Some Experimental and Theoretical Studies of Ferroelectricity in NaNO_2

概要

論文の詳細を見る
The dielectric constant of NaNO_2 crystal was measured in a temperature range from r. t. to 200℃ and in a frequency range from 60 to 10^6 cycles per second. It shows peak at 164.2℃ in heating and at 162.6℃ in cooling. Dielectric dispersion, similar to the one observed in other ferroelectrics, exists in all directions of the crystal principal axes in the paraelectric region as well as in the ferroelectric one. The spontaneous polarization was determined by the mcasuremeat of the pyroelectric current and the value was estimated to be ca 8.6 μC/cm^2 at r. t. The ferroelectricity in NaNO_2 was discussed in a phenomenological way, where the electrocaloric effect was taken into account. The free energy F was expressed as a function of the polarization P as F=A(T-T_0)P^2 +BP^4+CP^6, and the coefficients were determined by the dielectric properties as A = 1.22×10^<-3°>K^<-1>, B = 0.3×10^<-10> esu, C = 1.0×10^<-10> esu and T_0 = 436.2°K. From the dielectric measurements, it is concluded that the transition in NaNO_2 is probably of the first kind. It was pointed out by the consideration about the atomic arrangement that the main contribution to the spontaneous polarization comes from the relative displacement between Na^+ and NO^-_2 ions, and further that NaNO_2 crystal is a ferroelectric crystal which stands halfway between ionic and molecular crystal.
社団法人日本物理学会の論文
1961-12-05