ESR measurements of ${\mathrm{KH}}_2$${\mathrm{PO}}_4$ crystals doped with arsenic exhibit altered line shapes similar to those produced by an incommensurate phase. The modified line shapes occur in a range of temperatures extending approximately 17 K below the paraelectric-ferroelectric critical temperature ${\mathit{T}}_{\mathit{c}}$. The form and temperature dependence of the lines are in reasonable agreement with the predictions of the phase-soliton theory. The parameters ${\mathit{h}}_1$ and ${\mathit{h}}_2$ determining the variation of the resonant magnetic field show a power-law behavior as a function of temperature. The significance of the experimental results is discussed in the light of earlier studies which indicate a ferroelectric structure with four types of domains differing in electric polarization and in spatial orientation.

• Received 1 April 1991

DOI:https://doi.org/10.1103/PhysRevB.44.7297