Ferroelectric Properties Of BiFeO3 Research Articles

Magnetic, Antiferroelectric-like Behavior and Resistance Switching Properties in BiFeO3-CaMnO3 Polycrystalline Thin Films

The effect of ferromagnetic CaMnO3 (CMO) addition to structural, magnetic, dielectric, and ferroelectric properties of BiFeO3 is presented. X-ray diffraction and Raman investigation allowed the identification of a single pseudocubic perovskite structure. The magnetic measurement showed that the prepared films exhibit a ferromagnetic behavior at a low temperature with both coercive field and remnant magnetization increased with increasing CMO content. However, a deterioration of magnetization was observed at room temperature. Ferroelectric study revealed an antiferroelectric-like behavior with a pinched P–E hysteresis loop for 5% CMO doping BFO, resulting in low remnant polarization and double hysteresis loops. Whereas, high remnant polarization and coercive field with a likely square hysteresis loop are obtained for 10% CMO addition. Furthermore, a bipolar resistive switching behavior with a threshold voltage of about 1.8 V is observed for high doped film that can be linked to the ferroelectric polarization switching.

Effects of solvents and Al doping on structure and physical properties of BiFeO3 thin films

In this study, BFO and BFAO thin films were prepared on fluorine-doped tin oxide (FTO) substrates via spin coating with two different acid solvents. One is nitric acid solution (solvent I), the other is a mixture of 2-methoxyethanol and glacial acetic acid (solvent II). The structure, morphology, elemental valence states, and ferroelectric properties of BiFeO3 (BFO) and BiFe0.96Al0.04O3 (BFAO) films were investigated. X-ray diffraction (XRD) results show that all the films are R3c structure and have no impurity phase. The SEM results show that the BFO thin film prepared by solvent II is more compact, uniform, and has low porosity. Raman spectra show that Al doping causes structural distortion. Al doping can solve the problem of porosity and increase the density of BFO thin film. Therefore, the density of BFAO-II sample is better. X-ray photoelectron spectroscopy (XPS) shows that the presence of Al reduces the oxygen vacancy content. This is beneficial to reduce the leakage current density and improve the ferroelectric properties. The leakage current density of BFAO-II sample is 10-3 A/cm2, and the double residual polarization value is 110.2 μC/cm2. Compared with BFO-II sample, it is significantly improved. In addition, Al doping can reduce the band gap of BFO films. This work will be a new idea for the further application of Al doped bismuth ferrite films.

Dielectric and tunable ferroelectric properties in BiFeO3–BiCoO3–BaTiO3 ternary compound

The ternary compound BiFeO3–BiCoO3–BaTiO3 (BFO–BCO–BT) was prepared using the solid-state reaction method. The dielectric studies display strong frequency-dependent anomaly in the vicinity of Curie temperature (TC) ≈ 350 °K and exhibit strong diffusive relaxor behavior with (γ ≈ 1.61). The dielectric measurements confirm stabilization in BFO–BT solid solution due to BCO addition. The P–E loops display strong ferroelectric behavior and frequency variation indicating major dominant domain wall movement on high dielectric constant in the BFO–BCO–BT ternary compound. The magnetic field variation in the P–E loop displays strong magnetoelectric coupling originating from interfacial polarization with maximum coupling coefficient of 115 mV/cm-Oe at field of 500 Oe. The temperature variation of P–E shows enhanced configurational entropy due to increase in activation energy, with the highest isothermal energy (ΔS) = 0.15 J/kg/K obtained for E = 15 kV/cm and T = 125 °C. These studies provide tunable ferroelectric properties of BFO–BCO–BT for exploration of promising applications such as refrigeration and magnetoelectricity.

