Throne,
If you anneal ferrites and don't use the proper partial oxygen pressure @ the anneal temperature in your furnace, you can get segregation of Fe2O3. I assume you annealed in a too high partial oxygen pressure (atmosphere?) since you created the ironoxide with all Fe-ions in the highest oxydation state (III) while the ferrites are combinations of Fe(II) and Fe(III) ions. By annealing in a reduced atmosphere you can avoid this. It is also important to know if you quenched or slowly decreased temperature of the sample. If you slowly decrease the temperature, the partial oxygen pressure should also drop if temperature drops. The best way to do this is by reducing the atmosphere slowly to vacuum als you go down? If you quench the samples it is not important. The sample will not have time enough to take up oxygen.
Thank you, Peter, for the suggestion actually we have prepared both bulk and thin film in argon partial pressure because when we were preparing Mn Ferrite bulk( target for PLD in order to make the thin film ) in oxygen partial pressure we were getting the extra peaks of Mn oxides / Iron oxide.
Complex oxidation phenomena can occur in fine powders or thin films of manganese ferrites. See for instance Material Chemistry and Physics 17 (1987) 521-529. These phenomena lead to mixed valence defect ferrites with the spinel structure. But in air at quite high temperature the spinel structure is transformed and hematite or bixbyite appears.
Hi Throne,
When preparing your bulk material you might have been lucky with using Ar. Did this material show only one phase? I guess you sintered just long enough to create a ferrite with no phase separation. When you sinter long enough in only Ar, eventually the oxides will loose more O2 and you will get the Fe(II)O and Mn (II)O phase. Usually you have to sinter quite a long time on the right T-Po2 condition to get a single phase.At sinter temperatures of ca. 1100 C the Po2 for ferrites is usually around 0.2-1.0 atmosphere, depending on the material composition. As you go down in temperature the Po2 should also go down untill there is hardly any diffusion anymore (T
Hi Throne,
When you have a single target composition you only have to use the right sputter proces (I presume Ar or Ar with O2) and do athe anneal at the right T-Po2 condition.
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