Fast, reversible CO2 capture in nanostructured Brownmillerite CaFeO2.5

Electronic structure and magnetic properties of Al‐doped Ca2Fe2O5 brownmillerite compounds

“…Intrinsically, the vibrations below 150 cm −1 are associated with the movements of Ca ions. The modes at about 181, 254, 290 312, 379, 395, 427, 555, and 706 cm −1 are assigned to the A g symmetry, which are associated with the internal vibrations of FeO 6 octahedra . The other ones (212, 667, and 740 cm −1 ) with a low intensity could be due to the B g modes.…”

“…The other ones (212, 667, and 740 cm −1 ) with a low intensity could be due to the B g modes. Because vibrational modes are dependent on numerous factors (including the crystal orientation, bond strengths, particle size, different brownmillerite structures, and excitation energy), the position, intensity, and total number of Raman modes reported in the literature vary …”

“…In the case of the two strongest vibrations, however, one can see that the vibration at 254 cm −1 is less dependent on x (its change is approximately 3‐6 cm −1 ), while the other at 706 cm −1 is strongly affected by x , and vanishes as x ≥ 1.0. Because the mode at 254 cm −1 is attributed to the rotation of the FeO 6 octahedra, its position is not effected by Al doping. Meanwhile, the vibration at 706 cm −1 is associated with the symmetric breathing and stretching of the FeO 6 octahedra .…”

“…Among the brownmillerite oxides, the parent compound with A = Ca and B = Fe (i.e., Ca 2 Fe 2 O 5 ) has been of interest. This is due to Ca 2 Fe 2 O 5 showing many intriguing magnetic structures, novel applications in magnetoresistive devices, chemical looping H 2 production, reversible CO 2 ‐capture units for air purification, and electrochemical energy conversion devices …”

Crystalline and Electronic Structures and Magnetic and Electrical Properties of La-Doped Ca2Fe2O5 Compounds

“…5 At room temperature, it has brownmilleritetype orthorhombic structure in space group Pcmn with lattice constants a = 5.425 Å , b = 14.769 Å , and c = 5.598 Å . 6,7 This structure can be described as alternating layers of corner-sharing FeO 6 octahedra and FeO 4 tetrahedra.…”