Wyniki wyszukiwania - Biblioteka Nauki

1

Study of magnetic defects in NB2VSBO10 and NB6VSB3O25 compounds

100%

Typek J. , Bobrowska M.

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tom T. 5

93--98

EN

Introduction and aim: Two new compounds from the Nb-V-Sb-O system will be scrutinized as possible catalysts, because many compounds from this system has showed promising catalytic properties. Since there is often a direct link between the number of defects and catalytic activity of a compound, these two materials will be investigated by magnetic methods to detect existing defects and to determine their structure and properties. Material and methods:NB2VSBO10and NB6VSB3O25 are relatively new compounds synthesized in Department of Inorganic and Analytical Chemistry, West Pomeranian University of Technology, Szczecin. Two magnetic methods have been used - dc magnetisation and electron paramagnetic resonance (EPR) spectroscopy. Results: Although the nominal valences of metal ions in both compounds suggested non-magnetic properties, very complex magnetic response was registered in both magnetisation and EPR measurements. Non-homogeneous distribution of magnetic ions makes possible formation of different types of spin clusters and strongly interacting magnetic subsystems. Conclusion: NB6VSB3O25 seems to be more promising catalyst than NB2VSBO10 as there are more magnetic defects in this compound.

PL

Wstęp i cel: Dwa nowe związki z układu Nb-V-Sb-O będą rozważane jako potencjalne katalizatory, gdyż wiele związków z tego układu wykazuje obiecujące właściwości katalityczne. Ponieważ często pomiędzy ilością defektów a aktywnością katalityczną istnieje zależność proporcjonalna, dwa te związki będą badane metodami magnetycznymi aby wykryć istniejące w nich defekty oraz określić ich strukturę i właściwości. Materiały i metody: NB2VSBO10 and Nb6VSb3O25zostały zsyntezowane stosunkowo niedawno w Katedrze Chemii Nieorganicznej i Analitycznej Zachodniopomorskiego Uniwersytetu Technologicznego w Szczecinie. Zastosowano dwie metody badania właściwości magnetycznych - stałoprądową magnetyzację i spektroskopii elektronowego rezonansu paramagnetycznego (EPR). Wyniki: Chociaż nominalna wartościowość jonów metali w obu związkach sugeruje brak magnetycznych właściwości, zarejestrowano bardzo złożoną odpowiedź magnetyczną w pomiarach magnetyzacji i EPR. Niejednorodny rozkład jonów magnetycznych powoduje tworzenie się różnego rodzaju klasterów spinowych i silnie oddziaływujących podukładów magnetycznych. Wnioski: NB6VSB3O25wydaje się być bardziej obiecującym katalizatorem niż NB2VSBO10, ponieważ w tym związku jest dużo więcej defektów magnetycznych.

2

ESR study of spin dynamics in (Er0.5Y0.5)2Cu2O5 solid solution

100%

Typek J. , Guskos N.

Materials Science Poland

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2006

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tom Vol. 24, No. 4

901--912

EN

Powder samples of (Er0.5Y0.5)2Cu 2O5 have been synthesized by a solid state reaction method. Electron spin resonance (ESR) measurements have been carried out on a Broker E 500 X-band spectrometer in the 4-300 K temperature range. A single, almost Lorentzian-shaped resonance line has been recorded for the whole investigated temperature range and its ESR parameters (integrated intensity, linewidth and resonance field) displayed a strong temperature dependence. The integrated intensity of the resonance line showed a pronounced maximum in low-temperature range and vanished at the transition to the antiferromagnetic ordering at TN = 11 K. The temperature at which the ESR integrated intensity reaches its maximum is different for the heating and cooling runs. Below 40 K, on approach to TN, the linewidth exhibited a divergent behaviour due to the onset of three-dimensional magnetic order. At higher temperatures (about 220 K), variations in ESR magnetic susceptibility suggest the presence of dynamical processes in copper-oxygen chains leading to the formation of copper dirners. The observed changes of the ESR parameters are interpreted in terms of 2D magnetism of the copper-oxygen system in the (Er 0.5Y0.5)2Cu2O5 solid solution.

