Pressure and temperature effects on the one dimensional (1D) and higher-dimensionality correlations associated with the ferroelectric and antiferroelectric phase transitions in cesium dihydrogen phosphate were studied by means of the ${}_{}{}^{133}{}_{}{}^{}\mathrm{Cs}$ nuclear magnetic resonance (NMR) spin-lattice relaxation time $T_1$. We measured $T_1$ at 6.5 MHz at temperatures down to the ferroelectric (FE) Curie point $T_C$ at 1 bar and at 1.5 and 3.0 kbar, down to the triple point $T_t$=124.6 K at 3.3 kbar, and down to the antiferroelectric (AFE) Néel point $T_N$ at 3.6 kbar. With decreasing temperature, $T_1$ first decreases exponentially due to 1D fluctuations associated with the $J_b$ interactions in disordered hydrogen-bonded chains running along b. As the temperature falls further, $T_1$ then decreases linearly as the $J_c$ interaction between these chains in hydrogen-bonded planes comes into play. From these results and the known pressure derivatives of $T_C$ and $T_N$, we calculated pressure dependences for $J_b$, $J_c$, and for the interplanar interaction $J_a$. At 3.3 kbar $J_a$ changes sign, so the plane stacking becomes AFE instead of FE. Above 8.9 kbar, where $J_c$ extrapolates to zero, a new AFE phase with a checkerboard arrangement of FE b chains is predicted.

• Received 29 August 1988

DOI:https://doi.org/10.1103/PhysRevB.39.2549