Ab Initio Structure Evaluation of Aperiodic Structures in the Rare Earth – Ruthenium Systems

University essay from Lunds universitet/Centrum för analys och syntes

Abstract: Binary alloys comprising of the rare earth metals along with ruthenium, RE-Ru, have been noted to display superconductivity at low temperatures. Furthermore the alloys display interesting magnetic properties such as anomalies in magnetization measurements below the magnetic ordering temperature. In order to understand how some compounds obtain these intrinsic properties it is vital to investigate the crystallography of the compounds. In this thesis the structure, LaRux, of compounds comprising praseodymium, neodymium or lanthanum in the 35-38 at. % Ruthenium region has been investigated with modern x-ray diffraction techniques. Other compounds, Er3Ru2 and Y44Ru25, in the 30-40 at. % Ru region has been noted to show evidence of possible superstructure and has also been examined with x-ray diffraction in order to establish the connection between the two related crystal structures and to fully understand the extent and nature of the structures. The structure of the incommensurately modulated two composite compound Er3Ru2 was solved using the current (3+1)d superspace approach from structure data which was collected with x-ray single-crystal diffraction. The structure solution, performed with the charge-flipping algorithm, resulted in the non-centrosymmetric super-space group X3 (00γ)0 with a = b = 13.893 (4) Å, c = 4.0005 (12) Å q = 1.572 c'. The possibility for superstructure descriptions for the Y44Ru25 and the LaRux compounds could also be concluded. The diffraction patterns of both compounds contained satellite reflections, indicating superstructure. Furthermore the Y44Ru25 structure could be solved well with two symmetry incompatible lattices further strengthening the possibility of superstructure. Therefore it could be concluded that these compounds most likely can be well described with the superspace description. The task of describing them in higher-dimensions was not completed in this thesis and is considered future work.

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