5 research outputs found
Atomi- és mágneses szerkezetek neutrondiffrakciós vizsgálata = Neutron diffraction study of atomic and magnetic structures
KĂĽlönbözĹ‘, modern technolĂłgiákkal előállĂtott polikristályos anyagok atomi Ă©s mágneses szerkezetĂ©nek jellemzĹ‘it határoztuk meg neutrondiffrakciĂłs mĂ©rĂ©sek Rietveld-mĂłdszerrel törtĂ©nĹ‘ illesztĂ©sĂ©vel. MegállapĂtottuk, hogy a Sc-mal adalĂ©kolt hexaferritben alacsony hĹ‘mĂ©rsĂ©kleten inkommenzurábilis mágneses szerkezet alakul ki. A periĂłdushosszra 98 Angström adĂłdott, a kĂşp nyĂlásszögĂ©re pedig 40 fokot kaptunk. Kimutattuk, hogy a FeAl2 ötvözet anomális mágneses viselkedĂ©sĂ©t inkommenzurábilis mágneses szerkezete okozza, szemben az irodalomban elterjedt spinĂĽveg állapottal. A töltĂ©srendezĹ‘dĂ©s okozta rácstorzulás - kristály-szimmetriaváltozások - Ă©s a lehetsĂ©ges töltĂ©s-Ă©s mágneses rendezĹ‘dĂ©st tanulmányoztuk a hĹ‘mĂ©rsĂ©klet fĂĽggvĂ©nyĂ©ben kĂĽlönbözĹ‘ összetĂ©telű Bi-alapĂş manganát-oxid perovszkitokban. Nem-lineáris optikai tulajdonságokkal rendelkezĹ‘ ittrium-aluminumborát kristály szerkezeti paramĂ©tereit határoztuk meg Er ill. Yb dĂłpolás hatására. KĂĽlönbözĹ‘ összetĂ©telű nátrumboroszilikát alapű ĂĽvegeket állĂtottunk elĹ‘, Ă©s a szerkezet jellemzĹ‘it vizsgáltuk neutrondiffrakciĂłs mĂłdszerrel Ă©s a kĂsĂ©rleti adatok fordĂtott Monte Carlo (RMC) szimuláciĂłjával. Meghatároztuk a hálĂłszerkezet legfontosabb paramĂ©tereit, a parciális atomi párkorreláciĂłs fĂĽggvĂ©nyeket, a kötĂ©stávolságokat, a koordináciĂłs számokat, a szerkezetet felĂ©pĂtĹ‘ egysĂ©geket, Ă©s egyszerűbb összetĂ©telekre a kötĂ©sszög- Ă©s gyűrűeloszlást is. Sikeresen adalĂ©koltunk UO3-at az ĂĽvegbe, Ă©s azt tapasztaltuk, hogy az urán beĂ©pĂĽl a hálĂłszerkezetbe Ă©s stabilizálja az ĂĽveg szerkezetĂ©t. | We have determined the characteristic atomic and magnetic structure parameters for various polycrystalline materials prepared by novel techniques using neutron and x-ray diffraction experimental techniques, and Rietveld analysis data treatment. Formation of an incommensurate magnetic order with 98 ? periodicity length and 40? cone angle has been established in the Sc-substituted hexaferrite. The anomalous magnetic behaviour of FeAl2 alloy was explained by an incommensurate magnetic structure instead of the commonly accepted spin glass structure. Lattice distortion, crystal symmetry changes and charge-magnetic ordering effects were analysed in Bi-based manganese oxide perovskites in dependence of temperature. Changes in lattice parameters and atomic positions were analysed in Er and Yb substituted Yttrium-Aluminum borates. Sodium borosilicate matrix glasses are known as most suitable materials for radioactive waste material storage. We have successfully prepared these matrix glasses with various compositions, and the network structure was analysed by reverse Monte Carlo (RMC) simulation of the neutron diffraction spectra. Several partial atomic pair correlation functions have been revieled, and the characteristic parameters were determined, like the atomic bond distances, coordination numbers, the basic structural units, and for the simple glasses the bond angle- and the ring size distributions, as well. It was found that addition of UO3 stabilizes the network structure
FolyadĂ©kok Ă©s amorf anyagok szerkezetvizsgálata diffrakciĂłval Ă©s számĂtĂłgĂ©pes modellezĂ©ssel = Structural investigations of liquids and amorphous solids by diffraction and computer modelling
