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First-principles study of rare-earth effects on grain growth and microstructure in beta-Si3N4 ceramics

Painter, G. S.; Becher, P. F.; Shelton, W. A.; Satet, R. L.; Hoffmann, M. J.

Abstract:
Rare earth (RE) and group III oxide additions are frequently used to
optimize densification during the processing of ceramics. Silicon
nitride ceramics frequently serve as model cases, and in these systems
the effects of rare earths are important. Additions often determine the
morphology of beta-Si3N4 crystallites that grow in the multiphase
ceramic, thereby affecting the microstructure and mechanical toughness
of the ceramic. The influence of different rare earths has recently
been experimentally characterized in terms of their effects on grain
growth aspect ratios. In the study reported here, a new energy
parameter is introduced that provides a first-principles based
understanding of these effects. Grain growth aspect ratios measured for
various RE additions in silicon nitride correlate well with
corresponding differential binding energies (DBE) calculated within the
partial wave self-consistent field atomic cluster model. The DBE
provides a second-difference measure of relative site stabilities of RE
vs Si atoms in regions of variable O/N content. The physical mechanism
that underlies anisotropic grain growth is f ... mehr


Zugehörige Institution(en) am KIT Institut für Keramik im Maschinenbau (IKM)
Publikationstyp Zeitschriftenaufsatz
Jahr 2004
Sprache Englisch
Identifikator ISSN: 1098-0121
KITopen-ID: 1000007654
Erschienen in Physical review / B
Band 70
Heft 14
Seiten 144108
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