Influence of a weak dc electric field on tricritical phase transition in TGSe: evidence of different 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 the range between 5 and 175 V cm−1 and close to transition temperature (0.2 K), shows different behaviour on cooling and on heating at a temperature variation rate of ± 0.03 K h−1; for T<Tc−0.5 K all sets of data match each other. The experimental data have been fitted to the 2–6 Landau potential obtained for E = 0; a term −ξQ, taking into account the coupling between E (ξ being dependent on E) and the order parameter Q, is included. This potential fits well with the experimental data in the ferroelectric phase. The different relation between ξ and E obtained on heating and on cooling runs is discussed and it is concluded that data on heating correspond to the thermal equilibrium.

First order phase transition in deuterated triglycine selenate under an electric field: experimental study and analysis in the frame of Landau theory

“…A similar behaviour was recently reported [4,21] for tricritical phase transition in TGSe after studying the influence of the electric field on the specific heat. Ferroelectric phase data for E = 0 were also explained by considering an effective field higher than the applied field.…”

“…Taking into account that the experimental values are lower than the predicted curve and that the electric field decreases c at each temperature, the effect on the specific heat would be similar to that of an effective field (higher than the applied field) acting on the sample. A similar behaviour was previously found for specific heat in TGSe under electric fields lower than E < 175 V cm −1 , including the fact that the influence of the electric field becomes more significant on the ferroelectric to paraelectric phase transition [21].…”

“…It is noteworthy that a similar behaviour was observed in the tricritical phase transition of non-deuterated TGSe [13] where data on heating and cooling runs were found to match to each other for a zero-field experiment. On the other hand, they differ within a narrow temperature interval of 0.2 K around the transition temperature for applied electric fields lower than 175 V cm −1 [21]. A similar behaviour was also observed after a uniaxial pressure was applied along the ferroelectric axis in TGSe [13].…”