A new phase formed at high temperature with composition (Y2/3La1/3)2Si2O7 was found among the reaction products of a hot pressed Si3N4-based material (with Y2O3 and La2O3 as sintering aids) after oxidation experiments. This phase was also directly synthesized from oxide precursors (SiO2, Y2O3, La2O3) at 1600C, under the condition of a silica excess. After identifying a proper monoclinic cell, the structure of such a compound was success fully refined by Rietveld method starting from the existing model of G-form of La2Si2O7. 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.
Structural Data from X-ray Powder Diff raction of a New Phase Formed in the Si3N4-La2O3-Y2O3 System After Oxidation in Air
F Monteverde;G Celotti
1999
Abstract
A new phase formed at high temperature with composition (Y2/3La1/3)2Si2O7 was found among the reaction products of a hot pressed Si3N4-based material (with Y2O3 and La2O3 as sintering aids) after oxidation experiments. This phase was also directly synthesized from oxide precursors (SiO2, Y2O3, La2O3) at 1600C, under the condition of a silica excess. After identifying a proper monoclinic cell, the structure of such a compound was success fully refined by Rietveld method starting from the existing model of G-form of La2Si2O7. 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
