Influence of a weak dc electric field on tricritical phase transition in TGSe: evidence ofdifferent specific heat behaviour on cooling and heating runs

Abstract

The para-ferroelectric tricritical phase transition of a single crystal of triglycine selenate (TGSe)has been studied in the neighbourhood of the transition temperature, under weak electric fields,E, using a highly sensitive calorimetric technique. The specific heat,cE, under fields in therange between 5 and 175 V cm−1 and close to transition temperature (0.2 K), shows different behaviouron cooling and on heating at a temperature variation rate of ± 0.03 K h−1; forT<Tc−0.5 K all setsof data match each other. The experimental data have been fitted to the 2–6 Landau potential obtained forE = 0; a term−ξQ, taking into accountthe coupling between E (ξ being dependenton E) and theorder parameter Q, is included. This potential fits well with the experimentaldata in the ferroelectric phase. The different relation betweenξ and E obtained on heating and on cooling runs is discussed and it is concluded that data onheating correspond to the thermal equilibrium.