3

Synthesis and ESR study of (TbxY1 - x)2Cu2O5 solid solutions

80%

Typek J. , Kostrzewa J. , Guskos N.

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tom Vol. 23, No. 4

929--938

EN

Polycrystalline samples of (TbxY1 - x)2Cu2O5, where x = 1.0, 0.75, 0.50, 0.38, 0.25, 0.125 and 0, were synthesized by the solid-state reaction technique. XRD measurements showed that the obtained samples are single-phase and belong to the orthorhombic space group Pna21. The observed linear change of the lattice parameters and unit cell volume with terbium concentration is in agreement with Vegard's law. A thermogravimetric study of the decomposition process of the obtained samples revealed small sampledependent mass losses in the temperature range 1030-1050 °C, and a larger, intrinsic mass loss in the range 1100-1150 °C. The former are probably due to the 4 CuO › 2 Cu2O + O2 transformation, while the latter is related to the reaction 2Y2Cu2O5 › 4YCuO2 + O2. The peak temperature of the main decomposition stage varies linearly with terbium concentration, which could be explained by an increasing distortion of coordination polyhedra around the copper ion, caused by the substitution of the larger Tb3+ cation. The ESR spectra of (TbxY1 - x)2Cu2O5 solid solutions showed a complicated structure due to the presence of various copper clusters (tetramers, trimers). Moreover, the ESR spectra were anisotropic in an external magnetic field, despite originating from powder samples.

4

Magnetic resonance study of SbVO5 thermal decomposition products

80%

Typek J. , Filipek E. , Maryniak M. , Guskos N.

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tom Vol. 23, No. 4

1047--1054

EN

A new SbVO5 compound, which can be synthesized from an equimolar mixture of Sb2O3/V2O5 or ?-Sb2O4/V2O5 oxides by heating in air to temperatures below 650 °C, is stable in air up to 710 °C and in argon atmosphere up to ~645 °C. At higher temperatures it decomposes into a phase with a rutile-type structure. Using electron spin resonance (ESR) we have studied the magnetic properties of the thermal decomposition products of SbVO5 in air (sample 1D) and in argon atmosphere (sample 2D), as well as two phases of the of the rutile-type structure (samples 3S and 4S) synthesized at conditions similar to the previous two samples. The ESR spectra of all four samples consisted mostly of two types of lines: a narrow line (designated as the N component) and a very broad line (designated as the VB component). Close inspection of the ESR parameters for these components allowed the samples to be grouped according to the environment they were annealed in (air or oxygen-free argon). The origin of these lines and the implications concerning the phase composition of the decomposition products are discussed. ESR results confirm that the solid decomposition product of SbVO5 in air is a nonstoichiometric compound with a rutile structure and formula Sb0.95+V0.13+V0.84+ 0.2O4 and in argon a near-stoichiometric V4+Sb5+O4.5.

5

Magnetic ordering processes in manganese(II) di(hydrogen malonate) dihydrate complex studied by ESR spectroscopy

80%

Marczyński S. , Typek J. , Grech E. , Kołodziej B.

Materials Science Poland

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2006

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tom Vol. 24, No. 4

1139--1144

EN

A new manganese complex of malonic acid CH2(COOH) 2źMnCO3źH2O was synthesized. Temperature dependence of the electron spin resonance (ESR) spectrum of Mn(II) was investigated in the 4.2-295 K. temperature range. The obtained ESR spectra were successfully fitted by using a Lorentzian-shape function. The fitting revealed existence of about 2% of a spurious phase of the manganese(II) complex. Strong magnetic interactions have been observed in the investigated temperature range with expected magnetic phase transition at TN approximately equals 2.5 K. The integrated intensity, linewidth and resonance field of the ESR spectrum have shown that the spin dynamical fluctuations essentially influence the magnetic system. An anomalous behaviour of the ESR resonance field parameter has been observed below 100 K. and with decreasing temperature the resonance field shifted to higher magnetic fields.

6

Photoacoustic study of a new neodymium(III) hydrazone complex

71%

Guskos N. , Paschalidis D. G. , Majszczyk J. , Typek J. , Maryniak M.

