Bismuth Ferrite Films Research Articles

Valence-driven electrical behavior of manganese-modified bismuth ferrite thin films

BiFe0.95R0.05O3 (Mn2+, Mn3+, and Mn4+) thin films with (110) orientation were fabricated on SrRuO3/Pt/TiO2/SiO2/Si(100) substrates via rf sputtering. With the increasing valence of Mn in BiFe0.95R0.05O3, the concentration of Fe2+ increases, whereas the concentration of oxygen vacancies decreases. The electrical properties of BiFe0.95R0.05O3 are correlated with the valence of Mn. Their leakage current density is dependent on the concentration of oxygen vacancies caused by different valences of Mn. Their P-E loops become better with the increasing valence of Mn owing to a lower leakage current density in high electric field regions, and a large remanent polarization of 2Pr ∼ 145.2 μC/cm2 is obtained for the Mn4+-doped film. For the Mn2+-doped bismuth ferrite film, the space-charge-limited conduction and Schottky barrier dominate its leakage behavior under a negative electric field, the Ohmic conduction and Schottky barrier are involved in the leakage behavior under a positive electric field, and the interface-limited Fowler–Nordheim tunneling is their dominant mechanism in a high electric field region. In contrast, an Ohmic conduction dominates the leakage behavior of Mn3+- and Mn4+-doped films regardless of negative and positive directions or measurement temperatures.

Investigation of nanodomain pattern and piezoelectric behavior of mixed phases in epitaxial BiFeO 3 films

Abstract Mixed phases of rhombohedral and tetragonal ferroelectric variants have been recently observed to coexist through epitaxial constraints in bismuth ferrite films. They form stripe-like domain patterns with orientations closely parallel to the substrate edges and exhibit unusually large piezoelectric response in the stripe areas. Here a model is developed for explaining the peculiar domain orientations as well as the enhancement of piezoelectricity in the mixed phase. The former is determined by the relative magnitudes of elastic and depolarization energy, whereas the latter is ascribed to the strain-driven softening in dielectric stiffness. The predictions show the similar trend as those observed in recent experiments.

Domain pattern and piezoelectric response across polymorphic phase transition in strained bismuth ferrite films

A model is developed to investigate the domain pattern and piezoelectric response across the polymorphic phase transition in strained epitaxial bismuth ferrite films. The orientations of stripelike pattern of the mixed rhombohedral and tetragonal phases are predicted as the consequence of competition between elastic and depolarization energies. The abnormally large piezoelectric response is attributed to the strain-driven softening in dielectric stiffness. The results are in good agreement with recent experimental observations and provide a guidance for developing similar strain-driven polymorphic phase transition in other related perovskite material systems.

Thin ferroelectric Nd-doped BiFeO3 films with orthorhombic structure

X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on MgO substrates reveal their orthorhombic symmetry Fmm2 (a = 7.914 A, b = 7.913 A, and c = 7.937 A).

Structure and lattice dynamics of heterostructures based on bismuth ferrite and barium strontium titanate on magnesium oxide substrates

Bismuth ferrite films doped with neodymium on MgO single-crystal substrates with an epitaxial barium strontium titanate thin (1–2 nm) sublayer have been prepared by rf sputtering of ceramic targets at an elevated oxygen partial pressure and at temperatures below the ferroelectric and magnetic transition temperatures. It has been revealed using X-ray diffraction and Raman scattering spectroscopy that, in these bismuth ferrite films, a new phase (not observed in bulk samples) is formed. The symmetry of this phase is monoclinic, the unit cell contains two formula units, and the spontaneous polarization vector deviates from the [111]cub direction and can have different components along the x, y, and z axes.

Optical characterisation of BiFeO3 epitaxial thin films grown by pulsed‐laser deposition

AbstractEpitaxial thin films of bismuth ferrite, BiFeO3, were deposited by pulsed laser deposition (PLD) on SrTiO3 (100), Nb‐doped SrTiO3 (100) and DyScO3 (110) substrates. Ellipsometric spectra are obtained in the energy range 0.73‐9.5 eV by combining Variable Angle Spectroscopic Ellipsometry (VASE) and vacuum ultraviolet (VUV) ellipsometry with synchrotron radiation. The optical constants of BiFeO3 films were determined by analysing the ellipsometric spectra with a model that describes the optical response of a system consisting of air, film and substrate. The shift towards higher energies of the refractive index and extinction coefficient of the film deposited onto Nb‐doped SrTiO3 as compared with that deposited onto DyScO3 was attributed to a more compressive in‐plane epitaxial strain. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Unraveling Deterministic Mesoscopic Polarization Switching Mechanisms: Spatially Resolved Studies of a Tilt Grain Boundary in Bismuth Ferrite

AbstractThe deterministic mesoscopic mechanism of ferroelectric domain nucleation is probed at a single atomically‐defined model defect: an artificially fabricated bicrystal grain boundary (GB) in an epitaxial bismuth ferrite film. Switching spectroscopy piezoresponse force microscopy (SS‐PFM) is used to map the variation of local hysteresis loops at the GB and in its immediate vicinity. It is found that the the influence of the GB on nucleation results in a slight shift of the negative nucleation bias to larger voltages. The mesoscopic mechanisms of domain nucleation in the bulk and at the GB are studied in detail using phase‐field modeling, elucidating the complex mechanisms governed by the interplay between ferroelectric and ferroelastic wall energies, depolarization fields, and interface charge. The combination of phase‐field modeling and SS‐PFM allows quantitative analysis of the mesoscopic mechanisms for polarization switching, and hence suggests a route for unraveling the mechanisms of polarization switching at a single defect level and ultimately optimizing materials properties through microstructure engineering.

