PB-BASED AND BI-BASED FERRATES OF TYPE-2212

The extent of Pb → Bi substitution in the series of ferrates of type 2212 is studied by XRD, SEM, EDXA, DC resistivity, DC magnetic susceptibility, and vibrational spectroscopic measurements. It is shown that the 2212 structure has an extended field of stability including a pure Pb representative, PbSr4Fe2O9+z; a simultaneously Bi/Pb substituted series, Bi3-yPbySr2Fe2O9+z; and the pure Bi system Bi3-xSr2+xFe2O9+z. All compounds are basically antiferromagnetic and semiconductlng. However, from the observed discontinuity in the magnetic and electrical properties, combined with important differences in the hole concentration, the absence of a simple scheme of substitution follows. The correlation between hole concentration, crystal structure, and physical properties is discussed. © 1994 Academic Press, Inc.