Oxygen Displacement Research Articles

Atomic Level Engineering of Structural and Functional Properties of Transition Metal Oxides

Metal-oxygen bonds are responsible for a broad spectrum of functional properties of transition-metal oxides, and engineering the bonds is a key for exploring their properties. Artificial oxide heterostructures with chemically abrupt interfaces have provided a platform for engineering bonding geometries that could lead to emergent phenomena not seen in bulk oxides. In this paper, we demonstrate that interfacially engineering oxygen displacement is a good route for exploring structural and functional properties of oxides. Our high-resolution annular bright-field scanning transmission electron microscopy observations revealed that interfacial oxygen displacement determines metal-oxygen bond angles in entire heterostructures and the magnitude of the displacements can be adjusted by controlling propagations of the oxygen octahedral rotations across the heterointerface. We also show that by heterostructuring an itinerant ferromagnet SrRuO3 with Ca0.5Sr0.5TiO3 (0–4 monolayers thick) grown on a GdScO3 substrate, structural phase and magnetic anisotropy of SrRuO3 can be controlled through the interfacial engineering of its oxygen displacement.

Metal-Insulator Transition in Copper Oxides Induced by Apex Displacements

High temperature superconductivity has been found in many kinds of compounds built from planes of Cu and O, separated by spacer layers. Understanding why critical temperatures are so high has been the subject of numerous investigations and extensive controversy. To realize high temperature superconductivity, parent compounds are either hole-doped, such as {La$_{2}$CuO$_4$} (LCO) with Sr (LSCO), or electron doped, such as {Nd$_{2}$CuO$_4$} (NCO) with Ce (NCCO). In the electron doped cuprates, the antiferromagnetic phase is much more robust than the superconducting phase. However, it was recently found that the reduction of residual out-of-plane apical oxygens dramatically affects the phase diagram, driving those compounds to a superconducting phase. Here we use a recently developed first principles method to explore how displacement of the apical oxygen (A-O) in LCO affects the optical gap, spin and charge susceptibilities, and superconducting order parameter. By combining quasiparticle self-consistent GW (QS\emph{GW}) and dynamical mean field theory (DMFT), that LCO is a Mott insulator; but small displacements of the apical oxygens drive the compound to a metallic state through a localization/delocalization transition, with a concomitant maximum $d$-wave order parameter at the transition. We address the question whether NCO can be seen as the limit of LCO with large apical displacements, and elucidate the deep physical reasons why the behaviour of NCO is so different than the hole doped materials. We shed new light on the recent correlation observed between T$_c$ and the charge transfer gap, while also providing a guide towards the design of optimized high-Tc superconductors. Further our results suggest that strong correlation, enough to induce Mott gap, may not be a prerequisite for high-Tc superconductivity.

Practical methods for mitigating microbial degradation of ignitable liquids in soil samples

In fire debris analysis, it is commonly accepted that soil samples can potentially cause degradation of ignitable liquids through microbial activity. Temperature- and solvent-based mitigation methods have been explored, but space and practical application limitations potentially cause problems for these mitigation methods. Alternate mitigation methods using carbon dioxide cartridges, dry ice, and oxygen-adsorbent pouches were cursorily explored as possible practical options to slow microbial activity through the displacement or removal of oxygen within the sample cans. Sample cans were left at room temperature, refrigerated, or treated with a mitigation agent and tested for up to four weeks after application of the gasoline, with cans prepared in triplicate for each time point and storage condition.The carbon dioxide cartridges were ultimately found to be unreliable and widely variable with respect to ignitable liquid contamination. Dry ice did not mitigate the microbial degradation and added additional safety concerns. The oxygen-adsorbent pouches prevented the degradation of gasoline for up to four weeks in the examined soil and did not introduce contamination or safety hazards. Further research is needed to more fully evaluate this potential mitigation method prior to introduction into the field.

Anisotropic suppression of octahedral breathing distortion with the fully strained BaBiO3/BaCeO3 heterointerface

While the physiochemical effects of octahedral tilting and rotating distortions have been studied extensively, octahedral breathing distortion (OBD) at heterointerfaces has rarely been explored. Here, we investigated OBD in fully strained BaBiO3 (BBO) epitaxial films by making a new type of oxide heterointerface with non-breathing BaCeO3 epitaxial films. The integration of first-principles calculations with experimental observations of optical spectroscopy revealed that the oxygen displacement modes in BBO became disordered within six unit cells at the heterointerface and the surface. Controlling OBD in perovskite oxide thin films provides a means to exploit emerging material properties.

