Structural data from X-ray powder diffraction for new high-temperature phases (Y1-xLnx)2Si2O7 with Ln = Ce, Pr, Nd

• Published in: Journal of the European Ceramic Society 2002, Vol.22 (5), p.721-730
• Main Authors: MONTEVERDE, F, CELOTTI, G
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Inorganic compounds; Physics; Salts; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/S0955-2219(01)00338-7

In an investigation on possible mixed phases with composition (Y1-xLnx)2Si2O7 formed at high temperature under oxidising conditions in silicon nitride samples doped with Y2O3 and Ln2O3 as sintering aids, the compounds with Ln = Ce, Pr, Nd were synthesised and structurally characterised by Rietveld whole powder pattern refinement. Some fluctuations in the x values were found as well, but all the compounds were monoclinic (space group P21/c), with lattice parameters close to those of the previously studied (Y2/3La1/3)2Si2O7. Further efforts with Sm (and Dy) failed to produce the expected G-form phase, indicating that the family does not extend beyond Nd. In these cases, Ln ions partially substitute Y in its already known alpha- and delta-disilicates. Under the adopted experimental conditions (1 atm, ambient air), an explanation of the impossibility of obtaining the phase in question containing lanthanides with Z equal to or greater than 62 was attempted on the basis of lattice strains introduced by foreign ions larger than Y. 7 refs.