Structural data from x-ray powder diffraction of a new phase formed in the Si3N4-La2O3-Y2O3 system after oxidation in air

A new phase formed at high temperature with composition (YLa)SiO was found among the reaction products of a hot pressed SiN-based material (with YO and LaO as sintering aids) after oxidation experiments. This phase was also directly synthesized from oxide precursors (SiO, YO, LaO) at 1600°C, under the condition of a silica excess. After identifying a proper monoclinic cell, the structure of such a compound was successfully refined by Rietveld method starting from the existing model of G-form of LaSiO. The new phase turned out to be isostructural with it, showing however a characteristic inhomogeneous substitution of Y atoms by La ones in only half the cell positions and a rather distorted arrangement of Si-O tetrahedra.