Optical studies of order parameter fluctuations in solid solutions based on lead germanate crystals

Abstract

The approach for interpreting fluctuations seen in optical activity is suggested based on the first fluctuation correction to the Landau theory. Quantitative analyses of the fluctuation effects for Si-, Ba-and Bi-containing crystals of lead germanate family show applicability of the model. Critical indices governing temperature behaviour of the order parameter of ferroelectric phase transition are found for the crystals under study.

Optical activity and critical exponent of the order parameter in lead germanate crystals.1.The case of diffused phase transition in Pb5Ge3O11 doped with Cu, Ba and Si ions

“…Let us remind that this temperature point agrees with that experimentally obtained as a maximum of the slope of field-induced optical activity. As one can see, the fitted curve However, the range of phase transition diffusing derived from the data [19] is mach narrower than our value 14 K T ∆ = . (Pb Ba ) Ge O [22].…”

“…For example, the electrogyration coefficient 333 γ in Pb 5 Ge 3 O 11 :Cr 3+ [16,17] 6 3 ↔ . Moreover, it has been shown in the recent papers that the temperature behaviour of electrogyration effect induced by spontaneous polarisation may be used for obtaining the data concerned with critical fluctuations occurred in the vicinity of phase transitions [18], in particular for the case of lead germanate crystals [19,20]. The other known fact is that the temperature dependence of optical activity in the lead germanate may be used for deriving the critical exponent of temperature dependence of the order parameter.…”

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

“…Notice that S k represents anomalous part of the linear thermal expansion coefficient. It is known [10,21,22] that the both derivatives should behave similarly to the heat capacity and can be described, at least qualitatively, by power-law relationships like phases, and α the critical index determined by both the thermal fluctuations and the influence of structural defects [23].…”

Electrogyration effect in lead germanate crystal family

“…Characteristics of spontaneous EG for the doped LG:X crystals. The data for the pure LG crystal are taken from [11,15]. Table 1 gives the results shown in Table 1.…”

“…In order to gain reliable information regarding the influence of the impurities on the phase transition in LG and the critical fluctuations accompanying the phase transition, we have analysed the data of Fig. 1 using the technique described in our previous work [15].…”