Effect of Mechanical Treatment on Polymorphic Transformation in Copper Ferrite

Abstract

Effect of mechanical treatment on the polymorphic transformation in copper ferrite was investigated by X-ray diffraction analysis. The results obtained are as follows: 1) The transformation from cubic to tetragonal structure at temperatures between 320°C and 360°C was promoted by the mechanical treatment such as pressing or milling. The transformation isotherms were represented by Dander's equation, and the activation energy of the transformation was about 45k cal/mol, which was independent of the mechanical treatment and agreed with that of the oxidation. 2) For long-time milled or ground samples, the trans-formation from cubic to tetragonal structure did not occur below about 500°C. However, after being annealed higher temperatures the transformation occurred. 3) The tetragonal structure transformed into the cubic one at room temperature by long-time milling or grinding. It is considered that the cooperative Jahn-Teller ordering was destroyed by lattice imperfections, such as dislocations and stacking fault generated by milling or grinding. 4) The residual tetragonal structure which had not been transformed was transformed into the cubic one by heating above about 360°C.