Wyniki wyszukiwania - BazTech

1

Wpływ substytucji kationowej na strukturalne i magnetyczne właściwości wybranych chromitów selenowych

Jendrzejewska I.

Wiadomości Chemiczne

|

2010

|

[Z] 64, 9-10

859-898

EN

Selenospinels with general formula ACr2Se4 (A = Zn, Cu, Cd) were doped with nickel and tin ions. The chemical synthesis was carried out based on solid phase reactions. To estimate the chemical composition of the mono- and polycrystalline compounds, the following methods were applied: JEOL scanning microscope and ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectrometry). For the obtained polycrystalline compounds, their structural parameters were defined using X-ray diffraction analysis and Rietveld method. Definition of structure of the monocrystals was carried out using KM4 four-circle diffractometer and SHELX software. Magnetic properties were investigated with strong stationary magnetic fields up to 14 T in the temperature range of 4.2-300 K using an induction magnetometer and with stationary magnetic fields up to 0.5 T in the temperature range of 1.8-300 K using a SQUID superconducting magnetometer. In the systems doped with nickel, depending on the reaction stoichiometry, nickel ions were directed to tetrahedral or octahedral positions. When the octahedral positions are fully occupied by chromium ions, small amounts of nickel directed to tetrahedral positions are able to occupy them. The increasing amount of Ni2- ions tends to occupy the octahedral positions in accordance with preference energy, leading to change in structure from cubic to monoclinic one [19, 37, 38]. Nickel ions present in the spinel crystal lattice influence the magnetic properties of these compounds. For ZnCr2-xNixSe4 system, an increase in values of effective magnetic moment and saturation magnetic moment accompanying the increase in nickel ions concentration was ascertained. It was caused by the presence of another magnetic ions in ZnCr2Se4 crystal lattice. The values of paramagnetic Curie-Weiss point and Néel point decrease with the increase in nickel concentration. It is associated with an increase in antiferromagnetic interactions in the system caused by nickel ions [39-41]. Like in the Cd1–xNixCr2Se4system, saturation magnetic moment does not depend on the amount of nickel built-in, and the crystals exhibit strong ferromagnetic interactions. Lack of a change in saturation indicates that nickel is built in with compensated magnetic moment, or in a low-spin state (S = 0). Cadmium and nickel ions occupy tetrahedral positions and chromium ions - octahedral ones [42]. In the systems doped with tin, the reactions carried out in the solid phase were aimed to build in tin ions in tetra-and octahedral positions. X-ray diffraction studies confirmed the presence of tin ions in selected chromites. Mössbauer spectroscopy applied for the complex system Zn1–xSnxCr2Se4 confirmed the presence of tin ions in two inequivalent positions: in tetrahedral and in octahedral environments. Based on theses considerations, the general formula of these compounds may be as follows: ZnxSnδCrySnηSe4, where δ – parameter describing the share of tin ions in tetrahedral sublattice, η – parameter describing the share of tin ions in octahedral sublattice [43]. Although tin ions does not contribute to a magnetic share, their presence in the crystal lattice promotes an increase in antiferromagnetic interactions in the studied compounds. Under the influence of tin ions, conductance changes from p-type (hole conduction) occurring in pure ZnCr2Se4to n-type (electron conduction) [44, 45]. In CuCr2-xSnxSe4 system, magnetic properties change from ferromagnetic for nominal value x = 0.2 to antiferromagnetic for nominal value x = 1.0. These changes are caused by the presence of Sn4+ ions in the system, generating Cr2+ ions. The observed change in structure is caused by Jahn-Teller effect, occurring in the presence of Cu2+ and Cr2+ ions [46].

2

X-Ray and magnetic investigations of the polycrystalline compounds with general formula ZnxSnyCrzSe4

Jendrzejewska I., Mroziński J., Zajdel P., Mydlarz T., Goryczka T., Hanc A., Maciążek E.

Archives of Metallurgy and Materials

|

2009

|

Vol. 54, iss. 3

723-730

EN

Seleno-spinels with the general formula ZnxSnyCrzSe4 (where x + y + z ≈3) were prepared as polycrystalline samples in the two nominal compositions: Zn0.9Sn0.1Cr2Se4 and ZnCr1.9Sn0.1Se4, using ceramic method. X-ray powder diffraction was used to analyse the obtained phases and to determine their crystal structure and lattice parameters. The obtained single-phase compounds crystallize in the spinel cubic structure – Fd3m. Tin ions are found to occupy both tetrahedral and octahedral sublattices. Chemical compositions of the obtained samples were determined using JEOL-type Scanning Microscope which also revealed a variation in local distribution of cations and the porosity of the samples. The magnetisation data for ZnxSnyCrzSe4 system, shows that the saturation magnetic moments depend on location of tin ions in crystal lattice of ZnCr2Se4. It was found that the magnetic properties correspond well both with the chemical composition and with the crystal structure. PACS: 61.05.cp; 61.66.Fn; 75.30.Cr; 75.50.Ee.

