Evidence of Landau tricritical behaviour in TGSe by calorimetric measurements: effect of aweak uniaxial stress

Abstract

The paraelectric–ferroelectric phase transition of a single crystal of triglycine selenateTGSe, whose first- or second-order character is controversial, has been studied using a highsensitivity calorimetric technique. The specific heat of a highly pure TGSe has beenmeasured and no evidence of latent heat has been found. The anomalous part of thespecific heat shows Landau tricritical behaviour. Experimental data have been fitted to a2–6 Landau potential, whose coefficients have also been obtained. A weak uniaxial stressapplied along the ferroelectric axis (10 bar) decreases the anomalous part of thespecific heat. This effect is different for cooling and heating runs. The equilibriumdata are those obtained on heating that fit to a 2–4–6 Landau potential, whichindicates that the transition shifts to second order with the effect of uniaxial stress.