Optical Properties Of BiFeO3 Research Articles

All oxide lead-free bismuth ferrite perovskite absorber based FTO/ZnO/BiFeO3/Au solar cell with efficiency ∼ 12%: First principle material and macroscopic device simulation studies

We report the photovoltaic response of bismuth ferrite (BiFeO3) multiferroic absorber based all oxide FTO/ZnO/BiFeO3/Au solar cell using density functional theory for materials optoelectronic properties and macroscopic device simulation-based hybrid approach. The structural, electronic, and optical properties of BiFeO3 are investigated using density functional theory (DFT). The band structure and density of states of R3c-BiFeO3 are computed considering the Hubbard parameter Ueff∼4.2eV for both Fe-3d and O-2p orbitals for matching the experimental bandgap of ∼2.5eV. The computed optical properties, such as absorption for rhombohedral R3c-BiFeO3, are used to investigate FTO/ZnO/BiFeO3/Au solar cell performance using a macroscopic device simulation approach. The thickness, acceptor concentration, defect concentration of the absorber layer, interface defect density, electron affinity of the electron transport layer, and the impact of series, shunt resistance, and metal back contact are investigated to optimize the photovoltaic response under realistic conditions. The optimum photoconversion efficiency (PCE) is ∼11.92% with open circuit voltage (Voc) of 1.033V, short circuit current density (Jsc) of 15.27mA/cm2, and fill factor (FF) of 75.59%. This study on BiFeO3-based absorber materials opens a way to realize lead-free perovskite absorber material with a potential for realizing all oxide solar cells.

Synthesis, characterization and machine learning assisted optical emission studies of dysprosium doped bismuth ferrites

Multiferroic (Bi1-xDyxFeO3 (0.0 ≤ x ≤ 0.08, step x = 0.02) was prepared by auto-combustion method. The effect of Dysprosium substitution on the structural and optical properties of BiFeO3 was studied. XRD analysis confirmed the space group (R3c) rhombohedral perovskite structure with average crystallite size in the range of 25–56 nm. Moreover, the substitution of Dy3+ into BFO ferrite was verified by XRD. The average grain size was also estimated using SEM and TEM. FTIR showed the vibrational modes in the range 425–548 cm−1 corresponding to the stretching of Fe-O bonds. UV–vis measurements revealed lowering of bandgap for doped samples (2.51–2.23 eV). Sample (x = 0.04) showed highest saturation magnetization and retentivity. LIBS analysis showed the presence of Bi, Fe, and Dy in samples. The McWhirter criteria were used to confirm the local thermodynamic equilibrium (LTE). The principal component analysis in conjunction with LIBS spectra is useful to classify the materials with minute concentration variations.

Synthesis and investigation of structural behaviour and optical properties of BiFeO3, YMnO3 and BiFeO3-YMnO3 nanostructures

In this paper, BiFeO3, YMnO3 and BiFeO3-YMnO3 compounds were synthesized and compared their structural, morphological and light absorption characteristics for the first time. The XRD analysis of the synthesized samples revealed that the crystal structures of BiFeO3, YMnO3 and BiFeO3-YMnO3 are rhombohedral, hexagonal and rhombohedral-hexagonal. SEM images were used to examine the particle shape of all the synthesized compounds. The optical band gap values were measured to be 1.95, 1.35 and 1.28 eV for the BiFeO3,YMnO3 and BiFeO3-YMnO3 samples, using Tauc plots.

Effect of (Zn, Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe1-2xZnxMnxO3 (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO3 (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10−6 A/cm2) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm2 was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm2. The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.

Optimizing phase formation of BiFeO3 and Mn-doped BiFeO3 nanoceramics via thermal treatment using citrate precursor method

In recent years, bandgap tailoring of ferroelectric materials has gained great attention in the scientific community owing to their favourable materials characteristics, and new endowing paths for developing multifunctional devices. In this study, an attempt was made to tune the optical bandgap of BiFeO3 (BFO) via chemical substitution and by controlling thermal treatment temperature and time. A series of BiFe1-xMnxO3 (x = 0.00, 0.03, 0.05) nanoceramic samples were prepared by adopting the citrate precursor method. The effect of Mn substitution, annealing temperature, and annealing time on structural, morphological, and optical properties of BFO was investigated using X-ray diffraction, field emission scanning electron microscopy, and UV–visible spectroscopy, respectively. The average crystallite size was found to decrease (from 44−17 nm) with Mn-doping and increase with increasing annealing temperature and time (from 17−27 nm) due to the agglomeration of nanoparticles. The FESEM studies revealed the inhomogeneous distribution of granular structured grains with negligible porosity. The optical bandgap energy of BFO nanoparticles was found to reduce significantly by 21% (2.08−1.62 eV) with a competing effect of Mn-substitution, annealing temperature, and annealing time. The optical bandgap studies of BiFe0.97Mn0.03O3 showed a direct correlation with annealing temperature and an inverse correlation with annealing time. Additionally, BiFe0.97Mn0.03O3 nanoparticles annealed at 550 °C for 2 h showed a 31% enhancement in absorption coefficient and 14% reduction in bandgap value without a structural phase transition. The results obtained in this study propose BiFe0.97Mn0.03O3 nanoparticles as a potential candidate for upcoming ferroelectric photovoltaic devices.

