Cs133nuclear magnetic resonance study of one-dimensional fluctuations inAuthor(s) - Paul J. Schuele, V. Hugo Schmidt

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 " Cs nuclear magnetic resonance (NMR) spin-lattice relaxation time T, . We measured T& at 6.5 MHz at temperatures down to the ferroelectric (FE) Curie point T& at 1 bar and at 1.5 and 3.0 kbar, down to the triple point T, =124.6 K at 3.3 kbar, and down to the antiferroelectric (AFE) Neel point T& at 3.6 kbar. With decreasing temperature, T& first decreases exponentially due to 1D fluctuations associated with the Jb interactions in disordered hydrogen-bonded chains running along b. As the temperature falls further, T& then decreases linearly as the J, interaction between these chains in hydrogen-bonded planes comes into play. From these results and the known pressure derivatives of Tc and Tz, we calculated pressure dependences for Jb, J„and for the interplanar interaction J, . At 3.3 kbar J, changes sign, so the plane stacking becomes AFE instead of FE. Above 8.9 kbar, where J, extrapolates to zero, a new AFE phase with a checkerboard arrangement of FE b chains is predicted.