Pure BiFeO3 Thin Films Research Articles

Study of A-site and B-site Doping on Multiferroic Properties of BFO Thin Films

The 12% Cerium (Ce) and 10% Manganese (Mn) were doped at A and B sites respectively in BiFeO3 (BFO) thin films along with incorporation of 5% excess Bi. Pure and undoped BFO thin film capacitors are fabricated on indium tin oxide (ITO) coated corning glass and silicon substrate by chemical solution deposition (CSD) method. Film becomes preferred oriented along (110) directions with introduction of Mn and Ce in the host BFO lattice. Leakage current density is reduced by about 4 orders from (4.59 × 10−3 A/cm2) to about 2.91 × 10−7 A/cm2 at 100 KV/cm field after 12% Ce doping in BFO (BCFO) thin film. Enhanced ferroelectric response with saturated P-E loop is observed for BCFO thin film in compare to that obtained for 10% Mn doped BFO (BFMO) thin film. Improved capacitance-voltage characteristics with good butterfly loop is obtained for Bi0.88Ce0.12FeO3 thin film, indicating an increased degree of ferroelectricity. However, enhanced M-H loop with well saturation magnetization (Ms ∼ 19.65 emu/g) is observed for BFMO thin films while wasp waist loops (pinched) are observed for BCFO thin films with slightly degraded ferromagnetic properties.

Effect of Substrate Temperature on Electrical Properties of BiFeO3 Thin Films Prepared by Sputtering Method

Pure BiFeO3 thin films with different substrate temperatures (600°C and 650°C) were prepared using sputtering method on Pt /Ti /SiO2 /Si(111) substrates. X-ray diffraction analysis reveals that no second phases existed and the structure changed with different substrate temperatures. According to the SEM results, the surface configuration of the BFO film was improved when sputtered at a lower temperature. The P-E curves show a well-shaped hysteresis loop for both BFO films. The spontaneous polarization of two films deposited at 600°C and 650°C is 56 μc/cm2 and 72 μc/cm2 respectively when measured at room temperature.

Structural and electrical studies on rare-earth-element-substituted (Bi0.9 A 0.1)(Fe0.975Ti0.025)O3+δ (A = Nd, Gd, Eu) thin films

Pure BiFeO3 (BFO) and rare-earth-metal-ion co-substituted (Bi0.9A0.1)(Fe0.975Ti0.025)O3+δ (A = Nd, Gd and Eu, denoted by BNdFTi, BGdFTi, and BEuFTi, respectively) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates via a chemical solution deposition method. A perovskite-based-distorted rhombohedral structure for the thin films were confirmed by using an X-ray diffraction and a Raman scattering analysis. Significant improvements in the electrical and the ferroelectric properties were observed for the co-substituted thin films. For the BGdFTi and the BEuFTi thin films, the measured leakage current densities were 8.17 × 10−5 A/cm2 and 4.96 × 10−5 A/cm2 at an applied electric field of 100 kV/cm, respectively, which are approximately three orders of magnitude lower than that of the pure BFO thin film. Furthermore, a large remnant polarization (2Pr) of 99.0 µC/cm2 at 1470 kV/cm was measured for the BGdFTi thin film.

Electrical properties of chemical solution deposited (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb) thin films

Pure BiFeO3 (BFO) and (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb, denoted by BHFCu and BTFCu) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The BHFCu and BTFCu thin films showed improved electrical and ferroelectric properties compared to pure BFO thin film. Among them, the BTFCu thin film exhibited large remnant polarization (2Pr), low coercive field (2Ec) and reduced leakage current density, which are 89.15C/cm2 and 345kV/cm at 1000kV/cm and 5.38×10−5A/cm2 at 100kV/cm, respectively.

