Structure Refinement of the 0201-1201 Intergrowth-Type Ferrite PbSr4Fe2O9: Powder Neutron Diffraction and Mösbauer Spectroscopy Studies
✍ Scribed by V. Caignaert; Ph. Daniel; N. Nguyen; A. Ducouret; D. Groult; B. Raveau
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 305 KB
- Volume
- 112
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The structure of the tetragonal ferrite (\mathrm{PbSr}{4} \mathrm{Fe}{2} \mathrm{O}{9}(a=3.8484) (\AA, c=30.683 \AA) ) has been refined from powder neutron diffraction data. The intergrowth of the two structures 0201 and 1201 with the (\mathrm{La}{2} \mathrm{CuO}{4}) and the (\mathrm{TISr}{2} \mathrm{CuO}{3}) types is confirmed as is the oxygen stoichiometry (\left(\mathrm{O}{9}\right)), which involve oxidation states III and IV for iron and lead, respectively. The structure of the ([\mathrm{PbO}]{\infty}) layers consists of two sets of (\mathrm{Pb}) sites (at the origin and on (8 i(x 00)) split positions) and one set of oxygen atoms (O(1)) on (8 j\left(x^{\frac{1}{2} 0}\right)) split positions. According to neutron diffraction, Mössbauer spectroscopy, and electric field gradient calculations, a splitting of the axial oxygen ([O(2)]) along the (c) direction appears also as most probable. It results in two highly distorted octahedral coordinations for (\mathrm{Fe}(\mathrm{III})), which can be better described as almost regular (\left[\mathrm{FeO}{5}\right]) pyramids. Similarly two coordination states are found for (\mathrm{Pb}(\mathrm{IV})) : a fiattened (\left[\mathrm{PbO}{6}\right]) octahedron and a distorted (\left[\mathrm{PbO}{4}\right]) tetrahedron. 01994 Academic Press, Inc.