Phonon scattering from ferroelectric domain walls: Phonon imaging in KDP

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Abstract
The ferroelectric domain wall is an ideal interface for studies of the boundary scattering of high frequency acoustic phonons. These internal interfaces have no contamination and can be reversibly created and destroyed by application of an electric field at the phase transition—122 K in KDP. Images of phonons in single- and multiple-domain cases show remarkable differences in the ballistic heat flux. Theoretical modeling based on acoustic wave reflection reveals that the domain walls act as nearly perfect grain boundaries.