Structural, Optical, Ferroelectric and Ferromagnetic Properties of Bi1−xGdxFeO3 Materials

Bi1−xGdxFeO3 (BGFO) (x = 0.00 ÷ 0.15) materials were prepared by a sol-gel method. The effect of Gd doping on the structural, ferromagnetic, and ferroelectric properties of BiFeO3 (BFO) were analyzed using x-ray diffraction, Raman scattering, energy-dispersive x-ray spectroscopy, ferroelectric hysteresis loop and magnetic hysteresis loop measurements. All samples showed a rhombohedral structure of the perovskite type. The a and c lattice parameters decreased with Gd content, obeying Vegard’s law, from 5.583 to 5.511 A, and from 13.869 A to 13.741 A, respectively. The optical band gap (Eg) also decreased with Gd content, from 2.02 to 1.60 eV at x = 0.00 to x = 0.15, respectively. The ferroelectric and ferromagnetic properties of the BGFO materials were enhanced compared with those of the pure BFO material. Maximum saturation polarization (Ps) and saturation magnetization (Ms) values of 6.88 μC/cm2 and 0.386 emu/g were obtained. We found that the optimum Gd doping content to enhance multiferroic properties of BFO material is in range from x = 0.10 to x = 0.125. The origin of ferromagnetic and ferroelectric properties of BGFO materials were also discussed.

Magnetism and ferroelectricity in BiFeO3 doped with Ga at Fe sites

Theoretical calculations were performed to investigate the effect of isovalent substitution of Fe with Ga on the magnetic and ferroelectric properties in BiFeO3 doped with 16.6% and 8.3% Ga. Such substitution will break the G-type anti-ferromagnetic order and enhance the magnetism of BiFeO3 by forming a stable ferrimagnetic order. The doped system maintains robust spontaneous polarization that is sufficiently large for practical applications at room temperature. The findings explain experimentally observed magnetism. The coexistence of magnetism and ferroelectricity in the doped BiFeO3 render it a candidate material for application to information storage and spintronics devices.

First principles study of phase stability and ferroelectric properties of Bi1−xRExFeO3 (RE = Y, La) solid solutions

The ferroelectric properties and phase stability of Bi1−xYxFeO3 and Bi1−xLaxFeO3 solid solutions have been investigated from x = 0 to 1 using density functional theory. It was found that BiFeO3 undergoes a phase transition from rhombohedral (space group R3c) to orthorhombic structure at x = 0.15 and 0.32 for Y and La, respectively. Up to x = 0.63 for both systems the polar (space group Pn21a) and non-polar (space group Pnma) orthorhombic phases coexist. For x > 0.63 only the non-polar structure is stable. The effect of hydrostatic pressure on the structural and ferroelectric properties of BiFeO3 has been also investigated. The hydrostatic pressure has the same effect on BiFeO3 as Y substitution. The enhancement of the ferroelectric properties of Bi1−xYxFeO3 for low x arises from the large off-centering of Y-O atoms, which are caused by the small radius of Y atoms and the mixing of 4d-5p orbitals of Y followed by the hybridization of Y-4d and O-2p orbitals. The calculated ferroelectric polarization for the hypothetical rhombohedral YFeO3 structure is 72 μC/cm2.

Multiferroic properties and frequency dependent coercive field in BiFeO3-LaMn0.5Co0.5O3 thin films

The effect of LaMn0.5Co0.5O3 (LMCO) adding on structural, magnetic, dielectric, and ferroelectric properties of BiFeO3 is presented. X ray diffraction and Raman investigation allowed the identification of a structural transition and permitted to shed more light on the influence of LCMO addition. By varying LMCO concentration, highest remnant polarization (Pr) and coercive field (Ec) with a likely square hysteresis loop are obtained for 10mol% addition. With increasing concentration to 20mol%, a change of P-E shape, a decrease of both Pr and Ec, and a frequency dependence of Ec are observed. The results are approached with both Ishibashi-Orihara and Du-Chen models.

