Microwave-assisted synthesis of nanocrystalline MWO4 (M: Ca, Ni) via water-based citrate complex precursor

Nano-sized MWO4 (M: Ca, Ni) powders, which have scheelite and wolframite type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 500 °C for 3 h. Crystallization of the CaWO4 and NiWO4 nano-sized powders were detected at 300 and 350 °C, respectively, and completed at a temperature of 400 °C. Most of the CaWO4 and NiWO4 powders heat-treated between 350 and 450 °C showed primarily spherical and homogeneous morphology. The average crystallite sizes of CaWO4 and NiWO4 were between 12 and 35 nm and between 14 and 29 nm, respectively, showing an ordinary tendency to grow with temperature.