Formation of nanocrystalline NiFe2O4

Coprecipitates, Ni(OH)(2) + 2Fe(OH)(3), were milled in a planetary mill, using an agate bowl and balls (99.9% SiO2), and then heated at a maximum temperature of 573 or 773 K. The Mossbauer spectra at 298 K of the ball-milled samples (not healed) showed the superposition of two quadrupole doublets. After heating at 573 K, the superposition of two doublets was preserved at 298 K with a slight increase in the quadrupole splitting for the sample ball-milled for 64 h. After heating at 573 K, the ball-milled samples showed at 80 K a central quadrupole doublet and a sextet with very broad lines. All the samples heated to 573 K were amorphous for according to X-ray diffraction while those heated to 773 K exhibited crystalline NiFe2O4 with broadened diffraction lines. At 298 K, superposition of two sextets in the Mossbauer spectra was observed for the samples obtained after heating at 773 K, indicating the presence of nickel ferrite as a single phase. The average sizes of NiFe2O4 crystallites were in the nanosize range (8-12 nm). The Fourier transform infrared spectra of the samples heated at 773 K showed two very strong bands with positions at 601-603 and 408-411 cm(-1), which can be ascribed to NiFe2O4.