Abstract
Formation of MnxCo3−xO4 yolk–shell microspheres via a solvothermal reaction of hydrated cobalt and manganese nitrates in ethanol is investigated. Spinel nanocrystals of cobalt oxide or cobalt-rich ternary oxide preferentially develop in the system, while manganese-rich hydroxide form Mn(OH)2-type nanosheets. Instead of continuing to grow individually, the nanocrystallites and nanosheets aggregate into large microspheres due to their strong inter-particle interaction. When the proportion of Mn-rich nanosheets is high, therefore the overall density is low, dehydration of hydroxide nanosheets and a surface re-crystallisation lead to formation of a dense and rigid shell, which is separated from a solid or hollow core via a further Ostwald ripening process. The proposed formation mechanism of the yolk–shell structures based on electron microscopic studies would help us to develop yolk–shell structure based multifunctional materials.
Highlights
A large number of functional materials with spinel (AB2O4) structures have increasingly attracted researchers in various elds
The crystalline phases of the samples were initially detected by powder X-ray diffraction (PXRD)
The produced specimens were designated as mmol in total (Mn)(x-t), where x is the Mn content in the nominal formula MnxCo3ÀxO4, and t is reaction time in hours
Summary
A large number of functional materials with spinel (AB2O4) structures have increasingly attracted researchers in various elds. The main phase in Mn(1.5-24) is solid yolk–shell microspheres, from which, the Mn/Co ratios are 1.08 in the shells and 0.84 in the cores.
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