First-principles study of structural, electronic, and ferroelectric properties of rare-earth-doped BiFeO3

We study the effect of the light rare earth ions La, Ce, Pr, and Nd on electronic structure, structural properties, magnetic states, and ferroelectric properties of BiFeO3 using density functional theory within GGA + U method. The supercell of 40 atoms is considered for four phases: R3c, Pnma, Pn2 1 a, Pbam. We show that, among potential phases, the R3c-G structure of BiFeO3 where one Bi substituted by one of the studied rare-earth elements has the minimal total energy. We predict the values of spontaneous electric polarization in RE-doped BiFeO3 to be above 80 μC cm−2 and a non-zero values of the magnetic moments in RE-doped BiFeO3 for R3c-G phase of the studied systems. Upon introduction of a rare-earth ion to a Bi site, the total magnetic moments are 0 μB, 0.99, 1.99, and 2.98 μB f.u.−1 for La, Ce, Pr, and Nd substitution, respectively. The results of total energy calculations show that the Pn2 1 a and Pnma phases of the BiFeO3 with Ce or Pr substitution of Bi occur on the same energy scale. This close energy scale suggests a coexistence of these phases beyond T = 0 K or under other conditions.

Enhancement of multiferroic in BiFeO3 by Co doping

The effects of Co doping on the structure, magnetic and the ferroelectric properties of BiFeO3 were predicted through ab initio calculation based on density functional theory (DFT), in conjunction with experimental verification. The calculated structure of BiFe0.83Co0.17O3 belongs to rhombohedral R3c, which matched well with that obtained experimentally. The calculations revealed that the magnetic properties of BiFeO3 can be enhanced significantly by Co-doping at B-site, and the net magnetic moment of unit cell was evaluated to be 0.93μB for BiFe0.83Co0.17O3. The enhanced magnetic moments should be ascribed to the superexchange interaction of Fe3+–O2−–Co3+. By using the Berry-phase method, the ferroelectric polarization was calculated to be 108μC/cm2, which is larger than that in pure BiFeO3 (93μC/cm2). The observed weak ferromagnetism and ferroelectric nature at room temperature indicates the multiferroic nature of BiFe0.8Co0.2O3 sample, whose magnetoelectric coupling was verified to be 4.82% in BiFe0.8Co0.2O3 estimated by the change of dielectric constant with external magnetic field. These results may shed some light on the controlling and tuning of the multiferroic properties of BiFeO3.

Synthesis, electrical and magnetic characteristics of Nd-modified BiFeO3

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.

The electronic, optical and ferroelectric properties of BiFeO3 during polarization reversal: A first principle study

Rhombohedral BiFeO3 which has a large spontaneous polarization is a candidate material for ferroelectric random access memory (FeRAM). And the polarization reversal is the key factor for the application of FeRAM. Here, the electronic, linear and nonlinear optical properties, structure and its stability of BiFeO3 during the continuous polarization reversal from reference cubic phase to ferroelectric R3c phase were systematically investigated by LSDA+U (local spin density approximation plus Hubbard U) and DFPT (density functional perturbation theory) method. We proposed that the nonlinear optical second order coefficients could be indicators to check the polarization reversal of BiFeO3 and our result showed that the coefficient reach its maximum between 20% distortion and 40% distortion during the half path of the reversal. The relationship between the nonlinear optical second order coefficient and the Bader charge was also compared and we found the coefficient is also dependent on the Bader charge. In addition, the linear optical absorption coefficient was calculated; the obvious change in absorption peaks was observed during the transition. By comparing the crystal orbital of the reference cubic phase and distorted R3c phase we found that the hybridized Bi 6s and O 2p is the main reason that causes the structure distortion. The local phonon density of states proves that the Bi and O interaction is the origin of the instability of cubic phase BiFeO3. The factor group analysis showed the change of Raman and IR modes during the transition.

