NMR Study of Phase Transitions in Rochelle Salt

Nuclear-magnetic-resonance techniques have been used to measure the spontaneous polarization of ferroelectric Rochelle salt in the vicinity of the higher-temperature Curie point ($T_C$). The polarization was found to be proportional to ${(T_C-T)}^{\frac{1}{2}}$, but the technique did not allow measurements closer than 0.1 °C to $T_C$. In addition, the ${\mathrm{Na}}^{23}$ nuclear quadrupole coupling constant and field gradient asymmetry parameter in the low-temperature phase were found to be 1363 ± 3.4 kHz and 0.737 ± 0.004, respectively. These values are in accord with the model of Blinc, Petkovsek, Zupancic, and with the notion of an antiferroelectric low-temperature phase.