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

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.