Journal
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
Volume 39, Issue 16, Pages 5373-5379Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jeurceramsoc.2019.08.002
Keywords
Germanate glass; Glass transition; Crystallization; Nano-crystal; Melting
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Funding
- National Natural Science Foundation of China [61368007, 51802236, 51772223]
- China Scholarship Council [201406950038]
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The nanocrystals play a critical role in generating and affecting functionalities of glass materials. Therefore, scientists have made considerable efforts in clarifying microscopic mechanisms of nanocrystal formation in glass to obtain the desired type of nanocrystals. However, the phase transitions of nanocrystals during heating have not been well understood. Here we report on a discovery of the reversible melting-formation of nanocrystals in an oxyfluoride germanate glass during heating-cooling circles. Using a differential scanning calorimetry (DSC), we detected a striking endothermic event at 925 K during heating, after the glass underwent a DSC upscan to a temperature between 925-986 K and subsequent cooling. Based on Raman spectroscopy, X-ray diffraction and transmission electron microscopy, the endotherm is attributed to the melting of nano-crystal BaGeF6 ((similar to)20 nm). An exothermal response was observed at 890 K during the DSC downscan, implying the re-formation of BaGeF6 nano-crystals. This suggests that the melting-formation of BaGeF6 nano-crystals is a typical first-order transition.
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