Analysis of the spontaneous polarization, susceptibility and the specific heat for the ferroelectric AgNa(NO 2 ) 2 using the Landau mean field model

We employ the Landau mean field model by expanding the free energy in terms of the spontaneous polarization [Formula: see text] for the ferroelectric–paraelectric transition in the ferroelectric AgNa(NO 2 ) 2 crystal. The temperature dependences of the [Formula: see text], the inverse susceptibility [Formula: see text] of [Formula: see text] and the specific heat C, which we obtain from the Landau model, are fitted to the experimental data from the literature. By using the power-law formula, [Formula: see text], [Formula: see text] and C are analyzed and the values of the critical exponents [Formula: see text], [Formula: see text] and [Formula: see text], respectively, are determined. Depending on the [Formula: see text] values and the temperature intervals studied, the exponent values determined, are not in agreement with those predicted from the mean field theory. Instead, they indicate that the ferroelectric–paraelectric transition in AgNa(NO 2 ) 2 is close to the tricritical or weakly first-order transition, as also suggested experimentally.