Pseudo One-Dimensional Ferroelectric Ordering and Critical Properties of CsH2PO4 and CsD2PO4

Abstract

The temperature dependence of the dielectric constant of Cs${\mathrm{H}}_2$P${\mathrm{O}}_4$ shows a crossover between a region ($3 \mathrm{K}<~T-T_c<~90 \mathrm{K}$) dominated by one-dimensional correlations and a region ($0 \mathrm{K}<~T-T_c<~3 \mathrm{K}$) dominated by three-dimensional correlations. A similar effect is observed as well in Cs${\mathrm{D}}_2$P${\mathrm{O}}_4$. The dielectric data allow for a quantitative determination of the ratio between the long-range interchain and the short-range intrachain coupling constants. ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ NMR data show that the ferroelectric transition is connected with an order of the H(2) hydrogens along the zig-zag chains.