Preparation and properties of rare earth (Eu, Tb, Ho) and transition metal (Co) co-doped BiFeO3 thin films

Ferroelectric (Bi0.9 RE 0.1)(Fe0.975Co0.025)O3-δ (RE = Eu, Tb and Ho) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates via a chemical solution deposition method. All thin films were crystallized in a distorted rhombohedral perovskite structure confirmed by using an X-ray diffraction and a Raman scattering analyses. Compared to the pure BiFeO3 thin film, improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 4.28 × 10−5 A/cm2 was measured at an applied electric field of 100 kV/cm for the (Bi0.9Ho0.1)(Fe0.975Co0.025)O3-δ thin film. This value is approximately three orders lower than that of the pure BFO thin film. Furthermore, a large remnant polarization (2P r) of 60.2 μC/cm2 and a low coercive field (2E c ) of 561 kV/cm at 980 kV/cm were observed from the (Bi0.9Ho0.1)(Fe0.975Co0.025)O3-δ thin film.

Controllability study on the preparation of pure phase BiFeO3 thin films by liquid phase self-assembled method

Pure phase BiFeO3 (BFO) thin films were prepared on the ITO/glass substrates covered with functionalized OTS self-assembled monolayers (SAMs) by controllable liquid phase self-assembled method. The hydrophobic surface of OTS-SAMs was changed into hydrophilic surface after UV irradiation, which is helpful to make BFO precursor solutions fully wet the substrate surface. A dense film was formed only on the hydrophilic silnaol group regions, which shows the selectively deposition of BFO precursors. Changing the pH value of BFO precursor solutions will affect the phase purity. The pure phase BFO thin films can be obtained under various pH values, which indicates that the liquid phase self-assembled method is controllable. All pure phase BFO films are dense, smooth, well-grown polycrystalline films, but the size of grains increased gradually along with the increase of pH values. The micropattern of BiFeO3 film has clear edges. The possible growth mechanism of BFO thin films was discussed.

Preparation and Properties of Multiferroic La-Doped BiFeO<sub>3</sub> Thin Film

Multiferroic La-doped Bi1-xLaxFeO3 thin films were prepared on conductive indium tin oxide (ITO)/glass substrates through a simple sol-gel process. The crystal structure of La-doped Bi1-xLaxFeO3 thin films annealed at different temperature was determined to be rhombohedral of R3m space and free of secondary phases. The grain size of La-doped BiFeO3 thin films tends to become larger and the grain boundary is gradually ambiguous compared to pure BiFeO3. The double remanent polarization 2Pr of Bi0.9La0.1FeO3 thin film annealed at 500°C is 6.66 µC/cm2, which is slightly improved than that of pure BiFeO3 thin film. With the increase of La-doping levels, the dielectric constant is increased and the dielectric loss is obviously decreased.

Optical properties of BiCrxFe1−xO3 films grown by sol-gel method

The BiCrxFe1−xO3 thin films were fabricated on Si substrate by sol-gel method with x range from 0 to 0.05. X-ray diffraction analysis shows that both pure BiFeO3 thin film and Cr-doped BiFeO3 thin films have rhombohedral structure with space group R3c. Moreover, the influence of different values of x on the extinction coefficient and refractive index were investigated in order to exploit their possible application in optoelectronic devices. The optical constants of the Cr-doped BiFeO3 thin films in the wavelength range 500–1100 nm were obtained by spectroscopic ellipsometry, and the band-gap energy of BiCr0.03Fe0.97O3 was found to be 2.40 ±0.02 eV, and that of BiCr0.05Fe0.95O3 was 2.30 ±0.02 eV.

Anomalous Enhancement in Magnetization of BiFeO3 – CoFe2O4 Heterostructure Multilayer Thin Films Deposited on SrTiO3 with Different Orientation

The magnetic properties of BiFeO3(BFO) – CoFe2O4(CFO) heterostructure thin films, grown on (100), (110) and (111) SrTiO3 (STO) substrates by employing pulsed laser deposition (PLD) method, have been studied. The XRD patterns of BFO-CFO multilayer thin films compared with the pure CFO and BFO thin films grown using under identical conditions evidenced that all peaks present correspond to CFO and BFO structure in two separate phases. Micro-Raman spectra analysis also reveals the presence of BFO and CFO in two separate phases in the heterostructures thin films. The anomalous enhancement in magnetization has been observed for BFO−CFO multilayer thin films, relative to pure BFO thin films in all three different orientations. The saturation magnetization for (100), (111) and (110) oriented BFO-CFO thin films are 44, 62 and 80 emu/cc suggesting that (110) is most preferable direction to achieve the magneto electric (ME) coupling effect.