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tom Vol. 23, No. 4

1029--1034

EN

The neodymium(III) hydrazone complex [Nd(DBH)2(NO3)3] has been synthesized and characterized using microanalysis and IR spectroscopy. High-resolution photoacoustic spectrometry has been applied for studying the complex. The obtained photoacoustic spectrum has been analysed and compared to a similar [Nd(PicBH)2(NO3)2]NO3 complex. The intensities of the f-f transitions in the photoacoustic spectrum of Nd(DBH)2(NO3)3 were two times greater than for the [Nd(PicBH)2(NO3)2]NO3 complex.

7

The linewidths and pintegrated intensities of the d-d transitions in photoacoustic spectra of polyamine copper(II) complexes

71%

Guskos N. , Typek J. , Papadopoulos G. J. , Maryniak M. , Aidinis K.

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tom Vol. 23, No. 4

955--960

EN

Photoacoustic spectra of the d-d transitions for three different series of copper(II) complexes of spermidines Spn (Spn323, Spn333, Spn343), Spm (Spm323, Spm333, Spm343) and Spc (Spc323, Spc333) have been investigated. Replacements of distant atoms, the presence or absence of water molecule in the structure, the kind of ligands surrounding the metal(II) ions have a strong influence on the crystal field splitting and the intensities of the non-radiative transitions. Non-radiative processes are involved in important mechanisms of the dynamic interactions between the electrons and the lattice. Studies of the intensities of the non-radiative transitions provide a very important data for the thermodynamic states of these systems. Photoacoustic absorption band of the d-d transitions could be decomposed into three lines (due to the crystal field splitting) with different intensities, positions and linewidths. The integrated intensities may yield information about the number of non-radiative processes, while the linewidths about the mechanisms of the relaxation processes.

8

Electron spin resonance study of copper(II) hydrogenmalonate dihydrate complex

71%

Marczyński S. , Typek J. , Guskos N. , Grech E. , Kołodziej B.

Materials Science Poland

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2006

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tom Vol. 24, No. 4

1077--1085

EN

Copper(II) hydrogenmalonate dihydrate complex has been studied by using the electron spin resonance (ESR) method. Numerically deconvoluted ESR spectra of Cu(II) ions have been investigated at 4.2-295 K temperature range. The powder ESR spectrum has been described by three g-factors and additionally 1.5% of the existing spurious phases of a copper(II) complex has been revealed. The temperature dependence of the integrated ESR intensity has shown a Curic-Weiss type behaviour, consisting of two terms with different Curie-Weiss temperatures. The observed ferromagnetic interactions suggest the presence of two different paramagnetic species. It is proposed that the [Cu(H2O) 4][Cu(mal)2(H2O)2] copper(II) dimer complex is responsible for the low-temperature (T less than or equal 50 K) behaviour of the investigated sample.

9

FMR study of gamma-Fe2O3 magnetic nanoparticles in a multiblock poly(ether-ester) copolymer matrix

61%

Guskos N. , Typek J. , Maryniak M. , Roslaniec Z. , Petridis D. , Kwiatkowska M.

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tom Vol. 23, No. 4

971--976

EN

Four samples containing gamma-Fe2O3 magnetic nanoparticles dispersed at a concentration of 0.1 % (samples I and I') and 0.3 % (samples II and II') in a polymer matrix have been prepared. The polymer filler was in two forms: as solid-state grains (samples I and II) and as a liquid solution in trichloromethane (samples I' and II'). The typical size of the magnetic nanoparticles was 10 nm. The samples were characterized by XRD and TEM spectroscopy. Ferromagnetic resonance (FMR) measurements were carried out at room (RT) and liquid nitrogen (LNT) temperatures for all four samples. An intense resonance absorption line from gamma-Fe2O3 was recorded, with a slightly asymmetric line shape. The FMR spectra at RT and LNT are almost the same, as could be expected for the composite matrix. For samples II and II', the resonance lines are centred at Hr = 3039(10) Gs and Hr = 3197 (10) Gs, respectively, with linewidths of deltaH = 1289(5) Gs and deltaH = 1364(5) Gs, respectively. For samples I and I', the following values of resonance line parameters were obtained: Hr = 3172(10) Gs for sample I', and Hr = 2958(10) Gs for sample I, with linewidths of deltaH = 1279(5) Gs and deltaH = 1200(5) Gs, respectively. In both cases the resonance field for samples obtained from a solid state filler is shifted to lower magnetic fields as compared to samples made from a suspension filler, which suggests stronger ferromagnetic interactions in these materials.

