NONSTOICHIOMETRY AND PHYSICAL-PROPERTIES OF THE 2-DIMENSIONAL SR1-XFEO4-Y SYSTEM(XND1)

The compounds Sr1+xNd1-xFeO4-y (x = 0 00, 0.25, 0.50, 0.75, and 1.00) with the K2NiF4 structure are prepared by a drip pyrolysis technique. X-ray powder diffraction analysis assigns all the compositions to the tetragonal system with decreasing lattice volume as x increases. Nonst oichiometric chemical formulas are formulated and identified by Mohr s alt analysis and Mossbauer spectroscopy, respectively. Oxygen vacancy formation is predominant rather than the oxidation of the Fe3+ ion to the Fe4+ ion with respect to the competitive compensation for the posi tive charge deficiency. The electrical and magnetic properties of thes e compounds, with the space group 14/mmm, are different from those of the corresponding three-dimensional perovskites. All the compositions of the two-dimensional Sr1+xNd1-xFeO4-gamma compounds are within the s emiconducting range with positive temperature dependence of the electr ical conductivity. Although the amount of Fe4+ ion is maximum at the c omposition of x = 1.00, its lowest electrical conductivity can be asso ciated, not with the conduction carrier concentration, but with the mo bility which depends on the amount of the oxygen vacancy and on the Fe -O-Fe bond distance. As a result of the magnetic measurement with a SQ UID, all the compositions follow the Curie-Weiss law and the anomalous effective magnetic moments of the compositions can be interpreted as a coexistence of low and high spins of the mixed valence state. (C) 19 96 Academic Press, Inc.