Combined mechanochemical/thermal annealing approach for the synthesis of Co9Se8 with potential optical properties
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Synthesis of Co9Se8 phase from metallic cobalt and selenium powders by one-pot mechanochemical synthesis in a planetary ball mill and subsequent thermal treatment in argon atmosphere is reported. Crystal structure and morphology of the products were characterized by X-ray diffraction, specific surface area measurements, and transmission electron microscopy. Our study revealed that only mixture with excess of Co resulted in the formation of higher fraction of the Co9Se8 phase. While milling of Co and Se in 13.5:8 ratio resulted in the synthesis of nanocrystalline hexagonal CoSe (freboldite) and only around 13 wt.% of the targeted Co9Se8 phase, additional isothermal treatment at 450 °C increased yield of the Co9Se8 phase to more than 70%. Optical properties of the product with the highest Co9Se8 fraction showed broad absorption in whole UV–Vis optical region and band-gap energy of 1.93 eV, blue-shifted relative to the bulk Co9Se8. Both UV–Vis and photoluminescence spectra indicated quantum size effect of the finest nanocrystals in Co9Se8 product. The new combined approach represents a simple, fast, and easy up-scalable route for the synthesis of Co9Se8.
This work was realized within the frame of the project “Infrastructure Improving of Centre of Excellence of Advanced Materials with Nano- and Submicron- Structure”, ITMS 26220120035, supported by the Operational Program “Research and Development” financed through European Regional Development Fund. The support of Slovak Research and Development Agency under the contract No. APVV-14-0103 and Slovak Grant Agency VEGA (project 02/0065/18) is also gratefully acknowledged. N. Daneu and M. Mazaj acknowledge the financial support of the Slovenian Research Agency within research program cores P2-0091 (Contemporary Materials and Nanotechnologies), P1-0021 (Nanoporous materials), and project No. J1-8146.
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