The effects of deuteration on the static ferroelectric properties of KH2PO4 (KDP)†

Abstract

A detailed study was made of the static ferroelectric properties of a group of (H1-xDx)2 crystals with nominal x values of 0, 0.35, 0.80 and 0.98. The properties investigated included the transition temperature Tc, the Curie constant C, the saturation polarization Ps, the coercive field Ec and the electric field strength Es required to achieve saturation of the polarization. As far as we know, this is the first systematic study of the effects of deuteration on these properties employing the same experimental apparatus and techniques. Relatively large isotope effects are found in all of these properties, and the results render comparisons among crystals with different x more meaningful and help to remove some of the ambiguities and discrepancies in the earlier literature. For KH2PO4, Tc = 122°K, C = 2925°K and Ps = 5.1 μC/cm2, and these quantities increase nearly linearly by 83, 40 and 22%, respectively, on complete deuteration. The coercive field and Es increase by ∼20-fold and ∼6-fold, respectively: these are the largest isotope effects on the static properties, and they point to important differences in the domain wall motion in these crystals. The results are discussed in terms of the order-disorder, the tunneling and the coupled proton-lattice models for the transition.