title: Structural investigations of the two polymorphs of synthetic Fe-cordierite and Raman spectroscopy of hexagonal Fe-cordierite.
abstract: The crystal structures of synthetic hexagonal and orthorhombic Fe-cordierite polymorphs with the space groupsP6/mccandCccmwere refined from single-crystalX-ray diffraction data toR1, hex= 3.14 % andR1, ortho= 4.48 %. The substitution of the larger Fe2+for Mg leads to multiple structural changes and an increase of the unit cell volumes, witha,c(hex) = 9.8801(16) Å, 9.2852(5) Å anda,b,c(ortho) = 17.2306(2) Å, 9.8239(1) Å, 9.2892(1) Å in the end-members. Furthermore Fe incorporation results in an increase of the volumes of the octahedra, although the diameters of the octahedra in direction of thec-axis decrease in both polymorphs. X-ray powder diffraction analysis indicates a high degree of Al/Si ordering in the orthorhombic polymorph, the Miyashiro distortion index is ~0.24. Estimations of site occupancies based on the determined tetrahedral volumes result in the following values for hexagonal Fe-cordierite: ~73 % Al for T1and ~28 % Al for T2. For the first time Raman spectroscopy was performed on the hexagonal Fe-cordierite polymorph. In the hexagonal Fe-cordierite polymorph most Raman peaks are shifted towards lower wavenumbers when compared with the Mg-end-member.
authors.affiliation: Institute of Mineralogy and Petrography, University Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: Udo
authors.initials: U
authors.lastname: Haefeker
authors.affiliation: MATERIALS - Institute for Surface Technologies and Photonics, Functional Surfaces, JOANNEUM RESEARCH Forschungsgesellschaft mbH, Leobner Straße 94, 8712 Niklasdorf, Austria.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kaindl
authors.affiliation: Institute of Mineralogy and Petrography, University Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Tropper
authors.affiliation: Institute of Mineralogy and Petrography, University Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: Hannes
authors.initials: H
authors.lastname: Krüger
authors.affiliation: Institute of Mineralogy and Petrography, University Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: Volker
authors.initials: V
authors.lastname: Kahlenberg
authors.affiliation: Institute of Mineralogy and Petrography, University Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: Maria
authors.initials: M
authors.lastname: Orlova