X-Ray Studies of the Ferroelectric Phase Transition in NaNo₂

Studies of the temperature dependence of Bragg reflections and critical scatterings of X-rays have been carried out for the ferroelectric NaNO 2 in a manner analogous to those made by Shibuya and Mitsui for (glycine) 3 ·H 2 SO 4 . Experimental observations agree with theoretical predictions which are based on an assumption that the phase transition in NaNO 2 is of the order-disorder type. A long-range order parameter and the spontaneous polarization are estimated as functions of temperature by using the temperature variation of Bragg reflections. The observed intensity of the critical scattering drops rather abruptly just above the Curie point in a manner similar to the case of (glycine) 3 ·H 2 SO 4 .