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In this study, we investigated the effect of microwave irradiation on the synthesis of ZnFe2O4 (ZFO) nanopowders. The structural, chemical, and physical features of the powders prepared via microwave-assisted heating (MWH) were analyzed with variation in the initial precursors and synthesis temperatures. Three different types of source batches, namely Zn(CH3CO2)2 · 2H2O and FeC2O4 · 2H2O (ZAHFOH), Zn(NO3)3 · 6H2O and Fe(NO3)2 · 9H2O (ZNHFNH), and ZnO and Fe2O3 (ZOFO), were prepared. The formation of ZFO compounds was achieved at 100 °C for ZAHFOH using MWH, which is much lower than the synthesis temperature of 700 °C using conventional heating (CH). The value of the activation energy (Q) for the ZAHFOH source in synthesis using MWH was approximately 7.9 kJ/mol, which is approximately one-tenth of the Q value (100.7 kJ/mol) for ZOFO using CH. It was determined that the inversion factors were approximately 5.4, 4.3, and 4.0, and the crystallite sizes were 57.7, 72.5, and 78.9 nm for the ZAHFOH, ZNHFNH, and ZOFO, respectively. The ZFO powders exhibited superparamagnetism for ZAHFOH and paramagnetism for ZNHFNH and ZOFO. Based on the crystallite size-related surface effects, redistribution of the Zn and Fe ions occurred. This phenomenon is attributed to the magnetic transformation of ZFO. Based on these results, it is expected that a sensitively tunable size and magnetic properties can be achieved using MWH.

Microwave-assisted solid-state reactions (MSSR) are investigated for their ability to synthesize nanocrystalline BaTiO 3 powders at low temperatures. Ba(OH) 2 •H 2 O and TiO 2 •xH 2 O are, respectively, initial precursors for Ba and Ti. In this study, these precursors were mixed according to their chemical stoichiometry and heated in a temperature range of 100-1000 °C by MSSR. Nanocrystalline BaTiO 3 powders having an average size of 26 nm were produced by MSSR, even at 100 °C. The crystallization-related activation energy for the formation of BaTiO 3 with the precursors by MSSR was ~ 9.6 kJ/mol, which is less than 1/10 of the value (120 kJ/mol) when the conventional solid-state reaction was applied. The nanostructural and physical features of the MSSR-based powders are compared with those prepared using the conventional solid-state reaction.

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