Measurement of O and Ti atom displacements in TiO2 during flash sintering experiments

AbstractIn‐situ flash experiments on rutile TiO2 were performed at the synchrotron at the Brookhaven National Laboratory. Pair distribution function analysis of total X‐ray scattering measurements yielded mean‐square atomic displacements of oxygen and titanium atoms during the progression of the 3 stages of flash. The displacements are measured to be far greater for oxygen atoms than for titanium atoms. These large displacements may signal an “elastic softening” of the lattice, which, recently, has been predicted as a precursor to the onset of flash.

Structure, dielectric and electric properties of diisobutylammonium hydrogen sulfate crystal

Diisobutylammonium hydrogen sulfate, a new organic-inorganic hybrid compound, was successfully synthesized and three structural phases in 298–433K temperature range were revealed by differential scanning calorimetry and X-ray powder diffraction studies. Single crystal X-ray diffraction data were used to describe the crystal structures in each particular case. In phase III (below 336/319K on heating/cooling) the crystal arrangement appears to be within the triclinic symmetry with P-1 space group. During heating in the 336–339K region (and 319–337K on cooling) the crystal exists in the phase II, characterized by monoclinic symmetry with P21/c space group. Consequently, above 339K (during heating, and 337K during cooling temperature sequences), i.e. in phase I the crystal exhibits orthorhombic symmetry (Cmce space group). Ferroelastic domain structure was observed in phase III. These phase boundaries (III→II and II→I) were accompanied by the presence of small anomalies, apparent in the dielectric permittivity and electric conductivity experimental data. Fast proton transport with activation energy of 0.23eV was observed in the high temperature phase I and related to phonon assisted proton diffusion conditioned by disorder of diisobutylammonium (diba) cations, as well as by high thermal displacements of oxygen and sulfur atoms of hydrogen sulfate anion (hs).

Directional dependence of the threshold displacement energies in metal oxides

Molecular dynamics (MD) simulations are performed to investigate the directional dependence and the values of the threshold energies (TDEs) for the displacements of the oxygen and metal atoms and for producing stable Frenkel pairs in five metal oxides of Cr2O3, Al2O3, TiO2, SiO2, and MgO. The TDEs for the Frenkel pairs and atoms displacement are calculated in 66 crystallographic directions, on both the anion and cation sublattices. The performed simulations are for metal and oxygen PKA energies up to 350 and 400 eV, respectively. The calculated probability distributions for the atoms displacement and average number of Frenkel pairs produced in the different oxides are compared. The results revealed unique symmetrical patterns of the TDEs for the displacement of the atoms and the formation of stable Frenkel pairs, confirming the strong dependence on the direction and the crystalline structure of the oxides. Results also showed that the formation of stable Frenkel pairs is associated with the displacements of the PKAs and/or of the SKAs. The probabilities of the TDEs for the displacement of the oxygen and metal PKAs are consistently lower than those of the atoms in the crystal. In SiO2, TDEs for the displacement of oxygen and metal atoms and those for the formation of stable Frenkel pairs are the lowest, while those in TiO2 are among the highest. The results for Cr2O3 and Al2O3, which have the same crystal structure, are similar. The calculated TDEs for MgO, Al2O3 and TiO2 are generally in good agreement with the experimental values and the probability distributions of the TDEs for the PKAs in TiO2 are in good agreement with reported MD simulation results.

Correlated oxygen displacements and phonon mode changes in LaCoO3 single crystal

X-ray diffraction and inelastic X-ray scattering studies have been performed across the spin (~100K) and semiconductor-metal (~500K) transitions in LaCoO3 single crystals. The quadratic increase with temperature of the oxygen displacement parameters parallel and perpendicular to the Co-O bond has been correlated with softening of the TO2 and hardening of the TO1 phonon branches along the [0 ξ ξ] high symmetry direction. The latter effect can be associated with the weakening of the Co-O bond strength derived from the increase of Co-O bond length and angle as expected upon increasing the high spin state population of the system with temperature.

