Crystal Structure and Properties of Ba₁₁FeTi₂₇O_66.5

Abstract

The crystal structure of Ba 11 FeTi 27 O 66.5 was determined using single-crystal and powder X-ray diffraction methods. This phase crystallizes in the monoclinic space group C2/m (No. 12) (a = 23.324(1) Å , b = 11.388(1) Å , c = 9.8499(3) Å , β = 90.104(3)°; Z = 2; ρ calcd. = 4.98 g/cm 3 ), and exhibits a 10-layer structure built from close-packed [O,(Ba,O) , with some preferential ordering suggested by analysis of bond valence sums. The structure features vertex-, edge-, and face-sharing of the [Ti(Fe)O 6 ] octahedra. Indexed X-ray powder diffraction data for a polycrystalline specimen are given. Ba 11 FeTi 27 O 66.5 and the 8-layer phase Ba 4 Fe 2 Ti 10 O 27 are built from the same types of polyhedral layers, some of which feature vacant sites between two Ba ions, which substitute for three oxygens in a row. The single-crystal results suggest that the basic structural formula of the phase is A 11 B 28 O 66+x , with the value of x (and hence the Fe/Ti ratio) determined by partial occupancy of one of these vacant sites. Variation of this occupancy factor with synthesis temperature may account for apparent slight differences in the stoichiometry of this phase in polycrystalline and single-crystal form. However, solid solution forma-

Structure-mining: screening structure models by automated fitting to the atomic pair distribution function over large numbers of models

“…6 (Jain et al, 2013)) and 0.6 for the COD (such as COD No. 34 (Vanderah et al, 2004)). The entire search process took 493.7 seconds for the MPD and 469.5 seconds for the COD.…”