Reinvestigation of the Fe-rich part of the pseudo-binary system SrO–Fe2O3

The phase relations in the Fe-rich part of the pseudo-binary system SrO–Fe2O3 (>33 mol% Fe2O3) were reinvestigated between 800 and 1500 °C in air. A combination of microscopy, electron probe micro-analysis, powder X-ray diffraction and thermal analysis was used to determine phase relations, crystal structure parameters and phase transition temperatures. M-type hexagonal ferrite SrFe12O19 (85.71 mol% Fe2O3) is stable up to 1410 °C. No indication of a significant phase width was found; Sr4Fe6O13±δ appears as a second phase in compositions with <85.71±0.2 mol% Fe2O3. Sr4Fe6O13±δ itself is stable between 800 and 1250 °C. Two other hexagonal ferrites were found to exist at high temperatures only: W-type SrFe2+2Fe3+16O27 is stable between 1350 and 1440 °C and X-type ferrite Sr2Fe2+2Fe3+28O46 between 1350 and 1420 °C, respectively, which is shown here for the first time. These findings in combination with previously published data were used to derive a corrected phase diagram of the Fe-rich part of the pseudo-binary system SrO–Fe2O3.