Bonding and Stability of Ternary Structures in the CeT2Al20 (T=Ta, W, Re) and YRe2Al20 Alloys

A-T-Al aluminides, where A = actinide, lanthanide or rare earth elements and T=transition metals, have attracted considerable attention as potential materials where heavy fermions may be formed. This led to the discovery of superconducting properties in cubic AT2Al20 compounds with CeCr2Al20-type crystal structure. Other Al-rich aluminides, belonging to these A-T-Al systems, exhibited different physical properties as a function of their crystal structure. Thus, predicting the stable structure of the Al-richest phase that will form in the A-T-Al systems is highly valuable. Stability of the crystal structures, forming in the CeT2Al20 and YRe2Al20 systems, was studied in current research using density functional theory (DFT) calculations. It is demonstrated that the total spin magnetic moment of the transition metal can be used as a descriptor for phase stability assessment in the AT2Al20 systems, where T is a 5d transition metal. Basing on crystallographic considerations, degree of distortion of the coordination polyhedrons, formed around T atoms, can be directly connected to the specific type of structure crystallizing in these systems.

The stability of coordination polyhedrons and distribution of europium ions in Ca6BaP4O17

Polyhedron-tilt-induced coordination structural transformation and the stabilities are intimately related to dynamic environments.

Studies of Structural and Electronic Properties of Uranium Compounds, by XANES Spectroscopy

X-ray absorption near edge structure (XANES) is a sensitive probe of the electronic structure, and can provide information about the valency, the unoccupied electronic states and the effective charge of the absorbing atom. In this paper, near edge x-ray absorption fine structure spectra are reported at the L3, M5 and N5 thresholds and used to determined structural and electronic properties of U(VI) within uranyl nitrate (UO2(NO3)2.6H2O) and perovskite (Ba2ZnUO6). Experimental data analysis by simulating the absorption edge allows to compare the coordination polyhedrons, identify the electronic transitions and calculate the density of states associated with the absorption spectra. Moreover, a coupling between simulations of the experimental spectra and quantum chemical calculations is performed, in order to improve the model describing the final states and better understand the bonding properties of the cation with the ligand.

Ein neues kationenreiches Oxogallat Zur Kenntnis von K2Li3GaO4/A New Cation Rich Oxogallate About K2Li3GaO4

The new compound K2Li3GaO4 was prepared from binary oxides (powder) and from LiGaO2/KO0.48 (colourless transparent single crystals) in a closed Ag cylinder at 600 °C. It crystallizes in the monoclinic space group P21/c with the constants a = 553.6(2) 6 = 880.4(3) c = 1093.1(4) pm β = 111.52(3)°. Z = 4, drö = 3.017 and dpyk = 2.97 g·cm-3 . [4-circle diffractometer data, 1333 I0 (hkl), Mo-Ka, R = 4.95 and Rw = 5.04%, anisotropic refinement.] The new structure type is complicated. The characteristical features are shown using Schlegel projections of the coordination polyhedrons. Extended Schlegel Diagrams, a novel application of graph theory, are used. They describe bijective how the coordination polyhedra are three-dimensionally combined.