Advances in the structure and microstructure determination of yttrium silicates using the Rietveld method

The Y₂O₃-SiO₂ 1:1 composition doped with a weak concentration of europium ions was prepared with the sol-gel technique and the products studied by X-ray diffraction as a function of temperature in the range from 900 to 1300 °C, using the method of Rietveld for quantitative evaluation of amorphous and crystalline evolving phases. The amorphous profile of the yttrium oxyorthosilicate glasses has been described following the “Rietveld for Disordered Materials” method and subsequently included in the patterns of semicrystalline samples that have been heat-treated for temperatures above 900 °C at 1000, 1100, 1150, 1200 and 1300 °C. The quantitative evaluation of the amorphous phase is obtainable from the Rietveld approach equivalent to the method after Ruland. This enabled us to study in fine detail the structural rearrangements and growth mechanisms that take place during the crystal-to-amorphous transformation in terms of coordination numbers, average interatomic distances, average crystallite size and microstrain and to identify the polymorphous transformation involving the Y₂SiO₅ phase from low-to-high-temperature forms, as well as some minor quantities of other phases namely α-Y₂Si₂O₇ phase, Y₂O₃ and Y_4.67(SiO₄)₃O.