10

FMR study of agglomerated nanoparticles in a Fe3C/C system

61%

Guskos N. , Typek J. , Maryniak M. , Narkiewicz U. , Kucharewicz I. , Wróbel R.

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tom Vol. 23, No. 4

1001--1008

EN

Three samples with various Fe3C/C ratios have been prepared by the carburisation of iron with ethylene or an ethylene-hydrogen mixture. Carburisation was controlled with thermogravimetry. After carburisation, the samples were characterized using XRD and scanning electron microscopy. XRD measurements have shown the presence of the Fe3C (cementite) phase only. The mean size of cementite crystallites estimated using Scherrer's equation was in the range of 40-46 nm. Ferromagnetic resonance (FMR) absorption signals were investigated at room temperature. In all samples an asymmetric, very broad, and intense FMR line shifted toward low magnetic field was recorded. The linewidth, intensity, and position of the resonance field depended strongly on carbon concentration. With increasing carbon concentration the linewidth and integrated intensities of the FMR spectra decreased, and the resonance line shifted towards higher magnetic fields. The separation of granules from each other by carbon could drastically influence the FMR absorption spectrum due to decreasing intergranular interaction with increasing carbon concentration.

11

Temperature dependence of the FMR spectra of Fe3O4 and Fe3C nanoparticle magnetic systems in copolymer matrices

61%

Guskos N. , Typek J. , Roslaniec Z. , Narkiewicz U. , Kwiatkowska M. , Maryniak M.

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tom Vol. 23, No. 4

1055--1063

EN

A binary magnetic nanoparticle system, consisting of Fe3O4 (35 wt. %), Fe3C (29 wt. %), and C (36 wt. %) filling in a PTMO-block-PET polymer at low concentration (0.3 %), has been synthesized. X-ray and SEM analyses have been carried out. The temperature dependence of the FMR spectrum of this system has been investigated. At higher temperatures resonance from Fe3O4 nanoparticles dominates the FMR spectrum, while at lower temperatures a more intense line from Fe3C is recorded. The temperature dependence of the FMR spectrum confirms that the nanoparticles of Fe3O4 reach the ordered state faster than Fe3C nanoparticles. In both cases, the spin-glass state is observed below 50 K.

12

Characterization and EPR studies of TiC and TiN ceramics at room temperature

61%

Bodziony T. , Guskos N. , Biedunkiewicz A. , Typek J. , Wróbel R. , Maryniak M.

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tom Vol. 23, No. 4

899--907

EN

Four samples, namely TiC/C, TiN/C, (TiC + FexCy + Fe)/C and TiN/amorphous carbon, have been prepared and investigated. In the former three samples titanium compounds were placed in a carbon matrix, while in the fourth one TiN was surrounded by an amorphous carbon. The samples have been characterized by XRD, SEM, and electron diffraction spectroscopy. The crystallite sizes and lattice parameters of TiC and TiN have been determined by the X-ray diffraction method. XRD measurements have shown that the lattice constants of nanosized samples were smaller than those of microsized samples. An essential influence of the carbon matrix during the crystallization process on the lattice parameters and grain size was observed. Electron paramagnetic resonance (EPR) measurements of the samples were carried out at room temperature. A narrow EPR absorption line has been recorded for the TiC/C, TiN/C, and TiN/amorphous carbon samples, whereas for the (TiC + FexCy + Fe)/C sample a ferromagnetic resonance spectrum, mainly of ?-Fe and cementite Fe3C, has been recorded. The narrow resonance EPR line is explained by carrier motion - free electrons in the case of the TiN/C sample and holes (carbon vacancies) in the case of TiC/C and TiN/amorphous carbon samples - which could lead to the creation of the pseudogap state in TiCx or TiNx compounds.

13

Magnetic resonance study of M3Fe4V6O24 (M = Mg, Zn, Mn, Cu, Co) compounds

61%

Guskos N. , Typek J. , Zolnierkiewicz G. , Blonska-Tabero A. , Kurzawa M. , Bosacka M.

