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Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P145
Linear instabilities in early transition metal oxide structures
Thomas Malcherek 1 , Ulrich Bismayer 1 , Carsten Paulmann 1
1 Mineralogisch-Petrographisches Institut, Universität Hamburg, Grindelallee 48, D-
20146 Hamburg
Early transition metals (e.g. M = Ti, V, Nb, Ta) frequently exhibit out-of-center distortions
within the octahedral coordination environment of common oxide structures.
Given an appropriate structural topology of trans-corner connected octahedra, the
distortions may align to form chains of alternating short and long metal-oxygen bonds
at low temperatures. Depending on symmetry, the formation of such chains may
give rise to ferroelectric, antiferroelectric or antipolar ground states. Compounds of
this type often show characteristic diffuse scattering extending along reciprocal space
planes upon transformation to their high temperature paraphase. In the perovskites
BaTiO3 and KNbO3 such effects have been related to dynamic long range correlations
of Ti-displacements parallel to 〈100〉 of the cubic paraphase by first principle computational
methods [1]. Synchrotron radiation provides the means to efficiently study the
weak scattering effects associated with these linear displacement correlations as well as
their temperature dependence. Several examples of planar diffuse scattering effects in
structure types containing trans-corner connected chains of MO6-octahedra are being
presented. The effects are discussed in relation to structural phase transitions occuring
in these oxide compounds.
[1] R. Yu et al., Phys. Rev. Lett. 74 (1995) 4067.