抄録
In order to obtain any relation between an electric field gradient (E.F.G.) at the site of 23Na nucleus in Sodium Nitrite crystals and spontaneous polarization, the observed E.F.G. along the b-axis in the ferroelectric phase is formally expanded with the long range order parameter S. The E.F.G. in a fictitious perfectly ordered state and in a disordered one are calculated as a function of temperature. The E.F.G. of both fictitious states are calculated in a point charge approximation on the basis of a simplified model. The calculated S from the first order expansion series in terms of the observed E.F.G. and the calculated E.F.G. shows a good agreement with the S obtained from the observed spontaneous polarization except in the vicinity of the transition temperature. An effect of the order-disorder rearrangement of NO2− ion is concluded to reflect the temperature dependence of the E.F.G. observed in the ferroelectric phase.
