Dielectric permittivity, ε22, spontaneous polarization, Ps, and coercive field, Ec, of triglycine sulphate (TGS) crystals doped with d-l alanine, orthonitroaniline, paranitroaniline or aniline molecules have been measured from room temperature up to the transition point. A remarkable displacement of the hysteresis loops of polarization along the direction of the field axis and a broadened transition from the polar to the non-polar phase are detected. An increase in the value of Ps and a decrease of both ε22 and Ec are also observed. The changes in both ε22 and Ps attributed to the creation by the dopants of an internal electric field, Eb. The internal bias affects the Curie constant and εmax in a way similar to that introduced by an external bias. The value of Eb in the vicinity of the phase transition and the parameters of the statistical dipolar theory of ferroelectricity have been calculated. ©1989 The Physical Society of Japan

The pyroelectric coefficient and the piezoelectric modulus of triglycine sulphate (TGS) single crystals doped with d-l-alanine, orthonitroaniline, paranitroaniline or aniline molecules has been measured from room temperature up to the transition point. The data are compared with those which the authors have previously obtained on pure TGS. A noticeable increase in the value of the pyroelectric coefficient of the doped samples over the whole temperature range is observed. A significant pyroelectric signal is still detected several degrees above the transition point of pure crystals. The spontaneous polarisation is calculated using data for the measured pyroelectric current. The piezoelectric modulus of the doped crystals reaches its maximum value at a temperature lower than the Curie point of pure TGS before it decreases steadily to zero. A relation between the piezoelectric modulus and the temperature just before the maximum value is deduced. The role of the internal bias created in the crystal after doping is also discussed

The pyroelectric coefficient and the piezoelectric modulus of triglycine sulphate (TGS) single crystals doped with d-l-alanine, orthonitroaniline, paranitroaniline or aniline molecules has been measured from room temperature up to the transition point. The data are compared with those which the authors have previously obtained on pure TGS. A noticeable increase in the value of the pyroelectric coefficient of the doped samples over the whole temperature range is observed. A significant pyroelectric signal is still detected several degrees above the transition point of pure crystals. The spontaneous polarisation is calculated using data for the measured pyroelectric current. The piezoelectric modulus of the doped crystals reaches its maximum value at a temperature lower than the Curie point of pure TGS before it decreases steadily to zero. A relation between the piezoelectric modulus and the temperature just before the maximum value is deduced. The role of the internal bias created in the crystal after doping is also discussed

The problem of the existence of a new ferroelectric phase transition at low temperatures in triglycine sulphate (TGS) crystals is discussed. The influence of some inorganic divalent and trivalent ions presented in the lattice of TGS on dielectric and AC conduction is examined. The internal biasing field caused by the existence of dopants in TGS crystals is found to have an effect similar to the effect of an external biasing field working on the crystal. A small thermal hysteresis in the dielectric behaviour is detected at the transition temperature. The AC conductivity and the activation energy of conduction both change as a result of the existence of the distorted lattice caused by the dopants. The resemblance between the behaviour of the dielectric constant and that of the AC conductivity with temperature is quite noticeable