measurement gives information on the environment of La atoms. Thus the combination of the three techniques can provide us with a detailed description of the structure of a ternary system. It has been found that the nearest Ni-Al and Al-Al distances are 2.38±0.02 Å and 2.73±0.02 Å, respectively. Both values are considerably shorter than the sum of corresponding atomic radii (2.67 Å and 2.86 Å). The Ni-Al coordination number calculated from the model is 6.2±0.3. It is remarkable that a good quality fit could be obtained by a configuration in which 98% of Ni atoms have exactly 6 neighbours. This value would suggest the presence of well defined atomic motifs (e.g. NiAl6 octahedra or trigonal prisms). A thorough investigation of the atomic configuration does not reveal any special local ordering around Ni.
Liquids – The structure of liquid antimony pentachloride SbCl5 and tungsten hexachloride WCl6 has been studied by neutron diffraction and subsequent RMC modelling. As the two liquids have not been studied before, basic information like the liquid state molecular geometry was missing. In liquid antimony-pentachloride we find that molecules take the shape of a trigonal bipyramid, with strictly straight axial Cl-Sb-Cl bond angles. It is now proven that liquid WCl6 can be considered as a real molecular liquid, consisting of molecules of octahedral shape. It may be concluded on the basis of our long-term systematic studies on molecular liquids that as the size of individual molecules increases (and for ’centre-ligands’ types, like the two liquids in question, this means also the sphericity), the importance of intermolecular (orientational) correlations seems to decrease compared to the intramolecular contributions, as exemplified by the cases of liquid antimony-pentachloride and tungsten-hexachloride.
Disorder in ice – Studying the structure of hexagonal (Ih) ice we showed that both the Bragg and the diffuse scattering parts of neutron powder diffraction data can be interpreted simultaneously by constructing large models of the structure that are consistent with the measured total scattering functions within errors (see Figure 2, part a). The RMCPOW (Reverse Monte Carlo for POWders) algorithm proved to be readily applicable for the purpose. It is found that proton disorder on its own cannot be responsible for the measured level and shape of diffuse scattering. The present results, particularly the O-H and O-O partial radial distribution functions (see Figure 2, part b) and the distribution of the O-H…O hydrogen bond angles suggest that small changes of the hydrogen bonded network are most probably responsible for the slightly different shape of the diffuse scattering signal at 120 and 200 K.
Incommensurate antiferromagnetism in FeAl2. — We have performed a neutron diffraction (ND) study on FeAl2 below the magnetic phase transition temperature (~30 K) with the aim of obtaining information on the character of the magnetic structure. The ND pattern at 1.5 K and the temperature dependence of the week magnetic satellite reflections have been determined (see Fig. 3). The position of, and the area under these peaks are temperature dependent. As the peaks are rather narrow, though slightly broadend compared to the nuclear reflections, a long-range ordering of the moments can be stated.
We have established the incommensurate nature of the magnetic structure with a period length of 1.1 nm. The magnetic moments are in the range of 0.3-0.5 µB.
0 1 2 3 4 5 6 7 8 0
5 10
0 1 2 3 4 5 6 7 8
Q [Å-1] 0
0.1 0.2 0.3 0.4 0.5
F(Q)
(a)
0 2 4 6 8 10 12 14
r [Å]
0 5 10 15
gxy (r)
O-O
H-H
O-H
(b)
Figure 2. (a) Large panel: measured powder diffraction pattern of (D2O) ice Ih at 120 K (symbols) and 200 K (solid line); the focus is on the diffuse scattering part. Insert: powder
diffraction pattern of ice Ih at 200 K. (b) Comparison of the partial pair correlation functions for the 120 K (solid lines) and 200 K (dashed lines) states. In both cases, systems
of 83 unit cells were applied.
Figure 3. Neutron diffraction pattern of FeAl2 at 1.5 K (λ=2.4266 Å). The insert shows the low angle part taken at different temperatures between 1.5-45 K. Arrows indicate the temperature dependent weak magnetic satellite reflections, showing the formation of long-range ordered incommensurate magnetic structure.
Non-destructive materials testing on archeological objects. — Restorers of the Hungarian National Museum appealed to us during their recent restoration work on a helmet, found at the beginning of the 20th century, which belongs to the Déri endowment.
