Littérature scientifique sur le sujet « Ferric Order Parameters - Ferroelectricity »

Recently, strain engineering has been shown to be a powerful and flexible means of tailoring the properties of ABO 3 perovskite thin films. The effect of epitaxial strain on the structure of the perovskite unit cell can induce a host of interesting effects, these arising from either polar cation shifts or rotation of the oxygen octahedra, or both. In the multi-ferroic perovskite bismuth ferrite (BiFeO 3 –BFO), both degrees of freedom exist, and thus a complex behaviour may be expected as one plays with epitaxial strain. In this paper, we review our results on the role of strain on the ferroic transition temperatures and ferroic order parameters. We find that, while the Néel temperature is almost unchanged by strain, the ferroelectric Curie temperature strongly decreases as strain increases in both the tensile and compressive ranges. Also unexpected is the very weak influence of strain on the ferroelectric polarization value. Using effective Hamiltonian calculations, we show that these peculiar behaviours arise from the competition between antiferrodistortive and polar instabilities. Finally, we present results on the magnetic order: while the cycloidal spin modulation present in the bulk survives in weakly strained films, it is destroyed at large strain and replaced by pseudo-collinear antiferromagnetic ordering. We discuss the origin of this effect and give perspectives for devices based on strain-engineered BiFeO 3 .

ABSTRACTSingle-phase multiferroic materials have attracted considerable attention among scientists, due to the strong drive in industry towards device miniaturization, addition of new functionalities, etc. Currently, most of the discovered materials have at-least one ferroic order active only at low temperatures, thereby hindering their induction into practical devices. κ-Al2O3-type AlxFe2-xO3 (x-AFO) oxides belong to a new class of metastable multiferroic compounds (space group: Pna21), with relatively high Curie temperatures. The current work investigates the effect of thin film deposition conditions on the ferroelectric and ferrimagnetic properties of Al0.5Fe1.5O3 (0.5-AFO). Substrate temperature and oxygen partial pressure during deposition were found to be the critical parameters in obtaining high quality films. Optimizing the deposition conditions of 0.5-AFO enabled observation of both ferroelectricity and ferrimagnetism at room temperature.

Study of multiferroics, materials simultaneously having more than one primary ferroic order parameter, is a hot topic of material sciences. The most extensively studied class of these compounds is the family of magnetoelectric multiferroics, where ferroelectricity can be induced by various types of magnetic orderings via the relativistic spin-orbit interaction. As a consequence of the cross coupling between spins and electric polarization, the spectacular control of the ferroelectric polarization by external magnetic field and the manipulation of the magnetic order via electric field can often be realized in these systems. Depending on the symmetry and microscopic mechanism of the multiferroicity the coupling energy between magnetic and electric ordering parameters can significantly vary. Classical neutron diffraction often fails in the precise determining of the complex magnetic structure in the multiferroics due to the presence of the statistically distributed domains in the macroscopic sample. Using spherical neutron polarimetry (SNP), known also as 3D polarization analysis, it is possible not only to precisely determine the complex magnetic structure, but also to investigate in-situ its evolution with external parameters and to control the magnetic domains distribution under the influence of the external electric or/and magnetic field. Here we will present some SNP results on few different multiferroic materials. In some of them, e.g. square lattice 2D antiferromagnet Ba2CoGe2O7, even strong electric field does not change the magnetic order. However rater week magnetic field is sufficient to create a mono-domain structure and to rotate spins in the plane. In other e.g. incommensurate (spiral) magnetic structure of the TbMnO3, solely electric field is sufficient to fully control the chirality of the magnetic structure. In the case of Cr2O3 both electric and magnetic fields should be applied in parallel in order to switch between the different antiferromagnetic domains.

The special issue of the CMP journal Ferroelectricity and Multiferroics contains the papers of theoretical and experimental investigations in a wide range covering physical effects, properties and applications of ferroics–crystalline oxide, chalcogenide and hydrogen bonded materials with a long- range order parameter–spontaneous polarization, magnetization or strain. The order parameter arises due to the phase transition taking place with the temperature decrease, and at pressure or chemical composition variation. The phase transitions on the temperature–pressure–composition diagrams are investigated using different methods (first principles and model calculations, molecular dynamics simulations, mean-field analysis of thermodynamic properties) with the aim to search for the materials (monocrystals, ceramics and nanoparticles) having effective functional parameters, especially for multiferroics that have more than one of the interacting long-range orders. The fundamental physical research of nonlinear processes in ferroics on the nanoscale, with controlling the size effects, provides a background for developing nanostructures favourably applied in nanoelectronics and information technologies.

