title: High-pressure phase transition of Bi2Fe4O9.
abstract: The high-pressure behaviour of Bi2Fe4O9 was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi2Ga4O9. The lower phase transition pressure of Bi2Fe4O9 with respect to that of Bi2Ga4O9 (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga3+ and Fe3+ in tetrahedral coordination at high pressure. A fit of a second-order Birch–Murnaghan equation of state to the p–V data results in K0 = 74(3) GPa for the low-pressure phase and K0 = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements.
authors.affiliation: Institut für Geowissenschaften, Abteilung Kristallographie, Goethe-Universität Frankfurt, Altenhöferallee 1, D-60438 Frankfurt am Main, Germany. friedrich@kristall.uni-frankfurt.de
authors.forename: Alexandra
authors.initials: A
authors.lastname: Friedrich
authors.forename: Jasmin
authors.initials: J
authors.lastname: Biehler
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Morgenroth
authors.forename: Leonore
authors.initials: L
authors.lastname: Wiehl
authors.forename: Björn
authors.initials: B
authors.lastname: Winkler
authors.forename: Michael
authors.initials: M
authors.lastname: Hanfland
authors.forename: Martin
authors.initials: M
authors.lastname: Tolkiehn
authors.forename: Manfred
authors.initials: M
authors.lastname: Burianek
authors.forename: Manfred
authors.initials: M
authors.lastname: Mühlberg
mesh_terms: D001729:Bismuth / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D044367:Phase Transition; D011312:Pressure; D013059:Spectrum Analysis, Raman; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D001729:Bismuth