Dresden 2017 – scientific programme

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KR: Fachgruppe Kristallographie

KR 3: Crystallography - poster session

KR 3.5: Poster

Wednesday, March 22, 2017, 18:00–20:00, P4

Ga³⁺ Substitution in the Brownmillerite-Type Phase Ca₂Fe₂O₅: Structural and Spectroscopic Investigations — •Quirin Stahl^1,2, Andreas Reyer¹, Reinhard Wagner¹, Gerold Tippelt¹, and Günther J. Redhammer¹ — ¹Department Chemistry and Physics of Materials, University of Salzburg, Austria — ²Institute of Structural Physics, Technische Universität Dresden

Brownmillerite-type compounds with the general formula A₂B_2−x^′B_xO₅, where A = alkaline earth metals and B’/B = group III or transition-metal atoms, are among the most frequently studied oxygen-deficient perovskites. 61 synthetic single-crystal samples of Ca₂Fe_2−xGa_xO₅ with 0.00 ≤ x ≤ 1.328 have been investigated by single-crystal X-ray diffraction at RT. We find that pure Ca₂Fe₂O₅ and samples up to x = 0.989 have space group Pnma, Z = 4, whereas samples with x > 0.989 show I2mb symmetry, Z = 4. We also performed a detailed Raman study of Ga³⁺ and Al³⁺ doped Ca₂Fe₂O₅. The polarized Raman measurements of Ca₂Fe_2−xGa_xO₅ single-crystals enable us to assign eleven of the thirteen theoretically predicted A_g modes. Furthermore the change from Pnma to I2mb space group symmetry is reflected by a significant change of two Raman modes below 150 cm⁻¹. These Raman modes are obviously linked to changes of the Ca-O bond lengths at the phase transition. To complete the study of the Ca₂Fe_2−xGa_xO₅ series, we have performed a detailed Mössbauer spectroscopic study as a function of the chemical composition, mainly to fix site occupation number by a second, independent method beside XRD.