The adsorption mechanisms for model hydrocarbons, 4-nitrophenol (PNP), and naphthalene were studied in a coagulation-based process using a ferric sulfate–lime softening system. Kinetic and thermodynamic adsorption parameters for this system were obtained under variable ionic strength and temperature. An in situ method was used to investigate kinetic adsorption profiles for PNP and naphthalene, where a pseudo-first order kinetic model adequately described the process. Thermodynamic parameters for the coagulation of PNP and naphthalene reveal an endothermic and spontaneous process. River water was compared against lab water samples at optimized conditions, where the results reveal that ions in the river water decrease the removal efficiency (RE; %) for PNP (RE = 28 to 20.3%) and naphthalene (RE = 89.0 to 80.2%). An aluminum sulfate (alum) coagulant was compared against the ferric system. The removal of PNP with alum decreased from RE = 20.5% in lab water and to RE = 16.8% in river water. Naphthalene removal decreased from RE = 89.0% with ferric sulfate to RE = 83.2% with alum in lab water and from RE = 80.2% for the ferric system to RE = 75.1% for alum in river water. Optical microscopy and dynamic light scattering of isolated flocs corroborated the role of ions in river water, according to variable RE and floc size distribution.

Multiferroic materials have attracted significant research attention due to their technological potential for applications as multifunctional devices. The scarcity of single-phase multiferroics and their low inherent coupling between multiferroic order parameters above room temperature pose a challenge to their further applications. We propose a 3BiFeO3/7BaTiO3 perovskite–perovskite composite that combines ferroelectricity and ferromagnetism. We demonstrate that the sintering temperature can tailor the ferroelectricity and ferromagnetism of the composites. The multiferroicity can be achieved at a low sintering temperature in the composite-like structure ceramics, and its multiferroic properties, especially the ferromagnetism, are superior to those of solid solutions. We also investigate the dynamic evolution of multiferroicity with sintering temperature. We adopt a nano–micro strategy to construct a composite-like microstructure, which results in optimized ferroelectric (1.62 μC cm−2) and ferromagnetic (0.16 emu/g) characteristics at a sintering temperature of 750 °C. We also found experimental evidence of the competition between antiferromagnetic and ferromagnetic interactions in the transition metal cation sublattice. Multiferroic BiFeO3/BaTiO3 composites with combined ferroelectric and ferromagnetic properties have significant potential for various applications.

The effect of zinc sulfate and ferric sulfate on the pyrolysis process of lignin was studied at three different heating rates by using the thermogravimetric analysis technique. It was found that the pyrolysis of pure lignin is barely affected with the change of heating rates between 10 to 100 °C/min, which is unexpected because of the kinetic nature of pyrolysis. The pyrolysis kinetics of this major component of biomass was studied by using three fitting methods: the differential method with reaction order model n, the isoconversional method, and the distribution of activation energies model, DAEM. The best fit, which allowed calculating acceptable kinetic parameters, was obtained using the last method. The results show the influence of the catalysts and the heating rate on the lignin pyrolysis processes in the presence of the sulfates under study, which is confirmed by obtaining different kinetic parameters. The results suggest that zinc sulfate and ferric sulfate change the kinetic mechanism of lignin pyrolysis.

In order to nondestructively characterize chemical forms of ferric hydroxides in weathered rock, charge-coupled device type visible microspectroscopy was applied to brown stains produced in weathered granite surfaces. The combination of visible microspectra and color parameters ( a* and b*) was effective in examining chemical forms of ferric hydroxides in the analytical area. Color parameters in an a*– b* diagram of the brown stains, mostly lying between goethite and ferrihydrite trends, indicated that the brown stains contain ferrihydrite or hematite in addition to goethite. Similarity of the visible microspectra of the brown stains and their first derivatives to those of goethite or ferrihydrite suggests that goethite and/or ferrihydrite are the main weathering products of the granite. Occurrence of ferrihydrite as well as goethite in the brown stains implies that crystallization of ferrihydrite to goethite might be hindered during the granite weathering. This fact suggests the possibility of toxic metal retention in ferrihydrite by its long-term persistence during water–rock interactions at the earth's surface.

A classification scheme of Pb()O3-type perovskites with respect to the B-site order parameters was proposed based on the theoretical calculation of the short-range order parameter (σ) using the pair-correlation model. The calculated order parameters predict that a Pb()O3-type perovskite without any charge difference between B′ and B″ cations [e.g., Pb(Zr1/2Ti1/2)O3 (PZT)] is represented by a completely disordered state with the absence of a finite coherence length. On the other hand, a Pb()O3-type perovskite system having different ionic charges is characterized either by the short-range ordering with a nanoscale coherence length or by the macroscopic long-range ordering, depending on the magnitude of ionic charge difference between B′ and B″ ions. The normal ferroelectricity in Pb()O3-type complex perovskites was then correlated either with a completely disordered state (σ = 0) or with a perfectly ordered state (σ = 0), whereas the relaxor behavior was attributed to the nanoscale short-range ordering (0 < σ < 1) in the configuration of the B-site cations.

