Characterization of Ternary Compounds in the BaO:Fe2O3:TiO2 System: Ba6Fe45Ti17O106 and BaFe11Ti3O23

Published

January 1, 1999

Author(s)

Terrell A. Vanderah, Winnie K. Wong-Ng, B H. Toby, V. M. Browning, Robert D. Shull, Richard G. Geyer, Robert S. Roth

Abstract

Single crystals of Ba₆Fe₄₅Ti₁₇O₁₀₆ and BaFe₁₁Ti₃O₂₃ were obtained as major and minor co-products, respectively, by slow-cooling an off-stoichiometric BaO:Fe₂O₃:TiO₂ melt. The former compound exhibits variable stoichiometry Ba₆Fe_48-xTi_14+xO₁₀₆, with the Fe:Ti ratio dependent upon the partial pressure of oxygen. The value of x corresponds to the equivalents of reduction that occur to maintain electroneutrality as the Ti-content increases. When prepared in air, this phase occurs at x = 3 with the stoichiometry Ba₆Fe₄₅Ti₁₇O₁₀₆, while in 100% oxygen the x-value approaches zero with the resulting stoichiometry Ba₆Fe₄₈Ti₁₄O₁₀₆ (all Fe^3+^ and Ti⁴⁺). The structures of Ba₆Fe₄₅Ti₁₇O₁₀₆ and BaFe₁₁Ti₃O₂₃ were solved using single-crystal X-ray diffraction methods. Ba₆Fe₄₅Ti₁₇O₁₀₆ was prepared in polycrystalline form and further structural details, including accurate Fe/Ti occupancy factors, were determined by a combined refinement using neutron and synchrotron powder diffraction data. (Ba₆Fe₄₅Ti₁₇O₁₀₆: Space group C2/m (No. 12); a = 19.390(1), b = 20.260(1), c = 10.076(1) , = 105.27(1) ; V = 3818.5(3) }³; Z = 2; ρ_calc = 5.08 g/cm³. BaFe₁₁Ti₃O₂₃: Space group C2/c (No. 15); a = 19.561(1) , b = 8.6614(7) , c = 10.120(1) , = 105.62(1) ; V = 1651.1(3) ³; Z = 4; ρ_calc = 5.08 g/cm³.) Both compounds adopt eight-layer close-packed structures built from alternating ccp and hcp [O,(Ba,O)] layers stacked along the a-direction with a (ch)₄ repeat sequence. Both structures feature octahedral sites occupied by a mixture of Fe and Ti as well as tetrahedral sites occupied by Fe³⁺; the structural formulas are ^XIIBa₆^IVFe₆^VI(Fe₃₉Ti₁₇)O₁₀₆ and ^XIIBa ^IVFe₂^VI(Fe₉Ti₃)O₂₃. Both compounds are partially reduced; the former contains 3 moles of Fe²⁺ (or Ti³⁺) per formula unit, and the latter contains 1 mole. The formation of Fe²⁺ is considered more likely than Ti³⁺, but could not be experimentally confirmed. Ba₆Fe₁₁Ti₃O₂₃ is apparently metastable in air when cooled from above the solidus and could not be prepared as a polycrystalline sample. Indexed experimental X-ray powder diffraction data for Ba₆Fe₄₅Ti₁₇O₁₀₆ are given. Poly-crystalline samples of this compound were used to measure its magnetic and electrical properties. The magnetic behavior of Ba₆Fe₄₅Ti₁₇O₁₀₆ above room temperature up to 1073 K was found to obey the Curie-Weiss law, which indicated a small effective magnetic moment (34 per mole Ba₆Fe₄₅Ti_17Od106^) and a large negative temperature intercept (-806 K). Electrical resistivity measurements between room temperature and 120 K revealed nonmetallic behavior with an activation energy on the order of 0.17 eV. At 347 MHz under ambient conditions, Ba₆Fe₄₅Ti₁₇O₁₀₆ exhibited a relative permitivity of 24 and a dielectric loss tangent of 0.10.

Citation

Journal of Solid State Chemistry

Volume

143

Issue

No. 2

Pub Type

Journals

Keywords

Ba₆Fe₄₅Ti₁₇O₁₀₆, BaFe₁₁Ti₃O₂₃, barrium iron titanates, conductivity, crystal structure, dielectric properties, magnetism

Citation

Vanderah, T. , Wong-Ng, W. , Toby, B. , Browning, V. , Shull, R. , Geyer, R. and Roth, R. (1999), Characterization of Ternary Compounds in the BaO:Fe₂O₃:TiO₂ System: Ba₆Fe₄₅Ti₁₇O₁₀₆ and BaFe₁₁Ti₃O₂₃, Journal of Solid State Chemistry (Accessed December 26, 2024)