Effect of Chemical Stoichiometry on the Copper Ferrite Phase Transition

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Abstract
Previous studies on copper ferrite report conflicting data as to the effect of quenching temperature on the transformation temperature. Data of the present study reveal that the reason for this disagreement has been insufficient attention to the influence of chemical stoichiometry. The transition temperature of copper ferrite with Fe/Cu=2.00 has been shown to be determined primarily by the distribution of the Cu atoms between the A and B sites of the spinel lattice. However, this distribution is not determined uniquely by the quenching temperature, as has been previously reported. Instead it is shown that the Cu distribution is also strongly affected by the oxygen stoichiometry. For constant quenching temperature, the amount of Cu on B sites increases with decreasing oxygen deficiency, and for the same oxygen content, the B‐site Cu increases with decreasing quench temperature. The change in transition temperature produced by varying the oxygen content for a 900°C quench is comparable to the temperature change produced at constant oxygen content by varying the quench temperature from 900° to 500°C. In these studies the Cu distribution was determined from the saturation magnetization at 1.4°K. The temperature of the phase transformation was determined by x‐ray diffractometer measurements. In view of these data it is clear that a systematic investigation of this diffusionless transition requires control both of stoichiometry and of thermal history.

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