Structural, electrical, and magnetic properties of multiferroic Bi1−xLaxFe1−yCoyO3 thin films

Bi 1 − x La x Fe 1 − y Co y O 3 (x=0, 0.1; y=0, 0.05, 0.1) polycrystalline thin films were fabricated on Pt/Ti/SiO2/Si(111) substrates via chemical solution deposition method. X-ray diffraction analysis revealed a phase transition in La–Co codoped BiFeO3 (BFO) thin films. Saturated ferroelectric hysteresis characteristics in La–Co codoped BFO thin films were observed, and the conduction behavior of Bi1−xLaxFe1−yCoyO3 thin films investigated to understand the leakage mechanisms. In the low applied field, the conduction mechanism of Bi1−xLaxFe1−yCoyO3 thin films was found to be dominantly Ohmic. In the high applied field, the conduction mechanisms of pure and La doped BFO thin films were found to be trap-filled-limited and Poole–Frenkel emission, and that of Co doped and La–Co codoped BFO thin films Schottky emission. The dielectric constant of Bi0.9La0.1Fe0.9Co0.1O3 thin film, in the frequency range of 1 to 2000 kHz, was nearly two times higher than that of pure BFO thin film while the dielectric loss tan δ was small at values below 0.07. It was found that saturation magnetization in BFO thin films could be enhanced by La or Co doping, and obviously by La–Co codoping too.

Evolution of phase purity and texture on annealing of BiFeO3 thin film prepared by sol-gel technique

We report preparation of phase pure BiFeO3 thin films on glass, ITO and Si(100) substrates through chemical route using spin coating technique. Sol-gel process was adopted to prepare the films using bismuth nitrate and iron nitrate as precursors. X-Ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO3 evolved on annealing the films at 500°C, but with Bi2Fe4O9 and Bi24Fe2O39 as impurity phases. Increasing the annealing temperature to 550°C caused a drastic reduction of the impurity phases and at 600°C, the films were phase-pure BiFeO3. Micro Raman spectra showed features consistent with the reported characteristic peaks of BiFeO3 crystalline phase for films annealed at 500 and 550°C. Crystallite size obtained from X-ray diffraction line width analysis are within 30 to 40 nm. Atomic force microscopy (AFM) however showed grain size of ∼192 nm, indicating polycrystalline nature of the grains.

Effect of Tb doping on electric and magnetic behavior of BiFeO3 thin films

The effect of Tb doping on crystal structure and electric and magnetic behavior of BiFeO3 thin films prepared via a solution processing on (111)Pt∕Ti∕SiO2∕Si substrates was studied. The substitution of Bi ions by a small amount of Tb ions could stabilize the valence of Fe3+ in BiFeO3 thin films, and as indicated by transmission electron microscope images and largely reduced leakage current in comparison with pure BiFeO3 thin films, the quality of the films was improved by Tb doping. Electric and magnetic behavior of Tb-doped BiFeO3 films was investigated with employing La-doped BiFeO3 films as comparison. Large enhancement in both remnant and saturation polarization and the polarization switching were observed in Tb-doped BiFeO3 films, while the inhomogeneous spin-modulated magnetic structure of BiFeO3 was not modified through Tb substitution but by La substitution.

Ferroelectricity of BiFeO<sub>3</sub> Thin Films by Pulsed Laser Deposition and Effect of Atmosphere

In this study, BiFeO3 (BFO) epitaxial film was deposited on SrRuO3 (100)/SrTiO3 (100) substrates using pulsed laser deposition (PLD). Phase pure BFO thin film was obtained. Introducing a mask between the target and substrate in PLD improved the surface roughness from 47.8 nm (RMS, without mask) to 7.7 nm (RMS, with mask). The composition and electrical properties of BFO thin film were assessed after annealing for 1 h in Ar, N2, or O2 atmosphere at 600°C. The P-E hysteresis properties improved only in the O2 atmosphere. After annealing under O2 atmosphere, the leakage current decreased from 6.1 × 10-2 A/cm to 2.9 × 10-2 A/cm at 200 kV/cm, as in the other annealing atmospheres, but 2Pr increased from 35 BC/cm2 to 50 BC/cm2.