E-mode splitting in the ferroelectric phase of hydrogen-bonded ferroelectrics

Results of laser Raman studies of the E-modes in KH 2 AsO 4 , RbH 2 AsO 4 and CsH 2 AsO 4 , their deuterated isomorphs, and KH 2 PO 4 are presented. In the ferroelectric phase, the results reveal splittings for many of these modes, which arise from non-reststrahlen effects and which are consistent with the predictions of the recent pseudospin-two-phonon theory of Young and Elliott (see ibid., vol.7, p.27121 (1974)). These results are used to discuss the temperature dependence of the central component amplitude in these materials.