BiFeO3 perovskites: theoretical and experimental investigations

Bismuth ferrite (BiFeO3) is one of the most studied multiferroic system. BiFeO3 has been synthesized by controlled hydrothermal process, where the particles of small sizes and with high purity were obtained. Structural analysis showed that nonannealed powder can be perfectly fitted to rhombohedral space group R3c as αBiFeO3 phase. In addition, a structure prediction has been performed and 11 additional BiFeO3 modifications have been proposed. In the next phase, an ab initio optimization of predicted structures has been performed and the structure of the γphase has been elucidated. In addition, electronic and magnetic properties of BiFeO3 were investigated using combination of experimental and theoretical methods. Theoretical studies were performed using a full potential linearized augmented plane-waves plus local orbital (FP(L)APW+lo) method, based on density functional theory (DFT). HRTEM analysis confirmed existence of twin stacking faults, which are responsible for enhanced magnetic properties. EPR measurements suggested existence of electrons trapped by vacancies or defects, while magnetic behavior of synthesized material was investigated by SQUID

Introduction of transition metal cations (Co2+ and Zn2+) into dealuminated NaY zeolite obtained by citric acid treatment

Aluminum ions were extracted from the framework of the faujasite type zeolite NaY (Si/Al=2.4) by citric acid treatment. Dealuminated CoY and ZnY zeolites of high cobalt and zinc content were prepared by replacing sodium ions with Co2+ and Zn2+ in dealuminated Y zeolites, with increased framework Si/Al ratio. Chemical and XRD analyses of zeolites were performed and the FTIR-ATR spectra were recorded. The results of physicochemical analyses are discussed in terms of unit cell (u.c.) composition

Palladium sorption by aminofunctionalized macroporous copolymer from chloride–nitrate solutions

Macroporous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) with attached diethylene triamine [PGME-deta] with high amino-group content was used for the investigation of the Pd(II) sorption kinetics from mixed chloride/nitrate aqueous solutions in acidic medium (pH 2.0) at T=298 K. Four kinetic models were employed in order to comprehend the mechanism of Pd(II) sorption. The maximum experimental Pd(II) sorption capacity at initial pH 2.0 and 298 K was 20 mg g-1

Thermal behaviour of some nonporous methacrylate polymers

Three nonporous methacrylate polymer samples were synthesized by suspension polymerization, and subsequently investigated. The surface area and the surface morphology of the spherical beads were examined by the BET method from the low-temperature adsorption isotherms and by scanning electron microscopy (SEM), respectively. Thermal behaviour of the two homopolymer samples, poly(glycidyl methacrylate) (PGMA) and poly(ethylene glycol dimethacrylate) (PEGDMA), and the copolymer sample poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (PGME) was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). All samples exhibit complex thermal degradation behavior. The copolymer is intermediate in stability between PGMA and PEGDMA

Synthesis, optical and magnetic properties studies of multiferroic BiFeO3

Nanosized bismuth ferrite powder has a potential application in the production of lead free piezoelectric materials for actuators as well as magnetoelectric sensors. The simple, low-costing and energy-saving hydrothermal method has advantages over the conventional methods. BiFeO3 powders were made using Bi(NO3)35H2O and Fe(NO3)3 9H2O as starting material and 8 M KOH as mineralizer. The particle size and morphology were analyzed using scanning electron microscopy (SEM). The phase composition of obtained samples was determined by X-ray diffraction (XRD) analysis. It revealed that synthesized material crystallize in space group R3c with cell parameters a = b = 5.5780(10) Å and c = 13,863(3) Å. IR and Raman spectroscopy have been performed on the synthesized bismuth ferrite (BFO) powders in order to confirm the formation of pure and well-crystallized BFO nanocrystallites. 57Fe Mössbauer spectroscopy was performed in order to provide information on Fe cation arrangement in the BiFeO3 phase. The magnetic and optical properties of properties of BFO samples were characterized by SQUID magnetometry, and ultraviolet–visible spectroscopy. Temperature dependence of magnetization shows antiferromagnetic-paramagnetic phase transition at TN = 220 K, while below this temperature weak ferromagnetic ordering is detected

Perrhenate sorption by amino-functionalized glycidyl methacrylate copolymer: investigation of rhenium as an analogue of radioactive technetium

In order to define the favorable conditions for radioactive technetium (99Tc) uptake, the sorption behavior of its non-active chemical analogue rhenium ( 75Re) on amino-functionalized macroporous hydrophilic copolymer was studied. The pseudo-second-order (PSO) model provided the best fit for the kinetic data, while the intraparticle diffusion (IPD) model indicated a pronounced influence of the porous structure on the sorption rates. The maximum sorption capacity was found to be 84 mg g-1 and 74 % removal efficiency was reached after 180 min in citrate buffer at pH 5.0

