Phase coexistence in highly deuterated ferroelectric triglycine selenate: Landau description

The phase transition in a 90% deuterated sample of TGSe has been investigated by calorimetric and dielectric measurements. As a consequence of the presence of an internal crack in the sample, the transition takes place in two stages separated by an interval where the paraelectric and the ferroelectric phases coexist without latent heat contribution. From the latent heat, the specific heat excess and the Curie law for the dielectric constant, it is shown that the transition follows a 2-4-6 Landau potential, whose coefficients are determined. This potential describes completely all the data, including those corresponding to the coexistence interval.