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DF: Fachverband Dielektrische Festkörper

DF 13: Electrical and mechanical properties

DF 13.1: Talk

Thursday, March 17, 2011, 10:15–10:35, MÜL Elch

High-pressure crystal structure and Raman spectra of Bi₁₂TiO₂₀ sillenite — •Leonore Wiehl, Alexandra Friedrich, Eiken Haussuehl, Wolfgang Morgenroth, and Bjoern Winkler — Institut für Geowissenschaften, Goethe-Universität Frankfurt/Main, Germany

Sillenites, Bi₁₂MO₂₀ (M = Si, Ge, Ti), show outstanding electric and optical properties used in many applications, especially the photorefractive effect and a high photoconductivity, which are assumed to be correlated with the stereochemical activity of the 6s² lone electron pair of Bi³⁺. At ambient conditions the Bi³⁺ lone pair is oriented towards an unoccupied corner in the distorted BiO₅☐ octahedron. Thus the stereochemical activity is expected to decrease under high external pressure. The crystal structure of Bi₁₂TiO₂₀ (BTO) was determined from a single crystal at 9.2(2) GPa in a diamond anvil cell by X-ray diffraction with synchrotron radiation at HASYLAB (D3), Hamburg. Powder diffraction experiments were performed with synchrotron radiation at ESRF (ID09A), Grenoble up to a pressure of 37 GPa. On pressure release of the same sample, Raman spectra were measured in the pressure range from 37 GPa to ambient conditions. The bulk modulus is B₀ = 50(1) GPa. The Bi³⁺ lone pair remains stereochemically active up to the highest pressure reached in this study.

Financial support from the DFG (HA 5137/3-1) and from HASYLAB is gratefully acknowledged. We thank HASYLAB and ESRF for synchrotron beamtime, Martin Tolkiehn for assistance at D3 and Michael Hanfland for assistance at ID09A.