Electric field dependent local structure of (KxNa1−x)0.5Bi0.5TiO3

The in situ X-ray Pair Distribution Function (PDF) characterisation technique has been used to study the behaviour of (Kx Na1-x)0.5 Bi0.5 TiO3, as a function of electric field. As opposed to conventional X-ray Bragg diffraction techniques, PDF is sensitive to local atomic displacements, detecting local structural changes at the Ångstrom to nanometre scale. Several field-dependent ordering mechanisms can be observed in x = 0.15, 0.18 and at the morphotropic phase boundary (MPB) composition x = 0.20. X-ray total scattering shows suppression of diffuse scattering with increasing electric field amplitude, indicative of an increase in structural ordering. Analysis of PDF peaks in the 3-4 Å range shows ordering of Bi-Ti distances parallel to the applied electric field, illustrated by peak amplitude redistribution parallel and perpendicular to the electric field vector. A transition from ‹110› to ‹112› type off-centre displacements of Bi relative to the neighbouring Ti atoms are observable with increasing x. Analysis of PDF peak shift with electric field show the effects of Bi-Ti redistribution and onset of piezoelectric lattice strain. The combination of these field-induced ordering mechanisms is consistent with local redistribution of Bi-Ti distances associated with domain reorientation and an overall increase in order of atomic displacements.