Structural, dielectric, ferroelectric and optical properties of Er doped BiFeO3 nanoparticles

In this work, an effort has been made to show the effect of Er doping on the dielectric, electrical, ferroelectric, and optical properties of BiFeO3 (BFO) nanoparticles prepared by the sol-gel route. XRD of Bi1-xErxFeO3 samples revealed that the rhombohedral (R3c) structure is stable for 0 ≤ x ≤ 0.08 with distortional changes, whereas a co-existence of two phases, rhombohedral (R3c) and orthorhombic (Pn21a) is present for x = 0.12. At room temperature, dielectric properties are slightly improved with the appearance of defects at a higher temperature. The ln σacvs. 1000/T plots revealed the presence of different Arrhenius-type thermally activated mechanisms and, for their analysis, were divided in five regions: the low temperature regions (I and II), followed by a small polaron hopping (intermediate region III) and a single and a double oxygen vacancies regions in the high temperature side (IV and V). Er doped BFO displays an improvement of the dielectric properties with respect to those of BFO, clearly reflected in better P-E loops. UV–Vis spectroscopy revealed the optical band energy lies in the 2.10 eV–1.70 eV interval, suggesting possible applications in the visible range of the spectrum. The multiferroic properties at room temperature make it a good candidate for future potential application in memory devices.

Effect of La doping on the ferroelectric and optical properties of BiFeO3: a theoretical-experimental study

Much work has been done already on pure and doped BiFeO3 (BFO), however, renewed interest has emerged when considered as a viable photovoltaic material. It has been shown that, for this purpose, spontaneous polarization and energy gap are relevant physical quantities. In this theoretical-experimental work, we have studied the possibility of enhancing the spontaneous polarization and reducing the BFO bandgap by replacing 10% of the site A ions of the perovskite structure with La. The structural, electronic and optical properties of (Bi0.9La0.1)FeO3 were investigated using pristine BFO as a reference. A rhombohedral crystal structure was determined after La substitution and its corresponding bandgap of 2.49 eV was smaller than that of pure BFO. Theoretically, the spontaneous polarization (Ps) of the BFO increased with the incorporation of La up to a value of 103 μC cm−2, showing its effect on the ferroelectric properties. Moreover, the theoretical results and experimental measurements of the optical properties demonstrated the reduction of the optical gap.

Synthesis, structure and optical properties of lithium and zinc doped BiFeO3 by sol gel method

BiFeO3 is one of the multiferroic materials and have a wide range of application. For that reason, pure BiFeO3 (BFO), Li and Zn doped BFO were synthesized by sol-gel method. Structure and optical properties of BiFeO3 were characterized by using X-ray diffractometer and UV-Vis spectrophotometer. Pure BiFeO3 and single phase Li-doped BiFeO3 were detected from XRD pattern. Two-phase were identified in Zn doped BiFeO3. The Structure parameters of the three samples seem altered. Doping Li and Zn decrease crystal parameter. The Energy gap was calculated from the UV-Vis absorbance pattern, and pure BiFeO3, Li and Zn doped BiFeO3 have energy gaps 2.81, 3.19 and 4.82 eV respectively. The decrease of crystallite structure caused by the doping would raise the band gap energy.

Theoretical and Experimental Evidence of Modified Structure, Magnetism and Optical Properties in Ba and Mn Co-Substituted BiFeO3

To improve the vacancy related defects associated with pure BiFeO3 (BFO) different Ba-Mn co-doped samples (Bi1-xBaxFeyMnyO3; x = 0.1; y = 0.0, 0.05, 0.1, 0.15) were prepared from sol-gel method. The influence of co-doping on structural, magnetic and optical properties of BiFeO3 has been studied in different experimental conditions. Particle size and magnetic properties were measured from SEM and VSM analysis respectively. Again band gap was calculated from UV analysis. The co-doped samples showed reduced particles size as well as better surface morphology. M-H loops suggest that the presence of Mn2+ increased ferromagnetic quantity at some levels. Still room temperature occurrence of ferromagnetism obtained from M-H loops of all samples showed weak ferromagnetic behaviour. In addition the incorporation of Ba2+ at Bi3+ site and Mn2+ at Fe3+ site decreased the band gap which was evidenced by increased optical property.