Inert Gas Asphyxiation: A Liquid Nitrogen Accident

SESSION TITLE: Poisoning and Drug Overdose 1 SESSION TYPE: Affiliate Case Report Poster PRESENTED ON: Tuesday, October 31, 2017 at 01:30 PM - 02:30 PM INTRODUCTION: Gasses such as nitrogen, helium, and argon are considered to be non-toxic and benign due to their inert nature. They are colorless, odorless gasses that are rarely reported to cause injury. However, the following case demonstrates the indolent ability of inert gasses to cause significant harm with minimal warning. CASE PRESENTATION: A 50-year-old female presented to the emergency department with shortness of breath, altered mental status, and burns. She had a pulse of 100 bpm, respiratory rate of 26, blood pressure of 170/116, and SaO2 of 100%. On physical examination, she was making incomprehensible sounds, not following commands, and opening her eyes spontaneously. Cold burns were reported over 30% of her body. She was subsequently intubated and infused with warm IV fluids. Chest x-ray revealed no acute cardiopulmonary processes, and carboxyhemoglobin levels were normal. She was an employee at a local sperm bank who was found collapsed on the ground while attempting to correct a liquid nitrogen leak. She was later transferred to the burn unit for management of her liquid nitrogen cryoinjuries. A police officer who attempted to rescue this employee succumbed to inhalation of the gas, while three other officers were treated with symptoms of shortness of breath and have since recovered. DISCUSSION: Inert gasses stored in a liquid state at high pressure such as nitrogen are capable of rapidly expanding at atmospheric pressure and temperature. Liquid nitrogen expands to 694 times its original volume at 1 atm and 20°C. Although ambient air contains 78% nitrogen, the rapid expansion can quickly displace oxygen in enclosed spaces with poor ventilation. Given that exchange of CO2 continues to occur freely, there is no hypercapnic response elicited by medullary chemoreceptors that would evoke the traumatic sensation of suffocation. The oxygen chemoreceptors do not have a significant response to hypoxemia until PaO2 reaches below 55 mmHg. An individual may experience loss of consciousness and subsequent death with few to no warning symptoms. The patients in this case were subjected to oxygen levels that reached 0.2% because of a liquid nitrogen leak at the sperm bank. At medical facilities, large amounts of liquid nitrogen are frequently stored for laboratory work and research. Nitrogen gas asphyxiation has been reported to occur about eight times per year with many of the fatalities from attempted rescues. CONCLUSIONS: Inert gasses such as liquid nitrogen are often disregarded as hazards. However, those who handle them should be aware of the potential danger of the rapid displacement of oxygen in enclosed spaces. Reference #1: Hazards of Nitrogen Asphyxiation. U.S. Chemical Safety and Hazard Investigation Board. 2006; No. 2003-10-B. Reference #2: Kim V, et al. Oxygen Therapy in Chronic Obstructive Pulmonary Disease. Proc Am Thorac Soc. 2008; 5(4): 513-518. Reference #3: “Regulation of Respiration.” Hall JE, Guyton AC. Guyton and Hall Textbook of Medical Physiology. Philadelphia: Elsevier; 2016. DISCLOSURE: The following authors have nothing to disclose: Ivan Morales, Jayanth Keshavamurthy, Nikhil Patel, Norman Thomson No Product/Research Disclosure Information

In situ disordering of monoclinic titanium monoxide Ti5O5 studied by transmission electron microscope TEM

The superlattice and domain structures exhibited by ordered titanium monoxide Ti5O5 are disrupted by low energy electron beam irradiation. The effect is attributed to the disordering of the oxygen and titanium sublattices. This disordering is caused by the displacement of both oxygen and titanium atoms by the incident electrons and results in a phase transformation of the monoclinic phase Ti5O5 into cubic B1 titanium monoxide. In order to determine the energies required for the displacement of titanium or oxygen atoms, i.e. threshold displacement energies, a systematic study of the disappearance of superstructure reflections with increasing electron energy and electron bombardment dose has been performed in situ in a transmission electron microscope (TEM). An incident electron energy threshold between 120 and 140 keV has been observed. This threshold can be ascribed to the displacements of titanium atoms with 4 as well as with 5 oxygen atoms as nearest neighbors. The displacement threshold energy of titanium atoms in Ti5O5 corresponding with the observed incident electron threshold energy lies between 6.0 and 7.5 eV. This surprisingly low value can be explained by the presence of either one or two vacant oxygen lattice sites in the nearest neighbors of all titanium atoms.