Effect of process condition on the ferroelectric properties in BiFeO3-(Bi,K)TiO3 ceramics

The Effects of the sintering temperature on the physical and the ferroelectric properties were investigated in 0.6BiFeO3-0.4(Bi0.5K0.5)TiO3 (0.6BF-0.4BKT) ceramics. 0.6BF-0.4BKT ceramics were fabricated by using a solid-state reaction and the calcined powders were pulverized by ball milling (BM) or attrition milling (AM). A single perovskite phase with a pseudo-cubic diffraction pattern was observed in the samples sintered at 950~1,050 °C. The AM ceramic sintered at 950 °C showed a density of about 93% the theoretical density while the BM ceramic sintered at temperature above 1,000 °C displayed a density larger than 90% the theoretical value. The BF-BKT ceramic had dielectric properties with stable frequency characteristics of and a well-saturated P-E hysteresis when sintered at temperatures higher than 1,000 °C in the BM sample and higher than 950 °C in the AM sample. Dielectric relaxations around 200 Hz and leaky P-E loops were observed in BF-BKT ceramics sintered at lower temperatures.

Enhancement of magnetic and ferroelectric properties of BiFeO3 by Er and transition element (Mn, Co) co-doping

BiFeO3(BFO), Bi0.8Er0.2FeO3 (BEFO), Bi0.8Er0.2Fe0.9Mn0.1O3 (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.

Compositional dependence of dielectric and ferroelectric properties in BiFeO3–BaTiO3 solid solutions

Polycrystalline (1−x)BiFeO3–xBaTiO3 (0.11≤x≤0.5) ceramics have been prepared by the solid-state reaction method to investigate their phase structure, dielectric, ferroelectric, and field-induced strain behaviors. The phase was found to change from rhombohedral in BiFeO3-rich compositions to pseudocubic at a BaTiO3 content of x=0.33. The room-temperature dielectric permittivity increased with increasing BaTiO3 content regardless of phase structure, except for a small dielectric permittivity peak additionally observed at x=0.33. The (1−x)BiFeO3–xBaTiO3 solid solutions displayed a maximum in permittivity at temperatures (Tm) above 300°C in the compositional range of 0.2≤x≤0.5. The frequency dependence of high-temperature dielectric properties suggests that BiFeO3–BaTiO3 is a relaxor ferroelectric. Normal ferroelectric loops and large electric field-induced strains were observed for the BiFeO3–BaTiO3 ceramics. The BiFeO3–BaTiO3 shows a promising candidate for high temperature ferroelectric applications.

High quality multiferroic BiFeO3 films prepared by pulsed laser deposition on glass substrates at reduced temperatures

Phase structure and ferroelectric properties of BiFeO3 (BFO) films grown on Pt(111) buffered glass substrates at various growth temperatures and oxygen pressures have been studied. The optimization of the 20-nm-thick Pt(111) bottom electrode enables BFO films to form perovskite single phase structure at reduced temperatures between 400–500 °C. Microstructure of fine grains and smooth surface is obtained, which is favorable for applications. Multiferroic properties including 2Pr of 15.1–124 μC/cm2, Ec of 351–680 kV/cm, and Ms of 5–8 emu/cm3 are achieved within the oxygen pressure range of 10–75 mTorr. The optimized ferroelectric properties are comparable to the reported values of BFO samples using Si and MgO single crystal substrates. The results of this study may broaden the possibility of the use of BFO films.

Structural and ferroelectric properties of chemical solution deposited (Nd, Cu) co-doped BiFeO3 thin film

Effects of (Nd, Cu) co-doping on the structural, electrical and ferroelectric properties of BiFeO 3 polycrystalline thin film have been studied. Pure and co-doped thin films were prepared on Pt(111)/Ti/SiO 2 /Si(100) substrates by using a chemical solution deposition method. Significant improvements in the electrical and the ferroelectric properties were observed for the co-doped thin film. The remnant polarization (2 P r ) and the coercive field (2 E c ) of the co-doped thin film were 106 μC/cm 2 and 1032 kV/cm at an applied electric field of 1000 kV/cm, respectively. The improved properties of the co-doped thin film could be attributed to stabilized perovskite structures, reduced oxygen vacancies and modified microstructures.

