Glass formation and confined melting in sol–gel derived nano-ZnO aggregates
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Sol–gel processing of ZnO nanocolloids has been revisited to prepare various alkaline metal acetate (MAc: K, Na, Li-acetates) containing ZnO nanopowders. Using differential scanning calorimetry and X-ray diffraction investigations, several new relationships between the morphology and the thermodynamic behavior in the aforementioned particulate ZnO/MAc nanocomposites were noticed: (1) large MAc melting depression shifts −ΔTm ~ 80 °C due to salt confinement within porous ZnO aggregates, (2) corresponding MAc crystallization and re-crystallization temperature depression shifts, (3) presence of multimodal pore size distributions within nanoaggregates and (4) glass formation at temperatures Tg between −40 and 130 °C. We also note that the Tg value drops with rising alkaline metal size, increasing water content and decreasing ZnO particle size. In contrast, Tg rises in the case of co-doped Fe–LiAc/ZnO compositions.
KeywordsNanoparticles Melting confinement ZnO Sol–gel glasses
We gratefully acknowledge our colleagues Prof. Marcel Poulain and Prof. Jacques Lucas for useful discussions. C.A., on leave from the Palacky University Olomouc is grateful for the possibility of passing two short research periods at the University of Rennes 1. LS thanks CEITEC—Central European Institute of Technology for financial support (Project CZ.1.05/1.1.00/02.0068).
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