PROPERTIES OF K2NIF4-TYPE OXIDES SR2FEO-SIMILAR-TO(4)

Slightly oxygen deficient samples of the K2NiF4-type oxide Sr2FeO4 with tetravalent iron have been prepared from the metal oxides in flowing O2 gas atmosphere and investigated by resistivity, magnetic susceptibility, and Mössbauer effect measurements. Sr2FeO∼4 is a Mott-type antiferromagnetic semiconductor with a Néel temperature TN of about 60 K. The Mössbauer spectra above TN consist of a single Fe4+ quadrupole doublet with an isomer shift δ of -0.017 mm sec-1. The Mössbauer spectra of the magnetically ordered phase reveal at least four Fe4+ hyperfine sextets which are evidence for local structural distortions associated with the phase transition. A charge disproportionation according to 2 Fe4+ → Fe3+ + Fe5+ which was found previously for some semiconducting perovskite-type oxoferrates(IV) was neither observed above nor below TN. The magnetic hyperfine fields Bhf derived from the Mössbauer spectra at 8 K range from 25 to 33 T which suggests a formal d4 high spin configuration with covalent Fe-O bonding for the tetravalent iron. The properties of Sr2FeO4 are compared with literature data of the perovskite SrFeO3 and the K2NiF4-type phases (A, A′)2M0.5Fe0.5O4(A = Ca, Sr, Ba, A′ = La, and M = Mg, Zn, Li). © 1994 Academic Press. All rights reserved.