NA-23 NUCLEAR MAGNETIC RESONANCE STUDY OF PHASE TRANSITION IN FERROELECTRIC SODIUM NITRITE, NANO2

The temperature dependence of the electric field gradient (EFG) at the sodium site has been determined in the ferroelectric and paraelectric phases of sodium nitrite (NaNO2). Special attentions have been paid to the narrow temperature range near the ferroelectric Curie point Tc where the antiferroelectric phase had been discovered. The main results obtained are: (1) the field gradient varies linearly with the square of the long range order parameter determined by the X-ray study in the ferroelectric phase; (2) a small, but abrupt, change at Tc in the field gradient fives an evidence for a phase transition of the first kind; (3) the existence of the antiferroelectric phase can not be evidenced from the present study;(4) slight anomalies exist at 168°C and 178°C in the temperature variation of the field gradient; and (5) the field gradient decreases linearly with increasing temperature in the temperature ranges between 168°C and 178°C and also between 180°C and 230°C. It has been shown that these unusual behaviors of the 23 Na field gradient have close relations with the molecular motions of NO2 - ions and the structural changes in the crystal which bring about the phase transition. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.