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The preparation of NiFe2O4in the solid‐state has been studied by means of thermo‐magnetic and thermo‐gravimetric continuous measurements and by X‐ray diffraction analysis. The method consists of the preparation of a crystallized organo‐metallic complex (NiFe citrate precursor), which on decomposition at moderate temperatures gave NiFe2O4. The yield of the product depends on the ambient atmosphere during decomposition. Optimal conditions for a high yield of nickel ferrite were pretreatment of NiFe citrate at 250°C in air followed by gradual heating under vacuum to 500°C. This is a relatively low temperature as compared to temperatures previously used in the preparation of NiFe2O4.

Oxygen was absorbed on cerium (IV) oxide which had been prepared by heating the cerium (III) oxalate at 1173°K in air. In addition to the naturally occurring isotope mixture of oxygen, an enriched 17O2(67%) was adsorbed. From the enriched mixture it was concluded that the anionic species obtained was O−2. It was also shown that part of the oxygen was adsorbed as a molecular species. On this sample no isotopic exchange took place between the adsorbed (17O 17O)−and (16O 17O)−anion molecules.

The effects of heating in vacuum, carbon monoxide, and hydrogen on cerium (IV) oxide and zinc oxide‐doped cerium (IV) oxide were investigated by ESR, and a difference in the behavior of the signals obtained for the two preparations was observed. The signal decrease g = 1.940 and g = 1.961 was faster and was obtainable at lower temperatures for the doped oxide than for the undoped sample. The effect of oxygen on these samples is reported and a mechanism is proposed.