Calculation of the spontaneous polarization for Pb1-xCaxTiO3 close to the tricritical point

We calculate the spontaneous polarization as a function of temperature for a mixed crystal of Pb1-xCaxTiO3 close to the tricritical pointdx (x = 0.4). This calculation of the spontaneous polarization is performed using the effective field approximation for the dipolar (PbTiO3) and higher order ( quadrupolar and octopolar) interactions for the mixed system of Pb1-xCaxTiO3 at concentrations from x = 0 to x = 0.45.