Investigation of ferroelectric properties of bismuth ferrite films by the second optical harmonic generation technique

The specific features of the ferroelectric polarization switching in bismuth ferrite thin films doped with neodymium ions are investigated by the optical second harmonic generation technique. The structure and nonlinear optical properties of the samples prepared are studied in the course of ferroelectric polarization switching in planar geometry over wide ranges of film thicknesses and electric field frequencies.

Spatial distributions of the intensity of optical emission lines studied during bismuth ferrite film deposition in high-frequency discharge plasma

We have studied spatial distributions of the intensity of optical emission lines in plasma of the RF discharge in oxygen during the deposition of bismuth ferrite (BiFeO3) films. The intensities of characteristic emission lines in the visible, near-UV and near-IR spectral ranges have been measured as functions of the distance from the probed plasma layer to the target. The intensity profiles of the emission lines of oxygen ions, oxygen atoms, and iron atoms exhibit different behavior. Differences in the spatial distributions of intensity have been also observed for the two characteristic emission lines (at 613.7 and 688.6 nm) of iron.

Characterization of laser-transferred bismuth ferrite lead titanate ferroelectric thick films

Thick films of 0.7BiFeO3–0.3PbTiO3 have been deposited on sapphire substrates by tape casting and sintering at 1000°C. Films 20μm in thickness were released from the fabrication substrate using KrF pulsed laser radiation, and epoxy bonded to platinized silicon substrates in order to demonstrate the low-temperature integration possibilities of xBiFeO3–(1−x)PbTiO3 films. Despite structural changes at the laser-released film interface, strain-electric field loops are typical of a ferroelectric, showing an ultimate strain of 0.09%. X-ray diffraction and scanning electron microscopy observations suggest that interfacial melting and migration of Bi2O3 is involved in the lift-off process.

Growth and characterization of tetragonal bismuth ferrite–lead titanate thin films

Thin films of tetragonal bismuth ferrite–lead titanate (1−x)BiFeO3–xPbTiO3 with x=0.9–0.7 were prepared by pulsed laser deposition (PLD). The films exhibit a dense columnar grain growth. XRD analysis reveals that the films have a perovskite structure and exhibit a preferred (111) texture. The film microstructure was studied using SEM. The ferroelectric properties of the films are discussed in the light of polarization-field hysteresis behaviour and impedance spectroscopy. The remanent polarization values ranged between 2Pr∼45 and ∼60μCcm−2 at a field amplitude of 500kVcm−1 and −10°C, while the dielectric permittivity of the films ranged between 375 and 1096 at a frequency of 2kHz.

The Influence of Acceptor Doping on the Structure and Electrical Properties of Sol-Gel Derived BiFeO3 Thin Films

Bismuth Ferrite (BFO) films doped with strontium resulting in a nominal composition of Bi 1−x Sr x Fe 1 O 3 (x = 0–0.15) were fabricated using a sol-gel process on Pt/TiO 2 /SiO 2 /Si substrates by rapid thermal annealed in air at 700°C. A decrease in the grain size (from 1 μm to 90 nm) with increasing Sr concentration from 0 to 15% was observed, coupled with the degradation of columnar grain growth. X-ray diffraction and raman scattering showed evidence of a structural change from rhombohedral to pseudocubic with increasing Sr concentration. Leakage measurements revealed that films with Sr acceptor doping showed increased leakage compared to pure BFO, however the film leakage did not increase with increasing acceptor concentration due to microstructural modifications.

Strain-induced effects in phase transitions in thin films of multiferroic BiFeO3 probed by optical second-harmonic generation

Optical second-harmonic generation (SHG) was applied to study the ferroelectric and magnetic properties of strained epitaxial BiFeO3 films deposited on (001) SrTiO3 substrates by metal organic chemical vapor deposition. A strong interplay between the ferroelectric and magnetic subsystems of bismuth ferrite films results in the pronounced temperature dependence of the SHG intensity. The decrease of the critical temperature of the ferroelectric phase transition and the expansion of the nonlinear transient area near Néel temperature were observed for the strained BiFeO3 films.

Studies on Leakage Mechanisms and Electrical Properties of Doped BiFeO[sub 3] Films

The effects of La and/or Ti doping on crystallization, surface morphology, and electric properties of bismuth ferrite (BFO) films were investigated. All films consisted of single perovskite phase without a second phase. Ti-doping (BFT) does not have significant effects on leakage and polarization-electric field (P-E) loop. La-doping (BLF) improves leakage but degrades ferroelectric properties. In contrast, (La, Ti)-co-doping (BLFT) not only improves the leakage, but also decreases the relaxation gap of P-E loop. The determined leakage mechanisms of BFO, BFT, BLF, and BLFT are space charge-limited conduction (SCLC) with deep traps, grain boundary-limited conduction (GBLC), Poole-Frenkel, and SCLC with both shallow and deep traps, respectively.