SUBSTITUTION AND PROPERTIES OF BI/PB-BASED FERRATES OF 3212-TYPE

Bi-based ferrates of type 3212 with three rocksalt-like layers between the Fe containing perovskite slabs of general formula (Bi, Pb, Sr)3Sr3Fe2O10+z are characterized by a hole concentration of about 0.25 h+/Fe ion. According to investigations by XRD, SEM, EDXA, Mossbauer, magnetic, electrical, and vibrational spectroscopic measurements, charge delocalization by hopping conduction is present at room temperature whereas at low temperatures a transition to antiferromagnetism with charge localization takes place. Increase or decrease of positive charge by partial substitution La3+ --> Sr2+ or Pb2+ --> Bi3+ is simply compensated by an insertion or depletion of oxygen from the rocksalt layers and no exchange of carriers between the perovskite slabs and the rocksalt layer is detectable.