Detection by means of electrical and magnetic measurements of Crn+ (n > 3) ions in polycrystalline ZnCr2O4 samples prepared by heating in air

Polycrystalline samples of zinc chromite (Zn2+Cr23+O4) were prepared by the standard ceramic technique (mechanical mixing of oxides and heating in air), with the purpose of selecting the optimum and relatively simple preparation conditions which would lead to samples suitable for applications. The oxygen-rich furnace atmosphere is responsible for the oxidation of Cr3+ ions and possible presence of higher valence chromium ions. These would account for the amount of open porosity in the samples and affect their electrical and magnetic properties. It was found from XRD and electrical and magnetic measurements that the samples were single phase with the characteristic properties of zinc chromite. These observations led to the conclusion that the influence of the furnace atmosphere was limited to the presence of open porosity and did not affect the electrical and magnetic properties of the samples, within the limits of error of the specific measurements, making them useful for applications in which the increased amount of porosity is not forbidding, or can be made use of. A number of other spinels were also prepared for comparison purposes.