The temperature dependence of ordering in magnesium ferrite

Cation ordering in magnesium and nickel ferrites was studied by X-ray diffraction measurements carried out at the temperature of equilibration and also on quenched specimens. The order parameters on quenched specimens agreed with results previously reported by others but not with values measured at temperature. Previous results on quenched specimens had been described by a simple mass action relation with constant ordering energy. The new results on equilibrated specimens require a modified Bragg-Williams-type relation in which the ordering energy varies with the degree of order. Both ferrites are inverted when in equilibrium at low temperature. Magnesium ferrite approaches a random distribution at high temperature with a Curie point at about 1070°C. Oxygen positional parameters were 0.243±0.001 for both ferrites at room temperature. The lattice parameter of nickel ferrite quenched from temperatures up to 1255°C was 8.3295±0.0001 Å. For magnesium ferrite the lattice parameter varied from 8.3775±0.0001 Å, when quenched from 784°C. to 8.3848, when quenched from 1271°C.