Optical studies of ferroelectric phase transition in deuterated triglycine sulfate crystals

Critical behaviour of optical birefringence near the normal–incommensurate phase transition in [N(CH3)4]2ZnCl4crystals under the influence of hydrostatic pressure

“…Let us analyse in brief formulae (1) with the purpose of deriving the parameters of critical behaviour of the birefringence. They originate from a general relation n * ∼ η 2 between the PT-induced birefringence and the mean [10,22,23]). In a few cases, we have dealt with insufficient numbers of experimental points closest to the PT.…”

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

“…This correlates well with the known fact that the PT in is more essentially smeared than that in (6). Unlike the method adopted in [16,19] though similar to that used in the studies of critical fluctuations for deuterated triglycine sulphate [20,21], we have put the fitting parameters Table 1.…”

“…One of the possible reasons for deviation of ) 2 2 ( + − λ λ from the unity may be worse calculation accuracy for the paraelectric phase, the number of data points for which is mainly too small, though the fluctuation region in that phase can be wide enough [21]. On the other hand, the deviation could be induced by the influence of defects of the "random local PT temperature" type.…”

“…Nonetheless, the analysis of fluctuations after the optical activity possesses an evident advantage in this respect, when compare with the analysis based on the optical birefringence or thermal expansion data (see [16,[19][20][21]). Namely, the derivatives of the latter quantities include extra fitting parameters.…”

Nonlinear background corrections to dielectric permittivity of ferroics and multiferroics

“…In particular, it would be natural to expect that the relative importance of the dielectric background should not be completely neglected for a large number of substances. These are weakly polar ferroics [9,10], ferroelectric-dielectric composites [11], finite-sized or confined [12,13] systems such as thin-film or nanoscale ferroelectrics [14][15][16], improper ferroelectrics [17] and ferroeleastics [18] in which the dielectric anomaly has a secondary character, ferroelectrics with relatively high defect concentrations [19,20] or nonstoichiometry [21], and mutiferroics [22][23][24]. For very different reasons, the critical part 𝜀 cr (𝑇) can be small enough in these ferroics, thus imposing a greater relative contribution of the background.…”