The physico-chemical process of coagulation-flocculation is very efficient and economical for the treatment of leachate. The latter can have considerable impacts on the environment. The leachate from the landfill of the city of Mohammedia is characterized by a high COD content which varies between 2200 and 2700 mg/l, a total Kjeldahl nitrogen concentration varying from 1080 to 1405 mg/l while the ammonium content has a concentration varying between 587 and 1410 mg/l. Organic matter is not readily biodegradable (BOD5/COD: 0.2 to 0.13). Metal concentrations ranged from 0.1 to 4.2 mg/l for Cr, 40 to 5 mg/l for Cd, and 0.3 to 0.8 mg/l for lead. For monitoring the leachate treatment, several coagulants and flocculants were used (FeCl3, Al2(SO4)3, Alginate, cationic flocculants, anionic flocculants). In parallel with the monitoring of the physicochemical parameters we followed the production of the volume of the settled sludge over time. Treatment with all coagulants and flocculants used is pH dependent. Ferric Chloride has been shown to be effective at a pH of 6.5 while for Aluminum Sulfate the optimum pH is 5.3. The results showed that coagulation-flocculation by Ferric Chloride and Aluminum Sulfate is very effective in reducing turbidity. This reduction reaches 95 and 98% respectively for FeCl3 and Al2(SO4)3, while the reduction in COD for the two coagulants is around 60%. Organic flocculants alone do not lead to a significant reduction in turbidity and COD, while their combination with coagulants marks a good reduction in pollution. Hydrated iron hydroxides precipitate more easily than flocs formed by aluminum, resulting in more efficient removal of pollutants than that obtained at lower pH values. The order of introduction strongly influences the coagulation flocculation. The optimal doses of the various coagulants and flocculants chosen for the study vary from one reagent to another. FeCl3 remains the most suitable coagulant to further eliminate organic and metal pollution. The cost associated with the treatment using flocculants remains much higher when the flocculant is used in admixture with a coagulant.

The solid particle erosion (SPE) of flow passage is a universal problem in modern high-parameter steam turbines. With the continuous improvement of the working parameters of the steam turbine, the problem of SPE is becoming more serious. This problem is caused by the ferric oxide exfoliations carried by steam from the inner wall of the boiler tube into the steam turbine flow passage, causing the stator blades, the rotor blades, and the shroud to be eroded under impingement and scuffing failure. The SPE cannot only destroy the blade profile, increase the roughness of the blade surface, and affect the aerodynamic performance of the blade, but it can also shorten the maintenance cycle, prolong the maintenance downtime, and even increase the cost for steam turbine maintenance thereby reducing the unit efficiency and safety. In order to simulate SPE in the governing stage of a high-parameter steam turbine, this study adopts the Lagrange method and the Finnie erosion model. The motion characteristics of five different kinds of solid particle, including the solid particle trajectory, are thoroughly analyzed. The regulation of the erosion distribution in the radial and axial directions to the stator and rotor blades is studied to present the mechanism of SPE. Simulated results show that before their collision with the blades, the particles of the small diameters flow with the main stream, and their trajectories are close to the steam streamlines. By contrast, the particles of the large diameters are hardly influenced by the external factors, and their trajectories are close to the straight line. The SPE distribution of the stator and rotor blades varies with the particle diameter. The eroded area in the stator blade is mainly located at the leading edge and the pressure surface, particularly the mid-rear part of the pressure surface, whereas no eroded area can be observed in the suction surface. The small particles greatly affect the erosion distribution of the stator blade. The eroded area in the rotor blade is primarily at the mid-rear part of the pressure surface and the suction surface, which is close to the leading edge. The eroded area takes on a typical slop shape, and the erosion position has an obvious upward trend. The proposed research reveals both the motion characteristics of the solid particles and the distribution regulation of the SPE in the steam turbine flow passage. The analysis results provide references for the governing stage of a high-parameter steam turbine to prevent SPE.

