Mössbauer Characteristics of the Nonstoichiometric Sr₂LaFe₃O_8+δ Perovskite Obtained by Electrochemical Oxidation

Abstract
The nonstoichiometry and the vacancy ordering in the perovskite Ca₂LaFe₃O₈ has been investigated in previous works [1,2]. More recently, the occurrence of a large nonstoichiometric domain has been shown in the Sr₂LaFe₃O_8+δ system [3]. Thus, we have used a new "Chimie Douce" method : electrochemical oxidation which has been developped in our laboratory [4] for obtaining Sr₂LaFe₃O_8.90 in alkaline medium. The starting material Sr₂LaFe₃O₈ has been characterized by XRD, chemical analysis and Mössbauer spectroscopy. This compound contains only Fe³⁺. The Mössbauer spectroscopy reveals, in the oxidized phase, the occurrence of antiferromagnetic interaction below T_N = 195 K with a good agreement with electric and magnetic measurements. At low temperature, the presence of two sextets can be explained in terms of a charge disproportionation :
2 Fe ⁴⁺ → Fe^(4-λ)+ + Fe^(4+λ)+ .