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 P s for the ferroelectric – paraelectric transition in the ferroelectric AgNa(NO 2 ) 2 crystal. The temperature dependences of the P s , the inverse susceptibility [Formula: see text] of P s 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, P s , [Formula: see text] and C are analyzed and the values of the critical exponents β, γ and α, respectively, are determined. Depending on the T c 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