The structural, ferroelectric and optical properties of (Gd, Cr) co-substituted BiFeO3 thin films

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.

Remarkable improvement of ferroelectric properties and leakage current in BiFeO3 thin films by nd modification

Ferroelectric and leakage properties are important for ferroelectric applications. Pure and Nd-doped (x=0.05-0.20) BiFeO3 thin films were fabricated by sol-gel method on FTO substrates. The phase structure, surface morphology, leakage current, ferroelectric properties, and optical properties of BiFeO3 - based thin films were investigated. The substitution of Nd3+ ions for the Bi3+ site converts the structure from rhombohedral to coexisting tetragonal and orthorhombic. Nd doping improves the crystallinity of BiFeO3 thin films. The leakage current of Nd-doped BiFeO3 decreases by two to three orders of magnitude compared with that of pure BiFeO3. Among the samples, 15% Nd-doped BiFeO3 exhibits the strongest ferroelectric polarization of 17.96 μC/cm2. Furthermore, the absorption edges of Bi1-x Nd x FeO3 thin films show a slight red-shift after Nd doping.

Experimental and first principles investigation of Bi1-xCexFeO3: Structure, electronic and optical properties

The effects of Ce substitution on the structural, electronic and optical properties of BiFeO3 (BFO) powders using a simple hydrothermal method were investigated. X-ray diffraction data and scanning electron microscope images reveal the lattice contraction and decrease of grain size for the Bi1-xCexFeO3 (BCFO) powders. The absorption in ranges of 250–900 nm is enhanced with the increase of Ce dopant. The optical band gap of BCFO powders extrapolated by the UV–Vis absorption data decreases from 2.69 (x = 0, pure BFO) to 2.39 eV (x = 15%), in good agreement with the first principles calculation. We further demonstrated that the tunable gaps were mainly attributed to the doped Ce-4f states. An additional peak shifted from 1.45 to 1.65 eV in the calculated absorption spectrum is owing to the intraband transition between the Ce-4f impurity band and Fe-3d states or O-2p states in the conduction band, indicating that the band gap can be adjusted in another band range. The two tunable bands will open a new avenue to discover and design optimal BFO compounds for optical applications.

Effects of Strain on Optical Properties of BiFeO<sub>3</sub>: A First-Principles Study

In order to investigate the effects of strain on optical properties of BiFeO3, electronic structure, dielectric properties and optical properties of BiFeO3 under different strain conditions were performed by first-principles calculations. Results show that the optical spectra of BiFeO3 is mainly determined by the contributions from transition from valence band O 2p to conduction band Fe 3d levels or even higher conduction band Bi 6s states in the low-energy region. Compared with equilibrium state, state density peaks shift to left side and state density peaks become broader and lower, and band gap becomes smaller under strain states. Furthermore, strain increases optical absorption coefficient peaks, energy loss coefficient peaks and reflectivity coefficient peaks, and extinction coefficient peaks, exhibiting that optical properites of BiFeO3 is improved under strain states. Our research provides theoretical guidance for future optical applications of BiFeO3, especially photovoltaic application.

Size Effect on Optical and Photocatalytic Properties in BiFeO3 Nanoparticles

In this work we study the influence of grain and particle size on the structural and optical properties of BiFeO3 (BFO) nanoparticles and the resulting photocatalytic activity. Unexpectedly, the photocatalytic activity is found to decrease while the expected surface reaction area increases by decreasing the particles size. We show that while the global structure, polarization, particle morphology, and band gap are only weakly altered, if at all, some optical features, namely, the Urbach energy and low-energy bands, in the absorption spectra are substantially changed. We argue that these optical modifications related to defects and local distortions are mainly affected at the skin layer that is inherent to oxides like BFO. By reducing the particle size of BFO nanoparticles, the skin layer is thus altered, which in turn changes the photocatalytic properties.

Self-interaction corrected LDA + U investigations of BiFeO3 properties: plane-wave pseudopotential method

The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poisson’s ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.

