The effect of uniaxial pressure on the ferroelectric phase transition of TGSe crystals

Isobaric studies of the influence of uniaxial pressure on the transitions of pure TGSe crystals for the three directions are reported. The critical exponents, and , from dielectric constant and hysteresis loop measurements, as well as the coefficients and of the fourth and sixth powers of P in the free-energy expansion under uniaxial pressure were determined. It has been found that uniaxial pressure applied along the -axis keeps the transition near a tricritical point for 0 < X < 200 bar, but that when it is applied along the b- and c-axes it strengthens the second-order phase transition behaviour. The tricritical behaviour of TGSe crystals is discussed and a possible driving mechanism for the change in order of the phase transition is proposed.

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