Synthesis and characterization of mixed valent Fe containing K2NiF4-type phases

Abstract

The phases LaSr1−xNaxFeO4 (x=0.00, 0.05, 0.10, 0.15, 0.20) with K2NiF4-type structure have been synthesized by standard ceramic method. The Rietveld analysis of the powder XRD data assigns tetragonal structures to all the compositions with I4/mmm symmetry. The lattice constant a almost remains constant, while there is increase in c with increasing x due to Jahn–Teller effect. The anomaly for x=0.2 is consistent with smaller ionic radii of Na+ than Sr2+. For all the studied samples the paramagnetic Curie temperature (θp) is negative, indicating the existence of antiferromagnetic interactions in them. The change in Weiss constant (θp) is attributed to the presence of Fe4+ content. All the compositions of two dimensional compounds LaSr1−xNaxFeO4 are within the semiconducting range. The electronic conduction in these materials is obtained via hopping of electrons from the occupied sites, Fe3+ ions, to the unoccupied sites, Fe4+ ions. The transport properties are dominated by the Arrhenius model with the decrease of activation energy with increasing x.