First principles study of structural, electronic and optical properties of BiFeO3 in ferroelectric and paraelectric phases

The structural, optical and electronic properties of BiFeO3 in ferroelectric and paraelectric phases have been investigated using first principles methods within the generalised gradient approximation based on the density-functional theory. Several magnetic configurations have been considered into our calculation, and the antiferromagnetic state is found to be the ground state in both phases. Electronic and optical properties at the antiferromagnetic state are calculated. The band gap of BiFeO3 is found to be 1·198 and 0.280 eV for ferroelectric and paraelectric phases. The analysis of the electronic structures of BiFeO3 in ferroelectric and paraelectric phases indicates that the O-2p electrons hybridise with Bi-3d and Fe-3d electrons, which suggests the presence of covalent bonding contribution in BiFeO3. The dielectric function, absorption, energy loss function and reflectivity were also calculated to discuss the optical properties. The low reflectivity and negligible absorption indicate that BiFeO3 is a transparent material in the infrared region.

Elucidating the real effect of Ba and Co doping on the magnetic and optical properties of BiFeO3

We present Ba/Co co-doping effects on BiFeO3 structure, optical, ferromagnetic, and ferroelectric properties at room temperature. XRD indicates a high distortion of the rhombohedral symmetry, confirmed by Raman spectroscopy, where a change in the intensity ratio of E-1/A1-1 vibrational modes is a result of the partial substitution of Fe3+ by Co3+. This induces an A-site disorder in the FeO6 octahedra. Co2+ acts as grain growth inhibitor reducing average grain sizes from 304nm (without cobalt) to 200nm (with cobalt) after sintering. The magnetization results show that the Co-cation impregnated samples have higher magnetization (31%) than doped and undoped samples.

Structural, dielectric, magnetic, and optical properties of Ni0.75Zn0.25Fe2O4–BiFeO3 composites

The magnetoelectric composites of spinel ferrite Ni0.75Zn0.25Fe2O4 (NZF) and BiFeO3 (BFO) with general formula xNi0.75Zn0.25Fe2O4 + (1 − x)BiFeO3 (x = 0, 0.10, 0.20, and 0.30) have been prepared via hybrid processing route. Subsequently, the effects of addition of NZF on structural, dielectric, magnetic, magnetoelectric, and optical properties of BFO have been investigated, and significant enhancements have been observed in physical observables such as grain size, dielectric constant, magnetization, and polarization in ferroelectric hysteresis loops. The variation of magnetization with temperature indicates the presence of spin glass behavior along with the ferromagnetic component. The magnetoelectric coupling is found with a value of magnetocapacitance to be 4.6 % for 30 mol% addition of NZF. The optical properties of the composites are also studied using UV–Vis diffuse reflectance spectroscopy, Photoluminescence spectroscopy, and FTIR spectroscopy.

Multiferroic, magnetoelectric and optical properties of Mn doped BiFeO3 nanoparticles

Mn doped BiFeO3 (5, 10 and 15 mol%) nanoparticles were synthesized using sol–gel technique. The influence of Mn doping on structural, dielectric, magnetic, magnetoelectric and optical properties of BiFeO3 was studied. Rietveld refinement of XRD patterns showed rhombohedral to orthorhombic phase transition for 15 mol% Mn doped BiFeO3 sample. Magnetic measurements revealed the enhancement of ferromagnetic property with increasing Mn doping in BiFeO3. The characteristic dielectric anomaly, expected in the vicinity of antiferromagnetic transition temperature TN (Neel temperature) was found in all Mn doped BiFeO3 samples. The magnetoelectric coupling was evidenced by the change in capacitance with the change in the applied magnetic field. On increasing Mn concentration from 5 to 15 mol% in BiFeO3, a change in magnetocapacitance from 1.46% to 2.6% showed the improvement of multiferroic properties. In order to explore the optical properties of Mn doped BiFeO3 nanoparticles, their photoluminescent properties were also investigated.

Optical properties of BiFeO3 and Bi0.9La0.1 FeO3 films on silicon substrates

BiFeO3 (BFO) and Bi0.9La0.1FeO3 (BLFO) thin films were deposited on Si (100) wafer by sol-gel technique. The microstructure and surface morphology of the films were characterized using X-ray diffraction and atomic force microscope. After annealing at 600 °C, all the films were well-crystallized, and the diffraction peaks corresponded to BFO standard pattern quite well. The optical properties of BFO and BLFO film were studied by spectroscopic ellipsometry in the wavelength range 420 to1700 nm. Compared with the BFO film, the BLFO film has lower refraction index and higher extinction coefficient in the wavelength range 600 to 1700 nm. The absorption coefficient of the BLFO film is greater than 1700cm−1 in total measured wavelength region. The results suggest that the potential role of La dopant improved the optical properties of BFO thin film and the BLFO film is a promising material for photovoltaic devices.