Effect of pore size on ferroelectric properties of multiferroic BiFeO 3 films prepared on porous silicon

The ferroelectric properties of BiFeO 3 (BFO) films spray deposited on porous silicon have been studied. The analysis of XRD and FESEM investigations show that the crystalline strain in the BFO films increases with pore size. The BFO films on porous silicon substrate showed improvement in ferroelectric fatigue behavior, remanent polarization and ferroelectric switching time. A maximum memory window of 5.54 V at 1 MHz and a large remanent polarization ( P r ) of 13.1 μC/cm 2 have been obtained at room temperature. The improvement in the ferroelectric properties of these films has been correlated to the crystalline strain.

Ferroelectric Properties and Raman Scattering Spectra of Bi<sub>1-x</sub>Gd<sub>x</sub>FeO<sub>3</sub> Ceramics

Multiferroic ceramic samples of Bi1-xGdxFeO3(x= 0, 0.05, 0.1 and 0.15) have been prepared by the rapid liquid phase sintering technique. The effect of Gd substitution on ferroelectric properties of Bi1-xGdxFeO3ceramics has been investigated. The results of x-ray diffraction (XRD) patterns show that the single-phase BiFeO3sample has a rhombohedral structure and Gd3+substitution for Bi3+has not affected the perovskite structure. Experimental results suggest that Gd3+substitution for Bi3+has markedly affected the Raman scattering spectra, and the ferroelectric properties of BiFeO3are improved by Gd3+doping. Whenx= 0.15, saturated ferroelectric hysteresis loop is observed at room temperature with the maximal 2Pr = 1.62 μC/cm2.

Effect of oxygen content during sputtering on the electrical properties of bismuth ferrite thin films

AbstractThe effect of oxygen content during sputtering on the leakage mechanism and the ferroelectric properties of BiFeO3 with a sintering aid of CuO (CuO‐BFO) was investigated, where all thin films with (100) orientation were grown on SrRuO3/LaAlO3(100) substrates by radio frequency sputtering with an oxygen content of 0–40%. The ferroelectric properties in CuO‐BFO are tailored by changing the oxygen content during sputtering, indicating a small growth window. The Schottky emission dominates the leakage behavior regardless of oxygen content. The thin film with an oxygen content of ∼20% during sputtering has a higher remanent polarization of 2Pr ∼ 184.7 μC/cm2, due to its lower leakage current density and an improved phase purity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of bottom electrode and resistive layer on the dielectric and ferroelectric properties of sol–gel derived BiFeO 3 thin films

The effect of RuO 2 electrodes and La 2O 3 resistive layer were analyzed on the electrical and ferroelectric properties of BiFeO 3 (BFO) films deposited on Pt/Ti/SiO 2/Si substrates using a chemical solution method. XRD patterns revealed that BFO films with RuO 2 and La 2O 3 layers appeared preferred (0 1 2) orientation. The surfaces of the BFO films with the La 2O 3 layer appeared uniform with dense grain clusters. The utilization of La 2O 3 and RuO 2 layers reduced the diffusion of Ti and Si into the BFO films. Leakage mechanism of the films found specific to applied electric field. At lower applied electric field space-charge-limited current found dominant and at an applied electric field >80 kV/cm surface-limited conduction (Fowler-Nordheim type) found the dominant. The BFO films grown with La 2O 3 resistive layers also contained lower concentrations of Fe 2+, which resulted enhancement of dielectric constant ( ɛ), remnant polarization and lower leakage current. Among the studied films RuO 2/BFO/La 2O 3/BFO/RuO 2/Pt/Ti/SiO 2/Si exhibited the best with value of relative permittivity ( ɛ r) 208.8, leakage current 5.503 × 10 −6 kV/cm 2, remnant polarization (2 P r) 3.80 μC/cm 2, and coercive field (2 E c) 78.22 kV/cm.