Ab initio molecular dynamics simulation of low energy radiation responses of \u03b1-Al2O3

In this study, an ab initio molecular dynamics method is employed to investigate the response behavior of α-Al2O3 to low energy irradiation. Different from the previous experiments, our calculations reveal that the displacements of oxygen dominate under electron irradiation and the created defects are mainly oxygen vacancy and interstitial. The experimental observation of the absorption peaks appearing at 203, 233 and 256 nm for α-Al2O3 under electron irradiations should be contributed by the oxygen defects and these defects will reduce the transmittance of α-Al2O3, which agrees well with the very recent experiment. This study demonstrates the necessity to reinvestigate the threshold displacement energies of α-Al2O3, and to introduce recombination center for oxygen defects to improve its optical properties and performance under radiation environment.

Structural refinement of Pbnm-type perovskite films from analysis of half-order diffraction peaks

Engineering structural modifications of epitaxial perovskite thin films is an effective route to induce new functionalities or enhance existing properties due to the close relation of the electronic ground state to the local bonding environment. As such, there is a necessity to systematically refine and precisely quantify these structural displacements, particularly those of the oxygen octahedra, which is a challenge due to the weak scattering factor of oxygen and the small diffraction volume of thin films. Here, we present an optimized algorithm to refine the octahedral rotation angles using specific unit-cell-doubling half-order diffraction peaks for the a−a−c+ Pbnm structure. The oxygen and A-site positions can be obtained by minimizing the squared-error between calculated and experimentally determined peak intensities using the (1/2 1/2 3/2) and (1/2 1/2 5/2) reflections to determine the rotation angle α about in-plane axes and the (1/2 5/2 1), (1/2 3/2 1), and (1/2 3/2 2) reflections to determine the rotation angle γ about the out-of-plane axis, whereas the convoluting A-site displacements associated with the octahedral rotation pattern can be determined using (1 1 1/2) and (1/2 1/2 1/2) reflections to independently determine A-site positions. The validity of the approach is confirmed by applying the refinement procedure to determine the A-site and oxygen displacements in a NdGaO3 single crystal. The ability to refine both the oxygen and A-site displacements relative to the undistorted perovskite structure enables a deeper understanding of how structural modifications alter functionality properties in epitaxial films exhibiting this commonly occurring crystal structure.

Is oxygen reduction a viable antioxidant strategy for oil‐in‐water emulsions?

The impact of 0, 40, 58, 79, 93, and 98% total oxygen reduction on lipid oxidation kinetics in a 1.0% fish oil‐in‐water emulsion (pH 3.0; 32°C) was determined. Atmospheres were modified using nitrogen/oxygen gas blends or high purity nitrogen. Headspace and dissolved oxygen were monitored throughout the study using a non‐destructive technique in which fluorescent sensors were fixed in sealed vials. Lipid oxidation, as measured by lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS), was inhibited at oxygen reductions ≥58%. However, meaningful protection against lipid oxidation was only achieved at oxygen reductions ≥93%. Potential commercial strategies, nitrogen flushing/sparging, and ascorbic acid, were inefficient at reducing oxygen to levels that could significantly inhibit lipid oxidation. Results suggest that near complete oxygen removal is necessary to protect oxygen‐sensitive ingredients, but a need still exists to identify new strategies that sufficiently reduce the oxygen content of emulsions.Practical applications: The practical application of this work is that there is a global demand to remove synthetic additives from food and beverage formulations, and as described in this work, defining the level oxygen reduction that provides meaningful increases in oxidative stability is necessary. Results suggest that the oxidative stability of 1% fish oil‐in‐water emulsions can be extended by reducing system oxygen by ∼58%, but to have a meaningful antioxidant impact greater than ∼93% oxygen removal is required. Further investigation into simulated commercial oxygen removal strategies (e.g., nitrogen displacement of oxygen and ascorbic acid) demonstrated that current industrial strategies are lacking and need to be optimized in order to enhance stability against lipid oxidation.In this work, we design and modify a fish oil‐in‐water emulsion system to have different oxygen concentrations that range from almost complete oxygen removal to atmospheric conditions. The resulting emulsions are characterized over time by non‐destructively measuring oxygen concentrations, both in the headspace and dissolved phase, as shown in the figure of two sensor patches inside a sealed glass vial. The impact of oxygen concentrations on lipid oxidation kinetics is measured and represented in the graphed data. Results suggest that near complete oxygen removal is necessary to provide meaningful protection against lipid oxidation in emulsified systems.

