Electrically and magnetically induced optical rotation in Pb5Ge3O11:Cr crystals at the phase transition. 1. Electrogyration effect in Pb5Ge3O11:Cr

We present the results of studies for temperature dependences of electrogyration (EG) effect and natural optical activity in Pb5Ge3O11:Cr crystals. Extremely high magnitude of EG coefficient is found for these crystals. We also demonstrate how the Curie-Weiss constant, the critical exponents of the order parameter and the dielectric permittivity, as well as the coefficients of thermodynamic potential, could be derived from the temperature dependences of optical activity and EG coefficient.