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Thermal expansion of ε-Co and β-Co nanocrystals in glass matrices

: Briese, L.C.; Deubener, J.; Selle, S.; Höche, T.


Materials letters 270 (2020), Art.127707
ISSN: 0167-577X
Fraunhofer IMWS ()

Metastable ɛ-Co nanocrystals precipitate in silicate glass matrices together with stable β-Co nanocrystals at temperatures up to 873 K, whereas rapid thermal decomposition of ε-Co is reported if formed by wet-chemical routes. Hence, high-temperature X-ray diffraction was used to determine the unknown coefficient of thermal expansion (CTE) of ε-Co stabilized in glasses. The liquid character of the matrix provides free expansion of ε-Co nanocrystals above the glass transition temperature (Tg), while a strain correction was performed for lattice constants below Tg using the co-precipitated β-Co as internal reference. It is found that CTE (298–873 K) of ε-Co nanocrystals is 10.1 ppm K−1, which is slightly larger than CTE of β-Co nanocrystals (9.4 ppm K−1).