Impurity induced effect for the paraelectric to ferroelectric transition in a NaNO2–KNO3 mixture observed by 23Na NMR

The spin-lattice relaxation rate for the 23Na NMR central transition in [NaNO2]1−x[KNO3]x (x=0, 0.2) has been investigated in the temperature range of 298–451K. In the mixture [NaNO2]0.8[KNO3]0.2, a non-exponential behavior of the magnetization recovery and the narrowing of the linewidth are observed at 415K. This anomaly appears to be attributed to the phase transition of KNO3 in the mixture, as shown in the result of differential scanning calorimetry (DSC). The transition temperature from the para- to ferroelectric phase in the mixture decreases slightly compared with that in the pure NaNO2. This can be explained in terms of the change of spontaneous polarization.