PL

Metodą ceramiczną otrzymano polikrystaliczne związki chemiczne o ogólnym wzorze ZnxSnyCrzSe4 (gdzie x + y + z ≈ 3) dla dwóch założonych składów Zn0.9Sn0.1Cr2Se4 i ZnCr1.9Sn0.1Se4. Skład chemiczny określono przy użyciu mikroskopu skaningowego JEOL (SE 6480). Dla związku o nominalnym składzie Zn0.9Sn0.1Cr2Se4 wyznaczono skład rzeczywisty jako (Zn0.87Sn0.048)Cr2.02Se4, natomiast dla związku o nominalnym składzie ZnCr1.9Sn0.1Se4 wyznaczono skład rzeczywisty jako Zn0.93[Cr1.95Sn0.05]Se4. Za pomocą rentgenowskiej analizy strukturalnej oraz metody Rietvelda wyznaczono strukturę i parametry sieciowe otrzymanych związków. Badania magnetyczne wykonane w silnych polach magnetycznych wykazały, że momenty magnetyczne nasycenia zależą od obsadzenia jonów cyny Sn2+ w sieci krystalicznej ZnCr2Se4. Dla otrzymanych zwiazków (Zn0.87Sn0.048)Cr2.02Se4 i Zn0.93[Cr1.95Sn0.05]Se4 zmierzone momenty magnetyczne nasycenia wynoszą odpowiednio 6.52µB/cz. i 5.56µB/cz. Wzrost nasycenia namagnesowania w (Zn0.87Sn0.048)Cr2.02Se4, gdzie jony cyny Sn2+ podstawiają się w miejsce niemagnetycznych jonów Zn2+, świadczy o tym, że jony cyny Sn2+ mają wpływ na momenty magnetyczne w (Zn0.87Sn0.048)Cr2.02Se4. Badania magnetyczne wykonane przy użyciu magnetometru nadprzewodzacego SQUID potwierdziły obecność antyferromagnetycznego uporządkowania w sieci otrzymanych spineli oraz wykazały wpływ jonów cyny Sn2+ na oddziaływania antyferromagnetyczne w tym układzie.

3

Thin sample in the XRF analysis. A new method of preparing microsamples of mono- and polycrystals and of silicate rocks

Jurczyk J., Sitko R., Buhl F., Jendrzejewska I.

Chemia Analityczna

|

1999

|

Vol. 44, No. 2

167-186

EN

The authors have described a new method ofpreparation ofthin samples, which consists in digesting of the material studied directly on the substrate. Investigations were carried out in the sub- and microanalytical area with mono- and polycrystals of spinel structure (samples' mass from D. I to 1.2 mg), and in the semimicroanalytical area with silicate rocks (samples' mass from 5 to 5D mg). Relative thicknesses of samples as well as errors resulting from the lack of linear relationship between concentration and intensity of radiation have been determined using simple mathematical methods. A simplified method of performing the calibration has been applied by using one standard of diversified masses In the case of submicroanalysis of mono- and polycrystals, a possibility of neglecting the interelement influences allowed for using a linear regres-sion in the calibration. In the semimicroanalytical area (rock analysis), the appropriate mathematical models have been used to improve the results

PL

Autorzy opisali nowy sposób przygotowania cienkich próbek polegający na roztwarza-niu badanego materiału bezpośrednio na podłożu. Badania przeprowadzono w obszarze sub- i mikroanalitycznym na przykładzie mono- i polikryształów o budowie spineli (odważki od D. I do 1.2mg) oraz w obszarze semimikroanalitycznym na przykładzie skał krzemianowych (odważki od 5 do 5Dmg). Stosując proste metody matematyczne wY-znaczono względne grubości próbek oraz blędy wynikające z braku liniowej zależności pomiędzy koncentt.acją a intensywnością promieniowania. Zastosowano uproszczony sposób wykonania kalibracji z wykorzystaniem jednego wzorca o zróżnicowanych masach. W przypadku submikroanalizy mono- i polik1-yształów możliwość zaniedbania wpływów międzypierwiastkowych pozwolił a na wykorzystanie regresji liniowej do kalibracji. W obszarze semimikroanalitycznym (analiza skał) do poprawy wyników wykorzystano odpowiednie modele matematyczne-