Critical Scattering from Piezoelectric Ferroelectrics

The complex asymmetric critical scattering observed in quasielastic neutron scattering measurements in K${\mathrm{D}}_2$P${\mathrm{O}}_4$ is explained as arising from the piezoelectric coupling between the acoustic waves and the ferroelectric fluctuations. Detailed calculations give good agreement with the available measurements. It is further proposed that this coupling provides a way of determining the atomic motions in the ferroelectric fluctuations and also leads to a change in the critical properties of these and related materials.