Crystal Structure and Properties of Ba5Fe4^Ti10O31

Published

February 23, 1998

Author(s)

T Siegrist, Terrell A. Vanderah, A P. Ramirez, Richard G. Geyer, Robert S. Roth

Abstract

Using single-crystal and powder X-ray diffraction methods, the crystal structure of the new compound Ba₅Fe₄Ti₁₀O₃₁ was determined and its magnetic and dielectric properties were measured. Ba₅Fe₄Ti₁₀O₃₁ crystallizes in space group P6₃/mcm (no. 193) (a=9.9886(2), c=42.226(2) Angstrom}; Z=6; P_calc=5.147 g/cc) and exhibits and 18-layer close packed structure built from vacancy-free [O,(Ba,O)] layers. Some Ba ions in the structure display anomalous (9+3) coordination with three unusually long Ba-O bond distances. The structure contains octahedral sites occupied by a mixture of Fe³⁺ and Ti^{4+, with some preferential ordering, and tetrahedral sites occupied by Fe}u3+^, one of which shares faces and is half occupied. Computation of bond valence sums about the cations using the observed bond distances reveals significant deviations from the valence sum rule, indicating that the structure of Ba₅Fe₄Ti₁₀O₃₁ contains residual strain not relieved by distortion. Indexed experimental X-ray powder diffraction data for Ba₅Fe₄Ti₁₀O₃₁ are given and are in excellent agreement with those calculated from the results of the single-crystal structure determination. The compound exhibits paramagnetism that deviates from Curie-Weiss behavior below 200K. Fits to the data above 200K yield an effective moment consistent with the presence of high-spin Fe³⁺ (S=5/2), and a negative Weiss constant (nearly equal to}-190 K) indicating cooperative antiferromagnetic interactions. The relative permittivity and dielectric loss tangent of a sintered polycrystalline disk of Ba₅Fe₄Ti₁₀O₃₁ were measured between 7.1 and 7.7 GHz, yielding values (corrected for theoretical density) of 32 and 3.3(+0.3)x10^-3, respectively, that were essentially independent of frequency.

Citation

Journal of Alloys and Compounds

Volume

274

Issue

1/2

Pub Type

Journals

Keywords

Ba5Fe4Ti10031, barium iron titanium oxide, crystal structure, dielectric constant, dielectric loss tangent, magnetic susceptibility, x-ray diffraction

Citation

Siegrist, T. , Vanderah, T. , Ramirez, A. , Geyer, R. and Roth, R. (1998), Crystal Structure and Properties of Ba₅Fe₄^Ti₁₀O₃₁, Journal of Alloys and Compounds (Accessed October 31, 2024)