Comprehensive Characterization of Multiferroic BiFeO3 Powder Fabricated by the Hydrothermal Procedure

Bismuth ferrite (BiFeO3) has recently drawn attention due to its outstanding multifunctional properties, as well as for being a lead-free ceramic material. In the current study, BiFeO3 nanoparticles were synthesized by strictly controlled hydrothermal process. High geometric molded particles of a small size and with high degree of purity (99.74 %) were obtained. We used nitrates of bismuth and iron as well as 8M potassium hydroxide as a basis for synthesis. The results of the X-ray diffraction study of the obtained polycrystalline material show single-phase bismuth ferrite that crystallizes with a rhombohedral lattice. Using the Rietveld method it has been determined that the particles of the synthesized powder are in a nanometric range with a particle size of about 30 nm. It was found that all reflec-tions of the obtained bismuth ferrite belong to the rhombohedral α-BiFeO3 phase which crystallizes in the space group R3c (No. 161). In addition, electronic and magnetic properties of BiFeO3 were investigated using combination of experimental and theoretical methods. HRTEM analysis confirmed existence of twin stacking faults, which are responsible for enhanced magnetic properties. EPR measurements suggested existence of electrons trapped by vacancies or defects. It has been pro-posed that Fe3+−OV defect complex could be created at elevated temperatures fol-lowed by formation of trivalent Fe ions, which intensely provide local 3d moments. The magnetic behavior of the synthesized material was studied by means of SQUID device and using a vibrating sample magnetometer (VSM). The temperature dependence of the magnetization shows the antiferomagnetic-paramagnetic phase transition at the temperature of TN = 220K, while below this temperature weak ferro-magnetic behavior has been detected. Theoretical studies were performed using a full potential linearized augmented plane-waves plus local orbital (FP(L)APW+lo) method, based on the density functional theory (DFT). In addition, a structure prediction has been performed and 11 additional BiFeO3 modifications have been pro-posed. In the next stage, an ab initio optimization of predicted structures has been performed and the structure of the γ-phase has been elucidated

The investigation of strong active sites of dealuminated Y-type zeolite by TPD of carbon monoxide

The active sites of hydrogen-exchanged Y zeolite (HY) and dealuminated (HDY) zeolites are investigated by TPD of carbon monoxide. Only the high temperature TPD spectra of CO (T(M)approximate to620-690degreesC) were observed, meaning that CO molecules interact with very strong acid sites. The amounts of CO bonded on these sites are small (less than 1 molecule per unit cell). The strong influence of dealumination on the coverage degree is found. The calculated values for kinetic parameters indicate chemisorption of CO in the investigated systems (E(des)approximate to240 kJ mol(-1), Aapproximate to10(11) s(-1)).8th European Symposium on Thermal Analysis and Calorimetry (ESTAC-8), Aug 25-29, 2002, Barcelona, Spai

Synthesis and electrochemical properties of Na1.2V3O8/LTX as anodic material in sodium ion batteries

In this paper, the synthesis of composite Na1.2V3O8/LTX by sol-gel method was described. The synthesized powders were characterized by X-ray powder diffraction (XRD) and thermogravimetric analysis (TGA) while the electrochemical performances were investigated by cycling voltammetry (CV) by different scan rate. After thermal treatment, the part of carbon was 7%. The initial discharge capacity was 100.44 mAhg-1. The most capacity fade was after 2nd cycle (14%) but capacity fade from 6th to 10th cycle was only 10%. The efficiency of Na1.2V3O8/LTX is around 95%

BiFeO3 perovskites: A multidisciplinary approach to multiferroics

Bismuth ferrite (BiFeO3) is one of the most studied multiferroic system with a large number of published articles. This is mainly because BiFeO3 material possesses both ferromagnetic and ferroelectric properties observed at room temperature, which opens great possibility for industrial and technological applications. Well crystallized single-crystal BiFeO3 nanopowder has been successfully synthesized with the hydrothermal method. The phase composition of the synthesized samples was determined by the x-ray diffraction (XRD) analysis, and the results showed that synthesized material crystallizes in the space group R3c as alpha-BiFeO3 phase, which was confirmed by the previous experiments. In addition, a structure prediction has been performed and 11 additional BiFeO3 modifications have been proposed. In the next phase, an ab initio optimization of predicted structures has been performed and the structure of the gamma-form has been elucidated. Furthermore, electronic and magnetic properties of BiFeO3 were investigated using combination of experimental and theoretical methods. Spectroscopic Ellipsometry has been used to study electronic properties of BiFeO3, while magnetic behavior of synthesized material was investigated by SQUID. Finally, theoretical studies were performed using a full potential linearized augmented plane-waves plus local orbital (FP(L)APW+lo) method, based on density functional theory (DFT)