Landau behaviour of the heat capacity of AgNa(NO2)2 close to the nearly tricritical ferroelectric phase transition

Abstract

The heat capacity of a single crystal of the uniaxial ferroelectric AgNa(NO2)2 was measured close to the nearly tricritical phase transition. In the ferroelectric phase a strong temperature dependence of the anomaleous specific heat is found which obeys a temperature law (θ f —T)−0.494. A small latent heat was detected nearT c. The thermal behaviour of AgNa(NO2)2 is described by a Landau type theory, from which the non linear coefficientsζ andζ of the free energy expansion are derived. The thermal data fit well to the known dielectric behaviour.