Neutron scattering study of the pressure dependence of short-range order in CsD2PO4

We present the results of a neutron scattering study of the pressure dependence of the order-disorder phase transition in Cs${\mathrm{D}}_2$P${\mathrm{O}}_4$. In an earlier study, it was shown that the dominant interaction propagates along one-dimensional chains of disordered hydrogen bonds linking phosphate groups along the $\overrightarrow{\mathrm{b}}$ direction. In the absence of applied pressure, the interchain ordering is ferroelectric; at high pressure, it is antiferroelectric. This is shown to arise from extremely small interactions along the $\overrightarrow{\mathrm{a}}$ direction between correlated $\overrightarrow{\mathrm{b}}-\overrightarrow{\mathrm{c}}$ planes; with increasing pressure, these effective interactions change character so as to favor an antiferroelectric stacking of ferroelectric planes, resulting in a doubling of the unit cell along $\overrightarrow{\mathrm{a}}$. Interchain and intrachain couplings are inferred from a comparison of the diffuse scattering data with the predictions of a model based on weak coupling between one-dimensional chains. These results are compared with those obtained in a recent study of the dielectric behavior.