Effects of Sc doping on phase stability of Zr1 – xScxO2 and phase transition mechanism: First-principles calculations and Rietveld refinement

Scandia doped zirconia (ScSZ) is a promising electrolyte candidate for Solid Oxide Fuel Cells (SOFCs). However, the cubic-tetragonal phase transition of ScSZ is a serious problem that blocks its extensive application. A systematic study of tetragonal and cubic phase stability of Zr1–xScxO2 as a function of x is carried out using density functional theory (DFT) calculations. The optimized atomic structures and total energies are obtained. The cubic phase becomes stable when x>0.18. The largest tetragonal and cubic phase's total energy difference appears at x=0.2188, which indicates that the cubic phase is most stable at this doping level. Furthermore, experiments have been carried out to verify the calculation reliability. The calculation results match well with our Rietveld refinement and Raman scattering observations. The relative phase transition mechanism has been analyzed systematically according to the calculated results and optimized atomic configuration. The phase structure transformation is shown to be closely correlated with cell volume difference, coordinated situation and oxygen displacement.

Non-invasive ventilation in the perioperative period

### Key points Maintenance of adequate perioperative respiratory function is of paramount importance for the safe delivery of anaesthesia and surgery and an uneventful recovery thereafter. Optimized tissue oxygenation plays a pivotal role in the preservation of organ function and is vital for wound healing and the protection of surgical anastomoses. ### Physiological changes in the perioperative period Surgical patients often experience profound physiological changes to their respiratory system. General anaesthesia reduces oropharyngeal tone and airway reflexes. A decrease in respiratory rate and tidal volumes from opioid and anaesthetic agents leads to reduced minute ventilation, hypercarbia, and displacement of alveolar oxygen. This may be compounded by a blunted central ventilatory drive. Furthermore, functional residual capacity (FRC) declines, reducing the effective oxygen reservoir. Closing capacity approaches FRC during general anaesthesia, causing small airway closure and atelectasis and ventilation–perfusion mismatch is exacerbated, leading to increased physiological deadspace and shunt. There is also increasing recognition of ventilator-induced lung injury as a contributory factor to postoperative pulmonary dysfunction. Patient factors such as advanced age, premorbid cardiorespiratory disease, smoking, obesity, and anaemia may all increase the likelihood of developing postoperative pulmonary complications (PPC). Surgical factors include positional changes, diaphragmatic splinting, and direct surgical injury to the lungs, pleura, diaphragm, chest wall, abdominal wall, or to the nerves supplying the respiratory …

Oxygen Displacement in Cuprates under Ionic Liquid Field-Effect Gating

We studied structural changes in a 5 unit cell thick La1.96Sr0.04CuO4 film, epitaxially grown on a LaSrAlO4 substrate with a single unit cell buffer layer, when ultra-high electric fields were induced in the film by applying a gate voltage between the film (ground) and an ionic liquid in contact with it. Measuring the diffraction intensity along the substrate-defined Bragg rods and analyzing the results using a phase retrieval method we obtained the three-dimensional electron density in the film, buffer layer, and topmost atomic layers of the substrate under different applied gate voltages. The main structural observations were: (i) there were no structural changes when the voltage was negative, holes were injected into the film making it more metallic and screening the electric field; (ii) when the voltage was positive, the film was depleted of holes becoming more insulating, the electric field extended throughout the film, the partial surface monolayer became disordered, and equatorial oxygen atoms were displaced towards the surface; (iii) the changes in surface disorder and the oxygen displacements were both reversed when a negative voltage was applied; and (iv) the c-axis lattice constant of the film did not change in spite of the displacement of equatorial oxygen atoms.

An analysis of the phonon dispersion curves of lead hafnate in the cubic phase using lattice-dynamical models

We have analyzed the phonon dispersion curves in the paraelectric phase of a lead hafnate crystal (PbHfO3) by means of two different lattice-dynamical models. Both the rigid-ion model and the shell one provided an acceptable description of the available experimental data. The atomic displacement patterns were qualitatively different for the two models. In the rigid-ion model the motion in the characteristic low-energy flattened transverse acoustic branch contained both lead and hafnium displacements, while for the shell model it corresponded mainly to lead displacements with the small contribution of oxygen displacements. The shell model allows simultaneous description of the phonon dispersion curves and the correct value of the dielectric constant.