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tom Vol. 23, No. 4

923--928

EN

Multicomponent vanadates, M3Fe4V6O24 (M = Mg(II), Mn(II), Zn(II), Co(II) and Cu(II)), have been synthesized by the solid-state reaction method using a stoichiometric mixture of MO, Fe2O3, and V2O5 oxides. They crystallize in the triclinic space ace group P1 and have a complicated structure with two metal ion subsystems. Electron paramagnetic resonance (EPR) measurements have been performed at room temperature and an intense, almost symmetric EPR lines were recorded for all investigated samples except Co3Fe4V6O24. The integral intensity and linewidth of this line essentially depends on the kind of M(II) metal ion in the crystalline matrix. The EPR line intensity for the sample Co3Fe4V6O24 is over one order of magnitude smaller than for all other investigated compounds, and the position of its resonance line is shifted towards lower magnetic fields. The difference in linewidths and intensities are due to the various magnetic interactions between magnetic ions in the lattice, especially for systems containing two different magnetic ions.

14

Magnetic characterization of nanocrystalline iron samples with different size distributions

61%

Typek J. , Zolnierkiewicz G. , Pelka R. , Kielbasa K. , Arabczyk W. , Guskos N.

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tom Vol. 32, No. 3

423—429

EN

Nanocrystalline iron was obtained by fusing magnetite and promoters. The oxidized form was reduced with hydrogen and passivated (sample P0). The average nanocrystallite size in sample P0 was d(P0) =16 nm and the width of size distribution was s(P0) = 18 nm. Samples of nanocrystalline iron with narrower diameter ranges and larger and smaller average crystallite sizes were also synthesized. They were: sample P1 (d(P1) = 28 nm, s(P1) = 5 nm), sample P2 (d(P2) = 22 nm, s(P1) = 5 nm), sample P3 (d(P3) = 12 nm, s(P1) = 9 nm). These four samples were studied at room temperature by dc magnetization measurements and ferromagnetic resonance at microwave frequency. Correlations between samples sizes distributions (average size and width of the sizes) and magnetic parameters (effective magnetization, anisotropy field, anisotropy constant, FMR linewidth) were investigated. It was found that the anisotropy field and effective magnetization determined from FMR spectra scale linearly with nanoparticle sizes, while the effective magnetic anisotropy constant determined from the hysteresis loops decreases with nanoparticle size increase.

15

Ferromagnetic and spin wave resonances in thin layer of expanded austenite phase

61%

Typek J. , Guskos N. , Zolnierkiewicz G. , Berczynski P. , Guskos A. , Baranowska J. , Fryska S.

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tom Vol. 32, No. 2

198—205

EN

Four samples of austenite coatings deposited by reactive magnetron sputtering on silicon substrate at four different temperatures and pressures were investigated by ferromagnetic resonance (FMR) method at room temperature. The expanded austenite phase S (gN) layers with thickness in the 160 – 273 nm range and concentration of magnetic atoms: 72 % Fe, 18 % Cr and 10 % Ni, were obtained. The coatings with nanometric size grains were strongly textured and grown mostly in [100] direction, perpendicular to the sample surface. Intense FMR spectra were recorded at various angles between the static magnetic field direction and the sample surface. A strong magnetic anisotropy of the main uniform FMR mode was observed and the effective magnetization 4πMe f f determined. Spin wave resonance (SWR) modes were observed in all investigated samples in out-of-plane geometry of the magnetic field. The resonance fields of SWR modes in our samples varied linearly with the spin wave mode number. The value of the effective magnon stiffness constant was determined assuming a parabolic shape of the magnetization variation across the sample thickness.

16

Effects of thermal treatment on magnetic properties of Ni2FeV3O11-.delta compound

61%

Guskos N. , Typek J. , Żołnierkiewicz G. , Błońska-Tabero A. , Los S. , Kempiński W.

