Critical Behavior of Electric Susceptibility in NaNO2

The uniform susceptibility in a sinusoidally antiferroelectric substance, NaNO 2 , has been measured over a wide temperature range up to the melting point. A clear deviation from molecular field nature has been observed above the Néel temperature, T N . The deviation has been examined whether or not it is caused by any unessential reason, for instance the contribution of the thermal expansion of the lattice constants which is possible to give rise to a part of the deviation. As a result of the examination, it has been made clear that the deviation is of attribute in the temperature dependence of the susceptibility of NaNO 2 . By applying a critical exponent expression, the data obtained above T N have been analysed as follows,