ABSTRACT
Electron-counting rules were applied to understand the stability, structural preference, and physical properties of metal disilicides. Following predictions made by 14 electron counting rules, the ordered semiconductor ReGaSi, the first ternary phase in this system, was proposed and successfully synthesized. It crystallizes with a primitive tetragonal structure (space group P4/nmm) closely related to that of MoSi2-type ReSi2, but with Ga and Si orderly distributed in the unit cell. The band structure, density of states, and crystal orbital calculations confirm the electron count hypothesis to predict new stable compounds. Calculations, based on 14 electrons per ReGaSi units, show a small indirect band gap of â¼0.2 eV around Fermi level between full and empty electronic states. Additionally, first-principles calculations confirm the site preference of Ga and Si, which is observed through the structural refinement. Experimental magnetic measurements verified the predicted nonmagnetic properties of ReGaSi.
ABSTRACT
Synthesis, characterization, and thermal modification of the new layered perovskite FeLa2Ti3O10 have been studied. FeLa2Ti3O10 was prepared by ion exchange of the triple-layered Ruddlesden-Popper phase Li2La2Ti3O10 with FeCl2 at 350 °C under static vacuum. Rietveld refinement on synchrotron X-ray diffraction data indicates that the new phase is isostructural with CoLa2Ti3O10, where FeII cations occupy slightly compressed/flattened interlayer tetrahedral sites. Magnetic measurements on FeLa2Ti3O10 display Curie-Weiss behavior at high temperatures and a spin-glass transition at lower temperatures (<30 K). Thermal treatment in oxygen shows that FeLa2Ti3O10 undergoes a significant cell contraction (Δc ≈ -2.7 Å) with a change in the oxidation state of iron (Fe2+ to Fe3+); structural analysis and Mössbauer studies indicate that upon oxidation the local iron environment goes from tetrahedral to octahedral coordination with some deintercalation of iron as Fe2O3 to produce Fe0.67La2Ti3O10.
