Emergence of Perovskite and Hashemite-type phases in chromium doped (Ba 0.90 Sr 0.10 )(Fe 1-x Cr x )O 3 ± δ oxides: Formation, Rietveld refinement and Raman spectra

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 (Ba 0.90 Sr 0.10 ) (Fe 1-x Cr x )O 3 +/- delta (x = 0 - 1.0) and characterized with regards to structure and Raman vibrations. It depicts (a) pure cubic (Ba 0.90 Sr 0.10 )FeO 3- delta phase, (b) cubic+orthorhombic, and (c) single orthorhombic (Ba 0.90 Sr 0.10 )CrO 4 phase for x = 0 -0.10, 0.20 - 0.80, and 1.0, respectively. It exhibits (i) decrease of cubic lattice parameter ( a c )as 4.020 - 3.926 & Aring;, (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-O2.84 & Aring;, Fe -O -2.04 & Aring; and Ba/Sr-O 1 - 3.227 & Aring;, Ba/Sr-O 2 - 2.893 & Aring;, Ba/Sr-O 3 -2.859 & Aring; have been derived for cubic (x = 0) as well as orthorhombic structure (x = 1.0), respectively. The bond angles e.g., Cr -O 1 -Cr - 129 degrees , CrO 2 -Cr - 104.3 degrees and Cr -O 3 -Cr - 83.3 degrees have been found for x = 1.0. Moreover, the bond Cr -O 1 is compressed and Cr -O 2 is more stretched than Cr -O 3 bond. The morphology has also been changed to bigger size (nm) and shows different nature with chromium content. Raman spectra for Hashemite-type (Ba 0.90 Sr 0.10 )CrO 4 reveal bands at -350, 360, 401, 425, 861, 886 and 904 cm -1 and arise due to symmetric ( upsilon 1 , upsilon 2 ) and antisymmetric ( upsilon 3 , upsilon 4 ) bending/ stretching mode. The present findings suggest potential applications of (Ba 0.90 Sr 0.10 )(Fe 1-x Cr x )O 3 +/- delta oxides.