Characterisation of polycrystalline perovskite ferroelectrics using high-energy X-ray diffraction: from phase diagrams to domain wall dynamics

QUICK INFORMATION
Type
Seminar
Start Date
05-02-2020 10:00
End Date
05-02-2020 11:00
Location
Room 337, Central Building
Speaker's name
Stefano CHECCHIA
Speaker's institute
Beamline FemtoMAX - Max IV Laboratory, Lund University, Sweden
Contact name
Eva Jahn
Host name
M. Di Michiel
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Ferroelectric materials have become indispensable to many current technologies owing to a wealth of functional properties: polarisation switching, piezoelectricity, high dielectric permittivity, electro-optic coupling. In most practical cases the functional materials are polycrystalline oxides, in which the chemistry-structure-property relations are the result of the complex interplay of crystal structure, grain boundaries, ferroelectric/ferroelastic domain walls, crystallographic texture and, generally, the anisotropy of local stresses and electric field in the material. Controlling the electromechanical response of a ferroelectric material requires understanding how these intrinsic (lattice-related) and extrinsic (microstructure-related) factors affect its dielectric and piezoelectric properties.

Here we present some crystallographic tools that contributed to such understanding. In general, high energy X-rays have benefited particularly the study of high-Z, millimeter-thick samples, both in their application conditions and ex situ. High speed diffraction revealed the time-dependence of lattice strain and domain reorientation under applied electric fields. Combined with simultaneous polarisation and strain measurements, it illustrated the polarisation switching mechanism in a prototypical tetragonal ferroelectric. Adjustable beam focusing allowed experiments to probe in turn large portions of the bulk and structurally graded layers between surface and bulk. For example, analysis from microbeam scanning experiments suggested a link between defect chemistry and functional surface layers in Pb-free relaxor ferroelectrics. In another application, spatially resolved scans of compositionally graded samples promptly identified morphotropic phase boundaries, compositions with peak piezoelectric properties, thus speeding up considerably the investigation of binary and ternary phase diagrams. Results from these studies are discussed in light of the new possibilities for diffraction beamlines after the ESRF-EBS upgrade.

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