Crystal Structure and Properties of Ba11Fe2Ti26O66 Crystal Structure and Properties of Ba11Fe2Ti26O66 Crystal Structure and Properties of Ba11Fe2Ti26O66

The crystal structure of Ba11Fe2Ti26O66 was determined using single-crystal and powder X-ray diffraction methods. This new phase crystallizes in the monoclinic space group C2/m (No 14) (a=23.324(1) Å, b=11.388(1) Å, c=9.8499(3) Å, b=90. 104(3)°) and exhibits a 10-layer structure built from close- packed [O,(Ba,O)] layers with a stacking sequence (ccchh)2. Octahedral sites are occupied by a random mixture of Fe3+ and Ti4+. Indexed X-ray powder diffraction data for polycrystalline Ba11Fe2Ti26O66 are given. The compound exhibits approximately paramagnetic behavior that deviates somewhat from the Curie Law. Application of this formalism to the 1/c vs. T data above 75 K yields an effective moment consistent with the presence of high-spin Fe3+ (S=5/2), and a negative Weiss constant (» -25 K) indicating weak cooperative magnetic interactions that are overall antiferromagnetic. The relative permittivity and dielectric loss tangent of a sintered polycrystalline disk of Ba11Fe2Ti26O66 were measured at 5.33 GHz, yielding values (corrected for theoretical density) of 55 and 7.7(±0.3)x10- 4, respectively, that were essentially independent of frequency.