Magnetic properties and valence states of the Fe ions in Bi0.5Sr0.5FeO3-y

Fe-57 hyperfine interactions in the cubic perovskite Bi0.5Sr0.5FeO3 - y have been studied by Mossbauer spectroscopy in the temperature range 87-670 K. The results indicate that its magnetic ordering temperature is 637(3) K, which is close to the N,el point T (N) of bismuth ferrite. Below T (N), the measured spectra have a partially resolved magnetic hyperfine structure with broadened lines, which is well represented by four sextets. Above T (N), the spectra each consist of four quadrupole doublets. From the room-temperature hyperfine magnetic field B and isomer shift delta, it follows that all of the Fe ions are trivalent. The two sextets identical in isomer shift (delta(1) a parts per thousand integral delta(2) = 0.37 mm/s) are due to Fe ions in octahedral oxygen coordination. The other two sextets correspond to squarepyramidal (delta(3) = 0.25 m/s) and tetrahedral (delta(4) = 0.17 mm/s) coordination.