The properties of nanocrystalline oxides depend on the chemical and phase composition as well as the size and the morphology of crystallites, it is important to control all these characteristics during the synthesis process. In this paper zinc oxide powders doped with Co were produced in two ways: a microwave-driven hydrothermal process and vapour-condensation of the hydrothermal synthesized powders in a solar furnace. The combination of the two methods allows controlling both Co concentration (0.0079 wt% of Co in the hydrothermal powders and 0.0075wt% in vapour-condensation powders) and crystallite morphology from spherical nanoparticles to nanowhiskers. The influence of the synthesis process on the ESR spectra and magnetic properties are discussed.

In the absence of reliable phase diagrams for the studied system, thermodynamic simulations provided important information for controlling hydrothermal/solvothermal methods. The experiments confirm the high potential offered by solvothermal chemistry in producing semiconductor oxides with controlled dopant concentrations due to the in-situ nucleation of oxides, as observed from ESR spectra.

Acknowledgement

The paper is a result of a cooperation supported by EGIDE, France, in the frame of ECO-NET project “Fun-Nanos” and FP6 SOLFACE.

Some authors acknowledge the financial support from Romanian Agency for Scientific Research – CEEX Programme, project 69 SINAPS.

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