Eff ect of oil fl ushing with nitrogen on the quality and oxidative stability of coldpressed rapeseed and sunfl ower oils

Oxidative stability means resistance to oxidation during purchase, processing and storage and is a key quality indicator of edible fats. Oils ought to be stored in dark-glass bottles, at low temperatures and with no access of light in order to effectively preserve their oxidative stability. Since all vegetable oils contain unsaturated fatty acids that can react with oxygen and deteriorate over time, displacement of oxygen with inert gases may result in a reduction of the rate of oxidation. In the study the effect of oil flushing with nitrogen on the quality and oxidative stability of cold-pressed rapeseed and sunflower oils was determinate. Commercial samples of cold-pressed rapeseed and sunflower oils were stabilized by generating anaerobic atmosphere in the bottles by blowing through with nitrogen and generation of a "nitrogen cushion". Oils were tested in accelerated at 63°C and long-term at 20°C storage tests. After 20 days of Schaal oven test, the peroxide value in the flushing with nitrogen rapeseed and sunflower oils was, respectively, 4 and 7 times lower than in the control samples (without nitrogen). In turn, of the long-term storage test (with access of light 20°C), the peroxide value of oil flushing with nitrogen after 6 months of storage was 2.3 to 2.8-fold lower, respectively, than in the control sample. In the oil samples flushed with nitrogen peroxide formation was inhibited, however, as a result of the breakdown of the peroxides already existed in the oil, gradual decrease of the oxidative stability (determined via Rancimat test) was observed along with prolonged storage of oils. Oil flushing with nitrogen was a very effective way to reduce the changes caused by oxidation in cold-pressed rapeseed and sunflower oil.

Magnetic structure of an incommensurate phase of La-dopedBiFe0.5Sc0.5O3: Role of antisymmetric exchange interactions

A 20% substitution of Bi with La in the perovskite Bi1-xLaxFe0.5Sc0.5O3 system obtained under high-pressure and high-temperature conditions has been found to induce an incommensurately modulated structural phase. The room temperature X-ray and neutron powder diffraction patterns of this phase were successfully refined using the Imma(0,0,g)s00 superspace group (g=0.534(3)) with the modulation applied to Bi/La- and oxygen displacements. The modulated structure is closely related to the prototype antiferroelectric structure of PbZrO3 which can be considered as the lock-in variant of the latter with g =0.5. Below T_N = 220 K, the neutron diffraction data provide evidence for a long-range G-type antiferromagnetic ordering commensurate with the average Imma structure. Based on a general symmetry consideration, we show that the direction of the spins is controlled by the antisymmetric exchange imposed by the two primary structural distortions, namely oxygen octahedral tilting and incommensurate atomic displacements. The tilting is responsible for the onset of a weak ferromagnetism, observed in magnetization measurements, whereas the incommensurate displacive mode is dictated by the symmetry to couple a spin-density wave. The obtained results demonstrate that antisymmetric exchange is the dominant anisotropic interaction in Fe3+ based distorted perovskites with a nearly quenched orbital degree of freedom.

Distortion induced magnetic phase transition in cubic BaFeO3

The electronic and magnetic structures of cubic BaFeO3 (BFO) in the ferromagnetic (FM) and antiferromagnetic (AFM) states are studied using density functional theory (DFT) with the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), with and without a Coulomb U term. Our LSDA/GGA and LSDA+U/GGA+U results show that cubic BFO has a FM ground state, in agreement with recent experimental studies. Two types of distortions, denoted as D1 and D2, are considered. The source of the distortion in the D1 (D2) case is the displacement of the oxygen (iron) atoms from their equilibrium positions. FM to ferrimagnetic (FIM) and FM to AFM magnetic phase transitions are found in the D1 and D2 distortions, respectively. Larger strains are required for the FM–AFM transition as compared to the FM–FIM. DFT+U calculations also show that the magnetic moments dramatically decrease at large strains due to strong overlapping between the iron and oxygen atoms. The origin of these transitions is discussed in terms of a competition between double exchange and superexchange interactions. From these results it is possible to conclude that oxygen and iron displacements are responsible for the magnetic phase transitions and the reduction of the magnetic moments in BFO.