Rietveld analysis and Raman spectroscopic investigations alpha-Y2Si2O7

Polycrystalline material of alpha-Y2Si2O7 has been obtained from the thermal decomposition of a precursor prepared by a sol-gel process and subsequently characterized by X-ray powder diffraction and Raman spectroscopy. The structure belongs to the so-called B-type of rare earth element disilicates and was refined using the Rietveld method. alpha-Y2Si2O7 is triclinic with a = 6.58620(3), b = 6.62895(4), c = 12.02723(7) angstrom, alpha = 94.4706(4)degrees, beta = 89.0681(4)degrees, gamma = 88.2347(4)degrees, V = 523.166(5) angstrom(3), space group P (1) over bar, Z = 4 and D-x = 4.39 g/cm(3). The structure (R-wp = 4.7 %, R-B = 2.9 %) is built from triple tetrahedral [Si3O10]-groups and isolated [SiO4]-units, i.e. from a structural point of view it belongs to the group of mixed anion silicates. The silicate anions are located in layers parallel to (1 (1) over bar 1). Linkage between the anionic groups is provided by Y cations having six and eight oxygen neighbours. The corresponding coordination polyhedra can be approximately described as distorted octahedra as well as bicapped trigonal prisms, respectively.