Crystal structure analysis of Ca₄YFe₅O₁₃by combining 1 MeV high-resolution electron microscopy with convergent-beam electron diffraction

Hard–soft synthesis of a new series of vacancy-ordered perovskites, CaCrO3−δ

“…The CaCrO 3Àd perovskite superstructures are based on stacking of tetrahedral (T) and octahedral (O) layers, with increasing T/(T + O) ratio d ¼ 0.33 / 0.4 / 0.5 as reduction proceeds. This structural mechanism was reported in CaTi 1Àx Fe x O 3Àx , 13 where Fe-content determines the T/(T + O) layer ratio and oxygen-deciency x, and x ¼ 0, 0.25, 0.33, 0.4 and 0.5 phases were found, but has not previously been reported for reduced ternary ABO 3Àd perovskites.…”

Crystal and magnetic structures of the brownmillerite Ca2Cr2O5

“…However, the Cr2O 4 tetrahedron is highly distorted with Cr2-O distances of 1.73-1.90 Å and opening of the O2-Cr2-O2 angle to 141°while other bond angles lie in the range 99-107°. The corresponding a Cell parameters a = 5.420(4), b = 14.770 (10), and c = 5.509(4) Å; isotropic thermal parameter U iso = 0.038(2) Å 2 ; residuals R wp = 0.066 and R p = 0.052. , as this cation generally has a strong preference for octahedral coordination which maximises crystal field stabilisation energy of the 3d 3 electronic configuration. The Ca 2+ site coordination is comparable to that in other brownmillerites, [14][15][16] with seven short Ca-O bonds in the range 2.43-2.62 Å while other Ca-O distances are >2.85 Å.…”

“…This structural mechanism had not previously been reported for reduced ternary ABO 3−δ perovskites but is found in CaTi 1−x Fe x O 3−x where Fe-content determines the T/(T + O) layer ratio. 10 Magnetic ordering transitions were observed for the three reduced CaCrO 3−δ phases at 150-200 K. 7 The most reduced CaCrO 3−δ phase, Ca 2 Cr 2 O 5 , has a brownmillerite (Ca 2 Fe 2 O 5 ) 11 type structure where tetrahedral layers are stacked out-of-phase with their neighbours resulting in the OTOT' stacking sequence shown in Fig. 1.…”

HREM and CIP Characterization of Complex Superstructures in Cu‐Co Related Perovskites

“…For instance, YBa 2 Fe 3 O 8 [4] is a threefold perovskite superstructure with iron in octahedral and square-pyramidal coordination according to the sequence ···PO h P···. [8] and Ca 4 YFe 5 O 13 [9] which stabilize three-, eight-, and tenfold superstructures, exhibiting the…”