Effect of A cation size on structural, magnetic and electrical properties of K2NiF4-type oxide LaSrFeO4

K2NiF4-type oxides La0.8R0.2SrFeO4 (R=La, Nd, Gd, Dy) have been synthesized by Pechini method and their structures were established by Rietveld refinements of the XRD data in the space group I4/mmm. Analysis of cell parameters shows that the decrease in the c from La to Dy compound is much larger than that in a. All the samples show antiferromagnetic behavior with increase in value of Θ with decreasing average site radius. For all compounds, semiconducting behavior persists in the whole temperature range and can be expressed by two conduction mechanisms - Arrhenius model and polaron hopping model. The results suggests that the transport properties are dominated by the adiabatic small polaron hopping mechanism. Both activation energy (Ea) and polaron hopping energy (Ep) decrease with decreasing average ionic radius of rare earth ion at A-site.