Az oxigénsztöchiometria hatása ABO3 típusú (A: Ba, Sr, Ca, lantanidák, B: Fe, Co) perovszkitok és rokon oxidok szerkezetére és fizikai tulajdonságaira = The influence of oxygen stoichiometry on the structure and physical properties of ABO3 type (A: Ba, Sr, Ca, lanthanoids, B: Fe, Co) perovskites and related oxides.

Kutatási projektünk legfontosabb témája a La0.8Sr0.2CoO3  vizsgálata volt emissziós Mössbauer-spektroszkópia segítségével. E kolosszális mágneses ellenállást mutató anyagon a paramágneses és ferromágneses fázis együttes jelenlétét eddig soha nem látott széles tartományban tapasztaltuk, amit változatos méreteloszlású ferromágneses klaszterek létrejöttével értelmeztünk. Megállapítottuk, hogy a Mössbauer-izomereltolódás értéke a ferromágneses fázisban kisebb, mint a paramágneses fázisban, és ez a ferromágneses fázis megnövekedett vezetőképességével hozható összefüggésbe. Ezzel először láttuk be, hogy egy ilyen CMR anyagban fémes vezetés ténylegesen csak a ferromágneses fázishoz kötődik. Először mutattuk meg, hogy az oxigéntartalom csökkenése a rácsban megjelenő vakanciák hatására csökkenti az átlagos mágnesesklaszter-méretet, mivel a hiányzó oxigének megszakítják a mágneses (dupla) kicserélődési kölcsönhatás láncolatát. Ezek az eredmények jelentősen hozzájárulnak a CMR-anyagok mágneses viselkedésének megértéséhez. | As a first proirity within our research project, we have investigated La0.8Sr0.2CoO3  by the help of emission Mössbauer spectroscopy. Co-existence of the ferromagnetic and the paramagnetic fraction was observed in an unprecedentedly wide temperature interval in this colossal magnetoresistant material. This was attributed to the formation of magnetic clusters of variuos sizes. It was found that the Mössbauer isomer shift in the ferromagnetic phase is lower than in the paramagnetic phase, which was interpreted on terms of increased conductivity in the ferromagnetic phase. It was verified at the first time that metallicity is connected solely to the ferromagnetic fraction of the sample. It was demonstrated also at the first time that oxygen removal from the material decreases the average size of the magnetic clusters through injection of vacancies. Oxygen vacancies cut clusters into smaller parts because the chain of double exchange interaction is interrupted due to missing oxygens. These results are important contributions to the understanding of the magnetic behavior of CMR materials

X-ray powder diffraction study of chromium-vanadium oxide compounds prepared by "soft chemistry" methods

A novel aqueous method was used to synthesise mixed chromium-vanadium oxide hydrates with various chromium content, via the reaction of peroxo-polyacids of chromium and vanadium. The resulting materials are gelatinous. The dehydration of the gels result in a brown coloured amorphous powder. Depending on the chromium content, the compounds have a different characteristic crystallisation temperature upon the further heating. The crystalline compounds, except for the low chromium ones, go on a phase transition and decompose with increasing temperature. By refining the XRPD measurement data of the compounds, the type and parameters of the unit cells were determined. The experimental data were in concordance with the calculated values, using the PWC code. The lattice parameters and the crystalline structure were changed with the variation of chromium content. (C) Versita Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved

Preparation and structure's analyses of lanthanide (Ln) -exchanged bentonites

K

Mágneses ellenállást mutató perovszkitok és spinellek vizsgálata Mössbauer-spektroszkópiával, mágneses és röntgendiffrakciós módszerekkel = Mössbauer spectroscopic, magnetic and x-ray diffraction studies of some perovskite and spinel materials possessing magnetoresistivity

