FERROELECTRIC PHASE-TRANSITION OF DTGS CRYSTALS UNDER UNIAXIAL PRESSURE

Isothermic and isobaric studies of the influence of uniaxial pressure on the phase transition of deuterated TGS are reported for three direc tions - X, Y, Z. The pressure coefficients gamma(i) (gamma(i) = partia l derivative T-c/partial derivative X(i)) are established. It has been found that the coefficient xi of the fourth power in the free energy expansion is practically not uniaxial pressure and temperature-depende nt in the range of uniaxial pressures investigated (up to 1kbar). Simi larities between purely stress and temperature-induced phase transitio ns are shown, and the results are analyzed using scaled variables. Phe nomenological theory and the molecular origin of the ferroelectric mec hanism for TGS crystals are also discussed.