The effect of Cu content on the structure of Ni1-xCuxFe2O4 spinels

A series of Ni1-xCuxFe2O4 (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 oC. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 oC to 350 oC. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu2+ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe2O4, showing different surface oxygen species from the spinel and CuO. Cu2+ substitution favors the occupancy of A-sites by Fe3+.