Abstract
The effect of grinding on the transformation from the cubic to the tetragonal structure of Cu-ferrite caused by subsequent heat-treatment was investigated by X-ray diffraction analysis.
The sample of cubic Cu-ferrite, which is metastable below 360°C, was prepared from powders of CuO and Fe2O3 by heating at 930°C for 3hr and subsequent quenching into water., The molar composition was Cu1.001 Fe1.999 O3.950. The sample was ground in a ball mill at room temperature for various periods of time up to 80hr. With increasing grinding time, the strain in the lattice increased and the crystallite size decreased. Each of the ground samples was heat-treated at 280∼340°C for 1hr. It was clear that the short-time ground samples showed more obvious progress of transformation from the cubic to the tetragonal structure than the original one, but the long-time ground samples did not transform into tetragonal structure. In the long-time ground samples, the small crystallite size and a number of crystal imperfections may suppress the occurence of the cooperative Jahn-Teller effect, thus blocking the phase transformation to the stable tetragonal structure.
The effect of chemical stoichiometry of Cu-ferrite on its phase transformation was also investigated. The samples with different oxygen contents were prepared by firing in the atmosphere having different partial pressure of oxygen. The result of the heat treatment of the samples at 350°C for 1hr revealed that the transformation from the cubic to the tetragonal structure becomes depressed with increasing oxygen deficiency.
