constants, aH=5·5876, cH=13·867 at room temperature. The space group is R3c with two formula units in the unit cell. The atomic positions have been determined employing both X-ray single crystal and neutron powder diffraction. The oxygen atomic positions could be determined only by neutron diffraction and are interpreted as a rotation of rigid octahedra around the trigonal axis by an angle ω=11°40' from the ideal perovskite positions.The X-ray intensities were visually estimated by the multiple film technique using a Weissenberg camera. The cation positions, refined by least-squares, are in good agreement with those determined from neutron powder diffraction analysis. The final results are given with a reliability factor R=0·02 for neutron powder data and R=0·09 for X-ray single crystal data. With respect to the ideal perovskite structure, the cations are shifted along the trigonal axis in accord with the observed dielectric properties.
A method is used to improve the electrical properties of BiFeO(3) thin films by modifying the Bi content in ceramic targets, where all thin films were prepared on SrRuO(3)/Pt/TiO(2)/SiO(2)/Si(100) substrates by radio frequency sputtering. The Bi content in the ceramic target strongly affects the electrical properties of BiFeO(3) thin films. BiFeO(3) thin films prepared by using the ceramic target of Bi/Fe ≈ 1.15 with a molar ratio demonstrate a low leakage current density and a low dielectric loss. Moreover, a larger remanent polarization of 2P(r) ≈ 167.6 μC/cm(2) is also demonstrated for the BiFeO(3) thin films prepared by using the ceramic target of Bi/Fe ≈ 1.15, together with an improved fatigue behavior. Therefore, it is an effective way to improve the electrical properties of bismuth ferrite thin films by modifying the Bi content in ceramic targets.
Migration kinetics of oxygen vacancies in BiFe(0.95)Mn(0.05)O(3) thin film were investigated by the temperature -dependent leakage current as well as the electric field and temperature-dependent impedance spectroscopy. The BiFe(0.95)Mn(0.05)O(3) is of an abnormal leakage behavior, and an Ohmic conduction is observed regardless of varied temperatures and electric fields. The temperature-dependent impedance spectroscopy under different resistance states is used to illuminate different leakage behavior between BiFe(0.95)Mn(0.05)O(3) and pure BiFeO(3). The impedance spectroscopy under a high resistance state shows that the first ionization of oxygen vacancies is responsible for the dielectric relaxation and electrical conduction of BiFe(0.95)Mn(0.05)O(3) in the whole temperature range of 294 to 474 K; the BiFeO(3) exhibits similar dielectric relaxation and electrical conduction behavior in the low-temperature range of 294-374 K, whereas the short-range motion of oxygen vacancies was involved in the high-temperature range of 374-474 K. The impedance spectroscopy under a low resistance state demonstrates that the dielectric relaxation and conduction mechanisms almost keep unchanged for BiFe(0.95)Mn(0.05)O(3), whereas the hopping electrons of Fe(2+)-V(O)(•)-Fe(3+) and Fe(2+)-Fe(3+) are responsible for its dielectric relaxation and conduction mechanism of BiFeO(3). Different impedance spectroscopy under low and high resistance states confirms that an abnormal leakage behavior of BiFe(0.95)Mn(0.05)O(3) is related to different migration kinetics of oxygen vacancies, obviously differing from that of BiFeO(3).
A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.
Dielectric and piezoelectric properties of Sb
- Z H Peng
- Chen Q Wu
Multiferroic properties of Bi
- C Sun
- Y P Wang
- Y Yang
Electrical control of antiferromagnetic domains in multiferroic BiFeO
- T Zhao
- A Scholl
- F Zavaliche
Leakage mechanisms in rare-earth
- H Y Qi
- Y J Qi
The development of BiFeO
- A Hussain
- X J Xu
- G L Yuan
Polarized raman scattering of multiferroic BiFeO
- K Singh
- H M Jang
- S Ryu