title: The solubility and site preference of Fe3+in Li7-3xFexLa3Zr2O12garnets.
abstract: A series of Fe3+-bearing Li7La3Zr2O12(LLZO) garnets was synthesized using solid-state synthesis methods. The synthetic products were characterized compositionally using electron microprobe analysis and inductively coupled plasma optical emission spectroscopy (ICP-OES) and structurally using X-ray powder diffraction and57Fe Mössbauer spectroscopy. A maximum of about 0.25 Fe3+pfu could be incorporated in Li7-3xFexLa3Zr2O12garnet solid solutions. At Fe3+concentrations lower than about 0.16 pfu, both tetragonal and cubic garnets were obtained in the synthesis experiments. X-ray powder diffraction analysis showed only a garnet phase for syntheses with starting materials having intended Fe3+contents lower than 0.52 Fe3+pfu. Back-scattered electron images made with an electron microprobe also showed no phase other than garnet for these compositions. The lattice parameter,a0, for all solid-solution garnets is similar with a value ofa0≈12.98 Å regardless of the amount of Fe3+.57Fe Mössbauer spectroscopic measurements indicate the presence of poorly- or nano-crystalline FeLaO3in syntheses with Fe3+contents greater than 0.16 Fe3+pfu. The composition of different phase pure Li7-3xFexLa3Zr2O12garnets, as determined by electron microprobe (Fe, La, Zr) and ICP-OES (Li) measurements, give Li6.89Fe0.03La3.05Zr2.01O12, Li6.66Fe0.06La3.06Zr2.01O12, Li6.54Fe0.12La3.01Zr1.98O12, and Li6.19Fe0.19La3.02Zr2.04O12. The57Fe Mössbauer spectrum of cubic Li6.54Fe0.12La3.01Zr1.98O12garnet indicates that most Fe3+occurs at the special crystallographic 24dposition, which is the standard tetrahedrally coordinated site in garnet. Fe3+in smaller amounts occurs at a general 96hsite, which is only present for certain Li-oxide garnets, and in Li6.54Fe0.12La3.01Zr1.98O12this Fe3+has a distorted 4-fold coordination.
authors.affiliation: Department of Materials Research and Physics, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: D
authors.initials: D
authors.lastname: Rettenwander
authors.affiliation: Department of Materials Research and Physics, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: C A
authors.initials: CA
authors.lastname: Geiger
authors.affiliation: Institute of Mineralogy and Petrography, Faculty of Geo- and Atmospheric Sciences, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Tribus
authors.affiliation: Institute of Mineralogy and Petrography, Faculty of Geo- and Atmospheric Sciences, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Tropper
authors.affiliation: Department of Materials Research and Physics, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Wagner
authors.affiliation: Department of Materials Research and Physics, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: G
authors.initials: G
authors.lastname: Tippelt
authors.affiliation: Department of Materials Research and Physics, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: W
authors.initials: W
authors.lastname: Lottermoser
authors.affiliation: Department of Materials Research and Physics, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: G
authors.initials: G
authors.lastname: Amthauer
keywords: 57Fe Mössbauer spectroscopy; Chemical composition; Ion conductors; Li-oxide garnet; Synthesis; X-ray powder diffraction