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Site Cation (site + cation)
Selected Abstracts4d Electronic structure analysis of ruthenium in the perovskite oxides by Ru K - and L -edge XASJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Jong-Young Kim The 4d electronic structure of ruthenium in the perovskite oxides, La2MRuIVO6 (M = Zn, Mg, and Li) and Ba2YRuVO6, has been investigated by the Ru K-and L-edge XANES and EXAFS analyses. Such X-ray absorption spectroscopic results clarify that the RuIV (d4) and RuV (d3) ions are stabilized in nearly regular Oh site. Comparing the Ru L-edge XANES spectra of perovskites containing isovalent ruthenium, it has been found that the t2g state is mainly influenced by A site cation, whereas the eg is mainly affected by neighboring B site cation. The experimental EXAFS spectra in the range of R ,,4.5 Å are well reproduced by ab-initio calculation based on crystallographic data, which supports the long-range structure presented by Rietveld refinement. [source] Prediction of the crystal structures of perovskites using the software program SPuDSACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2001Michael W. Lufaso The software program SPuDS has been developed to predict the crystal structures of perovskites, including those distorted by tilting of the octahedra. The user inputs the composition and SPuDS calculates the optimal structure in ten different Glazer tilt systems. This is performed by distorting the structure to minimize the global instability index, while maintaining rigid octahedra. The location of the A -site cation is chosen so as to maximize the symmetry of its coordination environment. In its current form SPuDS can handle up to four different A -site cations in the same structure, but only one octahedral ion. Structures predicted by SPuDS are compared with a number of previously determined structures to illustrate the accuracy of this approach. SPuDS is also used to examine the prospects for synthesizing new compounds in tilt systems with multiple A -site coordination geometries (a+a+a+, a0b+b+, a0b,c+). [source] Octahedral tilt twinning and compositional modulation in NaLaMgWO6ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Graham King A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9,Å, which corresponds to a 12ap× 2ap× 2ap superstructure of the simple perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a,a,c0 with tilt angles of ,,8° about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6ap. Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A -site cations is necessary to explain the experimental images. [source] Prediction of the crystal structures of perovskites using the software program SPuDSACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2001Michael W. Lufaso The software program SPuDS has been developed to predict the crystal structures of perovskites, including those distorted by tilting of the octahedra. The user inputs the composition and SPuDS calculates the optimal structure in ten different Glazer tilt systems. This is performed by distorting the structure to minimize the global instability index, while maintaining rigid octahedra. The location of the A -site cation is chosen so as to maximize the symmetry of its coordination environment. In its current form SPuDS can handle up to four different A -site cations in the same structure, but only one octahedral ion. Structures predicted by SPuDS are compared with a number of previously determined structures to illustrate the accuracy of this approach. SPuDS is also used to examine the prospects for synthesizing new compounds in tilt systems with multiple A -site coordination geometries (a+a+a+, a0b+b+, a0b,c+). [source] | ||||||||||