Specific heat and quadrupole interactions in uniaxial ferroelectrics

The inclusion of quadrupolar and higher order terms into the effective field in second order transition in uniaxial ferroelectrics is shown to describe well the jump in specific heat at T?T_c for crystals of the TGS family. It is shown that the numerical values for the coefficient g≡(γ/β)(Nμ)², corresponding to the quadrupolar interaction term, obtained (a) from specific heat data and (b) from spontaneous polarization data (both at T?T_c are in good agreement with each other for crystals of the TGS family.