Characterization of second-phase plates in a Gd5Ge3 intermetallic compound

TitleCharacterization of second-phase plates in a Gd5Ge3 intermetallic compound
Publication TypeJournal Article
Year of Publication2013
AuthorsCao Q, Chumbley LS
Journal TitleMicroscopy
Date Published12
Type of ArticleArticle
ISBN Number0022-0744
Accession NumberWOS:000328365600010
Keywordsalloys, behavior, energy dispersive spectrometer, gd-5(sixge1-x)(4), gd5si2ge2, identification, microstructure, phase-diagram, rare-earth intermetallics, scanning electron microscopy, silicon, system, temperature, transition, transmission electron microscopy

Rare-earth compounds based on the stoichiometry R-5(SixGe1-x)(4) (R = rare-earth elements) exhibit many unusual features, including possessing R-5(SixGe(1-x))(3) thin plates which always precipitate from the matrix despite efforts to suppress their formation. In an effort to better understand the unique relationship between these two intermetallic alloy systems, the bulk microstructure of the compound Gd5Ge3 was examined using scanning (SEM) and transmission electron microscopy (TEM) and optical microscopy. Surprisingly, SEM examination revealed a series of thin plates present in the Gd5Ge3 matrix similar to what is seen in Gd5Ge4. TEM observation revealed that a role reversal had occurred, with the thin plates possessing the orthorhombic structure and composition of Gd5Ge4. The orientation relationship between Gd5Ge4 thin plates and the Gd5Ge3 matrix was determined to be [1 0 (1) over bar 0] [1 (2) over bar 1 1)(m) parallel to [0 1 0] (1 0 (2) over bar)(p), the same relationship reported for Gd5Ge3 plates precipitating from a Gd5Ge4 matrix. However, by exchanging the respective roles of the phases as regards matrix vs. precipitate, the total number of precipitation variants seen can be increased from two to six. The persistence with which these two intermetallic systems co-exist is truly unique. However, understanding exactly the kinetic and thermodynamic conditions that lead to their unique relationship is hampered by the high formation temperatures at which the observed reaction occurs.

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