The project was originally aimed at investigating and developing new efficient methods for cost effective removal of ammonia (NH₃) and hydrogen sulfide (H₂S) from Concentrated Animal Feeding Operations (CAFO), in particular broiler and laying houses (NH₃) and hog houses (H₂S). In both cases, the principal idea was to design and operate a dedicated air collection system that would be used for the treatment of the gases, and that would work independently from the general ventilation system. The advantages envisaged: (1) if collected at a point close to the source of generation, pollutants would arrive at the treatment system at higher concentrations; (2) the air in the vicinity of the animals would be cleaner, a fact that would promote animal growth rates; and (3) collection efficiency would be improved and adverse environmental impact reduced. For practical reasons, the project was divided in two: one effort concentrated on NH₃₍g₎ removal from chicken houses and another on H₂S₍g₎ removal from hog houses. NH₃₍g₎ removal: a novel approach was developed to reduce ammonia emissions from CAFOs in general, and poultry houses in particular. Air sucked by the dedicated air capturing system from close to the litter was shown to have NH₃₍g₎ concentrations an order of magnitude higher than at the vents of the ventilation system. The NH₃₍g₎ rich waste air was conveyed to an acidic (0<pH<~5) bubble column reactor where NH₃ was converted to NH₄⁺. The reactor operated in batch mode, starting at pH 0 and was switched to a new acidic absorption solution just before NH₃₍g₎ breakthrough occurred, at pH ~5. Experiments with a wide range of NH₃₍g₎ concentrations showed that the absorption efficiency was practically 100% throughout the process as long as the face velocity was below 4 cm/s. The potential advantages of the method include high absorption efficiency, lower NH₃₍g₎ concentrations in the vicinity of the birds, generation of a valuable product and the separation between the ventilation and ammonia treatment systems. A small scale pilot operation conducted for 5 weeks in a broiler house showed the approach to be technically feasible. H₂S₍g₎ removal: The main goal of this part was to develop a specific treatment process for minimizing H₂S₍g₎ emissions from hog houses. The proposed process consists of three units: In the 1ˢᵗ H₂S₍g₎ is absorbed into an acidic (pH<2) ferric iron solution and oxidized by Fe(III) to S⁰ in a bubble column reactor. In parallel, Fe(III) is reduced to Fe(II). In the 2ⁿᵈ unit Fe(II) is bio-oxidized back to Fe(III) by Acidithiobacillus ferrooxidans (AF).In the 3ʳᵈ unit S⁰ is separated from solution in a gravity settler. The work focused on three sub-processes: the kinetics of H₂S absorption into a ferric solution at low pH, the kinetics of Fe²⁺ oxidation by AF and the factors that affect ferric iron precipitation (a main obstacle for a continuous operation of the process) under the operational conditions. H₂S removal efficiency was found higher at a higher Fe(III) concentration and also higher for higher H₂S₍g₎ concentrations and lower flow rates of the treated air. The rate limiting step of the H₂S reactive absorption was found to be the chemical reaction rather than the transition from gas to liquid phase. H₂S₍g₎ removal efficiency of >95% was recorded with Fe(III) concentration of 9 g/L using typical AFO air compositions. The 2ⁿᵈ part of the work focused on kinetics of Fe(II) oxidation by AF. A new lab technique was developed for determining the kinetic equation and kinetic parameters (KS, Kₚ and mₘₐₓ) for the bacteria. The 3ʳᵈ part focused on iron oxide precipitation under the operational conditions. It was found that at lower pH (1.5) jarosite accumulation is slower and that the performance of the AF at this pH was sufficient for successive operation of the proposed process at the H₂S fluxes predicted from AFOs. A laboratory-scale test was carried out at Purdue University on the use of the integrated system for simultaneous hydrogen sulfide removal from a H₂S bubble column filled with ferric sulfate solution and biological regeneration of ferric ions in a packed column immobilized with enriched AFbacteria. Results demonstrated the technical feasibility of the integrated system for H₂S removal and simultaneous biological regeneration of Fe(III) for potential continuous treatment of H₂S released from CAFO. NH₃ and H₂S gradient measurements at egg layer and swine barns were conducted in winter and summer at Purdue. Results showed high potential to concentrate NH₃ and H₂S in hog buildings, and NH₃ in layer houses. H₂S emissions from layer houses were too low for a significant gradient. An NH₃ capturing system was designed and tested in a 100-chicken broiler room. Five bell-type collecting devices were installed over the litter to collect NH₃ emissions. While the air extraction system moved only 10% of the total room ventilation airflow rate, the fraction of total ammonia removed was 18%, because of the higher concentration air taken from near the litter. The system demonstrated the potential to reduce emissions from broiler facilities and to concentrate the NH₃ effluent for use in an emission control system. In summary, the project laid a solid foundation for the implementation of both processes, and also resulted in a significant scientific contribution related to AF kinetic studies and ferrous analytical measurements.