Emergence of Perovskite and Hashemite-type phases in chromium doped (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides: Formation, Rietveld refinement and Raman spectra

Abstract

Perovskite- and Hashemite-type oxides are relevant due to their applications as oxidizing agent, photocatalyst, nutrient, fuel cells, gas sensors, batteries materials. An attempt has been made here to synthesize (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ(x = 0 – 1.0) and characterized with regards to structure and Raman vibrations. It depicts (a) pure cubic (Ba0.90Sr0.10)FeO3-δ phase, (b) cubic+orthorhombic, and (c) single orthorhombic (Ba0.90Sr0.10)CrO4 phase for x = 0–0.10, 0.20 – 0.80, and 1.0, respectively. It exhibits (i) decrease of cubic lattice parameter (ac)as 4.020 – 3.926 Å, (ii) expansion of orthorhombic unit cell, (iii) complete appearance of chromium in 6+ state for x = 1.0, and (iv) decrease of bond length and angle both with chromium. The bond lengths corresponding to Ba/Sr-O ∼ 2.84 Å, Fe-O ∼2.04 Å and Ba/Sr-O1 ∼ 3.227 Å, Ba/Sr-O2 ∼ 2.893 Å, Ba/Sr-O3 ∼2.859 Å have been derived for cubic (x = 0) as well as orthorhombic structure (x = 1.0), respectively. The bond angles e.g., Cr-O1-Cr ∼ 129°, Cr-O2-Cr ∼ 104.3° and Cr-O3-Cr ∼ 83.3° have been found for x = 1.0. Moreover, the bond Cr-O1 is compressed and Cr-O2 is more stretched than Cr-O3 bond. The morphology has also been changed to bigger size (nm) and shows different nature with chromium content. Raman spectra for Hashemite-type (Ba0.90Sr0.10)CrO4 reveal bands at ∼350, 360, 401, 425, 861, 886 and 904 cm−1 and arise due to symmetric (υ1, υ2) and antisymmetric (υ3, υ4) bending/ stretching mode. The present findings suggest potential applications of (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides.