On the tricritical behaviour of the Sn₂P₂S₆crystals

On the critical exponent of order parameter in Sn2P2S6 and Sn2P2(Se0.28S0.72)6 crystals

“…As seen from Table 1, the mean value of the critical exponent  is equal to 0.29 0.02  , i.e. it is the same as obtained by us in the work [17] from the birefringence data. Since the values of the critical exponent obtained from different physical parameters for the Sn 2 P 2 S 6 crystals agree well, it is quite probable that the temperature dependence 6 has been evaluated from all the dependences presented in Fig.…”

“…As demonstrated in our recent work [17], this diffuse character of the anomalies is caused by too high temperature change rates in the region of the phase transition. Of course, the temperature rotation of the spontaneous polarisation vector in the ac plane also can affect the accuracy of determination of the critical exponent, though this effect is probably quite small.…”

“…However, some other reasons can be responsible for the disagreement of the critical exponent data, too. In particular, as shown in [17], one cannot determine the exact phase transition point T C taking into account a diffuse character of anomalies of different physical parameters (e.g., the optical birefringence) near T C . As a consequence, the critical exponent could be estimated only roughly.…”

“…As a consequence, the critical exponent could be estimated only roughly. Nonetheless, the study [17] has presented a method for evaluation of the critical exponent from diffuse anomalies obtained experimentally. On that basis the exact value of the critical exponent  has been determined, which is equal to 0.3 for Sn 2 P 2 S 6 crystals.…”

Comparison of critical fluctuations in Sn2P2S6 and Sn2P2(Se0.28S0.72)6 crystals

“…The birefringence of SPS and SPSeS crystals grown with a vapour transport technique at the Uzhgorod National University was studied [15,16] at the wavelength = 632.8nm Fig. 1a) has no strict physical meaning and is intended only for reducing overlap of those curves.…”