Our contribution was the non-destructive structure determination on a given part of the helmet. Parallel neutron diffraction measurements were also made on different iron oxides to compare the spectrum obtained from the heavily rusted object. In spite of the off stoichiometric composition and the large amount of hydrogen it is reasonable to assume that, apart from the presence of iron, the second phase is most probably hematite.
E-Mail:
Margit Fábián fabian@szfki.hu Ildikó Harsányi harsanyi@szfki.hu
György Mészáros meszaros@szfki.hu Szilvia Pothoczki pszzse@freemail.hu László Pusztai lp@szfki.hu
Erzsébet Sváb svab@szfki.hu László Temleitner temla@szfki.hu
Grants and international cooperations
OTKA T 042495 Neutron diffraction study of atomic and magnetic structures (E. Sváb, 2003-2006)
OTKA T 048580 Structural studies of liquids and amorphous materials by diffraction and computer modelling (L. Pusztai, 2005-2008)
MTA-BAS (Hungarian-Bulgarian bilateral): Neutron scattering investigation of the structure of ordered and disordered magnetic and non magnetic materials (E. Sváb, 2004-2006)
Publications
Articles
K.1. Pusztai L, McGreevy* RL; On the structure of simple molecular liquids SbCl5 and WCl6; J Chem Phys; 125, 044508/1-7, 2006
K.2. Jóvári P, Pusztai L; Structural changes in liquid selenium with increasing temperature; J Mol Liq; 129, 115-119, 2006
K.3. Harsányi I, Pusztai L, Soetens* JC, Bopp* PhA; Molecular dynamics simulations of aqueous RbBr-solutions over the entire solubility range at room temperature; J Mol Liq; 129, 80-85, 2006
K.4. Saksl* K, Jóvári P, Franz* H, Zeng* QS, Liu* JF, Jiang* JZ; Atomic structure of Al89La6Ni5 metallic glass; J Phys: Condens Matter; 18, 7579-7592, 2006
K.5. Kaban* I, Jóvári P, Hoyer* W, Delaplane* RG, Wannberg* A; Structural studies on Te-rich Ge-Te melts; J Phys: Condens Matter; 18, 2749-2760, 2006
K.6. Hoppe* U, Brow* RK, Tischendorf* BC, Jóvári P, Hannon* AC; Structure of GeO2 -P2O5 glasses studied by X-ray and neutron diffraction; J Phys: Condens Matter; 18, 1847-1860, 2006
K.7. Somogyvári* Z, Sváb E, Krezhov* K, Kiss LF, Kaptás D, Vincze I, Beregi E, Bourèe* F; Non-collinear magnetic order in a Sc-substituted barium-hexaferrite; J Magn Magn Mat; 304, e775-e777, 2006
K.8. Fábián M, Sváb E, Mészáros Gy, Kőszegi L, Temleitner L, Veress* E; Structure study of borosilicate matrix glasses; Zeitschrift für Kristallographie; Suppl.23, 461-466, 2006
K.9. Harsányi I, Jóvári P, Mészáros Gy, Pusztai L, Bopp* PhA; Neutron and X-ray diffraction studies of aqueous rubidium bromide solutions; J Mol Liq; accepted for publication
K.10. Kaban* I, Jóvári P, Hoyer* W, Welter* E; Determination of partial pair distribution functions in amorphous Ge15Te85 by simultaneous RMC simulation of diffraction and EXAFS data; J Non-Cryst Solids; accepted for publication
K.11. Fábián M, Sváb E, Mészáros Gy, Révay* Zs, Proffen* Th, Veress* E; Network structure of multi-component sodium borosilicate glasses by neutron diffraction; J Non-Cryst Solids; accepted for publication
K.12. Fábián M, Sváb E, Mészáros Gy, Révay* Zs, Veress* E; Neutron diffraction study of sodium borosilicate waste glasses containing uranium; J Non-Cryst Solids;
accepted for publication Book chapter
K.13. Temleitner L, Pusztai L; Investigation of the structural disorder in ice Ih using neutron diffraction and Reverse Monte Carlo modeling; In: Physics and Chemistry of Ice; Ed. W.F. Kuhs, Royal Society of Chemistry, Cambridge, UK; accepted for publication
See also: D.2.