Materials Science Poland

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2006

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tom Vol. 24, No. 4

983--990

EN

Ni2FeV3O11-.delat samples have been synthesized by the solid-state reaction method using two different heat treatment processes (samples of the type A and B). The XRD measurements have shown the same diffraction patterns for both types of samples. The temperature dependences of the electron paramagnetic resonance (EPR) spectra have been recorded for the two types of thermal annealing processes of Ni 2FeV3O11-.delta. Strong differences have been observed in the EPR spectra of both types of Ni2FeV3O 11-.delta. An intense EPR line has been recorded at high temperatures; it is suggested that the line is associated with oxygen-vanadium clusters (ferromagnetic ordering). The linewidth, resonance field and integrated intensity of the EPR spectra have shown a strong temperature dependence down to 200 K. Additionally, in one sample a very broad EPR line of Fe3+ ions appeared at low temperatures while at high temperatures this line was overlapped by the other line. The temperature dependence of the integrated intensity of this broad line has shown the Curie-Weiss behaviour. In the vanadate oxide materials with two strong magnetic ions in the structure (iron(III) and nickel(II)), the spectrum of the Fe3+ ions is not observed. Different oxygen deficiency processes could explain the differences in the EPR spectra of both types of Ni2FeV3O 11-.delta compounds.

17

Neutron diffraction study of Mn3Fe4V6O24

51%

Bezkrovnyi A. , Guskos N. , Typek J. , Ryabova N. Y. , Bosacka M. , Blonska-Tabero A. , Kurzawa M. , Rychlowska-Himmel I. , Zolnierkiewicz G.

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tom Vol. 23, No. 4

883--890

EN

Mn3Fe4V6O24 compound was prepared using the solid-state reaction method. The magnetic and crystal structural studies were carried out by using neutron diffraction methods at the temperatures of 10 and 290 K. Down to 10 K no long-range magnetic order was observed. Essential differences in the positions of metal ions were observed as compared to similar systems (ß-Cu3Fe4V6O24 and Zn3Fe4V6O24) investigated by X-ray and neutron diffraction methods. In this system, a disordering process involving iron and manganese atoms in M(2), M(3), M(4) cation sites was found, which could be responsible for the significant differences in the physical properties observed for this type of compound.

18

FMR study of nanocarbon materials obtained by carburisation of nanocrystalline iron

51%

Narkiewicz U. , Arabczyk W. , Pełech I. , Guskos N. , Typek J. , Maryniak M. , Woźniak M. J. , Matysiak H. , Kurzydłowski K. J.

Materials Science Poland

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2006

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tom Vol. 24, No. 4

1067--1075

EN

Samples of nanocrystalline iron were carburised with ethylene and next reduced with hydrogen. Both carburisation and reduction were monitored by the thermogravimetry. The obtained samples were characterised using X-ray diffraction, high-resolution transmission electron microscopy and ferromagnetic resonance. The samples after carburisation contained cementite (Fe3C) and carbon deposit (nanofibres and nanotubes). As the result of reduction with hydrogen at 450 or 500 °C cementite was reduced to iron. A major part of carbon was also hydrogenated, only thin carbon nanotubes remained. The FMR spectra of the prepared samples were recorded at room temperature. The sample after carburisation has shown a wide FMR line with weak intensity while the resonance field has been shifted to lower magnetic field. This spectrum has been attributed to the presence of cementite. The FMR lines corresponding to samples after reduction are more intense and are connected with the presence of alfa-Fe nanoparticle conglomerates.

19

Effect of calcination and structural additives on EPR spectra of nanocrystalline cobalt oxides

51%

Guskos N. , Typek J. , Maryniak M. , Żołnierkiewicz G. , Podsiadły M. , Arabczyk W. , Lendzion-Bieluń Z. , Narkiewicz U.

Materials Science Poland

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2006

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tom Vol. 24, No. 4

1095--1102

EN

Samples of nanocrystalline Co3O4 were prepared at various calcination temperatures and with various amounts of structural additives (CaO and Al2O3). The samples were characterized by X-ray diffraction. The average size and size distribution of nanoparticles have been calculated. Electron paramagnetic resonance (EPR) spectra of the samples were recorded at room temperature. The spectra have been attributed to divalent cobalt ions. Samples calcinated at higher temperatures showed an almost symmetrical, intensive EPR line. Temperature of calcination determined the character of the EPR spectra. The intensities of EPR spectra depended on the presence of CaO and Al2O3 additives