57Fe Moessbauer spectroscopy studies of Sr2Fe1-xCrxMo1-xWxO6 double perovskite compounds

Polycrystalline double perovskites Sr2Fe1-xCrxMo1-xWxO6 with x = 0, 0.05, 0.10, 0.15, 0.20, and 0.30 have been prepared by sold state reactions. A continuous decrease of the tetragonal unit cell parameters α and c with increasing x values is observed. The highest Curie temperature TC = 426 K is recorded for the x = 0.10 compound. 57Fe Moessbauer spectroscopy measurements indicate a non-integral electronic configuration of ∼3d5.3 for the Fe ions at the ordered double perovskite structure for x ≤ 0.20, which reaches ∼3d5.4 for x 0.30. Fe-Mo/W anti-site and anti-phase boundary defects are observed in all samples in equal concentrations of around 3% of the total number of Fe ions in their structure.