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 Ba6Fe48-xTi14+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; ρcalc = 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; ρcalc = 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 Ba6Fe45Ti17Od106^) 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
Issue: No. 2
Pub Type: Journals
Ba<sub>6</sub>Fe<sub>45</sub>Ti<sub>17</sub>O<sub>106</sub>, BaFe<sub>11</sub>Ti<sub>3</sub>O<sub>23</sub>, barrium iron titanates, conductivity, crystal structure, dielectric properties, magnetism