FolyadĂ©kok Ă©s amorf anyagok atomi szintű szerkezetĂ©t határoztuk meg neutron- Ă©s röntgendiffrakciĂłs, valamint röntgen-abszorpciĂłs (EXAFS) kĂsĂ©rletekkel. A Reverse Monte Carlo (RMC) számĂtĂłgĂ©pes modellezĂ©si eljárás segĂtsĂ©gĂ©vel olyan 3 dimenziĂłs, több ezer atomot tartalmazĂł szerkezeteket generáltunk, amelyek teljes mĂ©rtĂ©kben (azaz a kĂsĂ©rleti hibán belĂĽl) konzisztensek voltak a felsorolt kĂsĂ©rleti adatok mindegyikĂ©vel. A vázolt procedĂşra-sorozat ('protokoll') több, egymástĂłl nĂ©ha meglehetĹ‘sen eltĂ©rĹ‘ folyadĂ©k Ă©s amorf anyag szerkezetĂ©nek megĂ©rtĂ©sĂ©t tette lehetĹ‘vĂ© a korábbiakban elkĂ©pzelhetetlen rĂ©szletessĂ©ggel Ă©s bizonyossággal. E rövid összefoglalĂłba csak nĂ©hány pĂ©lda emlĂtĂ©se fĂ©r: tetraĂ©der alakĂş molekulákbĂłl állĂł folyadĂ©kokban (pl. szĂ©n-tetraklorid) a molekulák orientáciĂłs korreláciĂłit tisztáztuk; vizes elektrolitoldatokban rögzĂtettĂĽk a diffrakciĂłs adatok által megengedett koordináciĂłs számokat Ă©s a hidrátszfĂ©rákat jellemzĹ‘ szög-korreláciĂłkat; a DVD-technolĂłgia alapjául szolgálĂł germánium-antimon-tellĂşr amorf ötvözet szerkezetĂ©t elsĹ‘kĂ©nt sikerĂĽlt rĂ©szletekbe menĹ‘en tisztázni. A támogatott kutatĂłmunka több mint 40, referált nemzetközi folyĂłiratban megjelent közlemĂ©nyt eredmĂ©nyezett, amelyek összesĂtett impakt faktora meghaladja a 90-et (azaz 1 impakt-faktor pont 'egysĂ©gára' kb. 150 eFt volt). | The atomic level structure of liquids and amorphous materials have been determined by neutron and X-ray diffraction, as well as X-ray absorption (EXAFS) experiments. By means of the Reverse Monte Carlo (RMC) computer modelling teachnique, 3 dimensional structures (containing thousands of particles) have been generated that were fully consistent (within experimental errors) with all of the aformentioned experimental data. The series of procedures ('protocol') outlined above made it possible to understand the structure of various (sometimes, rather different) liquids and amorphous materials at an unprecedented level and certainty. Only a few representative examples can be mentioned in such a short summary: we were able to clarify correlations between molecular orientations in liquids containing tethedral molecules (such as carbon tatrachloride); for some aqueous elctrolyte solutions, we have determined the range of coordinations numbers and angular corrrelations that are allowed by diffraction data; the structure of germanium-antimony-tellurium amorphous alloy that forms tha basis of DVD technology could be determined to fine details. The reserach supported by the present OTKA grant resulted in more than 40 publications in referred international scientific journals, with a cumulative impact factor that exceeds 90 (that is, the 'unit price' of 1 impact factor point was about 150 kHUF)
Magnetic cation distribution in a nanocrystalline Fe(3)O(4) spinel
Neutron diffraction study of nanostructured magnetite was performed at room temperature. The actual grain-size was determined from evaluation of X-ray diffraction profiles by the modified Williamson-Hall plot. The atomic structure parameters and the sublattice magnetic moments were determined using the Rietveld refinement of the neutron diffraction spectra. The sublattice magnetization at the octahedral sites decreases with decreasing grain-size, while it remains practically constant at the tetrahedral sites