Acosta Matias, Schmitt Ljubomira A, Cazorla Claudio, Studer Andrew, Zintler Alexander, Glaum Julia, Kleebe Hans-Joachim, Donner Wolfgang, Hoffman Mark, Rödel Jürgen, Hinterstein Manuel
Department of Geo- and Materials Science, Technische Universität Darmstadt, Alarich-Weiss-Strasse 2, 64287 Darmstadt, Germany.
School of Materials Science and Engineering, UNSW Australia, Sydney, New South Wales 2052, Australia.
Sci Rep. 2016 Jul 1;6:28742. doi: 10.1038/srep28742.
Coupling of order parameters provides a means to tune functionality in advanced materials including multiferroics, superconductors, and ionic conductors. We demonstrate that the response of a frustrated ferroelectric state leads to coupling between order parameters under electric field depending on grain orientation. The strain of grains oriented along a specific crystallographic direction, 〈h00〉, is caused by converse piezoelectricity originating from a ferrodistortive tetragonal phase. For 〈hhh〉 oriented grains, the strain results from converse piezoelectricity and rotostriction, as indicated by an antiferrodistortive instability that promotes octahedral tilting in a rhombohedral phase. Both strain mechanisms combined lead to a colossal local strain of (2.4 ± 0.1) % and indicate coupling between oxygen octahedral tilting and polarization, here termed "rotopolarization". These findings were confirmed with electromechanical experiments, in situ neutron diffraction, and in situ transmission electron microscopy in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3. This work demonstrates that polar and non-polar instabilities can cooperate to provide colossal functional responses.
