Structural and kinetic study of phase transitions in LaYSi{sub 2}O{sub 7}.

Journal Article · Wed Aug 01 04:00:00 EDT 2012 · Journal of the European Ceramic Society

DOI:https://doi.org/10.1016/j.jeurceramsoc.2012.03.009· OSTI ID:1042578

Fernandez-Carrion, A J; Escudero, A; Suchomel, M R; Becerro, A ^[1]

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1. X-Ray Science Division

Phase transitions in LaYSi{sub 2}O{sub 7} have been investigated as a function of temperature using XRD, NMR and TEM. Previously described empirical crystal structure guidelines based on average cation radius in rare-earth RE{sub 2}Si{sub 2}O{sub 7}-type disilicates predict a stable tetragonal A-LaYSi{sub 2}O{sub 7} polymorph at temperatures below 1500 C. This study demonstrates that A-LaYSi{sub 2}O{sub 7} is not thermodynamically stable at these temperatures and suggests that guidelines based on average cation size do not accurately describe the equilibrium behaviour of this silicate system. The A to G-type polymorph transition is extremely sluggish; complete transformation requires {approx}250 h at 1200 C, and more than 3 weeks of calcination at 1100 C. This observation is important when this type of material is used as environmental barrier coating (EBC) of advanced ceramics. Analysis of XRD and TEM data reveal complete substitution of Y and La on the rare-earth cation sites in both LaYSi{sub 2}O{sub 7} polymorphs, but indicate preferential site occupancies in the G-type polymorph.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1042578
• Report Number(s): ANL/XSD/JA-73491
• Journal Information: Journal of the European Ceramic Society, Journal Name: Journal of the European Ceramic Society Journal Issue: 10 Vol. 32; ISSN 0955-2219; ISSN JECSER
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
CALCINATION
CATIONS
CERAMICS
COATINGS
CRYSTAL STRUCTURE
KINETICS
RECOMMENDATIONS
SILICATES
SPECTROSCOPY
TRANSFORMATIONS
X-RAY DIFFRACTION