External Influences on the N NQR of Ferroelectric NaN02

NaN02 is a famous ferroelectric material with spontaneous polarization (Ps) along the crystallographic b-axis, which undergoes an order-disorder transition at Tc = 437 K [1 3]. The Ps, arising from the ordering of N 0 2 and the accompanying shift of Na, is sensitive to the environment. Information on the local structure in NaN02 has been obtained by employing N NQR [4 5]. A change of the local structure can be achieved by changing the external conditions. The influences of those are reflected in the N NQR. External influences, such as changes of the temperature [6], electric field [7 8], stress [9], gamma irradiation [10], and impurity doping [11 13], on the N NQR in NaN02 were studied for a long time in our laboratory. A substitutional impurity A in Na1_xAA.N02 (A = Ag, K) disturbs the electric field gradient (EFG) at the N site, resulting in line broadening and intensity weakening of the N NQR line [13]. This trend is similar to the effect of gamma irradiation on NaN02 . The N NQR spectra obtained in the presence of an external electric field, stress, or a change of temperature show a frequency shift or line broadening. In this work, the results of previous investigations are reviewed and explained in terms of the spontaneous polarization of NaN02 . The spontaneous polarization in ferroelectric NaN02 was derived by Yamada et al. [14] as Ps = tanh[(Tc/T)(Ps + PZ\)], (1) 1-0 CL