Tetragonal-Cubic Transformation in CuFe2O4 by Grinding and Heat Treatment

Abstract

The effects of grinding and heat treatment on the structure of CuFe2O4 have been investigated by X-ray diffraction analysis.The sample of tetragonal CuFe2O4 was ground in water in a ball mill at room temperature for varying times up to 190hr, and cubic CuFe2O4, up to 70hr. From the results of the X-ray diffraction analysis, it has been observed that the tetragonal structure was gradually transformed into the cubic one with increasing grinding time, and that the reverse transformation did not occur. In both cases, the strain in the lattice increased and crystallite size decreased with grinding time. This fact indicates that lattice imperfections such as dislocation and stacking fault increase with grinding. It can be considered that a cooperative alignment in the tetragonal CuFe2O4 is gradually destroyed with an increase in the lattice imperfections, and that the tetragonal structure has consequently been transformed into a cubic one.When each of the samples of the ground cubic CuFe2O4 was heated for 4hr at 350°C, what was ground for a short time has been transformed into the tetragonal structure, while those samples which have been ground for a long time have not been transformed. When each sample of the CuFe2O4, which had been substantially transformed from the tetragonal into the cubic structure by grinding for a long time, was heated at varying temperatures up to 800°C for 2hr and then cooled slowly, the reflection line (311) of the cubic structure remained unchanged below 500°C. At the heating temperatures above 600°, the transformation from the cubic into the tetragonal structure progressed with rising temperature. The heating temperatures above 600°C closely corresponded to those of the recovery process of the induced strain and the reduced crystallite size.