I. Kutatásunk legfontosabb eredménye, hogy összefüggést tudtunk felmutatni a vizsgált kobaltát perovszkitok lokális elektromos és mágneses szerkezete és az általuk mutatott mágneses ellenállás között. Sikerült felvázolni a La0.8Sr0.2Co1-yFeyO3 (0 < y < 0,3) perovszkitok mágneses fázisdiagramját, részletesen elemezni tudtuk a különböző fázisok természetét, valamint a lantánionok európiummal való cseréjével megállapítottuk a ritkaföldfém lokális elektromos állapotát. Egy újabb kísérletsorozat során elkészítettük, karakterizáltuk és megvizsgáltuk a La1-xSrxFe0.025Co0.975O3 (0 < x < 0,25) összetételű perovszkitokat is. Eredményeink alapján megállapítottuk, hogy a mágneses ellenállás kiváltó oka a vizsgált perovszkitokban a nanoméretű elektromos-mágneses fázisszeparáció lehet. II. A pályázat másik kutatási témájának keretén belül növények vasfelvételi mechanizmusait vizsgáltuk Mössbauer-spektroszkópia segítségével uborka és búza felhasználásával. Bizonyítottuk az ún. I. stratégiai csoportba tartozó növények redukción alapuló vasfelvételi mechanizmusát és rámutattunk a Cd vasfelvételt (és transzportot) gátló hatásaira. Emellett biomineralizációs és szintetikus folyamatokban képződő jarozitok szerkezetét tanulmányoztuk PXRD és Mössbauer-spektroszkópiai módszerekkel. UV-látható spektrofotometria és Mössbauer-spektroszkópia alkalmazásával megvizsgáltuk a növényélettani szempontból jelentős indol-3-ecetsavnak a vas(III)-mal történő reakcióinak mechanizmusát és kinetikáját. | I. Our primer finding is that we were able to correlate the observed local electronic and magnetic properties of the investigated cobaltate perovskite samples with their magnetoresistance. We presented the magnetic phase diagram of La0.8Sr0.2Co1-yFeyO3 (0 < y < 0.3) perovskites, and we analyzed the nature of the depicted magnetic phases. Moreover, by replacing the lanthanum ions with europium, using 151Eu Mössbauer spectrometry we have determined the local electronic structure of the rare-earth cation, as well. We have also prepared and characterized La1-xSrxFe0.025Co0.975O3 (0 < x < 0.25) samples and performed several experiments on them. Due to our results, we were able to determine the possible source of the magnetoresistance of the investigated family of perovskites, being the nanosize electronic-magnetic phase separation. II. In the second part of the project, the iron-uptake mechanisms of plants were investigated by Mössbauer spectroscopy, using cucumber and wheat as model plants: direct evidence for the strategy I iron-uptake mechanism was given and the inhibitory effects of Cd on the iron-uptake and transport were demonstrated. The structure of jarosites formed during biomineralization and synthetic processes were studied with the help of PXRD and Mössbauer spectroscopy. The mechanism and the kinetics of the reaction of the plant hormone indole-3-acetic acid with iron(III) was discussed in detail using UV-Vis spectrophotometry and Mössbauer spectroscopy

Novel iron complexes with glyoximes, schiff bases and boric acid derivatives : synthesis, physico-chemical analysis and biological study

Iron(II) clathrochelate complexes obtained with glyoximes are macrobicyclic ligand systems, which completely encapsulate the metal ion, and are formed under mild conditions with high yields [1]. In particular, the riblike-functionalized clatrochelates both with the inherent and with the terminal closo-borate substituents synthesized recently have been proposed as new radiopharmaceuticals for boron neutron capture therapy of cancer [2]. In our research work new iron(II) complexes were synthesized with -glyoximes, boric acid derivatives, amines, Schiff bases, such as [Fe(Me-Pr-Glyox)3(BO–Et)2], [Fe(Et-BuGlyox)3(BO–R)2] (R = methyl, propyl, butyl), [Fe(phenyl-Me-GlyoxH)2(amine)2], [Fe(Et-BuGlyoxH)2(amine)2], [Fe(2-heptanone)2(en)(amine)2], where GlyoxH, Glyox = mono- or bideprotonated glyoxime, en = ethylenediamine and the used amines: dibutylamine, 3-picoline, 4-aminopyridine, 6-amino-3-picoline, 3-amino-1-propanol, imidazole, 2-aminopyrimidine, 3- methylpiperidine, 3-amino-1H-1,2,4-triazole. For preparation ironII -sulfate was dissolved in water and mixed with alcoholic solution of the glyoxime, then the corresponding amines and the other complexing agents were added. The mixture so obtained was refluxed under inert atmosphere. The molecular structures of our products were studied by IR, Mössbauer and UV–VIS spectroscopies, mass spectrometry (MS) and thermoanalytical measurements (TG-DTG-DTA). The biological activity, like antimicrobial effect, was studied for a few bacteria

