Crystal structure and properties of Ba 5Fe 4Ti 10O 31

Abstract

Using single-crystal and powder X-ray diffraction methods, the crystal structure of Ba 5Fe 4Ti 10O 31 was determined and its magnetic and dielectric properties were measured. Ba 5Fe 4Ti 10O 31 crystallizes in space group P6 3/mcm (No. 193) ( a=9.9886(2), c=42.226(2) Å: Z=6: ρ calc=5.15 g cm −3) and exhibits an 18-layer close-packed structure built from vacancy-free [O,(Ba,O)] layers. The structure features octahedral sites occupied by a mixture of Fe 3+ and Ti 4+, with some preferential ordering, and tetrahedral sites occupied by Fe 3+, one of which shares faces and is half occupied. Some Ba ions in the structure display (9+3) coordination with three unusually long Ba–O bond distances. Computation of bond valence sums about the cation sites using the observed bond distances reveals significant deviations from the valence sum rule, indicating that the structure of Ba 5Fe 4Ti 10O 31 contains residual strain not relieved by distortion. Indexed experimental X-ray powder diffraction data for Ba 5Fe 4Ti 10O 31 are given and are in excellent agreement with those calculated from the results of the single-crystal structure determination. The compound exhibits approximately paramagnetic behavior that deviates somewhat from the Curie Law. Application of this formalism to the 1/ χ vs. T data above 250 K yields an effective moment consistent with the presence of high-spin Fe 3+ ( S=5/2), and a negative Weiss constant (≈−190 K) indicating cooperative magnetic interactions that are overall antiferromagnetic. The relative permittivity and dielectric loss tangent of a sintered polycrystalline disk of Ba 5Fe 4Ti 10O 31 were measured between 7.1 and 7.7 GHz, yielding values (corrected for theoretical density) of 32 and 3.3(±0.3)×10 −3, respectively, that were essentially independent of frequency.