F. Monteverde et G. Celotti, Structural data from x-ray powder diffraction of a new phase formed in theSi3N4-La2O3-Y2O3 system after oxidation in air, J EUR CERAM, 19(11), 1999, pp. 2021-2026
A new phase formed at high temperature with composition (Y2/3La1/3)(2)Si2O7
was found among the reaction products of a hot pressed Si3N4-based materia
l (with Y2O3 and La2O3 as sintering aids) after oxidation experiments. This
phase was also directly synthesized from oxide precursors (SiO2, Y2O3, La2
O3) at 1600 degrees C, under the condition of a silica excess. After identi
fying a proper monoclinic cell, the structure of such a compound was succes
sfully refined by Rietveld method starting from the existing model of G-for
m of La2Si2O7. The new phase turned out to be isostructural with it, showin
g 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. (C) 1999 Elsevier Science Limited All rights reserved.