Új Fe(II)-komplexek előállítása α-dioximokkal, bórsavval sé észtereivel, szemi- és tioszemikarbazonokkal, schiffbázisokkal, valamint fizikai-kémiai és biológiai vizsgálatuk

In our research project new iron(II) complexes were synthesized with azomethines, such as [Fe(1,4-dibromo-2,3-butane-GlyoxH)2(3-HO-aniline)2], [Fe(1,4-dibromo-2,3-butaneGlyoxH)2(2-amino-pyrimidine)2], [Fe(4-benzyl-2-HO-propiophenone-GlyoxH)2], [Fe(5- methyl-2-hexanone)2(en)], [Fe(5-methyl-2-hexanone)2(1,2-pn)], [Fe(5-methyl-2-hexanone)2 (1,3-pn)], [Fe(5-methyl-2-hexanone)2(o-fen)], [Fe(2,4,5-trimethoxy-acetophenone-SC)2], [Fe(2,4,5-trimethoxy-acetophenone-TSC)2], [Fe(5-methyl-2-hexanone-SC)2], [Fe(5-methyl-2- hexanone-TSC)2], [Fe(Me-Pr-Glyox)3(BOH)2], [Fe(Me-Pr-Glyox)3(BOMe)2], [Fe(Me-i-BuGlyox)3(BOH)2], [Fe(Me-i-Bu-Glyox)3(BOMe)2], [Fe(Me-i-Bu-Glyox)3(BO-n-propyl)2] (en = ethylenedianine, pn = propylenediamine, fen = phenylenediamine, SC = semicarbazone, TSC = thiosemicarbazone), by reacting iron(II)-chloride with different glyoximes, Schiff-bases, semi- or thiosemicarbazones in suitable solvent. The Schiff-bases were obtained with the condensation of 5-methyl-2-hexanone, with diamines. The semi- or thiosemicarbazones were prepared by the condensation of 2,4,5-trimethoxy-acetophenone or 5-methyl-2-hexanone with semicarbazide or thiosemicarbazide. We analyzed their physicochemical properties using mass spectrometry, infrared-, NMR-, UV–VIS-, Mössbauer-spectroscopy, powder-XRD and thermal analysis (TG, DTG and DTA). The biological activity of complexes, especially their antibacterial activity was also explored. The importance of this class of compounds is gained in biochemistry, since some of them act as antibacterial agents and potential anticancer drugs. Furthermore, some members can play role as catalysts in organic chemistry transformations [1–2]

Structure and magnetism of Fe–Co alloy nanoparticles

We report the hydrothermal synthesis and structure of FexCo1−x alloy nanoparticles with considerable stability against oxidation under ambient atmosphere. Powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma mass spectrometry (ICP-MS), 57Fe Mössbauer spectroscopy and magnetization measurements are applied to characterize the composition, morphology, crystal structure, atomic order and magnetic properties of the nanoparticles. As-prepared samples are composed mainly of the bcc FexCo1−x alloy phase. TEM images of heat-treated samples confirm the nanoparticle nature of the original alloys. A consistent analysis of the experimental results leads to x ≈ 53% and x ≈ 62% Fe atomic ratio respectively in two analogous alloy samples, and suggests that the atomic level structure of the nanoparticles corresponds to that of a fully disordered (A2-type) alloy phase. Exploration of the effect of cobalt on the 57Fe hyperfine parameters of iron microenvironments suggests that in these alloys the electronic state of Fe atoms is perturbed equally and in an additive manner by atoms in their first two coordination spheres