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Dresden 2017 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 16: Crystallography - Poster Session (KR with DF)

DF 16.5: Poster

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

Ga3+ Substitution in the Brownmillerite-Type Phase Ca2Fe2O5: Structural and Spectroscopic Investigations — •Quirin Stahl1,2, Andreas Reyer1, Reinhard Wagner1, Gerold Tippelt1, and Günther J. Redhammer11Department Chemistry and Physics of Materials, University of Salzburg, Austria — 2Institute of Structural Physics, Technische Universität Dresden

Brownmillerite-type compounds with the general formula A2B2−xBxO5, 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 Ca2Fe2−xGaxO5 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 Ca2Fe2−xGaxO5 single-crystals enable us to assign eleven of the thirteen theoretically predicted Ag 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 Ca2Fe2−xGaxO5 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.

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