Premium
Crystal Structure and Properties of Ba 11 FeTi 27 O 66.5
Author(s) -
Vanderah Terrell A.,
Siegrist Theo,
Roth Robert S.,
Ramirez Arthur P.,
Geyer Richard G.
Publication year - 2004
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200300945
Subject(s) - crystallography , octahedron , crystallite , monoclinic crystal system , chemistry , crystal structure , feti , single crystal , valence (chemistry) , x ray crystallography , stoichiometry , diffraction , physics , domain decomposition methods , finite element method , optics , thermodynamics , organic chemistry
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 C 2/ 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)] layers with a stacking sequence ( cchhc ) 2 . Octahedral sites are occupied by a mixture of Fe 3+ and Ti 4+ , 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 formation was not observed for polycrystalline specimens. A comparison of the crystal structure obtained for Ba 11 FeTi 27 O 66.5 with that previously proposed for “Zr 4+ ‐stabilized Ba 2 Ti 5 O 12 ” indicates that the phase “Ba 2 Ti 5 O 12 ” is actually a ternary compound which forms upon addition (either deliberately or inadvertently) of a trivalent ion such as Fe 3+ or Al 3+ . The specimens Ba 11 Al 2 Ti 26 O 66 , Ba 11 Al 2 Ti 24 Sn 2 O 66 , and Ba 11 Al 2 Ti 24 Zr 2 O 66 were also prepared and were found to form the A 11 B 28 O 66+ x ‐type phase. Ba 11 FeTi 27 O 66.5 exhibits paramagnetic behavior that deviates somewhat from the Curie−Weiss Law below 75 K. Application of this formalism to the 1/χ vs. T data above 75 K yields an effective moment consistent with the presence of high‐spin Fe 3+ ( S = 5/2), and a negative Weiss constant (about −25 K) indicating weak cooperative magnetic interactions that are overall antiferromagnetic. The relative permittivity and dielectric loss tangent of a sintered polycrystalline disk were measured at 5.33 GHz, yielding values (corrected for theoretical density) of 55 and 7.7(±0.3) × 10 −4 , respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)